Popping on throttle roll-off a reliable lean indicator?

When I had my '05 XR650L stock and lean, it popped like popcorn when I rolled off the throttle. (Near sea level elevation.) I uncorked it and changed to 55/158 jets (from 50/152 stock). When I did, the popping practically stopped.

So does popping on throttle roll-off always indicate a lean condition? I'm asking because I should get my Supertrapp IDS2 slipon within a few days :thumbsup:. If the popping returns with a vengeance, do you think I need to up the jets again? Maybe 55/162?

I think your going to be OK the way it is. I believe that system is a disk type of system so that gives you some tune ability also.

Actually, I've heard it both ways. I always thought popping was from being lean, however, I've also heard that it could come from afterburning the extra fuel in the cylinder from being to rich after abruptly shutting off the throttle. I've been running my 650R quite rich (blackened plug/exhuast) for some time, and I still had popping on deceleration.

For that matter, I've also heard from 'jetting masters' that some popping is totally natural on thumpers. I've never totally gotten rid of it on my bikes.

55/158 might be a touch lean with an aftermarket pipe.

Only way to tell for sure, check the plug color.


My understanding is that the popping on the L was primarily related to the smog thingy. I took it off, rerouted the breather/carb tubes, installed the blockoff kit.........no more popping. However, at the same time I removed the snorkel, uni filter, carb mods 55/158 at 3500 feet, shimmed the needle .025, drilled 3/32 slider holes, White E series disc type exhaust, oh yea fuel screw out 2 1/2 turns.

You should also check the torque on your header pipe connection with the cylinder. Any air leaks will generate popping. I've pulled header pipes that didn't have the gasket installed. Without the gasket: messed up engine, with the gasket smooth. Actually air leaks anywhere along the circuit will cause various problems with acceleration/deceleration.

I had done the smog block off first and before I did the jetting and it didnt seem to change the lean poping at all. I new it was lean and I had planed on rejetting any way. I new I had to get rid of the octapuss just because it had no right to be there.

[snip]...I've been running my 650R quite rich (blackened plug/exhuast) for some time, and I still had popping on deceleration...[snip]

Your quite possibly still too lean on your pilot circuit. You can be rich on your main jet and/or jet needle but if your getting popping on off-throttle deceleration...that's generally a signal of a lean pilot circuit. Different circuits/jets control the fuel-air mixture at different throttle openings.

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