Xr600r dies on sudden throttle decrease

So I don't seem to find my specific issue so here I am asking. 

I have a 1997 Xr600r. It was recently re-jetted and has ran really well ever since until more recently it has begun to have this issue.

Everything works fine. Kicks right away, nice and easy. Runs great, sounds great, purs. But when I'm downshifting and slowing down to a stop, if I let my hand off the throttle that's when it just dies. I found that I can counter this by lightly holding the throttle as I down shift (so I'm revving quite a bit during downshift).  But it hadn't done this before. 

The only thing I've done that I suspect may have been an issue on my part was when I pulled out the engine to change the valve cover gasket and upon doing so perhaps when connecting the carb back to it, I may have missed something or made a crack in the boot? 

Any ideas? Thanks 

Turn the idle speed up until it stops doing it.  That's what I did on my XR650L.

Thanks ScottRNelson, 

You know, I actually tried that and it doesn't work very much, and when it seems to work, it is turned up so high that it is nearly impossible to kick start.. also at at certain point it stops working too.

but I plan to try that again and see what happens..

 

Possibly a pinched carb vent hose. This issue would seem to be somewhere in the fuel system.

Are you saying that there IS a crack in the intake boot? Or that you are just considering it as a possibility?

An air leak could definitely cause this issue.

Check the float level in the carb. I have seen it cause that problem before and also the float needle for wear

2 hours ago, firsthere said:

Possibly a pinched carb vent hose. This issue would seem to be somewhere in the fuel system.

Hmm, ok I can check those out.

2 hours ago, Backwoods-Bomber said:

Are you saying that there IS a crack in the intake boot? Or that you are just considering it as a possibility?

An air leak could definitely cause this issue.

I was just considering it as a possibility, seeing as the boot looks kind of old. Not sure if previous owner had replaced it in who knows how long. 

I was leaning to an air leak. However I inspected the boot pretty thoroughly, not sure it's to do with the boot.

8 minutes ago, nightbasser said:

Check the float level in the carb. I have seen it cause that problem before and also the float needle for wear

Okay, thanks, will do.

Possibly popped the air cutoff diaphram if compressed air was used.

So I think I've gotten a temporary fix.. for now.

I checked everything, save for pulling the carb out and opening and all seemed to check out, so I set the fuel screw to its previous setting (2 1/2 screws out) and proceed to try and kick it. It wouldn't kick, so I gradually turned it in until it kicked.. I didn't keep track but my guess was a whole turn in. Then it finally kicked and all seems well, the dying on downshift stopped and I really tried to get it to do it. Thanks again ScottRNelson.

However, I only consider this temporary seeing as the fuel screw setting isn't at where it was originally. 

With that being said I do recall that during the last jetting there was some fuel residue building up in the carb. So I suppose that will be my next step to a complete fix. 

Hmm, I wonder, if that is the case, will I just need to clean the carb or does that mean it's almost time for a new carb...

Edited by Xr600guy

 The ACV is a plate on the side of the carb with two screws, no carb removal, maybe the gas tank though. The valve will change the pilot circuit so maybe worth a look.

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