85 VF500F Carb Question

Any ideas what could cause fuel to pour out of one of the diaphragm air inlet hoses? Cranking the engine over trying to start it fuel begins to pour out of the tube. Blowing gently into the tube the fuel is coming out of seems to affect the second from the left and right most carb (oriented as if you were sitting on the bike).

Any ideas? Torn Diaphragm?

Thanks
Mike

 

I'm confused. Not really sure of what you are trying to say.
The carbs are numbered according to the cylinders they mount to

As sitting on the bike:

1__4
2__3

The only time I've heard of gas coming out of those plastic tubes is if an air tube is attached where a fuel tube is supposed to go.

 

A float is stuck letting the gas pour out, check the screw on the carb to drain the bowls.. ??

 

I think it's 2_4
1_3 as sitting on bike. It's hard to determine what hose he's talking about.

 

Sorry, I thought it was pretty clear. When you remove the carbs, the fuel feed line from the pump attaches to what I'll call the left most carb, #1 if you wish. Then a metal tube connects the fuel feed from #1 to #2. Then an arrangement of plastic elbows connects #2 and #3, and finally back to a metal tube to connect #3 and #4. Those are all fine and connected correctly.

There is a plastic tube that connects to #1 and #3 with a nipple in the middle of it. There is a long hose connected to the nipple that runs to the bottom of the bike and connects to nothing. There is also a plastic tube that connects #2 and #4 with the same nipple and hose arrangement. When you crank the bike, fuel pours out of the rubber line connected to the plastic tube connecting carbs #2 and #4.

When you crank the bike, fuel begins to pour out of the rubber hose that's attached to the plastic line that connects carbs #2 and #4.

I assumed that those tubes allowed ambient air pressure to one side of the slide diaphragm. It's possible it's a float sticking. That could allow the bowl to overflow, but wouldn't that just fill the cylinder and hydrolock the motor? I don't understand how it could end up coming out of that tube.

And this bike has been totally hacked into in it's life. It's totally possible that the hoses that are connected to the plastic tubes linking the carbs aren't run where they're supposed to go either.

Thanks for the replies.

Mike

 

I guess reading over the replies again I understand the carb/cylinder # confusion. Even though the motor is a V4, the carbs are lined up in a row. Since the intakes are staggered it allows the carbs to mount side by side. Since I didn't know which cylinder is considered #1 I figured it was easier to describe them in terms of left to right as if you were sitting on the bike. With the carbs off the bike, it's pretty obvious which ones I mean, but I realize that not many people will have the carbs off the bike to answer my question.

Mike

 

I believe, but I'm not sure that the tubes with the nipples on them you refer to were originally routed into the metal air plenum.

But in later years, the holes in the plenum were removed and a hose was run under the plenum connecting the two together.

Try the above and see if it works...

The 1_3 carb might also have a tube with a nipple that faces the up toward the rear of the air plenum and should have a "J" shaped hose on it that vents to the atmosphere. The "J" hose is to prevent water getting into the carbs.

 

still seems likely you have a leaky fuel inlet valve.......tapping lightly on the float bowls sometimes cures the problem, and some air blown into fuel inlet hose might blow out small debris in the valve.....

 

It seems pretty obvious to me that the problem is a stuck float. The fuel is leaking from the bowl vent lines, a typical indication of the problem.

Did we get off the subject with the whole carb numbering thing? Just wondering...

 

I guess we did. So those tubes I'm talking about that aren't the fuel supply tubes are bowl vent tubes?

 

Is it possible that the float level is off so the float hits the housing before it pushes the needle all the way closed?

 

From your description it sounds like that's what you are talking about. If so the problem is a stuck float, usually something in the needle/seat that isn't allowing it to close off. Often that 'thing' is a piece of the plastic screen that is part of the needle/seat assembly.

 

Well the carbs are apart now, so I'll work on them later this week and let you guys know how things turned out.

 

It's been a little while, but I took the float bowls off, checked all the floats, checked all the float valves and seats and found nothing. It was obviously a float sticking, but disassembly found nothing out of sorts. I think that my flipping the carbs around, over, under and through while replacing the o-rings on the steel transfer tube from the first carb bowl to the second bowl managed to shift one of the floats enough to stick it. I probably could have fixed it on the bike by just tapping the bowls with a wrench until it freed up.

So we put the assembly back on the bike, and fired it up. It caught immediately and just as immediately began pouring fuel out of the center of the carbs. Back off came the carbs. Inspection found that those stupid 90 degree elbows that link the center two carbs float bowls was leaking. So no I must do the one thing that I have gathered you must never do. I have to unbolt that top plate and separate the carbs!!!!

It actually wasn't that bad. I took the plate off, carefully separated the middle carbs just enough to work out that goofy plastic assembly, replaced the three o-rings and reassembled the top plate. The only tough part was reinstalling the two small throttle linkage springs that came off when the carbs pulled apart. :strong:

Back on the bike and she fires up and runs with no fuel leakage.

Thanks for all the help. :thumb: