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Old 06-21-2012, 04:34 PM
JosephM JosephM is offline
Join Date: Apr 2012
Location: Atlanta, Ga.
Posts: 34
Backfire Fix for 1981 XS1100H

Previous owner replaced airbox w/4 individual pod filters. Replace original exhaust with free flow exhaust. Starts, idles, accelerates perfectly. However, upon letting off the gas and engine braking, I get a pop pop pop and then a loud backfire - not a good thing to have happen in the city of Baltimore!

1. Is there an easy adjustment?
2. Rejet the carbs?
3. Replace the original airbox & baffles?
4. Any other suggestions?
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Old 06-21-2012, 05:00 PM
BA80's Avatar
BA80 BA80 is offline
Doctor of XSology
Join Date: Oct 2010
Location: Tulsa, Ok
Posts: 9,852
Try backing the idle mixture screws out a half turn and see if that makes a difference.

Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.

― Albert Einstein

80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

The list changes.
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Old 06-21-2012, 06:44 PM
TopCatGr58's Avatar
TopCatGr58 TopCatGr58 is offline
Join Date: Jul 2002
Location: Portsmouth, Va.
Posts: 12,620
Hey Joseph,

Aside from Greg's advice, you need to find out what jets are in the carbs, because with those mods....it's possibly running too lean anyways, and you don't want to burn holes in your pistons!

Even though the manuals say that the carbs might have staggered sizes... smaller outer cylinders, larger inner....most have found the OEM setup to be the same sized jets across all 4. My 81SH had 110's across stock. Those types of intake/exhaust mods calls for about 3 sizes UP on the mains, as well as possibly 1 up on the pilots...but many have been able to just adjust the OEM pilots with a few extra turns out.

Also....you could set the idle a little higher as well, which would keep the butterflies open a little more when you drop the throttle completely and would be less lean to help reduce the decel popping.

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Old 06-21-2012, 06:48 PM
James England's Avatar
James England James England is offline
XS-XJ Super Guru
Join Date: Oct 2010
Location: North of England
Posts: 3,039
It's definitely too weak, I'd say. Pops and bangs on the overrun are usually the sign. Those pods (not my favourite mod) will allow more air in the mixture, assisted by the freeflow exhaust. Personally, I'd fit the OEM airbox and filter! That will richen things up
XS1100F 1980 European model. Standard. Dyna coils. Iridium plugs. XS750 final drive (sometimes). Micron fork brace. Progressive front springs. Geezer regulator/rectifier. Stainless 4 into 2 exhaust. Auto CCT (Venturer 1300) SOLD. New project now on the go. 1980 European model.
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