Jetting problems (250r)

[Dynofox]

While riding my 86 ATC 250r if I am 1/2 throttle or above for any lenght of time and then let off the machine starts to act up. It starts to surge, the rpms will go down then back up to normal, back down then up again (almost acts like it is running out of fuel and tring to stall). When its doing this if I give it some gas it seems to help. My trike is stock other than a full fmf system and my jetting for cental NY (around 800ft) is:

Main: 150
Pilot: 42
Needle pos: 3rd slot

I've tried moving the needle clip to position 4 to richen it up but it made no difference. Should I try a larger pilot? Doesn't seem like a main jet problem since it happens when I'm off the gas, not on it. I've checked my intake boot for cracks and found none and have recently installed a billet exhaust flange with dual o-rings. Anyone have any tips? Thanks!

[hrc85250r]

hmm check the plug....clean the $#!T out of your carb, and you might need a size or two larger jet due to the pipe, but it shouldnt be too far off.....sounds like a dirty carb to me tho...

[x.system]

While riding my 86 ATC 250r if I am 1/2 throttle or above for any lenght of time and then let off the machine starts to act up. It starts to surge, the rpms will go down then back up to normal, back down then up again (almost acts like it is running out of fuel and tring to stall). When its doing this if I give it some gas it seems to help. My trike is stock other than a full fmf system and my jetting for cental NY (around 800ft) is:

Main: 150
Pilot: 42
Needle pos: 3rd slot

I've tried moving the needle clip to position 4 to richen it up but it made no difference. Should I try a larger pilot? Doesn't seem like a main jet problem since it happens when I'm off the gas, not on it. I've checked my intake boot for cracks and found none and have recently installed a billet exhaust flange with dual o-rings. Anyone have any tips? Thanks!

Thats a hard one to diagnose but I would check the air screw, that will determain if you have the right pilot jet in it. Minumum is 1 and 1/2 turns out, max is 2 and 1/2. If yours is in that range you should be fine with your pilot.

May want to check your float level to when you have your carb apart to clean it.

Check the throttle cable also for frays or binding but it sounds like you are getting air somewhere, maybe the carb top? Is the gasket on the cap?

[Dammit!]

Spray some starting fluid everywhere it could be sucking in air while it's running. A visual inspection won't always get the job done.

[Hornetpowerspor]

Spray some starting fluid everywhere it could be sucking in air while it's running. A visual inspection won't always get the job done.

Good call , it sounds like it could be sucking air somewhere and leaning out. After spraying either around all the gasket surfaces while running, dont forget to remove the stator cover and spray some in there to see if your crank seal is leaking.

[TravEX]

I know this is old, but Dyno what did you find out?

[Dynofox]

Well I have since rebuilt my whole motor (top and bottom) and have went back to the OEM exhaust and played with my jetting. Am now running 150 main, 40 pilot and 3rd clip position and it seems to fun pretty well. I also dropped a tooth on the front sproket to give it more low end power and to keep my RPMs up in the tight woods riding we have around here. I have not noticed the situation that I described in my first post here in central NY, the problem I was having was at TF in Indiana. I am assuming I was running into a lean condition at TF and that was the cause of the surging.