riddle me this............03 f4i....bike starts up runs good but stumbles on hard acceleration till about 2,500....now this is where it gets good....i have a chopped stock pipe...i take it off the stumble goes away........i have a M4-pipe put it on same thing still stumbles till about 2,500...only way it will clutch up is with out a pipe on it....gotta have a pipe for the spots i ride in dont wanna attract any unwanted attention.....its SF,kleen air mod ,tip sensor mod,idle mods are all done ive changed them back to stock same thing........


someone anyone

 

sorry for the dbl post pos computer

 

Could be a bad fuel regulator, coil pack, spark plug or a little of all three I would change the plugs first then the coil packs. Somethimes could be the regulator but most of the time that will just make it bogg. Pull the plugs and check them and the gap on them. I guess you are not getting any codes?

 

already swapped fuel press reg out ...same thing,,,nope no codes.... its so weird that it only runs like this with the muffler on...

 

definatly sounds like a fuel issue(I wish honda had put a shreader valve on the rail to test pressure) Ive seen f4i pumps break apart from a hard crash,on 2 different bikes. both bikes still started but didnt want to rev up fast,not really same symptom as yours but might look into it if you run outta options. oh and the damage is obvious once you pull the pump out.