hi, i got a fiddy w/ 88cc big bore kit, big card, intake, fast 50s pipe and CDI box. it has miles of torque down low but starts missing at high revs. It also sputters / pops a bit when I gtake my hand off the throttle, after nailing it.

any suggestions on how to make it run better at high revs?

 

at full throttle if it sounds like it has a rev limiter on it.... its too fat. go down 1 size jet and try that. if it pops out the exhaust after letting off at full throttle.... its too lean. another way to check is by running it at full throttle, and killing the engine right while its breaking up. coast to a stop and check the color of the plug. when it looks like coffee with creamer, u are in good shape. good luck man.

 

http://www.ngksparkplugs.com/techinf...000&country=US
http://www.strappe.com/plugs.html
read both

 

good info, thanks to you both ...

 

Make sure your choke isnt turned on.

 

yea i have the same problem i had to buy a jet kit and also i saw on xr50.com the have a hot plug kit for the big engin but its like 300 and im not spending that but try the jet kit and make sure your valves where floated right that gave me a problem also