305 mercruiser 898

[inflagstaff]

I have Rochester 2bbl carb. that is running very rich and this fouls the plugs up. The float valve is set correctly and the needle valve can be shut down completely without shutting the motor down. The carb is clean, overhauled and the plugs are new. I suspected a vacuum leak at the base of the carb but I recleaned it to no avail. Still runs very rich and the needle valve can be screwed in all the way without shutting off the motor. Any ideas?

 

[Bondo]

Re: 305 mercruiser 898

I have Rochester 2bbl carb. that is running very rich and this fouls the plugs up. The float valve is set correctly and the needle valve can be shut down completely without shutting the motor down. The carb is clean, overhauled and the plugs are new. I suspected a vacuum leak at the base of the carb but I recleaned it to no avail. Still runs very rich and the needle valve can be screwed in all the way without shutting off the motor. Any ideas?

Ayuh,... A vacuum leak causes a Lean condition, not rich...

My guess is the carb is Junk, or ya ain't rebuildin' it right....

Unless it happens in a fully equipped reman shop,...
Carb rebuilds are a 50/ 50 shot, at Best...

 

[inflagstaff]

Re: 305 mercruiser 898

Ya it was done at a professional shop..just trying to think of another issue I could be missing.

 

[Bondo]

Re: 305 mercruiser 898

Ya it was done at a professional shop..just trying to think of another issue I could be missing.

Ayuh,... Mechanical fuelpump diaphram torn,..??

 

[inflagstaff]

Re: 305 mercruiser 898

I think the clue here is the needle valve closing all the way and it does not shut down the motor

 

[gulfvet]

Re: 305 mercruiser 898

are you talking about the low speed adjustment? If so, you won't be able to adjust it until the motor is warmed up. I had the same problem after a re-build and it ended up being a weak coil and the valves needed adjusted(intakes not closing all the way) A rich condition can be so many things. To check for a vac leak, spray some carb cleaner at the base of the carb when it's running and if you get a fog out the exhaust or it stumbles you got a leak. But start with letting it warm up before you try to adjust that low speed. Sounds to me like you don't have a hot enough spark to completely burn that fuel.

 

[franktrav]

Re: 305 mercruiser 898

I think the clue here is the needle valve closing all the way and it does not shut down the motor

at idle?
then your carb is leaking gas internally....look for gas dribbling/running from boosters at idle...
or if too much of the idle transfer slot is exposed beneath the throttle blades,,,the needle valve will not have much of an effect on the idle...this is more likely with a hot cammed motor that needs a slightly higher idle speed ..

 

[greg82255]

Re: 305 mercruiser 898

I had the exact same problem with the needle valve on the exact same motor, 898 with a rochester 2 bbl. It turned out that the rebuild kit came with 2 different needle valve o-rings, and you need to use the thicker ring. I used the thinner one at first and the motor ran alittle rich, and the needle valve did not close all the way and fuel still leaked in even when the motor was turned off. I installed the thicker o-ring and the problem was solved.