xs1100 - carb rejet

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Last year I replaced the factory exhaust. This was not by choice. Unfortunately the factory exhaust literally rusted in half. I had it welded back together but that only bought me a few months before it rusted apart again. No fault of the exhaust, 30 years is a pretty good run.


I fitted an aftermarket exhaust. This exhaust flowed more freely than the original exhaust. That, combined with a K&N air filter the previous owner fitted, and the bike was running a little lean. I didn't put 2 and 2 together at the time though. I cleaned the carbs, set float level, balanced them, then repeated this process. Finally I drilled out the caps on the air idle mixture screws and cranked them up from the factory setting (1-1/2 I think) to 5 turns. On this carb model the idle setting affects the entire RPM range. This made idle way to rich but corrected the mid and top end lean condition. It idled only okay and, more annoyingly, I could smell gas when I was stopped.


The bike stayed in this state for about 200 miles before I decided to go for a rejet. The BS34 carbs used on the 1981 XS1100 Special (SG) use 110 main jets and 42.5 for pilot jets. Its the same for all 4 carbs.


I picked up 115 and 120 main jets so I had two sizes up to play with. Likewise I also picked up 45 and 47.5 pilots. I started by just installing the 115 main jet and 45 pilot jet. I set the air idle mixture screw back to 1-1/2 turns out.


Upon reassembly, the bike runs really well in the mid and upper throttle range. It has an acceptable idle but stumbles a little just off idle when not fully warmed up yet. It also has a slight burp when decelerating. I think I am running a little lean now at idle. As soon as I have some time I will try 2 or 2.5 turns out on the air idle mixture screws and see if that helps.


Preview Image Size
main jet unscrewed. This one was missing the washer... doh.
pilot jet removed
really difficult to read but this jet is a 110
new jets from mikesxs. same carbs used on the xs650
slide needle is not adjustable on this carb model, though you can install a washer to raise it

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