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Discussion Starter · #1 ·
'01 SVS, totally stock but has had muffler drilled (or something done by previous owner, sounds like crap).

Took the SV on some mountain roads for the first time a couple weeks ago, and had a few backfires on decel before a few turns at roughly 5000 rpm's or so. Sometimes it would happen with the clutch engaged (with the throttle cracked just a hair), and a couple times it did it on decel when I pulled the clutch in.

Not just ready to re-jet the bike just yet, but I did pull out the needles and shimmed them. Figured 1 shim would be okay but ended up putting in 2 for the hell of it. Bike seems to run a little better overall, but when I took it back into the mountains yesterday I still got the same occasional backfires.

I figured the bike is a bit lean, shimming didnt change anything. Since it's happening on decel, is this probably an issue with the idle screw? The carbs need to be removed to get access to them, correct? Should I go back in and go with just 1 needle? Should I be concerned about these backfires or are they just an inconvenience?

Thanks for any help!
 

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Dont worry, normal for I think all bikes pretty much, even if it is properly jetted you will get that when you have the throttle closed or almost because you are on a different part of the jetting or fuel map as opposed to the rpm's your engine is running.
 

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I found out last weekend that vacuum leaks can cause some pretty nasty backfiring on decel. I had a bad plug-end (sliced it with the tank when I was finishing up) on my carb-synch port. Maybe not the problem on your bike, but easy to check.
 

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the bike is running lean for some reason or other. could be a vacuum leak, gummed-up jets, overly free-flowing air-filter or exhaust, etc.
 

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Discussion Starter · #6 ·
Thanks for the suggestions, I'm not quite ready to rejet just yet but I may take a shot at unplugging the idle screws and going out on them a little bit.
 

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backfire on decel usualy means lean, if it was so lean it was running hot then your fan would stay on so i would chalk this one up to anyance, at least until you can rejet........i am saving for slip on and jet kit but while waiting i drilled out stock muffler, basicly removed layer between outer shell and inner pipe at rear just leave enough that inner pipe doesnt rattle, helped it rev better and picked up middle and top end power but hurt bottem end power it sounds like a strait pipe, thats a good thing to me maybe not for you
 
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