Mercruiser 120 sputtering low rpm

[Nijkampr]

Hi all,
I just bought my first boat; a 1982 Panther with a Mercruiser 120 engine.
The boat was running great until we pulled into the dock where the engine was running poorly. While trying to figure out the problem, I pulled the idle screws out of the carb thinking it was a fuel problem. I later got the boat running again by replacing the points and consdenser. The ignission system is pretty much brand new as the coil and distributer cap have also been replaced.
However, it would appear that I messed things up when changing the idle screws. Here are the symptoms.
Boat idles great. No miss firing.
The boat pulls great from ~ 2000 rpm to full throttle.
When slowly applying throttle without load, the engine behaves as expected.
When stabbing at the throttle without load, I get a backfire through the carb and if I don't back off, the engine stalls.
Under load, you need to be very careful with the throttle until the engine rpm is high enough to not backfire.
I have done some searching online for idle screw adjustment but I haven't had any luck getting it back to the way it was.
Any ideas?
Thanks in advance!
Rob

 

[Bondo]

Re: Mercruiser 120 sputtering low rpm

Hi all,
I just bought my first boat; a 1982 Panther with a Mercruiser 120 engine.
The boat was running great until we pulled into the dock where the engine was running poorly. While trying to figure out the problem, I pulled the idle screws out of the carb thinking it was a fuel problem. I later got the boat running again by replacing the points and consdenser. The ignission system is pretty much brand new as the coil and distributer cap have also been replaced.
However, it would appear that I messed things up when changing the idle screws. Here are the symptoms.
Boat idles great. No miss firing.
The boat pulls great from ~ 2000 rpm to full throttle.
When slowly applying throttle without load, the engine behaves as expected.
When stabbing at the throttle without load, I get a backfire through the carb and if I don't back off, the engine stalls.
Under load, you need to be very careful with the throttle until the engine rpm is high enough to not backfire.
I have done some searching online for idle screw adjustment but I haven't had any luck getting it back to the way it was.
Any ideas?
Thanks in advance!
Rob

Ayuh,... Run it in to just snug, 'n back it out a turn, 'n 1/2 to start,... I don't that's all of the problem though,...

It sounds like the carb needs to be rebuilt, or replaced,...

 

[Nijkampr]

Re: Mercruiser 120 sputtering low rpm

Thanks for the reply.

Found my problem. Turns out that the points slipped and the gap closed. Once fixed the boat runs like a top once more.

 

[Silvertip]

Re: Mercruiser 120 sputtering low rpm

Did you check the dwell and timing? Anytime you change the points you need to check the dwell (point gap) and adjust the timing (in that order).

 

[Nijkampr]

Re: Mercruiser 120 sputtering low rpm

Did you check the dwell and timing? Anytime you change the points you need to check the dwell (point gap) and adjust the timing (in that order).

Thanks Silvertip. Did you see my response? It was in fact the dwell. I did not test timing as I did not turn the distributer. I am currently at the cottage and don't have all my tools with me. Is it recommended that I also check timing? If so, why?

 

[cedgo]

Re: Mercruiser 120 sputtering low rpm

A change in the point gap will also change the timing.

 

[Nijkampr]

Re: Mercruiser 120 sputtering low rpm

A change in the point gap will also change the timing.

That makes sense. Thanks guys.