1972 XL250 Tuning

[pmmcmullen94]

Hi Everyone I have a 1972 Honda XL250 with a big bore kit to I believe 290cc. I can't remember the exact bore that i got. I have a Mikuni carb on it with jetting 30/165 and the clip is in the middle. Before the big bore, I had it at the same settings and it ran perfectly. Now, it will pull fine from 5K and up and runs decent maybe a little rich from 1-4K. The area from 4K-5K it will jerk around and pop once the engine is hot. We tried working around with richer jets to see if the fuel was getting cut off but it ran better as I went leaner. Should I drop the pilot down to a 25 and see if that is the issue?

When I pulled the plug it wasn't completely covered but it was fairly black. Definitely darker than the caramel color desired. I put a new plug in and did a high speed run and it came out looking almost brand new so I know that the main isn't running too rich. Could my pilot be running too rich causing it to hesitate at the upper end of the pilot circuit? By this I mean, once you are getting to right around 1/4 throttle where the pilot starts to cut out, could there be too much fuel dumping in causing it to bog at 4K? Please give me any suggestions. I didn't know if I should go leaner or richer on each jet after boring it out 15% over its normal displacement.

Also forgot to add that it will idle perfectly but if I try to pop the throttle at any RPM it will bog out. It won't die unless I hold it open for a long time but it won't regain itself I have to let off and then roll on the throttle. It also pops out the exhaust when it gets hot (~4K).

Extra info:

Stock Muffler/Pipe (May be slightly restrictive)

Fully rebuilt engine

Pod filter

Stock gearing

New Coils/Points

Timing Calibrated

Edited July 8, 2013 by pmmcmullen94