1985 18HP sputters at idle and full throttle

[bhgkiks]

Symptom:
Motor starts fine. It has trouble idling, and when i am putting around it runs good but has an occasional JOLT or short SPUTTER. It sounds like this mmmmmmmmmmmmDUNKmmmmmmmmmmmmmmmmmDUNKmmmmmmm and the motor violently shakes ONE time on the 'dunks'.

It will continue to run fine like this but when i apply full throttle it sputters and never develops full speed.

Under no load it will go to full throttle. In reverse, it will go to full throttle although i dont keep it there for very long and it may be just b/c there isint as much load on the motor.

Ok, attempted fixes:
Inspected plugs and spark coming from both.
Cleaned Carb.
Changed fuel tank, added glass filter so i could watch fuel flowing through.


Dont know what else to do?

I am sort of maybe suspecting an igntion problem but i dont SEE anythign out of the ordinary. It all looks good from the naked eye. COuld it be as simple as de-carbing the motor???

Thanks in Advance!

 

[bhgkiks]

Re: 1985 18HP sputters at idle and full throttle

OK, got an update on this one:

Top cylinder has 127psi of compression
Bottom cylinder has 123psi of compresion

Both plugs spark like crazy when i test them against the block.

I have removed the ground wires for the coils and the powerpack to clean them and reinstall.

I have also removed the carb for a 2nd time to see if there was anything i missed.

Any suggestions???

Hellooooooooooooooooo, anybody? ? ? ? ?

LOL
Thanks!

 

[tashasdaddy]

Re: 1985 18HP sputters at idle and full throttle

does it feel like maybe the engine hit something. if so it sounds to me like the clutch dog is bumping out of gear. this is the item in the lower unit that moves between the forward and reverse gears, when they get worn on the forward side, and you are cruising, it feels and sounds like you hit a log. doing it a full throttle is what leads me to this. if it were and idle cough or sneeze, then is would say it's running rich or lean. but doesn't sound like it.

 

[bhgkiks]

Re: 1985 18HP sputters at idle and full throttle

No, it feels more like a momentary depression of the kill switch. It never makes it to full throttle, and it doesnt do that exact same thing trying to get there. Its more like a long bog when I open up the throttle. I have tried choking the carb(by putting my hand over the inlet) when the throttle is wide open and the motor is bogging, and that doesnt really seem to change anything.

It could be a rich/lean condition but when i pull the plugs they dont show a drastic color either way. I am starting to wonder if its one of the coils.

Anybody got a way to test them other than to try a new one?

does it feel like maybe the engine hit something. if so it sounds to me like the clutch dog is bumping out of gear. this is the item in the lower unit that moves between the forward and reverse gears, when they get worn on the forward side, and you are cruising, it feels and sounds like you hit a log. doing it a full throttle is what leads me to this. if it were and idle cough or sneeze, then is would say it's running rich or lean. but doesn't sound like it.

 

[frednick1]

Re: 1985 18HP sputters at idle and full throttle

Hi,

I only have anecdotal advice.

I have a Mariner 90HP that did the same thing. It started, ran ok but coughed and wouldn't get up to full power at full load.

After much diagnostic brain twisting, I was told by these guys and it turned out to be that I needed a new power pack which I got (used) on eBay for 40.00.

Now it runs like a champ.

I bought another used power pack to have in reserve for 40.00 just to have in case the first one was a dud. Still less than a new on at the marina store which was 225.00. Probably would have been 500.00 if they fixed it. So, these guys saved me a bundle.

I did replace the coils, too. Just for fun. But I am sure it was the power pack. Everyone said it was probably not the coils.

Good luck.

frednick1