Jump to content
Sign in to follow this  

Troubleshooting FCR jetting/AP

Recommended Posts

Since I live in Wisconsin, and we're in that wonderful time of year where the weather can swing 50 degrees in a matter of one day, I've had the chance to see how my FCR performs at different temperatures, and it turns out it needs some adjustment. I think I've got it figured out, but I want to give my theory a sanity check.

I'll describe whats happening based on the temperature, since it was 40 to 50 degrees yesterday, and its 60 to 70 degrees today. I should also mention that I bought this FCR from Epic, and put it on my bike without opening it up to see how it was jetted, so I have no idea whats in there for jets.

Temperature: 40-50 deg F

  • Quarter throttle stutter when moving, clears up when the throttle is opened or closed.
  • Popping on decel
  • Hitting the throttle from a walking speed (5-10 mph) results in a wheelie (as it should)
  • Bike revs cleanly with clutch pulled in
  • 50-100% throttle opening seems to run fine

Temperature: 60-70 deg F

  • Quarter throttle stutter is gone
  • Popping on decel is all but gone (one pop every couple seconds)
  • Hitting the throttle from a walking speed results in bucking and stuttering for a half second or so, then the bike pulls away, but not all that strong, no wheelie, or very small one
  • Bike does not rev cleanly with clutch pulled in, sputters
  • 50-100% throttle seems fine still, at least from my butt dyno

So, based on that, I'm going to guess that the bike is mostly jetted right for 60-70 degrees, and the AP is providing too much fuel, leading to flooding when the throttle is opened in warmer temps?

Does this seem like the case to anyone else? Is there any way to adjust the AP to provide less fuel without tearing it apart and replacing the leak jet?

Edited by Mattydiah

Share this post


Link to post
Share on other sites

What needle (and clip setting) is in the bike?

AP appears to be working fine (no bog). What happens when not moving really is insignificant. it does not have a leak jet. They are only used on the smaller bore engines.

Expect some decel popping as your carb does not have an ACV (Automatic Coast Valve).

Share this post


Link to post
Share on other sites

So the stuttering in throttle open doesn't point to the AP? That seems weird to me.

Share this post


Link to post
Share on other sites

Right, and what I'm saying is that accelerating from a slow speed makes the bike stutter and buck. That quarter throttle stumble, I agree points to the pilot, but on acceleration, that would point to ap

Share this post


Link to post
Share on other sites

At walking speed you would be at idle...with an fcr dumping the engine with full throttle at this rpm is a big ask...you could try turning your AP screw in 1/2 a turn...For simplicity, a remember where your starting point is whenever you move the AP screw so you know where to come back to is needed...

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×