1999 Yamaha 250 surging problem

[23parker]

The motor surges between about 2200 and 3000 rpm's. It runs great at WOT and at idle and low speed. Just a problem in the mid range.
1. Checked and cleaned VST
2. Changed plugs
3. Decarboned engine
4. Replaced fuel filters
5. Replaced O2 sensor
6. Replaced stats (just because they had not been changed in awhile.
7. Replaced the three fuel pumps

What do you think the problem is?

 

[cousinabe]

Re: 1999 Yamaha 250 surging problem

check your tps is in spec throughout the throttle range. make sure no dead spots.

Have you checked the fuel pressures (lp and vst) while problem occurs?