PCS Pipe & carb Problems

[jkeatts]

I just installed a new pcs pipe on a 70 limited. At full throttle it was cutting out some with a 100 jet. I changed to 120 jet and it made things worse. Also installed new plug and clean filter. Any ideas as to where to start trying to solve the cutting out at full throttle?
Thanks for the help
James

[riding4fun]

Probably need more info. What 70 motor, what carb and size of carb. standard ignition or pvl.

[jkeatts]

Some details on the 70

Keihin 24mm Carburetor
Performance Intake and Reed Cage
Pod Filter
High Performance Head (air cooled)
I think it is standard ignition

[riding4fun]

Did you do a "plug chop" If so, what did it look like?

[thequadfather+2]

back it up to a 110-115, make a couple wide open passes and cut the quad off while its wide open and check the plug color. 100 to 120 may have been to big of a swing although, our 70 is lightly modded with a PCS pipe and we are running a 120 main. We have ran 118-115 in the summer months and it was great. As riding4fun asked, what is the plug looking like at WOT?

Also, make sure you dont have a leak around that intake, put it on a stand, idle it up a good bit and spray around the intake with carb spray and listen for RPM changes.

We had the same thing happen on our 70, drove me crazy for a week. Swapped the intake and all was better.