fuel delivery?

[Guest]

ok. interesting problem.. in the "on" position the bike will run for about a mile, mile and a half, switch to prime, and it runs great. boring, no interesting problem here, right?

i dunno, i'm stumped. I have a:

new petcock
new vac line
new fuel line
checked all the previous lines for pinches and blockages
carbs fully cleaned and soaked just over a month ago.
took the inline fuel filter off.

it seems that the bowls are running out of fuel.. when in the on position.
i also checked the petcock when i hooked it up, when i suck on the vac line, it dumps fuel.

so uh. i'm stumped. i searched some of the fuel threads but they usually lead back to issues listed above.

ideas?

[tkent02]

How does it run on RES?

[seuadr]

How does it run on RES?

you know, i didn't try. i have about a half tank of gas though. i'll try it tommorow.

i'm gonna feel like a freaking idiot if i got down to needing reserve :P

[Dogma]

You switch to prime for normal running, or you simply mean that it runs while on prime?

[seuadr]

i had to switch to prime for it to run.

[hikermikem]

Did this just happen out of the blue? Or after you replaced/checked something.

Make sure your vac line from the carb is connected snugly, and the line isn't leaking at any connection. Same type/length of vac line as compared to the one you replaced??

Don't know... that's a weird one!

[Dogma]

i had to switch to prime for it to run.

Yeah... that ain't right. It sounds like the new petcock has a leaky diaphragm. When you tested it for fuel flow, did you test both On and Prime? I suspect that if you test it on prime, the fuel will slow to a trickle and maybe stop fairly shortly. I know the petcock is new, but it sounds like it's time to double-check the things you know are right.

[Jon Burke]

Is it possible that you're losing vacuum on the line to the petcock via a hole in the line? Maybe a vacuum leak elsewhere dropping the vac being supplied to the hose?

[Nessism]

Maybe fuel tank is not venting properly? When the bike is starting to fuel starve, try removing the gas cap to see if there is a suction lock.

[ironsheik]

Maybe fuel tank is not venting properly? When the bike is starting to fuel starve, try removing the gas cap to see if there is a suction lock.

Wouldn't that cause the issue on the prime setting as well? I'll bet the vacuum line or petcock are faulty as previously mentioned.

[cvmgtwowheels]

All good ideas to check but also check to make sure you are getting vacuum at the carb you may have the wrong carb hooked up, as in my case.

[seuadr]

All good ideas to check but also check to make sure you are getting vacuum at the carb you may have the wrong carb hooked up, as in my case.

0.o you have more than one vacumme hookup?

[ned37]

i used to have a hinckley triumph that did that. it was related to a misrouted fuel line getting an air bubble up high above the petcock. turning to reserve always overcame the bubble because of the higher feed pressure (lower pickup pipe). prime is just a manual reserve with the pickup on the bottom of the tank. make sure your fuel line just goes straight in and down with no upward loop.

[cvmgtwowheels]

On my bike only one carb has the vacuum port the on other carbs the same nibble are vents.

[seuadr]

weird, i thought i replied to this yesterday but the post is gone..

anyhow, i'm an idiot. 4.4 gallons pumped into the tank.. pretty sure it's a 4.5 gallon tank