XS650 Jetting/backfires

drunkaroos

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Hey all
Before I put my bike away for the winter I am trying to fix a problem I have with it. Ever since I removed the beat-up stock silencers and slapped on some cheap slash-cut mufflers(sounds amazing btw) I've been getting a decent bit of popping on deceleration and when I let off on the throttle. Adjusting the cam chain has toned it down a bit but it's still pretty noticeable. Could this be the fault of not having correct jetting for the new exhaust setup, and what jetting would fix this if so?
Picture of me on my bike for attention
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Nice looking Green XS there.
BS34 carbs. Sounds like you will need to richen up the mixture a tad?
Many other members have jetting experience with the BS34's hope you get nice advice here.
-R
 
Could this be the fault of not having correct jetting for the new exhaust setup, and what jetting would fix this if so?
Yes, less restrictive mufflers will change your jetting. You could try adjusting your mixture screws to stop the popping, but it's likely you're lean all across the throttle range. There's no correct answer to the second part. You could start by going one up on the pilots and mains. Best you read the carb guide in the Tech section. It's an excellent source for rejetting.
 
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Thanks! Yes, they are bs34 carbs. They were pretty gunked up when I got the bike but I rebuilt them. I'll be sure to check the mixture. I also have a pair of bs38's that I've been considering installing that I've heard allow for more fuel flow out of the box. Would that potentially help?
 
Thanks for the info, I'll be sure to check out the carb guide. What would be the best way to check if I'm running lean? I've heard theres a method involving running the engine for a short while and checking the plugs.
 
. I also have a pair of bs38's that I've been considering installing that I've heard allow for more fuel flow out of the box. Would that potentially help?
BS38's Hmm, which year or series? The late BS38's with Uni Pod filters may be a fun upgrade. I've had such good luck with those that I just stay with those years. Its all what you are comfortable with I suppose.
 

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Might not be a carburetor problem at all. There are vent holes front and back in the outer layer of the head pipe, to allow heated air to escape when it expands. If the hole in back opens into the muffler, it will cause popping under engine braking when cold air is drawn into the muffler. Pamco Pete posted one solution: use an adapter to block the rear hole.
 
It could very well be one (or both) of the things mentioned in the last 2 posts. But, you should be aware that the BS34s came jetted very lean from the factory, border-line too lean even on a totally stock machine. Make any changes to intake and/or exhaust and it usually requires some re-jetting.
 
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