How I solved my pigs sticking idle problem

PROBLEM: My XR650R ran fine but it would sometimes fail to return to idle when I came to a stop. I’d have to blip the throttle three or four times to get it to settle down. After first determining there was no friction or interference in the throttle cable and linkage, I suspected I had a lean condition caused by either a loose manifold boot or something afoul in the pilot circuit.

SOLUTION: Your probably familiar with the sage advice of changing one thing at a time when your jetting a carb. Well I did not follow that advice, I fixed my problem, but I don’t know what to attribute the cure to.

1st I disabled the AJCV (Air Jet Cut Off Valve) by placing a tab of electrical tape on top of the 1/8” o-ring prior to reassembly. I read else ware someone advising cutting the plunger off the back side of the diaphragm, that to would disable the “deceleration softening circuit” but would be otherwise irreversible, so I went the PVC tape route.

2nd I reamed the 65s pilot jet with a paper clip (too big), then with a B string from my guitar (too small) then I found that a bread twist tie with the paper striped off made a perfect ream. Buttoned up the beast took her for a spin. Not once did the idle hang, she just settles down to a loping thump. Tomorrow I’ll pull the tape and see what effect it has.

BTW what is the consensus for removing the spring loaded backfire flap from the choke plate? I wouldn’t want that plate and spring sucked into my topend, but I would like to retain full choke.

FWIW, reaming a jet is typically a no-no. Carb cleaner and compressed air is the best method for cleaning them.

I removed the backfire plate with zero problems. With a properly jetted pilot circuit you shouldn't have any starting issues doing that mod.

A hanging idle will also be caused by the idle simply being set too high. Typically, the pilot jet is a bit too lean. When started cold the bike runs like crap and doesn't idle well. This is due to the air intake being cold. Cold air is more dense, which mean more O2 per volume of air, worsening the lean condition. It will appear that the idle speed is too low and adjust it up. After the bike warms up, the incoming air is heated and becomes less dense, meaning less O2 per volume, richening the air/fuel mixture. Now the bike runs better as the air fuel mixture is closer to optimum. But, now the idle is set too high and will 'hang'.

Lower your idle when the bike gets good and warm and see if that doesn't fix the 'hanging idle' problem. Also notice that the bike still idles good as the idle is now set closer to proper.

The solution is to set your fuel screw richer (righty tighty is lean, lefty loosy is rich). However, if you best idle condition is above 3 turns out from fully closed, then you need to install a one step richer pilot jet (then re-adjust your fuel screw down to about 1.5-2 turns out from closed). The richer pilot circuit will make cold starts better.

There may be other factors involved but I know that the above can add to the problem, as I've experienced it myself. Good luck.

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