My EX bogs/dies at high rpm, put new plug in and still does it, the old plug was black as night. I pretty sure I'm runnin rich and I want to know how to fix it, it would be nice if I didn't have to buy and new jets.

 

put a smaller main jet (i cant really say from here) OR get some performance mods to make up for it. Exhaust, air filter may make up for it. if still rich get a cam

 

a cam will make you run leaner??? humm whats your setup man......stock pipe and filter??? let us know that and then we might can help ya out better

 

if not cam get porting and boring

 

umm oh it is the main jet for sure cause thats what controls....3/4 to full throttle....also check inside you carb the linkage that picks up the slide is connected right.......I put mine in wrong and is dissconected and would rev up but then bog and sputter....and yea the plug was very black!.....try that

 

Thanks a lot for the help. My bike is stock performance wise. But last week I had to strip down the top end and I got new head bold and piston pin and rings so I think it is running higher compresion so now it's too rich, how do I adjust the main jet? do I just need to buy a smaller one?

 

Raising the compression will not make your engine run rich. If the fuel/air mixture was OK before you changed pistons, then don't mess with the jets. It may be that your new rings haven't seated yet(although they should have) or maybe you have another problem in the cylinder(i.e. bad gasket, broken ring, etc). If you can get a compression gauge, do a compression test. I don't know what the book calls for on the 300EX, but I'm sure that someone on this forum has the data. What I'm getting at, is that it may be oil that is fouling your sparkplug, not fuel. Good Luck.

 

umm you'll have to go to your honda shop and get the 120 the stock is 122.....just get a few different sizes smaller than 122. you gotta take off the tank off...flip the carb up side down....unscrew the 17mm scrw on the bottom....pull your main jet and screw the new one in....if you want anymore help with jetting just e-mail I'll be glad to help out.....later