Backfiring through exhaust - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
 
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post #1 of 9 (permalink) Old 09-29-2016, 03:03 PM Thread Starter
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Backfiring through exhaust

2003 Vstar 1100 Custom:
I purchased max air PMS screws for my Carburetor so I can adjust them on the fly. I have a clymers manual that states europian and Australia models are 3 turns out on both carbs. Well I'm not sure that's right as I turned out both to 3 turns and am getting backfiring on acceleration through first and second gear. I do have a cobra exhaust on it so I'm sure it must be adjusted but I'm not sure how many turns out I need to be. I'm assuming its running lean is why it is backfiring but at 3 turns out seems it would run rich. I'm no expert jut wondering if anyone has any insight. Also I have to remove the air filter housing every time I want to adjust them so it's not a ride and turn thing, gotta make a short loop around the neighborhood firing off shotgun blasts to pull back in park it and remove the air filter housing to adjust it. Any thoughts and tips are appreciated. Thanks guys
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post #2 of 9 (permalink) Old 09-29-2016, 03:58 PM
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The PMS controls fuel supply with a closed throttle. If it is backfiring on acceleration you have a totally different issue. Vacuum leak, plugged pilot or main jets, stuck or popped out needle. It could also be improperly adjusted valves.

Sick Mick* 2006 V Star 1100 Custom

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Last edited by Sick Mick; 09-29-2016 at 08:16 PM.
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post #3 of 9 (permalink) Old 09-29-2016, 04:06 PM
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http://redirect.viglink.com/?format=...2Fcarb-jetting scroll down to table A. for stock intake and slipons 2 turns. backfiring thru the carburator is usually a lean condition.backfiring thru the exhaust is too rich, or a air leak. an air leak can cause a lean condition too. with slip-ons you can turn the screws out a half turn or there abouts
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post #4 of 9 (permalink) Old 10-12-2016, 12:38 AM
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Originally Posted by Sick Mick View Post
The PMS controls fuel supply with a closed throttle. If it is backfiring on acceleration you have a totally different issue. Vacuum leak, plugged pilot or main jets, stuck or popped out needle. It could also be improperly adjusted valves.
Would improperly adjusted valves cause a back fire when you blip the throttle? I've had that issue for a while now but only when I quickly crack the throttle. It seems like it's coming from the front of the engine though.

Last edited by roblox84; 10-12-2016 at 12:42 AM.
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post #5 of 9 (permalink) Old 10-12-2016, 08:40 AM
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Possibly...

Checking the valves is just plain general maintenance and should be done at least once a year. If you;re not doing it...I'd advise you to start.

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--- Striping, lettering and paint by Sick Mick 6* Tree - 2" extended forks 21" front wheel - HK Sideburners - Progressive rear shock Pods Sick Mick solenoid delete - Spring seat - and other stuff
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post #6 of 9 (permalink) Old 10-15-2016, 07:43 PM
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I do, it's just that the gap tends to shrink as you tighten down the valves and I want sure if I might have let one slip too much.

It doesn't backfire all the time, just when I rev the bike up and before the rpm's fall I rev it again and that's when it'll do a little backfire.
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post #7 of 9 (permalink) Old 10-16-2016, 06:18 PM
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These are vacuum slide carbs...they are not meant to be "tested" that way. You rarely, if ever, make those type of radical throttle movements while you are actually riding. So you are creating an abnormal condition. The vacuum slides require a split second to recover after radical movement..... in other words....quit it!.

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--- Striping, lettering and paint by Sick Mick 6* Tree - 2" extended forks 21" front wheel - HK Sideburners - Progressive rear shock Pods Sick Mick solenoid delete - Spring seat - and other stuff
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post #8 of 9 (permalink) Old 10-16-2016, 06:40 PM
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Lol, I kind of figured I was messing with it. I guess I was trying to see if it'll eventually go away.
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post #9 of 9 (permalink) Old 10-16-2016, 07:33 PM
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I had many air cooled VWs over the years
you could make them backfire while driving by

turning the key off,
pumping the gas pedal to the floor quickly,
turning the key back to the run position: BANG!

It sounded better with headers,
split a $100 quiet header muffler in half once showing off

anytime you pump more gas through the piston than it can handle, the next stroke that fires will ignite the fuel in the exhaust.

Im not sure if that is a bad thing to do to your engine... But I can tell you about mufflers.
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