OMC 4.3 still with idle issues

[welch181]

Ok guys, still need a little help here. I have a 93 OMC 4.3. Ran great up until about 3 weeks ago. Coming back to ramp, when slowed to no wake speed, engine stalled at idle. Started back had to feather throttle to keep from stalling. Thought it was a spark plug problem. Changed out plugs still will not idle less than 1000 rpms. Changed fuel filter, changed wires, tested ignition module, still will not idle less than 900 rpms, and that is really rough at that speed. Compression is good on all cylinders between 135 and 145 on all. Engine still runs great at anything over 1000 rpms, purrrs like a kitten, still reaches 4400 at WOT.

Started looking around the carb, pulled vacuum hose from the auto choke, doesnt change the idle at all, covered air intake on side of carb, doesnt change the idle at all.

So what am I missing here, what should I check next? Should pulling that vacuum hose make the idle change? Should covering the air intake make it change?

Kinda stumped on this one, needing some help, boat has had to sit the past 3 weekends, not happy

 

[skeat]

Re: OMC 4.3 still with idle issues

Not really sure but I have the same engine and have worked on it somewhat. It might just need a rebuild. some dirt could have messed up just the low idle end of the carb which is why it runs fine at higer rpm's. There are 2 separate systems (?) in the carb, one for idle and the other when the throttle plates are open.

Shawn

 

[Bondo]

Re: OMC 4.3 still with idle issues

Ayuh,....

It sounds like some Crap has invaded your carbs low speed circuit,....

Tear it down,.. Soak the hard parts in carb cleaner,.. Blow out all the tiny passages with compressed air,+ Reassemble it with the new parts provided in the carb kit.....

 

[welch181]

Re: OMC 4.3 still with idle issues

Thats about where I was at, was hoping for a different answer, lol. Is there any other way to clean the idle circuit, I noticed today that changing the mix screws causes a change in idle, at least something makes it change. How difficult of a job is a carb rebuild? Have never tackled anything like that but am fairly mechanically inclined and could probably get it done, is there a lot that a novice can screw up during the rebuild??

Thanks,

 

[achris]

Re: OMC 4.3 still with idle issues

I would also be looking at exhaust manifolds. If they are still original, then take them off and have them pressure tested... A small leak can cause water to be pulled back into the combustion chamber, particularly at idle. I hope the problem is just the carb.... But check everything else too....

Chris...........

 

[skeat]

Re: OMC 4.3 still with idle issues

is there a lot that a novice can screw up during the rebuild??

Thanks,

Just buy a rebuild kit for that carburetor, a can of gumout spray and follow the instructions. Take your time taking it apart and keep everything clean (write notes if you need to). If you've done other mechanical work then it shouldn't be difficult at all.

 

[achris]

Re: OMC 4.3 still with idle issues

Just buy a rebuild kit for that carburetor, a can of gumout spray and follow the instructions. Take your time taking it apart and keep everything clean (write notes if you need to). If you've done other mechanical work then it shouldn't be difficult at all.

I've found a cheap digital camera is now permanently on my work bench. Fantastic for 'as you go' photos....

Chris..........

 

[chiefalen]

Re: OMC 4.3 still with idle issues

Wait a second here. It is not all that easy to rebuild a carb.

Float has to be set correctly. It's a precision piece of equipment, that must run perfectly for the boat to run correctly.

If i were you i would take the carb to a pro. must be somewhere near you a pro carb rebuider.

Then i would clean all the fuel filters on the boat. So it don't happen again.

Maybe the guy will teach you how to rebuild it so then you can have the knowledge to perform the task yourself.