carburetor spitting fuel

Fjfreude

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1967 xs650c with BS38s. I did a thorough rebuild and clean of the carbs before it went to bed this winter and I know the float heights are correct. Bike starts fine but idles rough on the left side. On idle, the left side pops and sputters and the headers are significantly less hot. Runs better with the air filter off but I noticed that the carb is spraying a mist of fuel out of the right hole near the air filter (marked in the attached picture). The jetting seemed great when it got parked last winter and I did replace the valve stem seals over winter too. Im pretty confident I didnt screw up the valve spacing but I may go check. The right side is well behaved, which makes me think theres gunk or something in the left carb.

Any clear ideas here? Clean the carbs again via the carb guide? Any particular spots to check?
 

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Fjfreude

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Thanks Gary, I'll check that out when I clean out the pilot circuit. Although, I did replace all the fuel lines last year. Unless they getting eaten away by cleaner/seafoam and depositing junk. I didnt see anything in the bowls when I looked this weekend, though.

For anyone else with a similar problem, I'll leave these two links here. I think they will come in handy:

https://www.xs650.com/threads/carb-clean-idle-circuit.58321/

https://www.xs650.com/threads/rever...bs38-carburetor-pilot-circuit-idle-jet.42002/
 

Fjfreude

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Well, I took it apart, and alternated carb cleaner and the air compressor in the relevant ports. The problem is still there. Either I've got something reeaaallly stuck in there or its another issue. Maybe its time to soak some parts? Im not sure. Insight welcomed.
 

grizld1

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Float height is an indirect measure of fuel level. The problem cylinder fires better with the air filter off, which tells you that the left side fuel/air mixture is too rich, which tells you that fuel is being picked up by engine vacuum and passed to the cylinder. Set up a sight tube and find true fuel level; I'd bet dollars to donuts that it's too high. If so, inspect the float for leaks by immersing it in hot water and looking for bubbles.
 

Fjfreude

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Float height is an indirect measure of fuel level. The problem cylinder fires better with the air filter off, which tells you that the left side fuel/air mixture is too rich, which tells you that fuel is being picked up by engine vacuum and passed to the cylinder. Set up a sight tube and find true fuel level; I'd bet dollars to donuts that it's too high. If so, inspect the float for leaks by immersing it in hot water and looking for bubbles.
Hmm easy enough to check. I did all that when i rebuilt the carbs but there is always room for human error. Especially for me.
 

Jim

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Runs better with the air filter off but I noticed that the carb is spraying a mist of fuel out of the right hole near the air filter (marked in the attached picture).
Curious how you determined it was out the pilot air hole? If it was a mist, how could you tell? Reason I ask.... fuel mist out the air hole would tell me the pilot circuit is clear, at least clear enough for fuel to make it's way to the air mix section of the pilot passageways. Then, where is the pressure coming from to mist it out the air hole? The other end of the pilot circuit is in the throat... a low pressure area that sucks, not blows. And if it was blowing, it ain't plugged. Very curious.
I suppose it's possible you're seeing a slight amount of exhaust reversion, but that would be the bellmouth generally (entire carb inlet) and not the pilot air hole.
Without seeing it running, I suspect that's a rabbit hole and not the real problem. Follow Griz's float suggestion... then go from there.
Im pretty confident I didnt screw up the valve spacing but I may go check.
Might be worth checking. An intake valve not fully closing would blow back through the carb.
 

Fjfreude

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Curious how you determined it was out the pilot air hole? If it was a mist, how could you tell? Reason I ask.... fuel mist out the air hole would tell me the pilot circuit is clear, at least clear enough for fuel to make it's way to the air mix section of the pilot passageways. Then, where is the pressure coming from to mist it out the air hole? The other end of the pilot circuit is in the throat... a low pressure area that sucks, not blows. And if it was blowing, it ain't plugged. Very curious.
I suppose it's possible you're seeing a slight amount of exhaust reversion, but that would be the bellmouth generally (entire carb inlet) and not the pilot air hole.
Without seeing it running, I suspect that's a rabbit hole and not the real problem. Follow Griz's float suggestion... then go from there.

Might be worth checking. An intake valve not fully closing would blow back through the carb.

Oh yeah! That makes sense too. I can watch a cone of what i think is fuel coming out of the pilot hole. Also the clutch cable right behind the carb gets misted and wet. The other alternative is that the pilot hole is smoking, which looks like mist, and the back end of the carb is spraying the fuel.

However, why it would come out of either hole where air is supposed to come in certainly confuses me. Maybe a rabbit hole indeed.

All seems like good suggestions. Ill check floats, heights, and valves. Thanks!
 

5twins

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Did you insure that the pilot circuit passageway through the main carb body is clear? The fuel/air mix from the pilot jet enters the main body through the pilot inlet on the bottom of the carb .....

Pilot Inlet BS38.jpg


..... and exits into the main bore out 4 tiny holes .....

Pilot Outlets BS38.jpg


Yes, air is usually drawn into the air jet, but that's when it's being pulled up through the carb body. If that passageway is plugged, I think it's possible for the air rushing into the intake bell to pull the fuel/air mix from the pilot jet out the air jet.

I think I'd try back flushing the circuit. Remove the float bowl and the mix screw. Cover the 4 little holes in the main bore with a finger, squirt carb cleaner in the mix screw hole, and blow it through with compressed air. It should come out the pilot inlet on the bottom of the carb.
 

Fjfreude

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Thanks! I cleaned out the passages with air and cleaner but did not know where to look to see if things were going right (i.e. pilot inlet). Im also not sure I blocked all four of the little holes at once. Easy enough to go back through and check when im confirming float and heights.
 

Fjfreude

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Well folks, all the above was done and the spitting continues. I blew air out the mix screw (air came out the pilot), reset the float height (it was off-level by about 1.5 MM on one side), checked the float for leaks (no air bubble when submerged), checked the float valve (clean and it sprung), and checked the exhaust/intake valves (all good).

I did confirm that fuel is coming out of the pilot hole. When i stuck a paper towel where the air filter goes, theres a small wet spot where the pilot hole. When I pull the throttle, the carb really spits out fuel. The other carb is dry.

Perhaps I missed something when I did the above, maybe its something else. Current hypotheses include bad spark plug (unlikely because I switched them and the problem was the same), coil/wire issue, bad seal on the needle jet, and gremlins clogging the carb overnight.

What did I miss?
 
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Fjfreude

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What are the chances it has to do with the coil or spark plug wire? I say that because it had trouble starting up right after winter. I kept the wires on the coil end but switched the wires on the spark plugs and it started right up. Is that indicative of anything?

I have a "green monster" dual output coil, can one output go bad and the other be fine or does it all just go bad at once? Maybe the wire or coil to the left cylinder is just bad.

Edit: both plugs have a visual spark when I kick the bike over.

PS. I did change out the plug to a new one, but the carb kept spitting fuel.
 
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bosco659

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Did you insure that the pilot circuit passageway through the main carb body is clear? The fuel/air mix from the pilot jet enters the main body through the pilot inlet on the bottom of the carb .....

View attachment 211739

..... and exits into the main bore out 4 tiny holes .....

View attachment 211740

Yes, air is usually drawn into the air jet, but that's when it's being pulled up through the carb body. If that passageway is plugged, I think it's possible for the air rushing into the intake bell to pull the fuel/air mix from the pilot jet out the air jet.

I think I'd try back flushing the circuit. Remove the float bowl and the mix screw. Cover the 4 little holes in the main bore with a finger, squirt carb cleaner in the mix screw hole, and blow it through with compressed air. It should come out the pilot inlet on the bottom of the carb.
Wear a pair of safety glasses when doing this and keep your eyes out of the direct line of discharge from the orifice. Nasty stuff to get sprayed into your eyes.
 
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