Engine Sputter at 1,500 RPM's

[jcupo6]

Okay fellas I need some opinions. My 1978-1982 120 HP Mercruiser has acceleration issue. If I accelerate quickly the engine will sputter and sometimes stall at 1,500 rpm. If I baby the throttle and get passed 1500, I can then gun the motor to WOT and everything is fine. The following is what I have done.

1. Switched carbs
2. Changed Fuel water filter
3. Changed Fuel filter
4. Changed back to a mechanical fuel pump - The PO installed an electric pump, which I hated!
5. Replaced fuel lines, and made sure nothing was clogged

None of this fixed the issue. I plan on changing to Pertronix Electronic ignition, change all plugs and wires, change distributor and rotor and check the timing. Is there anything else I should do or am missing? I think it's strange that the issue is always at 1500 rpm. Besides the sputter the motor runs solid and idles great. I run about 26-30 at 3000rpm at WOT which is low, but I think this is a prop issue as the original motor was a 140hp engine and I have not changed the prop yet. Sorry for the long post, just trying to cover all the bases and be as clear as possible, thanks in advance for the help!

 

[EddiePetty]

Re: Engine Sputter at 1,500 RPM's

the timing. ......... I think it's strange that the issue is always at 1500 rpm............

....hum, same engine speed, consistently misbehaves?

Sounds like the mechanical advance is sticking to me.

Hook up the muffs and a timing light to verify

 

[jcupo6]

Re: Engine Sputter at 1,500 RPM's

Will do, thanks for the reply. We did look at the spring, which wasn't seized and seemed to be okay but I will take another more detailed look!

 

[jcupo6]

Re: Engine Sputter at 1,500 RPM's

Update:

Cleaned carb and replaced the fuel accelerator, the engine sputter issue is no more! The boat now takes off without any issues.