Holly Carb Question

[raritan]

I have a 650 double pumper on a 350.... At about 4000rpm it acts like its hit a rev limiter. It just wont go any faster. I put another single pump holly and its fine. The throttle plates are fully open. What could be the problem.

[Gearhead99]

The float level is too low.
Do the secondary throttle plates open too??

But, I would lean toward the float level too low.

What jets are you running??

[Donzified]

Carefull! if your running out of fuel you may be running too lean. To lean too hot.Too hot ...to bad.
The float leavel is easy to adjust. They sell clear inspection screws to replace the solid brass ones on the side of the carb.
The jets are easy also. Buy the more expensive re usable gaskets.
My 650 doulble pumper on the 350 started with size 66 jets primary,76 jets secondary. After upgrades I switched to 76 and 86, way to large.I am now runnig 68 and 78. I could go back with 66 and 76 but don't want to get too lean.
The holly takes time to dial in but once you get it right nothing gives you the responce the double pumper gives up right now!

[raritan]

I have had the float at every level you can think of. The secondarys fully open. Could the power valve cause this.... I really appreciate your help. This caused me a lot of headaches last summer. This engine is stock except for balancing and 60 over. What jets would you 350 people recommend and also where can I get the jets. Please let me know your thoughts on the jets and power valve.
thanks

[Rootsy]

Doubt it is the power valve, when they rupture you get an extremely rich condition. Are you getting fuel from the bowl to the venturi's? Are you sure that the needle and seat aren't sticking? Does your carburator have the filters in each bowl behind the fuel line fitting? Make sure they aren't plugged. Is the bowl vent unobstructed? If the throttle plates are fully opening you should see fuel spraying out of the main jet discharges on all 4 venturis, they should be even right to left, not necessarily front to rear depending on jetting. if you are seeing a lack of fuel you probably have a blockage somewhere along the line eh. Set the floats with the boat in the water. The fuel level should be right to the bottom of the sight plug. If the carburator has been apart or rebuilt make sure that no one bent the float arm... the float has a set height that should be checked whenever rebuilding. the float may be at the correct level but if the arm is bent the wrong way it'll hold the needle on the seat and the other way it'll have the needle off the seat too long and if too extreme, fuel pouring out of the vent tube on top. are you sure that the carburator doesn't have any vacuum leaks?

600 CFM dual feed, vac secondaries, 350, damn near stock.. 68 front 74 rear for jets... can't really go by those numbers but it'd be a starting point, no two carbs and engines are the same and the only way to tell is change em run and do a plug check... you can get everything ya need for your holley @ summit.com or jegs.com or a local speed shop if you have one near you...

[raritan]

This carb has mechanical secondaries..... Do you happen to know where on the net I might find a blowup of this carb. I believe it is a 4160... The boat is in storage for a few weeks so I am going biy memory.

[Donzi Dreaming]

If you have a speed shop close to you you should be able to get all the parts you need plus a diagram. I believe a diagram comes with a rebuild kit if you had to buy one- they usually go for 20-30 bucks. Also, while you are getting the carb set up coat the gaskets with a light coating of vaseline. It will keep the gaskets from sticking.

John

[Gearhead99]

One more far out one. Make sure that the float has "float drop" too. If the float isn't allowed to drop it can have the correct level, but won't drop enough to allow enough fuel to get by the needle and seat to refill the bowl fast enough.

It is adjusted by the tang on the float.

[Rootsy]

holley.com has blowups and rebuild directions in their tech section on just about all of their carburators... you can print em off there. for free

[Donzified]

I have been known to pound down the float arms by playing in the rough stuff. This has happened twice in ten or so years.Find the best carb rebuilder you can and pay the man.

[raritan]

I assume the jet sizes that you have given me are the Holley jet numbers and not the actual diameter of the hole in thousands.....is that correct. Also should I use genuine holley parts or does it make any difference. I am using a 6.5 power valve. Is that about right.
thanks again for the help

[Rootsy]

yep those are the holley numbers for the jet sizes... the 6.5 power valve pretty much comes standard in most rebuilding kits... doesn't mean it is correct for your setup though

[Blewbyu]

Read those plugs first.If you don't know which color means what,number them as you take em out,and have your favorite mechanic analyze them for you.
Agree with above-have it rebuilt by someone with a decent rep.Do NOT pay ANYBODY $400.00 to rebuild it like most shops charge.Local machinist or speed shop should do it for less than $150.00.
MONEY WELL SPENT!!!!!

[HELLERBOY]

gota love them,gota hate them.

[BillG]

Had the same problem a few years back. Take the sintered bronze filters out of inlets to the bowls. They may look clean, but they could be dirty. It worked on mine and the trouble never came back.
BillG

[JimG205]

Power valve will only affect acceleration,had that problem on my ski nautique with a 4160.ONLY use holley parts,your asking for problems with non holley.My money is on the float height or stic :D king needle float valves.The 4160 is a great carb! eek!

[Jamesbon]

I had an identical problem a few years ago. After trying everything in the book, I changed the ignition coil. Wa-La! That was it. The coil was too weak to produce good spark when the engine was under load and sounded like it was hitting a rev limiter. Just a thought...

Grab another coil from your buddys car or boat and give it a try.

Do you have points?

If you do decide to have a professional re-build the carb., I would suggest sending it to Nickerson Performance (http://www.nickersonperformance.com/marine/marine.html). They do the majority of HOT marine carbs on blower motors and naturally aspirated marine engines in the performance market. It'll cost you $250.00, but they completely tweak your carb. to your specific engine, then it's flow benched so there's NO more guessing. When you get it back, you simply bolt on and set the idle.

[AVickers]

One other thing...

Mechanical Secondary Carbs are very sensitive about the secondary accelerator pump. It makes a BIG difference if it's not working correctly.

Also, if I remember correctly, there's an idle/midrange circuit on the secondaries of the 4160. Make sure they're not plugged up.

I've got a mechanical spreadbore in the garage...I'll take a look at it tomorrow to see if there's anything else that could be fouled up.