my gas gas 300 seems to make a knock noise when letting off the throttle, ive tried to video it but it sonds abit tinny on the video, it sounds abit like the piston slapping... ive heard about pinking and wondered if it was this? any ideas how to cure it?

Edited July 14, 201214 yr by stu3y

Seems like the noise you get when your bike is overheating and the mixture has leaned off or you're getting fuel starvation....I guess you're not overheating as you would have mentioned it?

If I had to make a video guess,I would hope it's just a mixture problem.

That sounds like a lean knock to me, clean your carb ,check the needle is in the right position (clip/groove) turn your mixture screw to try and 'richen' things up..

I hope it's that simple.

Wayne

hmm, it does seem to get louder/more frequent when its hot... and when it is hot the fan on the radiator seems to stay on longer than what it used to on my last Gas Gas 300....

Gassers like good clean head! An excessive build up of carbon in the combustion chamber will cause a "lean knock" sound, but it is actually a slight pre-ignition. Remove the head and clean the piston crown and combustion chamber, most of the time that is all it will need.

Seems to be a common problem on 300's. As previously mentioned, decoke the head and all will be well. I do it regularly on my 300 when its starts to pink again...

my gas gas 300 seems to make a knock noise when letting off the throttle, ive tried to video it but it sonds abit tinny on the video, it sounds abit like the piston slapping... ive heard about pinking and wondered if it was this? any ideas how to cure it?

You may have a stock #35 pilot, try changing to a #38 before engine work.

Jon