90 horse carb problem???

[backwater dawg]

I have a 90 horse Force powerhead in a 1994 Merc sport jet---starts great-idles great-the problem is as I try to get on plane--It just seems to lack any power-this boat 1 month ago ran great so it just changed?? It seems to be a gas problem--seems to be a gas stavation issue---could 1 carbs float be sticking??? Any ideas??? Thanks

 

[QuadManiac]

Re: 90 horse carb problem???

Verify spark to all 3 cylinders. Look to see that all 3 butterflies open fully horizontal at WOT. Check your plugs and run a compression test while they're out.

Pull your cowl, see if problem persists. If it goes away, you have an exhaust leak into the powerhead area that's starving the engine of air.

If all these pass, then start looking at the more esoteric problems: fuel pump, carbs, stator, coils, etc.

Good Luck!

 

[jkp1]

Re: 90 horse carb problem???

I have the same problem on the same engine. Starts great, runs smooth just no power when you open it up. I'm on a 14' Sea Rayder which should be hitting 40 mph. Right now can only hit 28. Slow to get out of the hole as well.

Pulled the plugs, 1 & 2 were carboned up pretty good. #3 was very clean Replaced plugs & fuel filter - only saw a 1 mph improvement.

Good spark to all three plugs. I pulled the wires of each and noticed a corosponding drop in RPM & roughness each time.

Don't have a compression checker but the "thumb test" showed impressive compression out of each hole.

Inspected throttle advance on each carb and they are all advancing properly. I did not remove cowling or confirm the butterflys are in fact opening.

Could I be looking on the wrong end? The impeller looked OK. No damage or fouling but I did not remove it.

I'll pull the cowling and check the butterflys. Assuming thats OK, what should be next?

 

[QuadManiac]

Re: 90 horse carb problem???

Without a real compression test, all other troubleshooting may be a waste of time. My 'calibrated' thumb can't tell the difference between 150 and 80 PSI, but your engine's performance sure will.

#1 plug being so clean could be the result of 'steam cleaning' due to water getting past a leaky head gasket.

 

[jkp1]

Re: 90 horse carb problem???

Just an update. I checked the butterflys, they are operating properly. Opening the cowl did not make any improvement.

Trying to track down a compression tester.

 

[tnfreebird]

Re: 90 horse carb problem???

Hey J, I finally found you!

At the risk of being redundant, I questioned on another thread the fact your 90 powerhead is a Force. I had an F14 with a 90 and assumed, perhaps incorrectly, that it was a Mercury powerhead.

It doesn't matter at this stage of the game as it relates to your problem, but no doubt it will come into play later.

 

[jkp1]

Re: 90 horse carb problem???

Well, compression is good,

Cyl 1 = 155
Cyl 2 = 150
Cyl 3 = 145

Kind of backs up the sellers claim that the powerhead was replaced in 2003 and the boat only has 20 hours on it since then.

Saw another thread which suggest disabling the rev limiter. Disconnected the black & yellow/black wires but no change in performance.

I guess the only thing left is either the carb high speed jets or the ignition system. Based on what I've read, I bet the magnets on the flywheel, stator or trigger are messed up.

B.O.A.T. = Break Out Another Thousand

 

[backwater dawg]

Re: 90 horse carb problem???

Well---I started this and now I figuged mine out---A BIG HOLE IN THE MIDDLE PISTON---we all need to remember" A BOAT IS A HOLE IN THE WATER INTO WHICH WE THROW $$$$$$--oh well--I'm just going to replace the one piston and see how it runs--after all its a 1994 and if I'm going to spend any big $$$ on it I'm going to increase HP somehow--any suggestions---Thanks

 

[jkp1]

Re: 90 horse carb problem???

Hole in the piston? Sorry to hear that.

My guess is the offending cylinder was leaned out too much. Suggest you consider replacing all pistons, otherwise compression will not be balanced hole to hole.

 

[jkp1]

Re: 90 horse carb problem???

I may actually have a carb problem. Pulled off the bottom carb and and broke it open. What a mess! Reddish rusty grit and orange jelly stuff throughout.

I'm giving it a soak in carb cleaner, will hit it with compressed air and reinstall tomorrow. Keep your fingers crossed.

 

[bowhuntrrl]

Re: 90 horse carb problem???

I may actually have a carb problem. Pulled off the bottom carb and and broke it open. What a mess! Reddish rusty grit and orange jelly stuff throughout.

I'm giving it a soak in carb cleaner, will hit it with compressed air and reinstall tomorrow. Keep your fingers crossed.

You better do all your carbs or you will have further problems.

 

[backwater dawg]

Re: 90 horse carb problem???

Yep---I think I figured out mine--middle cyl was prob clogged up and ran to lean--over time burned the top layer off the piston--I am going to put it away for the winter(up here the lakes freeze solid from Nov to early April) and over the winter replace all the pistons-rebuild all 3 carbs--any other suggestions???? Thanks

 

[jkp1]

Re: 90 horse carb problem???

Sure enough, it was the carb. Yesterday, top end was only 28mph. Cleaned the suspect carb last nite and reinstalled today. Top end is now 39 mph.

And here I was thinking it was the ignition. Hope I didn't lean out the cylinder too much. Will clean up the remaining carbs this winter.