Carb Issues

spectra

XS400 Junkie
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Ok am beating my head against the wall.............bike was running great now well.......it is popping off idle and sluggish. Not sure wtf is going on. Once after 4K it runs great but sluggish now off idle.

Bike has one up size on pilots and one up on mains........everything else is stock to the 81........I think its about 3 turns out on the air mixture screws.

Carbs have been off a few times to go through and re adjusted the floats again........still have issues of fuel coming out the air cleaner if I dont shut the the petcock off.......aftermarket one and I think its a POS........

Let me know what you think as I am tearing them off tomorrow as I need a last of the season ride.........and all jets are genuine Mikuni from Jets R Us so no off brand crap.......
 
Am thinking the one size up pilot may be the issue..................

Cant remember what i did on my other bike but it runs great no issues what so ever.........
 
Could be the weather influencing jetting, as you tend to need more fuel when its cold.

Ive had popping exhaust syndrome from a hole in the exhaust, an air leak at the carb boots, and bad timing. If you have the aftermarket boots, the rubber is fragile. Ive torn them a couple times before and ruined them. Most recently, I forgot to put the rubber cap on a sync port and that caused a lot of popping on both sides. After I passed about 4k rpm when riding, performance picked up a bit and it was less noticeable, but I caught it soon after and made a huge difference.
 
Weather has been decently warm still in the 70s but only for a few more days. Am going to pull the tank today and mess with it.
 
Well call me stupid :laugh2: went out to mess with it and decided hey lets fire it up one more time before digging into it.........well left cylinder was dead and not firing.......raw fuel going through well go figure why its backfiring........popped in a brand new set of plugs and bam both cylinders fire and runs great.

I think all the messing around with it and just working the idle messed up the plugs as both were black.......still probably need to work on the carbs a bit but hey summer is almost over so going to do that in the winter........
 
Well call me stupid :laugh2: went out to mess with it and decided hey lets fire it up one more time before digging into it.........well left cylinder was dead and not firing.......raw fuel going through well go figure why its backfiring........popped in a brand new set of plugs and bam both cylinders fire and runs great.

I think all the messing around with it and just working the idle messed up the plugs as both were black.......still probably need to work on the carbs a bit but hey summer is almost over so going to do that in the winter........
hi fella just reading your posts😃I've got one of these bikes😬did you ever get it running right.🤔
 
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