Backfire Fix for 1981 XS1100H

[JosephM]

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?

[BA80]

Try backing the idle mixture screws out a half turn and see if that makes a difference.

[TopCatGr58]

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.

T.C.

[James England]

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