Mercruiser 3.0L Hesitates 1200-2100RPM

[sprobst]

I have a 1998 Mercruiser 3.0L (with a Merccarb carburetor) that idles fine (both in gear and in neutral). It also runs fine at cruising speed above 2100 RPM. But, anywhere in the range of 1200-2100RPM, it'll hesitate and slowly lose RPM (at which point I will have to increase or decrease throttle to keep it running). When throttling up from an idle zone, I can't really do it gradually. I have to throttle up quickly past 2100RPM or so. Then, I'm fine. Quick acceleration is fine. Gradual acceleration from idle is not.

Mostly, I've been living with the issue, but lately, I've been thinking about researching the possible cause. I'd be interested in any opinions on what I should check/replace first. I would think a carb rebuild would be my last resort.

 

[bigdan1]

Re: Mercruiser 3.0L Hesitates 1200-2100RPM

a carb rebuild is your solution ....

probably a stuck power piston in the bore ....

 

[EddiePetty]

Re: Mercruiser 3.0L Hesitates 1200-2100RPM

"Quick acceleration is fine. Gradual acceleration from idle is not."
....sounds more like a sticking mechanical advance in the distributor. Put an adjustable timing light on 'er and prove me wrong.

 

[fishrdan]

Re: Mercruiser 3.0L Hesitates 1200-2100RPM

anywhere in the range of 1200-2100RPM, it'll hesitate and slowly lose RPM (at which point I will have to increase or decrease throttle to keep it running). When throttling up from an idle zone, I can't really do it gradually. I have to throttle up quickly past 2100RPM or so. Then, I'm fine. Quick acceleration is fine. Gradual acceleration from idle is not.

Sounds like carb rebuilt time to me. Here's my SWAG, pumping the throttle between 1200-2100RPM shoots more fuel into the carb (accelerator pump), curing the loss of fuel/lean condition. Could be a fuel delivery problem too, carb running out of fuel. Have you checked the fuel filter(s) yet? There is a sticky at the top of this forum for testing a fuel system, might be worth looking at.

Checking the distributor weights as EP suggested is pretty quick and easy, take you all of 5 minutes to pop the dist cap, rotor and cover plate. Actually, turn the rotor by hand and see if it operates smoothly back and forth, no binding, and that the advance springs pull the rotor back.

 

[sprobst]

Re: Mercruiser 3.0L Hesitates 1200-2100RPM

I will attempt to manually rotate the distributor rotor, next chance I get. This is an interesting idea that I hadn't thought of. That would be easy to check.