What he is experiencing is very close to what my problem is. At 5500 rpm the car starts missing and labors to go higher, no codes, not fco. I have a stock 7mgte, except for 3” exhaust and a boost controller set at 11.3 psi. About 4 weeks ago I added a Walbro 225l w/o a 12v mod everything was fine. Car ran good, 14.5 quarter mile. Last week I replaced the plugs, Autolite, gapped at .28 that is when it started, car ran OK but at 5500 + it miss’s. I rechecked the plugs, cleaned the air filter, no change, put the old plugs back in and removed the a/f no change.
So after reading all these post I am wondering if I
should remove the “J” tube, and do the 12v mod or maybe something else?
I have never checked the fuel pressure so I will do that today.