All other rpms the afr is good at 3800 its 14 to 15 range then at 3900 it stumbles and bucks and goes very lean. Then at 4000 to redline it goes from 12.5 to 11.5. No codes. What could cause this. Its the same place everytime. Engine is stock with afp regulator and walbro, 3 inch down pipe to open 3" exhaust. It does this with and without load.
Last edited: