Thread: 25 hp johnson runs 1/2 throttle,than makes strange sound if you go full throttle

Sounds to me like the timing is not advancing. That is all located up under the flywheel. The chatter sound, funny noise you hear is the air fluttering past the carb plates, plenty of fuel and air, but will not run as timing is messed up......defective. Once you get it running you will have to sync the carbs to get top rpm out of it.

Kit

I'm going with leaning or timing also. Be careful though...as if you mix your fuel/oil, if you are running lean, you are also running lean on oil. I know you have to test to figure out the problem, just might stick a bit of extra. I like an old 2 stroke to smoke a bit at idle...not much...but I'd rather keep it decarbed with seafoam and change plugs more than ever have to worry about enough oil.

Like defar was saying on the leaning out, it could also be a fuel line/bulb problem. He asked about the gray hose because its about as sorry as it gets. Life of about a year. You might try having someone pump the bulb as you throttle up. If its a pump/bulb/line issue you should here it try to go on and rev as you pump and keep the bowls full as the main jet kicks in.

You'll need a manual or do alot of online reading to checking your electrical system and setting timing. Its not hard...but you have steps to follow, and ranges things are supposed to be in. Try to find an oem manual if you can.

A can of seafoam couldn't hurt either...its as close to a miracle in a can as it comes! lol.