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I have an 84 FXRP with an EV-3 cam,Screaming Eagle 40mm carb from around 1986 or so(Its been rebuilt),and Supertrapp 2/1 SS exhaust.I am having a bitch of a time getting it adjusted the way it should be.When its fully warmed up,it stumbles off idle like its cold or something.Ive tried adjusting the idle mixture,and idle speed and also the acceleratorpump cam and it IS somewhat better,but still has a bit of a "chug" or cough when ya suddenly open it up.It catches itself after a second,but that initial burp agravates the hell outta me.
Now is there something Im missing somewhere?Could it need rejetted or perhaps rebuilt again?Maybe the fuel injection on the 06 has me spoiled but it seems like it didnt do that before.Any advise will be appreciated.
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Usually a stumble off idle means a too rich mixture. But when you say it coughs or chugs, I start thinking "too lean". So I'm twiddling my thumbs here!
If it's coughing back out the carb, remove the air cleaner completely. That'll lean it out, and you can try it to see if it improves, or gets worse. That might give you an idea of what direction to go.
Might grab a handful of low speed jets on either side of what is in there now. Swap 'em out and see what happens.
Does that carb have an accelerator pump? (Showing my ignorance here, but I'm not familiar with anything newer than a Keihin butterfly carb.) If it does, try setting the adjustment so it doesn't quite squirt as much gas.
Does it stumble off idle before it is warmed up?
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It does sound like a 'carb' issue, like was posted...You probably need to rejet the carb because of the cam/exhaust/air cleaner setup. And possibly go with a different needle or adjustable needle to make it run smooth through the transitions.
Unfortunately, I'd have to recommend that you find a shop with someone that knows how to use a dyno to tune a carb. You can 'play around' with it, maybe even 'get it right'...But you're never gonna know what's happening until it's run on a dyno and the various air/fuel mixtures are read. Trust me, it was the best $$$ I ever spent on my 93 EVO (stock CV carb, EV27, SE air cleaner, Supertrapp slipons-18 discs, dyna2000 ignition).
I havent tuned up my 06 on the dyno yet.I just tuned it till it felt right with the PC and the SERT.
On my 84 fxrs I do all my own stuff sence it was new.It dosent cough back through the carb like a backfire,it just seems to sort of stumble for that second before it revs up.Like I said,I think it just needs rejetted.
The carb DOES have an accelerator pump,and ive adjusted it to where it IS somewhat better.
I think I will rebuild it again OR buy a Mikunismoothbore.
Stumble off of idle
