Carbs keep flooding into main throat.

CaseySmithersxs

CaseySmithersxs

XS650 Junkie
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Okay guys, I really dont post questions on here unless I've tried everything I can think of. So here I am. My carbs "mainly left" keep flowing fuel into the main bore of the carb"throat" as I call it, its coming up through the brass fitting that the needle slide goes into. Petcock is OFF and NOT leaking, it drained all the fuel ou the line until its dry. Both float are set to 25.50 which is on the lean side. I also did the clear line test with the carbs level on my bench, the levels were not high "under the bowl flange". New needle and seat on left side, and right needle and seat seem to be performing correct, if so blow into the fuel inlet and the float is resting on the needle, it will NOT let any air through. I've also submersed both float in hot water for a fairly long time, and no bubbles or water in the floats.

So....
Float levels-25.50=check
Needle valves-no air flow when floats are resting=check
Floats-no leak=check

ONLY THING I CAN THINK OF IS THE BRASS PIECE THAT THE NEEDLE SLIDE GOES INTO IS LEAKING, But I dont know if thats even possible. Im out of ideas... Thanks in advance for the help.
 
CaseySmithersxs said:
Okay guys, I really dont post questions on here unless I've tried everything I can think of. So here I am. My carbs "mainly left" keep flowing fuel into the main bore of the carb"throat" as I call it, its coming up through the brass fitting that the needle slide goes into. Petcock is OFF and NOT leaking, it drained all the fuel ou the line until its dry. Both float are set to 25.50 which is on the lean side. I also did the clear line test with the carbs level on my bench, the levels were not high "under the bowl flange". New needle and seat on left side, and right needle and seat seem to be performing correct, if so blow into the fuel inlet and the float is resting on the needle, it will NOT let any air through. I've also submersed both float in hot water for a fairly long time, and no bubbles or water in the floats.

So....
Float levels-25.50=check
Needle valves-no air flow when floats are resting=check
Floats-no leak=check

ONLY THING I CAN THINK OF IS THE BRASS PIECE THAT THE NEEDLE SLIDE GOES INTO IS LEAKING, But I dont know if thats even possible. Im out of ideas... Thanks in advance for the help.
Click to expand...

On the BS38 carbs, 1970 to 1979, the needle jet has a rubber O-ring. If you look into the carbs, with the engine running, and see raw fuel coming out around the needle jet, then the O-ring is worn out, and must be replaced.
 

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It leaks fuel here when the engine is off also.. This is where its leaking. And how do I take those needle jets out? PS these are not my carbs lol. These look horrible.
 

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I know you tested, still, double check float needle valves. If you have spares (known good ones) laying around swap them in.

Sometimes they look good but will leak like sieves once gas is pushing through, depending on how higher up the petcock is.

Shouldn't take much to rule them out.

I've had to replace them in 3 sets of carbs, always thinking "it can't be that"...
 
Since you're referring to the needle jet as "the brass tube," it's pretty clear that you haven't bothered to follow the link to the XS650 Garage Carb Guide--too busy cutting things up to learn the machine, I guess? Anyway, you're creating a mystery where none exists; if the float system was adjusted correctly and sealing correctly, fuel couldn't rise to a level that would take it past the NJ into the venturi with the engine not running. One possibility is that a sloppy pivot could be causing the float to hang up. A fresh O-ring is definitely needed.
 
No I've actually read through the guide you and 5Twins created multiple times, and I use it ALL the time as a reference for different problems. So thanks for creating it, its a huge help. And are you meaning a sloppy pivot on the float itself? And I'm picking o-rings today. Could someone post a pic of where float levels need to be while doing the clear tube test? As I said ive check my float levels at least 8 times, both sides of the float are at 25.5 which should be lean... Believe me dont see now its possible either, thats why I posted on the forum. Sorry if I come off as an moron, or that I haven't taken the time to thoroughly reqd through your carb guide before bothering everyone on the forum. Because I have gone through it. Thanks for the help...
 
Yep, I mean the pivot on the float itself, the part that goes around the pin. If the pivot is deformed (common in Chinese repops) or worn sloppy, the float can cock and lock up. Anyway, your problem is somewhere in the float system, and if you're at 25.5 mm. with a sight tube showing the level to be below the flange, the float and/or valve has to be malfunctioning.
 
They are the original floats are are in good condition, no crimps or binding on the mounting post. With the sigh tube the level is just below the flange, thats too high? Where should it be?
 
Find and put in some float needles that are rubber tipped.. They are not only just plain superior, you can rule that out. I don't mess with any other kind.
 
I'm just lost... My float level is below the carb body where the bowl meets the carb, but fuel is still coming up through the needle jet... When the bowl is full at the correct float setting, is the fuel even high enough to reach the seat if the needle jet? And the leaking is worse when on the side stand.
 
CaseySmithersxs said:
I'm just lost... My float level is below the carb body where the bowl meets the carb, but fuel is still coming up through the needle jet... When the bowl is full at the correct float setting, is the fuel even high enough to reach the seat if the needle jet? And the leaking is worse when on the side stand.
Click to expand...

Everyone has been telling you the problem is with the float needle valve, so you should focus on that area. Your petcock(s) must be passing also.

Somethink to remember...................the float valve is not an isolation valve. Its a flow control valve, designed to do its job when the engine is running and consuming some fuel. That's why you need a good petcock, because its the isolation valve that does a complete shut off of the fuel.
 
Float valves are new from 650central. And my 1 manual petcock is NOT leaking either. The carbs drain the fuel lines dry, no more fuel is getting past the petcock... And the petcock is also new, all brass ball valve from lowbrow.
 
OK, one more time! You know that the float system is working when the carbs are level on the bench, the level you read with the sight tube is correct, and unless those float valves from 650 Central had "MXS" as the first characters of the part number, they're genuine Mikuni brass, and it doesn't get better than that. That brings us back to the float. If the pivot is too sloppy, it's going to be prone to malfunction when the bike is heeled over on the side stand. Try leveling the bike side-to-side and see what happens.
 
Okay dude, I'm not sure why it seems like everyone's got an attitude about this thread. And I also said it flooded when its level on my bench.... And as far as I know the float pivot looks fine.
 
grizld1 said:
unless those float valves from 650 Central had "MXS" as the first characters of the part number, they're genuine Mikuni brass
Click to expand...

That means CMXS... is a genuine part?


CaseySmithersxs said:
Okay dude, I'm not sure why it seems like everyone's got an attitude about this thread. And I also said it flooded when its level on my bench.... And as far as I know the float pivot looks fine.
Click to expand...

If you use good parts it will work. Just about that easy. Maybe post a pic so people can see if they're in right?
 
OK, Casey, I'm clear on what you're seeing now; I thought the carb checked out on the bench but not on the bike. You're right, the floor of the venturi is a good bit higher than the bottom of the flange, which is where your sight tube tells you the fuel level stops--but the gas entering the venturi is telling you otherwise. I'm stumped.
 

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