General engine question--expanding the audience

[Ghost]

Regarding the strength-of-spark needed to ignite the fuel-air mix: is the needed strength of the spark higher at higher RPMs?

Such that if spark is on the weak side, is it possible that the engine would run okay up to a certain RPM, and then above that, the spark would not ignite the mix consistently, and the motor could start to flood itself out?

All thoughts welcome.

Thanks,

Mike

[VetteLT193]

weak spark would cause a misfire... did you 'read' the plugs yet?

as far as RPM related I'd guess it's more related to the advance, or lack thereof.

Technically speaking I can't see a reason why more RPM would do anything other than exposing a misfire because of more frequent misses... I might be missing something though.

[Ghost]

Thanks. Plugs reek of gas, which I hear is definitely wrong. Nothing too visual I could assess--they're pretty new plugs.

My theory (and it was totally just theory, and I was curious if all the gearheads here would know from experience) was that as the spark advanced forward with increasing RPM, the fuel/air mix would be less compressed at spark time. And thus that fuel/air mix might be slightly harder to ignite as RPM climbed.

And that a weak spark that was on the ragged edge, just barely getting the job done at lower RPM might start missing once the RPM went up past a certain point. (And all the residual fuel that went uncombusted would only make it worse.)

And then the engine would flood itself a little, and wind down in RPM until it got down low enough for the advance to back off, and for the compression at spark time to increase a little, and thus for the spark to be strong enough again.

(The wind-down symptom is what I have.)

I assume the compression of the mix at spark-time HAS to decrease with spark advance. This seems like a given. But I have no idea if that change would make the mix harder to ignite, enough to require stronger spark.

[silverghost]

The answer to your question is this:
It all comes down to your ignition coil charge time!
The faster you go ~ the less time your coil has to charge-up for the next plug firing!
The faster you go ~ the less energy your ignition coil system will put out!
It all comes down to dwell or coil charge time.
Years ago dual point systems were popular to increase coil charge time.
There were also many other racer tricks used.
Electronic ignition and high energy CD systems helped this problem a bit~
BUT~
If you have any weak links such as~
Partially shorted & failing Coil
Worn-out Ign points (if you still have them)
Failing condenser
leaky or higher than normal resistance plug wires
Dirty or worn-out spark plugs with too wide a gap
Dist cap or rotor with dirty or burned corroded contacts
Low ign battery voltage because to the system because of corroded & high resistance connections..
All of the above will have an effect the faster that you go!
In almost any conventional Ignition system Electronic or point systems the faster you go the less spark at the plug gap.
That's just a fact of science!
The above problems only compound this low voltage energy problem at your plugs!
This is why drag & other racers use high energy & magneto systems & dual ignition!
With a magneto the faster you go the more spark energy you have~ The exact inverse of a conventional ignition system!
What's your real answer here?
Keep your system components in tip top condition by doing a complete major ignition tune-up!
These systems work well up to about 6000RPM !
After that you need a racing Magneto or High Energy CD race type system such a built by MSD or Mallory !
Hope this helps? !

[Ghost]

The answer to your question is this:
It all comes down to your ignition coil charge time!
The faster you go ~ the less time your coil has to charge-up for the next plug firing!
The faster you go ~ the less energy your ignition coil system will put out!
If you have any weak links such as~
Partially shorted & failing Coil
Worn-out Ign points (if you still have them)
Failing condenser
leaky or high resistance plug wires
Dirty or worn-out spark plugs with too wide a gap
Dist cap or rotor with dirty corroded contacts
Low ign battery voltage because of corroded high resistance connections..
All of the above will have an effect the faster that you go!
I almost any conventional Ignition system Electronic or point systems the faster you go the less spark at the plug gap.
The above problems only compound this low voltage energy problem at your plugs!
This is why drag & other racers use high energy & magneto systems!
With a magneto the faster you go the more spark energy you have~ The exact inverse of a conventional ignition system!
What's your answer?
Keep your system components in tip top condition by doing a complete ignition tune-up!

Wow, thanks, good stuff. I think I know what to do next. (I've replaced plugs and gapped them, and replaced the dist cap and rotor. And the new plug wires are in front of me, my next thing.)

One question: have you ever seen a "wind down" condition from exactly the weak-spark causes listed above, or is the typical symptom something else. (When I've needed dist caps or rotors in the past, I did not see this. I saw a couple of unwilling starts, then a motor that would not fire at all. But never saw a "wind down" like I see now.")

Thanks,

Mike

[VetteLT193]

That is a great point on a failing coil...

I could see a 'wind down' on an old and dying coil.

the plugs smelling like gas though is kind of odd... I'd think if you really didn't have a problem at lower speeds it would burn off the excess gas at lower speeds.

Are all the plugs equal?

[silverghost]

Just my gut feeling~
It sounds to me more like a fuel delivery problem!
Clogged fuel filter
Fuel pump problem
Carb or Fuel Injection issue
Restricted fuel line or fitting etc.
Could be ignition~
But without being there to see the problem first hand it really sounds more like a fuel delivery issue!

[Ghost]

That is a great point on a failing coil...

I could see a 'wind down' on an old and dying coil.

the plugs smelling like gas though is kind of odd... I'd think if you really didn't have a problem at lower speeds it would burn off the excess gas at lower speeds.

Are all the plugs equal?

Equal? Yes, same type, same gap, all very new. Can't say I could see or smell a difference from one to the next.

[Ghost]

Just my gut feeling~
It sounds to me more like a fuel delivery problem!
Clogged fuel filter
Fuel pump problem
Carb or Fuel Injection issue
Restricted fuel line or fitting etc.
Could be ignition~
But without being there to see the problem first hand it really sounds more like a fuel delivery issue!

Thanks. Practically the only thing left in the fuel system would be a carb rebuild, which was next on my list after doing the rest of the ignition. My separators are new and huge (90 gph per motor). Filters are pretty new. Etc. Beyond that, the fuel pump and the hose itself is about all that's left.

[silverghost]

It might help us troubleshoot your problem If we knew what engine you are running?
What year?
Model #
Points or Enectronic Ign.?
Carb or Fuel Injection?

[VetteLT193]

Equal? Yes, same type, same gap, all very new. Can't say I could see or smell a difference from one to the next.

I agree with silverghost, except I think your fuel delivery problem is too much fuel. More info please, Carbed? what type? when do the secondaries open? what's the deal on the overall problem... new engine, new problem? old engine new problem just cruising along one day?

My best guess is you are over-carbed, or something broke in the carb and is dumping fuel in when the secondaries open. That puts you in a super rich, un-burnable fuel scenario.

[Ghost]

It might help us troubleshoot your problem If we knew what engine you are running?
What year?
Model #
Points or Enectronic Ign.?
Carb or Fuel Injection?

2003 PCM 5.7 310 HP carbureted

I *think* the (factory) Mallory distributor has the newer electronic guts such that it does not have a condensor and points to replace.

[VetteLT193]

Thanks. Practically the only thing left in the fuel system would be a carb rebuild, which was next on my list after doing the rest of the ignition. My separators are new and huge (90 gph per motor). Filters are pretty new. Etc. Beyond that, the fuel pump and the hose itself is about all that's left.


Do you smell gas in the oil? Now I'm guessing fuel pump, assuming it's a mechanical pump.

[Ghost]

what type? when do the secondaries open? what's the deal on the overall problem... new engine, new problem? old engine new problem just cruising along one day?

My best guess is you are over-carbed, or something broke in the carb and is dumping fuel in when the secondaries open. That puts you in a super rich, un-burnable fuel scenario.

Dunno when secondaries open, good question. (I know this sounds idiotic, but any thoughts on a good, safe way to observe/assess this?)

New problem. Engine has started sounding rougher lately, then this most recently.

I've felt the same way about too much fuel as opposed to too little. Thus your over-carbed point makes a lot of sense to me with the secondaries.

(And, I could swap the carbs--the other motor is running ok. I've been trying to understand as much as I could and learn some theory along the way, rather than just do a lot of swapping and such, not knowing much about why it might be happening.)

[Ghost]

Do you smell gas in the oil? Now I'm guessing fuel pump, assuming it's a mechanical pump.

Have not noticed a gas smell in the oil, but not sure I would have.

Electrical pump. Not a 2-stage with a return, but one stage high-volume/low pressure. I think somewhere in the 6-10 psi range, as it is feeding a carb and not an injector system.

[silverghost]

If the plugs are wet with excess gasoline & you are flooding you just may have a simple carb float needle valve that is not seating properly!
Could be as simple as a speck of dirt or bad needle valve.
Float level could be also improperly set too high!
Do you have a fuel pressure regulator between the fuel pump and carb?
If so regulator may be failing or set to too high a fuel pressure and popping float needle valves off their seat?
What kind of carb and fuel setup do you have?

[VetteLT193]

Dunno when secondaries open, good question. (I know this sounds idiotic, but any thoughts on a good, safe way to observe/assess this?)

New problem. Engine has started sounding rougher lately, then this most recently.

I've felt the same way about too much fuel as opposed to too little. Thus your over-carbed point makes a lot of sense to me with the secondaries.

(And, I could swap the carbs--the other motor is running ok. I've been trying to understand as much as I could and learn some theory along the way, rather than just do a lot of swapping and such, not knowing much about why it might be happening.)


Ok... probably not the fuel pump...

The best way I have found for the secondaries is to:
-Engine off throttle the handle forward until the secondaries just start to open. It will take a few trips back and forth between the stick and the engine to get it right.
-When you find the point, put a piece of tape on the throttle housing, or some other indicator, so you know.
-Add a couple of other pieces while you are at it for other stages... 25% open, 50% open.

Then run the boat... see what happens relative to the tape. That assumes MECHANICAL secondaries. Vacuum... well, find a very non accident prone and careful friend. don't let him have beer until you are done testing. LOL

[Ghost]

Ok... probably not the fuel pump...

The best way I have found for the secondaries is to:
-Engine off throttle the handle forward until the secondaries just start to open. It will take a few trips back and forth between the stick and the engine to get it right.
-When you find the point, put a piece of tape on the throttle housing, or some other indicator, so you know.
-Add a couple of other pieces while you are at it for other stages... 25% open, 50% open.

Then run the boat... see what happens relative to the tape. That assumes MECHANICAL secondaries. Vacuum... well, find a very non accident prone and careful friend. don't let him have beer until you are done testing. LOL

LOL, thanks. Mechanical I think, so this should work. Good idea. (Bonehead me didn't think that one through before asking...)

[silverghost]

The more we talk about this~
The more I think it is a simple float needle valve issue !
The float needle valve might not be seating properly because of dirt, varnish, or a bad rubber tip.
This would allow fuel to just dump out of the carb jets into the engine creating a very rich fuel condition!
I have seen this many times~
It's a very simple fix!

[VetteLT193]

The more we talk about this~
The more I think it is a simple float needle valve issue !
The float needle valve might not be seating properly because of dirt, varnish, or a bad rubber tip.
This would allow fuel to just dump out of the carb jets into the engine creating a very rich fuel condition!
I have seen this many times~
It's a very simple fix!

+1 on this.

[Ghost]

If the plugs are wet with excess gasoline & you are flooding you just may have a simple carb float needle valve that is not seating properly!
Could be as simple as a speck of dirt or bad needle valve.
Float level could be also improperly set too high!
Do you have a fuel pressure regulator between the fuel pump and carb?
If so regulator may be failing or set to too high a fuel pressure and popping float needle valves off their seat?
What kind of carb and fuel setup do you have?

No regulator--pretty sure it's all just the rigid tube from the pump to the carb.

I take it the carb rebuild is the way to deal with the stuff you listed? (Or is there something short of that to try?)

I forget which carb model it is, but I will double check the model #. A pretty common marine Holley 4 barrel, with one fuel entry at one end, not two.

BTW, I am about to disappear for a few hours most likely. I really appreciate all the help from you guys.

Mike

[BlownCrewCab]

I agree on the carb being the problem, Have you had any good Backfires lately? that could have damaged parts in the carb (depending on what kind you have) or the float levels way off or stuck and it's just dumping fuel.

[Ghost]

The more we talk about this~
The more I think it is a simple float needle valve issue !
The float needle valve might not be seating properly because of dirt, varnish, or a bad rubber tip.
This would allow fuel to just dump out of the carb jets into the engine creating a very rich fuel condition!
I have seen this many times~
It's a very simple fix!

Oooh, this sounds like something to hope for---what's the way to clean the tip?

[Ghost]

I agree on the carb being the problem, Have you had any good Backfires lately? that could have damaged parts in the carb (depending on what kind you have) or the float levels way off or stuck and it's just dumping fuel.

Zero backfires.

[Ghost]

Gotta run--back later this evening. Thanks again for all the help guys!

Mike

[BlownCrewCab]

Oooh, this sounds like something to hope for---what's the way to clean the tip?


4 bolts that hold the float bowl on, usually can save the gasket if your carefull.

[silverghost]

Carefully pop the entire top off your carb after dis-connecting all carb linkage and check the needle valves!
On Holley you need to pop-off the side fuel bowl/s not the top as on Carter etc.
Pull the float pivot pin and pull out the needle valve/s!
Turn carb upside down and gently blow into fuel inlet.
With carb top upside down float valve should shut off all air flow!
If not~
Check needle valve/s thmselves for dirt etc.
Very simple to do~
You might not really need a full carb re-build.
Be very careful not to let any small parts drop into the intake manifold & engine!

[VetteLT193]

sometimes a little taaaaappy tappy tappy fixes it.

most of the time, pull the bowl off and clean that first. it's usually simple and pretty obvious.

[silverghost]

If it's not the needle valves then it must be a power valve issue!
This is why he asked you about a backfire!
A backfire can blow-out a power valve quickly in your Holley Carb!
This too is an easy Do it yourself fix!
Power Valve failures have always been a common big problem with these carbs!
There is a back-fire check valve kit that prevents this common power valve blow-out Holley problem!
Any good speed shop should carry Holley float needle valves, power valves, and the check valve retrofit kit !
These are inexpensive parts!
Make sure you get the exact power valve for your Holley carb.
It is located on the main jet metering block behind the float chamber casting!
I have replaced dozens of Holley needle & power valves, and Accelerator pump diaphrams over the years !
These are the weak links in any Holley Carb!

[smbarcelow]

These are the weak links in any Holley Carb!

Weak links but, fortunately, easy repairs. Also, those are good parts to keep in a spare parts bin. Having a few of them handy may save an afternoon of boating. :cool:

[silverghost]

I don't want to start a riot here but Holley Carbs on boats have a number of well known problem issues!
The Holley has been around in many forms almost forever!
It is a good carb.
It is easy to re-jet and tune while still on the engine without taking the carb completely off the manifold.
Float levels can be adjusted on most models externally using a sight hole in side of fuel bowl and extrnal float adjustment & float valve assemblys can be easily removed externally on many models.
Parts are easy to find at speedshops & auto stores.
Most racers & good mechanics understnd this type of carb!
Now the Downside~
Holley uses rubber diaphram parts on the power valve & accelerator pump.& vacuum secondary diaphram.
A single back-fire can blow-out the power valve/s.
I have replaced dozens over the years!
There is a retrofit kit called a power valve blow-out preventer that you can buy that has a small check valve and tools to help install it.
It is a simple carb mod!
It works in 90% of back-fires~BUT not always.
Holley also uses a rubber pump diaphram/s on it's accel. pump/s. & secondary Vacuum Diaphrams
These rubber pump & power valve parts & diaphrams can be ruined by new fuel blends and additives!
Winter boat storage with long terms of non-use can dry-out and crack these rubber diaphrams
You can't avoid the carb drying out over the winter .
The result ~
Every Spring
Leaks & poor performance!
It got to a point with my Chevy 454 Boat Holley Double Pumper that each and every spring I could look foreward to replacing these rubber parts in my Holley!
EVERY YEAR~ What a pain!
I finally switched to a Edelbrock Performer AFB/AVS (Carter/Weber) and I have never looked back!
These do not use rubber diaphrams or power valves!
No more Spring Fit-Out Holley Diaphram leaks & replacment!
One Carter AFB Mod I like ~
I used the newer off-road needle float valves with a secondary float springs that are not included with the new Carter Marine Performer as I found these worked much better on a pitching & rolling boat application to control a stable float level & and I have not had to touch the carb in ten years after I first tuned it to my engine/boat application.
I love the old Carter AFB/AVS Edelbrock performer marine carbs!
Many of you Holley guys out there might not like the Carter AFB/AVS.
I used to be a Holley guy too.
But I am now glad I switched!
My old Holley Marine Double Pumper is now in a box on a shelf in my basement!
No doubt the rubber parts are now rotten again from sitting dry.
I do not miss it one bit !
I find I have fewer lay-up~ Rubber Dry Out problems with the Carter/Weber AFB/AVS
Just my experience!
More Fun time to actually use the boat & less time rebuilding the old Holley Carb!

[silverghost]

I have found that the newest Holley Carbs & pressure regulators have all sorts of quality control issues new-out-of-the-box !
Their casting & machining quality has really slipped! (Foreign Manufacture Issues?)
Made in China, Tiawan, & Mexico ?
Who Knows Why ? !
This is one of the many reasons Racers have switched to Deamon, Barry Grant, Edelbrock Performer, Etc, and other brands!
Holley quality is not what it used to be !
I guess we should all be thankful that anyone even makes any carbs at all today!

[BlownCrewCab]

I have found that the newest Holley Carbs & pressure regulators have all sorts of quality control issues new-out-of-the-box !
Their casting & machining quality has really slipped! (Foreign Manufacture Issues?)
Made in China, Tiawan, & Mexico ?
Who Knows Why ? !
This is one of the many reasons Racers have switched to Deamon, Barry Grant, Edelbrock Performer, Etc, and other brands!
Holley quality is not what it used to be !
I guess we should all be thankful that anyone even makes any carbs at all today!


I'm in the middle of rebuilding the small block 408 from my old donzi, I just got the new CROWER Lifters, I compared them to the ones I'm replacing (that I bought From Crower in 1998) and the quality Demise isn't even funny. the old lifters are quality pieces, the new ones are Very poor in comparison, They cost almost 2x as much though....

[BUIZILLA]

funny you say this about new lifters.... tomorrow i'd already planned on having my new set checked for hardness..

[Dr. David Fleming]

Carter AFB - Aluminum Four Barrel and AVS - Air Valve Secondary - these carbs were designed in the 1950's for automotive and appeared on some of the greatest Detroit engines. AFB was an older design and was cleaned up by GM and Carter in the 1967 era for the small block Chevy - this redesign was the AVS which had real clean secondaries and an air valve to eliminate the bog when the secondary came in quickly. GM used it for about a year then forgot about it. Chrysler picked it up and used it on the 383 Magnum and 440 Magnum street engines for about three years then it disapeared. It was a best loved carb and the bigger versions flowed about 810 cfm - cubic feet per minute of air. Racers always prefered the 4150 Holly - 750cfm and 850cfm - which was designed by motor guru Smokey Unick (sp)

I was trying to round up some spare parts from Carter in the 1980's and had a great conversation with some of their engineers. The Carter AVS and Thermoquad tooling was destroyed by plant workers in St. Louis, Mo. when they found out the company was going to have it manufactured in Italy. I lost track of them after that as fuel injection was the way of the future. Eldebrock the high performance parts folks suddenly resurfaced the AFB and called it the Competition Series. Mercury had the big Carter on its marine engines but called it a Webber which is made in Europe - same carb though.

Some of the advantages are the one piece float bowl that doesn't leak gasoline into the bilge - also all the calibrations are in the primary venturi clusters which are removable (idle jets, emulsion tubes, air bleeds, economizer bleeds etc. Main Jets are in the bottom of the float bowl though.

The 1967 - AVS General Motors redesign had no booster venturis in the rear barrels in the 60's just a couple of brass dump tubes to flow the fuel into big empty barrels which weren't venturi just cylindrical bored holes! - later AVS models made by Eldebrock seem to be a cross between AFB and AVS and have the secondary venturi clusters and sometimes the old little AFB airvalves inside the rear barrels as well as the AVS large air valve - sure like to know the engineering ideas behind that hybrid.

There was also and early tall AFB called the "D series" which had a small air horn diameter and later the "E serie" had a lower air horn which was bigger in diameter the choke stood up into the air cleaner on a sort of tower. Early Chrysler street hemi's all used the tall "D series" and the later GM prefered the shorter "E series" - AVS carbs were all "E series." Buick used duel AFB's so did Chrysler in those huge "long ram" big blocks in the 60's one carb over each front tire and this bellcrank throttle linkage - sort of like headers on the fuel intake system.

The big Carter and Holley four barrels produced a lot of horsepower - their downfall was their fuel mileage and emissions. Modern fuel injection like the Merc MPI, MAG MPI and 500EFI don't seem that much more powerful but they do have the emissions and mileage edge. The big Carter four-barrel was one of Americas great carburators and seeing it on a Mercury big block Chevy engine means only one thing - horsepower American style.

Dr. d

[silverghost]

The Dr. is correct !
The new units are an AFB/AVS cross-breed carb.
The Edelbrock Performer & new Carter carbs are all in fact made by Weber of Italy !
The Webber name & logo is in the lower main castings.
I have older AFB & AVS carbs and the new units are a cross-breed of the two old carter designed & built units with some minor improvements!
I really like these new carbs!
They are very tuneable and never give you problems!
The old Chrysler Thermoquad is another story~
The basic carbs plastic parts on it are a bit of a pain in the neck!
They do not age well & the engine heat distorts them!
They were an experimental composite unit that was way ahead of it's time!
The idea behind it was the idea that plastic would keep the fuel cooler than cast metal carbs! Thus the "Thermoquad" name!

[BlownCrewCab]

funny you say this about new lifters.... tomorrow i'd already planned on having my new set checked for hardness..


Good point, and I am in a building with just about every kind of Hardness checker made:yes: The difference between the 2 pieces (new & Old) is pathetic..

[joseph m. hahnl]

You can check to see if it's flooding from either a bad seat or fuel pump diaphram rupture. by romving the spark errestor and running the engine at idle. you will see fuel dribbeling from the trucks or from the fuel pump by pass hose. The power valve is for low vacume enrichment.


this link will show how to check the power valve with out removing the carbuerator
http://www.youtube.com/watch?v=6vKlAnKdcB4









POWER ENRICHMENT SYSTEM

The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to “time” this system’s
operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number “65” indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501, should be used when determining the correct power
valve to use. A competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8” Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5.
Most of the popular Holley “Street Legal” and “Street
Performance” carburetors incorporate a power valve blow-out
protection system. A special check valve is located in the throttle
body expressly for this purpose. This check valve is
designed to be normally open but will quickly seat to close off
the internal vacuum passage when a backfire occurs. Once
closed, the check valve interrupts the pressure wave caused by
the backfire, thus protecting the power valve.
If you have a carburetor older than 1992 (or you have experienced
an extreme backfire) and expect a blown power valve,
use this simple test. TEST: At idle turn your idle mixture screws
(found on the side of the metering block) all the way in. If your
engine dies the power valve is not blown.

THE TRUTH ABOUT POWER
VALVES USED WITH HOLLEY
CARBURETORS

There still seems to be a lot of misconception about
Holley carburetors blowing power valves. Nothing
could be further from the truth. Holley performance
carburetors built since 1992 have utilized a power
valve check system that effectively eliminated this
infrequent problem. Consisting of a spring, brass
seat and check ball, the check ball system is 100%
effective protecting the power valve diaphragm
from damage due to engine backfire.
The power valve check ball is designed to be
normally open but quickly seals to close off the
internal vacuum passage when a backfire occurs.
Once closed, the check valve interrupts the pressure
wave generated by the backfire, thus protecting the
power valve diaphragm. There is no way that the
power valve’s diaphragm can rupture due to an
engine backfire!
http://www.holley.com/data/TechService/Technical/power_valves.pdf

[Bamboo Loui]

I have really enjoyed this thread-- tons of info-- I know Mike has a problem as described-- and honestly-- though I am not any kinda wrench type guy-- which means I usually break something or do not finese something back into place--- which really means--I as doing it wrong because nothing ever SHOULD need forced--
I just (perhaps it is off thread-sorry) have a question-- I have had an old corvette-- 327/365 with a carter AFB-- I just sold a 67- 427-400 tri power vetter with original carbs-- the leaking was horrible on the 67--- internally-
If I was to ever repower my 22c-- what does the board feel-- carb- or EFI??-- so it would be 502 efi- 502 carbed? 502SC?
question has to do with the whole carb thing- as a older gen guy- I have had the forever-- but in my cars have enjoyed the reliability of the new computerized efi systems
thanks

again sorry if I am too off thread
Loui/doug

[Bamboo Loui]

I have really enjoyed this thread-- tons of info-- I know Mike has a problem as described-- and honestly-- though I am not any kinda wrench type guy-- which means I usually break something or do not finese something back into place--- which really means--I as doing it wrong because nothing ever SHOULD need forced--
I just (perhaps it is off thread-sorry) have a question-- I have had an old corvette-- 327/365 with a carter AFB-- I just sold a 67- 427-400 tri power vetter with original carbs-- the leaking was horrible on the 67--- internally-
If I was to ever repower my 22c-- what does the board feel-- carb- or EFI??-- so it would be 502 efi- 502 carbed? 502SC?
question has to do with the whole carb thing- as a older gen guy- I have had the forever-- but in my cars have enjoyed the reliability of the new computerized efi systems
thanks

again sorry if I am too off thread
Loui/doug

Sorry-- I meant I have had carb cars-boats forever- but the new EFIs seem so nice

[Ghost]

No worries at all. I've got lots of great info to work with for now, so hijack away and enjoy. Been some pretty interestiing history and discussion here. I hope to have a chance to try some stuff over the weekend. When I have more info, I'll report back. -Mike

[joseph m. hahnl]

I have really enjoyed this thread-- tons of info-- I know Mike has a problem as described-- and honestly-- though I am not any kinda wrench type guy-- which means I usually break something or do not finese something back into place--- which really means--I as doing it wrong because nothing ever SHOULD need forced--
I just (perhaps it is off thread-sorry) have a question-- I have had an old corvette-- 327/365 with a carter AFB-- I just sold a 67- 427-400 tri power vetter with original carbs-- the leaking was horrible on the 67--- internally-
If I was to ever repower my 22c-- what does the board feel-- carb- or EFI??-- so it would be 502 efi- 502 carbed? 502SC?
question has to do with the whole carb thing- as a older gen guy- I have had the forever-- but in my cars have enjoyed the reliability of the new computerized efi systems
thanks

again sorry if I am too off thread
Loui/doug



1971- inboard Model 324, 325hp, 427cubi inch - 4bbl carb -8.8:1 comp.
inboard Model 390, 390hp, 482cubi inch - 4bbl carb - 10:1 comp.
1973- inboard Model 325, 325hp, 427cubi inch - 4bbl carb -8.8:1 comp.
inboard Model 350, 350hp, 454cubi inch - 4bbl carb -8.5:1 comp.
1974- inboard Model 350, 350hp, 454cubi inch - 4bbl carb -8.5:1 comp.
1975- inboard Model 350, 350hp, 454cubi inch - 4bbl carb -8.5:1 comp.
1976- inboard Model 350, 350hp, 454cubi inch - 4bbl carb -8.5:1 comp.
1977- Alpha drive, 330TRS/TR, 330hp, 454 cu.in- 4bbl carb- 8.2:1comp.
1978- Alpha drive, 330TRS/TR, 330hp, 454 cu.in- 4bbl carb- 8.2:1comp.
1980- Alpha drive, 330TRS/TR, 330hp, 454 cu.in- 4bbl carb- 8.7:1comp
1984- Alpha drive, 330TRS/TR, 330hp, 454 cu.in- 4bbl carb- 8.8:1comp
Alpha drive, 370TRS, 370hp, 454 cu. in. - 4bbl carb- 8.8:1comp.
1985- Alpha drive, 330TRS/TR, 330hp, 454 cu.in- 4bbl carb- 8.5:1comp
Racing eng, 370TRS, 370hp, 454 cu. in. - 4bbl carb- 8.6:1comp.
Racing eng, 400TRS, 400hp, 454 cu. in. - 4bbl carb- 8.6:1comp.
Racing eng, 440TRS, 440hp, 454 cu. in. - 4bbl carb- 8.6:1comp.
1988- Bravo drive, 7.4Bravo, 330hp, 454cu. in. - 4bbl carb- 9.3:1comp
Bravo drive, 454MAG, 365hp, 454cu. in. - 4bbl carb- 8.8:1comp.
Racing eng, HP 420, 420hp, 454 cu. in. - 4bbl carb- 8.8:1comp.
1989- Bravo drive, 7.4Bravo, 330hp, 454cu. in.- 4bbl carb- 8.5:1comp.
Bravo drive, 454MAG, 365hp, 454cu. in. - 4bbl carb- 8.8:1comp.
1999- Bravo drive, 7.4MPI, 310hp, 454cu. in. fuel injection- 9.3:1comp.
Bravo drive, 454MAG/MPI, 385hp, 454cu.in fuel inject-8.6:1comp
Bravo drive, 502MAG/MPI, 415hp, 502cu.in fuel inject-8.75:1com

[BlownCrewCab]

I was never a fan of EFI...Until I learned How it worked..... AND HOW WELL IT WORKED!!!! If you can get all the neccesary sensors in the required locations it is the Best (The Sh*t, The Bomb, etc...) No carb could ever keep up under all conditions. a good efi systym knows how much air is coming in (MAF, Mass Air Flow sensor) then the processor adds fuel based on your throttle position (TPS Throttle Position Sensor) while Checking for Knock (knock sensor, not on all efi's) then Ultimately checking the O2 sensor to see if it needs to add or subtract "Minute" amounts of fuel to get the required "Perfect" air fuel ratio, something a carb could never do all of. I agree a properly tuned carb is Great, but it can't adjust it's self to be perfect like efi can. I used to think it just squirted fuel in and was no big deal bla bla bla, until I learned how perfect it can be, it is the best....

[Dr. David Fleming]

Your question about the EFI or the carburator is a good one. Merc EFI is expensive and unless you get the whole engine and set it up stock you have some expensive tuning to do.

Take for example the Merc 502/454 MAG MPI which is a great fuelie set up. There were three different computors, fuel rails and at least two types of fuel pumps.

The early 502/454 MAG MPI had a MEFI 1 computor (Mercury Electronic Fuel Injection) it used a small fuel rail with small injectors and a high pressure fuel canister or what ever it was on the top of the engine. This motor can be identified by the paper air filter element. This engine also used v type fanbelts. I believe this engine used a mechanical and electric fuel pump system.

The second 502/454 MAG MPI had the MEFI 2 computor housed in an electrical box on the top of the engine. They did away with the high pressure fuel canister and changed the paper air filter for a spark arrestor. I believe this engine used a serpentine drive belt with different pully brackets holding the accessories also a different oil filter mount and the valve covers had different openings. Mechanical fuel pump was eliminated.

The third 502/454 MAG MPI had the MEFI 3 computor bolted on the side of the exhaust manifold and a larger fuel rail with bigger injectors. This engine used the serpentine belt, spark arrestor as the earlier model but the computor was substancily more powerful. There was also a fuel injector change late in the year. This was the last model 502MAG MPI because of the new 496HO engine.

I don't believe the carburated engine is anywhere near as complicated. Just bolt on the old Carter/Webber and go. The EFI setup is also very hard to troubleshoot if there are problems you need the diagnositc tools.
With a carburator you can figure out most of the problems in your head.

Dr. d

[Pismo]

I was never a fan of EFI...Until I learned How it worked..... AND HOW WELL IT WORKED!!!! If you can get all the neccesary sensors in the required locations it is the Best (The Sh*t, The Bomb, etc...) No carb could ever keep up under all conditions. a good efi systym knows how much air is coming in (MAF, Mass Air Flow sensor) then the processor adds fuel based on your throttle position (TPS Throttle Position Sensor) while Checking for Knock (knock sensor, not on all efi's) then Ultimately checking the O2 sensor to see if it needs to add or subtract "Minute" amounts of fuel to get the required "Perfect" air fuel ratio, something a carb could never do all of. I agree a properly tuned carb is Great, but it can't adjust it's self to be perfect like efi can. I used to think it just squirted fuel in and was no big deal bla bla bla, until I learned how perfect it can be, it is the best....

EFI is the best when it works. When it quits it is not just a 1minute diagnosis and a quick repair, it can take months of hunting down which sensor(s) is out. Lots of threads on here about just that.

[VetteLT193]

I was never a fan of EFI...Until I learned How it worked..... AND HOW WELL IT WORKED!!!! If you can get all the neccesary sensors in the required locations it is the Best (The Sh*t, The Bomb, etc...) No carb could ever keep up under all conditions. a good efi systym knows how much air is coming in (MAF, Mass Air Flow sensor) then the processor adds fuel based on your throttle position (TPS Throttle Position Sensor) while Checking for Knock (knock sensor, not on all efi's) then Ultimately checking the O2 sensor to see if it needs to add or subtract "Minute" amounts of fuel to get the required "Perfect" air fuel ratio, something a carb could never do all of. I agree a properly tuned carb is Great, but it can't adjust it's self to be perfect like efi can. I used to think it just squirted fuel in and was no big deal bla bla bla, until I learned how perfect it can be, it is the best....

Merc uses the older, more simple setup. No MAF, just a MAP sensor. No 02 either. TPS is commonly misconceived in any EFI setup. it's mainly used for delta value to make sure the engine doesn't stall on a quick pull back and allows to quickly add fuel on quick throttle ups.

On a boat the jury is still out for me. EFI/MPI whatever is nice, but a well tuned carb will hang in there without the headache of bad sensors. Plus, as a worst case for a few hundred bucks you can change the entire thing out. Modifications are much easier with carb too. All the base EFI system can really account for over a carb system is altitude and temperature. Great in the automotive world, but how often do boaters change altitude? Temp, that's good too, but most of us boat in nearly the same conditions every weekend.

[BigGrizzly]

One other thing a short rotor eg too short not short circuit. In chevy's back in the day they put short rotors on some engines to slow them down. The old hot rod trick was to pit an early rotor on it.

[Ghost]

One other thing a short rotor eg too short not short circuit. In chevy's back in the day they put short rotors on some engines to slow them down. The old hot rod trick was to pit an early rotor on it.

Interesting. What's the effect of a short rotor and how come? Seems to me like it would make things run rough as much as weaker, but I have no doubt I just don't understand.

Mike

[Dr. David Fleming]

Yah, short!

Don't be caught short when the time comes.

I need a short rotor to do my thing!

[BigGrizzly]

What happens is the spark gap between the rotor and cap reduces the intensity at the plug. This is why you should always replace the cap and rotor at the same time. The truth is the rotor wears faster then the cap. This actually happened to my dads 40 foot cruiser going through the Mansquan inlet.We were lucky in that we made it out in time. Another friend of mine was with me at the time and he knew exactly what was happening. we flew down stairs and pulled the hatches and changed then one at a time, to keep the boat under power. Dad was so impressed that when we got back to the dock he took us all out to the Lobster Shanty for dinner.

[Ghost]

I'm totally with you about the intensity being reduced at the plug with a short rotor. The part I don't get is what that translates to.

If the spark is reduced enough, the cylinder will not fire at all. Mix in some of those with mostly successful fires and I'd think it'd be running rough, not smoothly but a little weaker.

But I assume I must be wrong about that given that people put in short rotors deliberately to drop the power a little. Dialing down the power by causing some misses seems nuts, so I figure that ain't it.

My thinking goes:

If the spark intensity is just enough, ignition happens. If not, it doesn't.

It seems to me like the range from "not enough to ignite" to "enough to ignite" would be pretty small. So, it'd be hard to even land in that range consistently. Just a little natural variation might create intermittent misses.

But it sounds like this is not so, and that there must be a wider range of spark intensities where there are "strong" sparks that ignite as well as a range of weaker sparks that ignite, and the weaker ones are not likely to miss but do produce a weaker stroke. And thus you can pick a rotor length that will put you squarely into the weaker-spark part of the spectrum, and the motor will run smoothly, but with a little less power.

I would not have guessed there was such a range of detonation strengths (and thus power in the stroke) based solely on spark intensity, with all else equal. It just seems like it would be near binary, ignition or not, with a sharp edge between. But the fact that people made short rotors suggests the range of detonations is far wider.

Am I getting this right, or am I completely off? (It's so counter-intuitive to me that I don't trust any assumptions I'm making.)

Thanks,

Mike

[BigGrizzly]

This reduced spark acts as a governor. Except it wears the rotor faster the shorter it gets. Most of what you said id correct. I once though I knew all this stuff, but the older I get the more I realize I don't know. Its a never ending learning curve. There isn't a day at Garry's that I don't learn something new, and I worked with Honda R&D.