Backfiring through carb - Kawasaki Vulcan Forum : Vulcan Forums
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post #1 of 27 (permalink) Old 07-12-2016, 04:48 PM Thread Starter
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Backfiring through carb

96 vn800
Mods- intake, intake ports cleaned up on the heads(nothing crazy) cobra pipes and EPA delete
Jetting is 52/175
Idles ok, backfires through the carb with light throttle.I would think it's a lean condition, but it dies on the choke. Pulls pretty good at wot. Any ideas
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post #2 of 27 (permalink) Old 07-12-2016, 06:05 PM Thread Starter
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Update, I turned the idle screw in to 1 1/2 out, was alittle better. Backfiring went down a little. So then I turned it to 1 1/4 out backfiring was a little worse
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post #3 of 27 (permalink) Old 07-12-2016, 06:23 PM
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Put 2.5 turns shim needle going through same thing


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post #4 of 27 (permalink) Old 07-12-2016, 06:25 PM Thread Starter
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I'll give it a try and see what happens. What jetting are running, the same as I have
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post #5 of 27 (permalink) Old 07-12-2016, 06:29 PM
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Yes 52 pilot 170 main cut the air box I couldn't get the bike to take any throttle stock needle shimmed with number 4 washers from lowes


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post #6 of 27 (permalink) Old 07-12-2016, 06:30 PM Thread Starter
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Ok cool thanks
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post #7 of 27 (permalink) Old 07-12-2016, 06:59 PM Thread Starter
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It doesn't like 2 1/2. I have two shims and about 1 3/4 out runs perfect, but as soon as I go to put it on choke it dies
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post #8 of 27 (permalink) Old 07-12-2016, 10:24 PM
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First off, is it really backfiring through the carb? True backfiring, especially on bikes with electronic ignition, is very rare. True backfiring is either caused by a valve timing issue or by the ignition being so far out of proper setup that the spark plug fires when the intake valve is open and ignites the incoming air/fuel mix before the intake valve is closed. So in this case "backfiring" is probably not the issue.

With the mods you made, I bet what you hear is exhaust popping due to a lean fuel to air ratio on closed throttle on decel (light throttle). On way to know for certain, next time you hear the popping pull in the clutch. If the popping stops immediately, then you have proof it is not backfiring. Decel popping causes no harm at all to the engine, but a modded exhaust will cause the popping noise to be more evident. Turning the idle screw only slightly keeps the throttle plate slightly more open on decel and adds air to the mix, slightly reduces the vacuum through the venturi and reduces the fuel draw.
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post #9 of 27 (permalink) Old 07-13-2016, 11:18 AM Thread Starter
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It does it without moving too. Not as much. I turned the screw in and it doesn't pop as much. I noticed yesterday when I took it out, I did wot for a couple gears felt pretty good. When I let off and and went to ride slowly it popped a little bit. Still won't run on choke. I might try and put the 50 back in
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post #10 of 27 (permalink) Old 07-13-2016, 11:21 AM Thread Starter
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Also if I put it at 1 1/2 the popping is worse but it will some what run on choke. 1 3/4 runs better but won't run on choke. It kinda has me a little confused
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