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Buell Forum » Old School Buell » Archive through October 14, 2009 » Pop back thru carb -- « Previous Next »

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Randy_spann
Posted on Wednesday, September 23, 2009 - 03:04 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Anyone know what causes pop back thru carb? Happens infrequently (worse when engine is cold), but every once in a while... Could the fuel mixture be too lean?
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Fast1075
Posted on Wednesday, September 23, 2009 - 03:13 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Fuel mixture is definately too lean...fatten it up a bit..or it has a vacuum leak.
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Kalali
Posted on Wednesday, September 23, 2009 - 03:23 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

This may or may not apply to you but those "pop backs" or backfires thru the intake tend to put tremendous stress on the butterfly shaft, specially during cold start ups (when the throttle plate is mostly closed). I ended up with a broken shaft only after half dozen backfire episodes. Fortunately nothing was sucked into the motor. Just visually inspect the butterfly to be sure. Especially check the screws holding the plate to the shaft for tightness.
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Buell_bert
Posted on Wednesday, September 23, 2009 - 08:14 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

First of all let it warm up. Unless your leaving a bank under unusual circumstanse
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Billetmetallic
Posted on Friday, September 25, 2009 - 01:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

mine did this progressively worse as my intake seals leaked more and more, it started off just as you describe. I would say replace your intake seals, and while you have your carb off take the top (or bottom, depends on perspective) off and make sure you have the 190 main and 45 pilot jets in there (if you have intake and exhaust mods that is) But i would bet that its your intake seals, from what I understand, they dont last long

-g
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Billetmetallic
Posted on Friday, September 25, 2009 - 11:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

oh, and 2.5 turns out from bottom on the mixture screw with above mentioned jets and mods
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