Flames from carb on throttle

Fingerscrossed

XS650 Enthusiast
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Hi, so I’ve recently gone through my ‘75 as it was running on one cylinder, replacing the coil fixed that. I also put on a new (old) set of BS38s that I cleaned, just with carb cleaner and an air compressor.

So it starts first kick, but upon throttle there are flames coming out of the left carb, that I can see through the air filter… it is consistent upon throttle.

The mix screws are set to 2 1/4 turns out, they are 77-78 carbs so are to spec.

I went through the point gap, and valve clearances but haven’t touched timing. Could it be I’ve set one sides valve clearances wrong? I did notice the left side (flame side) exhaust was getting hotter quicker than the right side.

I couldn’t find any threads on actual flames coming out from the carb, it’s on every throttle at idle which is a bit concerning. It’s not backfiring, there is no sound, and any help would be appreciated!
 
Last edited:
Hi, so I’ve recently gone through my ‘75 as it was running on one cylinder, replacing the coil fixed that. I also put on a new (old) set of BS38s that I cleaned, just with carb cleaner and an air compressor.

So it starts first kick, but upon throttle there are flames coming out of the left carb, that I can see through the air filter… it is consistent upon throttle.

The mix screws are set to 2 1/4 turns out, they are 77-78 carbs so are to spec.

I went through the point gap, and valve clearances but haven’t touched timing. Could it be I’ve set one sides valve clearances wrong? I did notice the left side (flame side) exhaust was getting hotter quicker than the right side.

I couldn’t find any threads on actual flames coming out from the carb, it’s on every throttle at idle which is a bit concerning. It’s not backfiring, there is no sound, and any help would be appreciated!
Others have competence, me not so much specific to these bikes. However...if y'all have flames and sparks and gasoline it's probably a good idea to have a way to put out a fire...

Advice> assume nothing, create truth table. work through every aspect taking notes.
 
The timing was way off 👍 valves were spot on although when doing the covers back up one of the bolts stripped, so got an oil leak…

It has happened a few times on this bike, is that pretty common? The oil drain plug needed a pretty big breaker bar to get undone so it could be that the PO was just very extreme…

Also there is still some popping out of one cylinder, mostly on decel. The boots seem good, I have two pairs so could try swapping but I haven’t replaced the butterfly seals, is that recommended? Only thing putting me off is potentially rounding the heads as I’ve heard it’s tricky
 
The timing was way off 👍 valves were spot on although when doing the covers back up one of the bolts stripped, so got an oil leak…

It has happened a few times on this bike, is that pretty common? The oil drain plug needed a pretty big breaker bar to get undone so it could be that the PO was just very extreme…

Also there is still some popping out of one cylinder, mostly on decel. The boots seem good, I have two pairs so could try swapping but I haven’t replaced the butterfly seals, is that recommended? Only thing putting me off is potentially rounding the heads as I’ve heard it’s tricky
For removing butterfly plates, using a Dremel tool, carefully grind the backs of the screws off where they have been peened over. Use a good JIC screwdriver to remove the screws, applying good downward pressure, but not enough to bend the throttle shafts. Some use a piece of wood to support the back of the throttle shaft to support it while removing the screws. This requires slide removal. I’m sure other will chime in on this subject. When I remove throttle shaft screws, I apply slight forward and backward twisting motion of the screwdriver until the screws break free.
 
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