Full tank of fuel.......but it's not flowing?

[Geers]

Ok so I am running a sportster tank on my 78 XS650 with mikuni vm 34s. My problem is my glass fuel filter will not stay full. I am running a vented cap with 5/16 fuel line and my entire set up is gravity fed. The filter is just after the petcock. While the bike is running down the road the carbs must be sucking just enough fuel to keep it running but when I come to a stop the bike really wants to cut out. Also if I loosen the hose clamp at the petcock a little bit the glass fills up completely. But In turn the fuel starts leaking. Am I missing something or what? Please help

 

[ippytattoo]

Have you tried to run without the gas cap? sounds like it could be a bad vent.

 

[Geers]

Yup does the same with cap off. That was my first thought.

 

[Detale]

I had the same issue with the small glass filter. I found that if the hose was too long it would create some kind of unexplainable suction in there and finally I just gave up on it. Plastic filter for me now with no issues.

 

[Geers]

What exactly do you mean by the hose being too long? I have might set up in the straightest shot possible without kinking the line.

 

[Detale]

I had a hose coming from the petcock to the filter and the from the filter to the carb. Ah I forgot to mention it was on my rebel. I couldn't get a straight shot so the total length was longer with the filter in there, bout an inch if I recall. Someone explained to me what the problem was when the hose was too long. Ill try and find it when I get home. For the life of me I can't remember what the problem was, but when I shortened the hose it got better but not quite fixed so I gave up.

 

[weekendrider]

A bubble in the filter won't hurt anything. As long as it will flow.
You could loosen the line at the filter to bleed it.

 

[Geers]

I have loosened the line to bleed it as well. It will just suck the filter dry and only a small amount is visible. In my opinion that filter should be 100% full all the time.

 

[weekendrider]

Ok. The bubble bothers you.
But if it flows does it matter?

 

[Geers]

Well that's the problem it doesn't flow! While running down the road I believe just enough is getting by to keep the float bowls full. It's when I slow down to an idle she revs up and wants to cut out because there is no available fuel in the line after the filter.

And I never said anything about a bubble in the filter. I would love to see bubbles that would mean the filter actually had fuel in it!

 

[weekendrider]

My problem is my glass fuel filter will not stay full......... Also if I loosen the hose clamp at the petcock a little bit the glass fills up completely.

Sorry my assumption was you were seeing a bubble.
A case (again) of what I read isn't what your are saying.

Take the line loose at the exit side of the filter and run it to a catch pail.
Open the valve if it drains the tank without "gulping" I'd say flow isn't the problem.
If it does gulp then you have venting problems.
If it flows slowly you've got a restriction. Could be a wad of plumbers tape(why would people use that on gas lines), thread burr, or the petcock through hole isn't big enough or not lining up with the holes.
Another thought would be the "fittings" on the lines, filter and / or petcock aren't sealing.
Even gravity sucks air easier than fluid.
Waiting for more educated minds to enlighten us.

 

[XSLeo]

If it runs well while riding but won't idle it does sound like an air leak, but not in the fuel filter. Check for air leaks between the carb and head. It could also be a sticky advancer rod. If the advancer sicks advanced the bike idles way high.
Some filters are designed to work after a fuel pump and flow well under pressure. Some are designed to flow well using just gravity.
If your filter was designed for a fuel pump then it won't flow well with just gravity.
If you want to know for sure if it's the filter, run a line without the filter, if it still acts the same it's not the filter.
Leo

 

[Geers]

Thanks for the input. I will troubleshoot and keep you posted

 

[Geers]

So I used the clear plastic style filter and no more flowing issues. The glass style filter was from Drag Specialties. The only thing I can think of is this style filter is only supposed to be used with a fuel pump. Or the filter could be junk. But it works so..... thanks