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Post by randall on Dec 31, 2012 10:13:11 GMT -5
OK, My Diamo has a gravity fed fuel system with a vacuum petcock. Where the fuel line connects to the petcock, is only maybe an inch higher than the carbs fuel inlet. The filter is about halfway between them. What's happening is that as the tank goes below about a third, sloshing lets air into the line which collects in the filter as a bubble. If that bubble gets big enough fuel doesn't flow out of the filter and the bike runs out of gas. I then have to jiggle the filter to get it flowing again, then crank a few times to fill the bowl and I'm on my way again.
So, my question. I want to solve this once and for all. Is there a fuel filter that anyone knows about that has a 90 degree inlet and outlet that I can mount right at the output of the petcock? Something short and stubby would be best. I'm thinking this would more easily expel its air bubble back to the tank, as the horizontal kind always seem to have some amount of bubble.
Any other ideas?
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Post by tortoise on Dec 31, 2012 10:32:19 GMT -5
fuel filter that anyone knows about that has a 90 degree inlet and outlet |
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Post by dyoung1167 on Dec 31, 2012 11:38:37 GMT -5
i don't understand how you are getting air from your tank to the filter. as said it is gravity, not suction fed. physics says it can't. if you have a small crack or other leak at or below the filter you may get a bubble that slowly builds up, but it's not coming from your gas tank. air will always rise, this is why you can run the tank and entire system dry, put fuel in and go (not counting the few cranks for vacuum to operate the petcock)
make sure all flow is up/down depending on how you look at it. most filter will have a small bubble in the small space just before and above the tank side nipple unless it is oriented directly vertical but this affects nothing.
you may also have trash in your petcock keeping it from flowing enough. or, if the bubble is on the carb side of the filter element within the filter it's probably clogged.
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Post by 50cc on Dec 31, 2012 12:16:46 GMT -5
Try shortening the fuel lines
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Post by randall on Dec 31, 2012 12:31:21 GMT -5
i don't understand how you are getting air from your tank to the filter. as said it is gravity, not suction fed. physics says it can't. Gas sloshes left, feed tube is no longer submerged allowing air, albeit a small amount, into the line. Gas sloshes back to the right, gravity forces fuel in and pushes the little bubble down the line ending up in the filter. Get enough of these in the filter and lose flow as it gets below the filters outlet. Petcock might be sluggish at low vacuum. That's something I'll have to check. At high vacuum, cranking, closed throttle, I can fill a cup in about 30 seconds. System is tight. Applied 15 psi to the filler tube and not a leak in sight. |
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Post by randall on Dec 31, 2012 12:33:50 GMT -5
fuel filter that anyone knows about that has a 90 degree inlet and outlet That's the ticket. I'm on it! |
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Post by dyoung1167 on Dec 31, 2012 15:44:37 GMT -5
it doesn't work that way. as long is the line is going down the fuel will not carry the air with it. it weighs more than air and will always drop below it and the air will always travel back up no matter how many times the the opening gets uncovered.
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Post by randall on Dec 31, 2012 16:48:13 GMT -5
It does if the bubble is small enough. It doesn't have enough buoyancy to break the fuels surface tension. I have a clear line from the tank and can watch the bubble appear and travel down the line while my buddy throttles it up and we rock the bike to slosh a quarter tank back and forth.
I'm going to go with the vertical orientation filter. The 90 degree one will give me enough room. Not enough vertical space in that run to use an inline. Going to change the petcock too.
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Post by Blueboy5000 on Jan 1, 2013 7:26:10 GMT -5
I don't see why a 90 degree inlet on a fuel filter would make any difference as it's hydraulics we're talking about here.
You should not be getting air bubbles in your fuel filter, the only way this can happen is if you have a defective petcock (specifically if the diaphragm inside the petcock fails).
Yes the petcock is indeed underrated for most GY6 with gravity feed petcocks. Use a Mikuni style petcock (a passive/ gravity fed style petcock) instead of those tiny ones that usually come stock on our bikes.
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Post by randall on Jan 1, 2013 9:25:46 GMT -5
Blueboy, my thoughts exactly. I ordered this yesterday: www.scootertronics.com/fuelvalve.htmlThe 90 degree filter will just help a lot with the line run. I've got space restrictions, a 24 inch run with only about a 3 inch drop. My plan is to come out of the tank, right into the filter, then 12" of line with a nice steady slope, into the mikuni valve, then about 8" into the carb, steady slope. This keeps the vacuum line short too, always a good thing. I like the filter before the valve. Keeps it from getting mucked up. |
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