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View Full Version : loss of 700 rpm??



HyperDonzi
07-28-2002, 08:14 PM
earlier this season, i was pushing 5200rpm at wot. the other night i was only able to pull 4500. this is a 4.3l merc. engine. the boat did sink july 2 2000. i am thinking of trying that carbon buster. anyone else have any suggestions?

mattyboy
07-28-2002, 08:18 PM
think it could be the weather??

HyperDonzi
07-28-2002, 08:33 PM
well, it has been hotter and more humid, but do you think 20 deg will +/- 700 rpm? if so i will now be doing my boating in 30deg temps...

MOP
07-28-2002, 09:13 PM
If all else checks out like good spark secondary barrels opening if you have a four barrel no funny sounds ETC. Maybe you should check compression, a sinking that far back should have shown up bad stuff long before this.

HyperDonzi
07-28-2002, 09:18 PM
new platinum plugs (less than 5hrs) only prob is a tach that shows i am at a few k rpm at idle, knocking on glass fixes this problem tho. it is a 2 barrel, how do i check compression?

MOP
07-29-2002, 07:28 AM
When checking compression I like to crack the spark plugs loose then just snug them back in with the engine cold. Run it at 10-1200 till up to atleast 140, shut it down ground coil, easily pull Hot plugs, set carb to full throttle, check and record each cylinders reading. With 4 strokes a 25% margin between readings is acceptable. Usually if I find the readings all over the board but within the 25% I will run carbon buster through. Raw water cooled engines, especially ones that have long canals to idle down seem to be the worst for cold stuck rings. Recheck compression usually you will see improvement. I do my engine just before layup, I do all of my engines once a yaer no matter what. My once of prevention!

MOP
07-29-2002, 07:30 AM
P.S. use a decent screw in type compression gauge.

rong
07-29-2002, 08:10 AM
What's your recommendation on a carbon buster?

HyperDonzi
07-29-2002, 09:29 AM
how much is a compression gauge? ill check at the local dealer.

carbon buster gets the carbon off carbon stuck rings, from what i understand, it will not hurt to run it im guessing it is like dry gas but i have never used this before.

MOP
07-29-2002, 03:24 PM
Carbon buster is extremely caustic, it will burn paint off, burn your skin, not real quick. You must follow the directions and hose any residue off of you and your machinery. It will clean carbon off piston tops un-stick carbon stuck rings (NOT SCORE STUCK RINGS)it will generaly eat most all the carbon off everything in you engine. If you suspect carbon stuck rings you must use a squirt oil can if it does not have the squirt tube with the can to shoot it into the cylinders and it has to sit over night for it to be able to work its way into the ring groves. the next day you will have to spin it over with the plugs out. Good idea is to get rags in place so it does not shoot all over you compartment. And make sure you hose down good, you absolutely must change the oil and filter afterwards or it will eat things it is not suppose to. It is really great stuff but you must be carefull with it. I have land in Costa Rica, I bring several cans down each year and do my friends and relitives motors they think its magic. They have lousy gas down there.

HyperDonzi
07-29-2002, 07:05 PM
i think it was your post earlier this month that got me thinking about that. lot more than shooying a bottle of stuff down there. i will wait till the end of the season.

MOP
07-29-2002, 10:12 PM
Some things are better done before things gat any worse. If it spooks you try to find an outboard tech most all of them use it on a regular basis if they are worth thier salt. If its not on thier shelf and being used Don't take your boat there for repairs.

Moody Blu'
07-30-2002, 01:59 AM
wow thats some good info, wink

rong
07-30-2002, 08:56 AM
M.O.P. - What do you think about the spray in while running de-carbon, as maintenance if the gas your running is good? Is the method your talking about the only one that works?

HyperDonzi
07-30-2002, 10:40 AM
rong your thinking just like spraying fogging oil for winterization.

MOP
07-30-2002, 02:06 PM
For regular de carbonizing follow directions on can most say let sit 30-45 minutes, for serious stuff let it sit longer or do it again. Just remember if left in the engine for longer than the can directions change the oil and filter. It runs about $6-10 a can depending on whos brand on alot of things it is pretty amazing on other things no change, usually have to explore the problem deeper.

harbormaster
07-30-2002, 03:36 PM
MOP,

Got any tricks for cleaning out a radiator or engine waterjackets?

MOP
07-30-2002, 07:38 PM
Is that thing still cooking? I would not think that you would have much junk in the block. From what I have been told most of what plugs up radiators is mineral build up. Calcium, sulfur, you name it. Ok did you pull the thermostat and try it? Is the clutch fan Ok? did you remove the belt or belts start it and watch for bubbles in radiator, you can not check for air with the belts on they whip up the water, it should be done cold with clear water. Did you pressure check system? Ok on to my thoughts have you tried to check for a lean condition? All that clattering noise kinda spooks me, hsd the engine gotten hot already by the time you tried flooring it. If not maybe get it to a shop theat can put an exhaust probe in the pipe and give you a yeah or neah on the lean thought. A lean engine will get hot pretty fast.

HyperDonzi
07-30-2002, 08:07 PM
now today, yet another problem....
accelerating, no waves, trim down and suddenly theres no load on the engine. i turn the key off immediatley. is there some way the drive may have gone into neutral for a few secs? i know the throttle wasnt in neutral.

MOP
07-30-2002, 08:46 PM
When you re-started it were you able to idle back in or did you have no drive power at all?

MOP
07-30-2002, 08:57 PM
More questions, did it go into gear and work Ok afterwards? You had an overheat, a commonly overlooked thing is to inspect the shift cable to the drive. I have seen it get ruined by a hot exhaust, we all know that Mercs an OMCs have to maintain good cable adjustment. If the cable gets burned (melted housing) It can and will eventually screw up and you will blow the clutch dog. before you run it again feel the cable carefully down near any hot parts, if it feels rough change it out and re adjust you settings. Please use the book and measure carefully. This may not apply in your case but anyone who overheats should check the cable to the drive. This just happened about a week ago to a fairly close Bud.

HyperDonzi
07-30-2002, 08:59 PM
it worked to get back, where is this cable at? i dont have thru hull if your thinking about that.

MOP
07-31-2002, 12:00 AM
If you have a Merc or OMC the cable goes down and through the transom shield, usually routed down next to the exhaust left side looking from the cockpit toward the transom. Just run your hand down the shift cable to where it goes out of sight, it should be smooooooth along its length. No bubbles or flat spots its plastic and does melt on occasion.

MOP
07-31-2002, 12:09 AM
Ok I did not mention Volvo, it also has the same basic setup. But for some reason maybe the cone shift can have a pretty ratty cable and still work fine.

P.S. If the cable appears to be good check your ajustment carefully, like I said the clutch dog and usually the forward gear will give up the ghost it must engage fully. I go just a little extra by going 1/2 turn more on the cable adjuster further into forward, a slight pre load some will argue the point but I have done it for years.