Hey guys,

1992 FXRP, stock except air cleaner. 5th gear, between about 3500 rpm to 4000 rpm there’s a flat spot in the throttle response.
I can give more throttle and pull through it but if I just smoothly accelerate it feels like I don’t have much power there. Once or twice my bike...coughed(?) in this zone, may have been a backfire but I’m not sure.
Any ideas?

 

Based on your stock bike carb set up, and that you put on an aftermarket air cleaner, I would say you need to increase the size of your main jet. To really make your bike run better, you should get a more free flowing exhaust, and do a little CV carb modification. This site provides lots of great info and proven suggestions:http://www.nightrider.com/biketech/hd_cv_mods.htm

 

Jetting changes can be done with carb in place
but on a 28 yr old machine I would politely suggest pulling it and replacing the rubber “compliance fittings” at intake manifold
cheap insurance

jmo

edit: punch out the plug in stock mufflers
pilot jet number 45
main jet number 175

 

before we all dive into the weeds:
is this bike new to you OR is it a new occurrence on a machine you’ve had for years?
big difference

 

Sorry, that’s a good point. I’ve had the bike for a couple of years. Can’t really say when this flat spot started showing up. Last month or three would be my guess. I did replace the carb maybe a year so so ago with a new CV carb.

 

Holy crap, and I thought "60 Minutes" only gave us HALF the story!

 

yeah, sorry guys-should’ve included that in the first post

 

I would suggest going through the carb and see what jets you have. When you replaced the CV carb, did you replace all gaskets associated with it. Even if you did, something has changed, and with a "flat spot" that is intermittent and or happening more frequent, I would go back to the last thing you did to the bike, and that's with changing out the carb. Good luck.

 

Did you replace the compliance fittings last year with the new carb?

if yes , I would check the nuts for tightness

if no I would do so now

 

I’m sure I replaced everything-but I will start there. Check tightness and condition.