Mercarb Issue?

I have a mercruiser 3.0 (2000) with a mercarb 2 barrel on it. Now the problem that I am having with it to me is a brain number. With the choke closed I can start the motor and have it idle at around 700 Rpm's and then slowly increase to 1000 RPMS as the motor warms up and the choke opens. Once the choke opens to a certain point ( I would say about 3/4 of the way open) the engine dies. So i would appear that there is an air leak and the engine is getting too much air. NOw in order to restart the motor I have to place the throttle at 3/4 throttle and when the engine starts I have to continually rev the engine to keep it running. After revving the engine it sometimes will allow me to let it "idle" at 2800 rpm. If it does this then I can return the throttle back to neutral and have the engine idle at 700 RPM's. I do not understand how one minute it acts fine (initial startup) then acts like it has an air leak and then returns to a normal idle????
I have tested all over the place for an air leak and have found none. The carb was rebuilt last year by the dealer, and was working fine. I have replaced the fuel pump and have tried running from an alternate fuel source. I am fresh out of ideas and fully frustrated.

Re: Mercarb Issue?

mudcat88 said:

I have a mercruiser 3.0 (2000) with a mercarb 2 barrel on it. Now the problem that I am having with it to me is a brain number. With the choke closed I can start the motor and have it idle at around 700 Rpm's and then slowly increase to 1000 RPMS as the motor warms up and the choke opens. Once the choke opens to a certain point ( I would say about 3/4 of the way open) the engine dies. So i would appear that there is an air leak and the engine is getting too much air. NOw in order to restart the motor I have to place the throttle at 3/4 throttle and when the engine starts I have to continually rev the engine to keep it running. After revving the engine it sometimes will allow me to let it "idle" at 2800 rpm. If it does this then I can return the throttle back to neutral and have the engine idle at 700 RPM's. I do not understand how one minute it acts fine (initial startup) then acts like it has an air leak and then returns to a normal idle????
I have tested all over the place for an air leak and have found none. The carb was rebuilt last year by the dealer, and was working fine. I have replaced the fuel pump and have tried running from an alternate fuel source. I am fresh out of ideas and fully frustrated.

Click to expand...

Ayuh,... A carb rebuild only lasts til the next time Crud is introduced to the fuel...

It sounds like there's crud restricting the Idle Circuit...

The choke partially closed is compensating for the restriction in the Idle circuit...

Re: Mercarb Issue?

Sounds like a blockage in the idle circuit. Pull the carb and strip and clean it. Use carb cleaner and DRY compressed air.

Re: Mercarb Issue?

And when you get it fixed, change the fuel filters and always use a fuel system treatment to keep things clean.

Re: Mercarb Issue?

Silvertip said:

And when you get it fixed, change the fuel filters and always use a fuel system treatment to keep things clean.

Click to expand...

Ayuh,... 'n if ya don't already have a canister type fuel filter,... Get 1, 'n plumb it in, ahead of the fuel pump...

Re: Mercarb Issue?

This is where I am confused then. If the idle circuit is blocked why does the engine return to a proper idle (700 rpms)after I rev the engine and keep it at 3000 rpms. I would think that if the circuit was blocked and the choke is fully opened then the engine would not idle and would die.

Re: Mercarb Issue?

mudcat88 said:

This is where I am confused then. If the idle circuit is blocked why does the engine return to a proper idle (700 rpms)after I rev the engine and keep it at 3000 rpms. I would think that if the circuit was blocked and the choke is fully opened then the engine would not idle and would die.

Click to expand...

Not unheard of for 'blockages'/dirt to move around... If enough fuel is getting passed the dirt it could run sometimes....

Chris........