92 OMC 4.3 running rich

[jdoane3414]

Hello,<br />I have a 1992 OMC 4.3L that has been running very rich, producing black smoke all over my swim platform. I have replaced the two fuel filters(canister and the small basket filter in the carburetor), put new plugs, wires, cap, rotor and it is still smoking at low RPMs ( < 1500 RPM). <br /><br />I just noticed yesterday that I might have a caburetor float problem. After running my engine for a while the temperature rises but my float does not open. On the side of my carburetor is the controller for the float but unless I am at high RPM's the float remains closed. Should this float open when the engine is warm? <br /><br />I also noticed that there is a missing vacuum line on the starbort side of the carburetor. There is a fitting for a hose but the hose is missing. The fitting is also pulling air in. Does someone have a similar engine they can look at to see if they have a hose there and if so where does it go?<br /><br />Thanks for the help!<br />Jeff

 

[JB]

Re: 92 OMC 4.3 running rich

Hi, Jeff.<br /><br />Welcome to iboats. <br /><br />Check out our menu. We have fora for just about everything to do with boating and a few that have nothing to do with boating.<br /><br />This forum is for discussions about outboards that do not include problems or repairs.<br /><br />Since you have a problem, and your engine is not an outboard, there must be a better place to post your question.<br /><br />I will move this to the I/O and Inboard engines forum.

 

[deputydawg]

Re: 92 OMC 4.3 running rich

Float open? You probably mean the choke. In case your not familiar with carbs, the hole on the top or the air inlet of the carb has a plate or butterfly valve that can close and shut this opening off. It is designed to close during cold temps allowing less air and more fuel to enter. When it warms up, usually after 3 to 5 minutes running time or less it should open. <br />Some here will disagree with me but after you get the engine warmed up, shut it down. Open this butterfly valve and prop it open. I like using clothespins for this, the wood won't scar anything and they will clamp so you won't lose it. However you can, prop it open securely so as not to obstruct the opening. Put the spark arrestor back on and run it to see if it helps. If it helps you need to adjust the choke, it is an easy thing to adjust. <br />Post again and let us know how it goes.<br />Oh yeah, I almost forgot, never ever ever look straight down into the top of the carb while it is running. Never have any body parts or clothing over the top either. Carbs have a habit of backfiring at the wrong time and this can cause serious burns!

 

[jdoane3414]

Re: 92 OMC 4.3 running rich

Thanks for the suggestions deputydawg. Sorry about the typo, I did mean the choke. The choke is down all the time. <br /><br />When I prop the choke open with a screwdriver my engine seems to run a little smoother. I'm not sure about the smoke. I've already winterized my boat but I will definitely try the clothespin in the spring to see if the boat still smokes.<br /><br />I was hoping I could find someone that has the same engine and could see if I was missing a vacuum line or some line that helps the carburetor open the choke.<br /><br />Thanks,<br />Jeff

 

[Lou C]

Re: 92 OMC 4.3 running rich

Which carb do you have, the 2bbl or 4 bbl Rochester? My 88 4.3/4bbl has a spring mounted in the intake manifold that opens the choke as the motor warms up. There is a vaccum pull off diaphragm that is supposed to pull the choke open a fraction so it will keep running during a cold start. The things you can do is to replace the spring and make sure the vacc break works, the linkage has some adjustment in it. The 2bbl has a different system. See if you can get ahold of an OMC shop manual, that will spell it out for you. You may also have to adjust the idle mixture if it still runs rich after fixing the choke.

 

[deputydawg]

Re: 92 OMC 4.3 running rich

I figured you meant to say choke.<br />There might be a round mechanism mounted on the side that the choke shaft runs into. The end of this should have a black cover with 3 screws holding it. Loosen these screws and turn the black plastic cover, this will loosen or tighten the choke spring which is attached to the plastic. A rule of thumb is when the engine is warm, or on a hot day the choke plate should be open with no tension from the spring. It should be turned so the tension to close is just releived.

 

[Don S]

Re: 92 OMC 4.3 running rich

You have either a Holley 4 or 2 bbl carb on that year engine. The only vacuum line that I can think of on either carb would be one shown in the picture below. The arrow is pointing at a plug that goes over the fitting.<br />You also have an electric choke coil. Make sure you have power to it. It usually gets power from the AC tap off the alternator. If the choke coil is bad, you need to replace it. <br />Another thing that can cause problems with the Holley carb is a bad power valve. It will cause idle ploblems and smoke if bad. They can go bad with just a backfire<br />But before you get into taking the carb apart, get a manual.<br /><br />

 

[jdoane3414]

Re: 92 OMC 4.3 running rich

Don and others,<br />Thanks for the information. I wasn't sure if I had a Holley or Rochester 2-bbl but the more I look at it and comments from Don I'm pretty convienced it is a Holley. I found the section in the shop manual where they talk about choke thermostat adjustments. I think that might be the source of my problem. I do not recall seeing any wires attached to the choke but I will have to look at this again in the spring. If there is supposed to be a plug on that line in your picture, I might be missing that as well. Hopefully the spring will come soon! <br /><br />Thanks again for all the suggestions.