1990 25hp Stuttering Johnson tiller

[redfury]

http://www.youtube.com/p.swf?video_...FyiU/2.jpg&t=OEgsToPDskKfyHLi24_lyOEt4FxHhPmq

That is a video of the engine running for those that have the "ear" for this kind of thing.

It runs great at WOT, but off idle as you can hear, as well as at idle, I get a stuttering problem.

I checked for spark, both cylinders are fine. I just got this boat from my dad and this spring and he only had initial start up issues with it. Once it's fired up, it starts back up just fine. Pretty strong motor when I was out with him, and ran strongly with my family of 4 in the boat. I'm concerned with the stuttering problem though as I don't want to damage this motor by ignoring the problem.

I have to get ahold of a manual, I know that much. I won't ever work on a boat motor without SPECIFIC instructions. I just want opinions on what I should focus on.

Oh, the water pump works without issue on the lake and on the muffs ( running low water pressure to avoid damaging the impeller ).

 

[tashasdaddy]

Re: 1990 25hp Stuttering Johnson tiller

got the this linkm scroll down and read the posts on decarbing the engine. you can use Seafoam in a spray bottle, and add to the fuel, no need to buy Deep Creep aerosol. same stuff. when were the carbs last totally cleaned and rebuilt with new kit. over all it doesn't run that bad.

 

[redfury]

Re: 1990 25hp Stuttering Johnson tiller

I dunno about when the carb was redone. I got the boat from my dad this spring and I know it hasn't been done for at least a couple of years and usage was minimal during that time.

I tried a different tank of gas today and it ran the same. I pulled the 2 plugs and found the upper soaked and the lower dry, but carbon coated. I also did not mention that you can feel a vibration once you start to increase RPM.

Is it possible that I may need to replace the reed valves if I'm fouling out one cylinder on a single carb engine, or would I foul out the upper cylinder before the lower on a poorly tuned carb? While the engine was running, I could see gas/oil forming at the lip of the carb ( outermost part ) within the bore. I'm leaning towards a carb problem, but the upper cylinder fouling makes me raise an eyebrow, along with the vibration ( though I suppose that could be from the one cylinder fouling out more ).