86 OMC 3.0 Carb Questions.

[misiek]

I have a 1987 Thundercraft with a 3.0 OMC 140 HP engine. I am trying to troubleshoot the carburetor problems. The boat has starting problems I have to crank for quite a while to have it started. In order to start I have also to adjust the screw so the engine get some RPMS and warms up. Then the engine idles nicely but when I hit the gas it bogs down immediately with a slight pop from the fire arrestor. It takes some slight back and forth movement for the engine to jump into higher RPMS and from then it flies with no problems until I stop and restart again. Do I have a carb issues or timing issues. Please throw me some bones here. Thank you.

 

[proshadetree]

Re: 86 OMC 3.0 Carb Questions.

Sounds like you need to rip the carb down and clean it. Install a fresh kit and then check you timing with a light. Have you checked to see if the accell pump is working.

 

[misiek]

Re: 86 OMC 3.0 Carb Questions.

You mean if it squirts fuel down the barrels when I pull the throttle down?

 

[Big_Eddy]

Re: 86 OMC 3.0 Carb Questions.

Check the choke linkages. Assuming it is a Rochester 2 bbl, on the starboard side of the carb there will be a heat actuator unit and a vaccuum actuator.

Sounds to me like the heat actuator is not moving freely. With the engine cold, the arm should be almost horizontal to close the choke plate. Then when the engine warms up, the arm will drop down. I'll bet yours is stuck partly open making it hard to start cold. Manually move the arm to the horizontal position and see if the engine will start more easily.

The bogging when you go to accelerate is the same issue. When you advance the throttle past a certain point, it forces the choke to wide open. With the choke stuck partly open/closed everytime you give it fuel it bogs down. Push it over the stop and you're good until the next time the engine has to start cold. If you try to gently advance - it will bog and bog and you keep backing off. Ram it over - it backfires once and then it goes. (Or could actually flood and stall - but then will go after the restart)

To confirm this is the issue- after starting the engine from cold - warm it up at low speed - shut down - open throttle all the way then return to neutral - restart - problem should be gone.

Lubrication may be all that is required to free up the linkages.

 

[misiek]

Re: 86 OMC 3.0 Carb Questions.

I knew it had something to do with the choke. I've replaced the spring a couple months ago. I am having problems with setting it correctly. Any ideas how to set it correctly?

 

[Big_Eddy]

Re: 86 OMC 3.0 Carb Questions.

Lots of good information here.

http://www.oldcarmanualproject.com/manuals/Carbs/Rochester/2-Jet/Manual/MCarbRoch1973__2G.htm