bike will only run with the gas tank off ? Help

So here the deal, I just got the bike out today and it not running right. So I took the tank off and put a funnel on the gas line and filled it wilth gas and it start right up. But when I put the tank back on it it is really hard to start and then when I do get it running with the tank on it only will run for a little bit. What Im thinking is the carbs need to be flushed seafoam . I just had them rebuilt last summer so there pretty clean. The other thought was that there might be a hole in the line that pressurizes the tank?
Not sure. if you guys have any ideas let me know. Just in case its a 86 vf500.I am only home for a week then I go to india for 9 weeks So i dont have alot of time.

 

....."Pressurizes the tank" ??????

Most likely cause--if bike runs OK when "bottle fed"--is a loose connection or hole or crack in the vaccum line from behind the petcock to its connection on left rear cylinder.

Pull fuel line off petcock, apply suction to small tube, and fuel should flow. If not, try cleaning the filter screen on the tube located above the petcock.

 

Or your fuel lines are crossed, or your tank isn't venting...

 

or a tweaked fuel pump

 

No fuel pump on an '86 500 i think.......gravity is more reliable.

 

yeah I dont have a fuel pump. Im gunna try and work on it tonight .

 

+1 on what Sman and Crusty said.

I would put my money on either a petcock issue or a tank venting issue. A simple test for the tank venting issue is to open the gas cap and try to run it with the tank open. If all goes well then your vent line is blocked somehow. If it doesn't then I bet you could disconnect the line after the petcock but before the carbs and find that you simply have an inadequate fuel supply reaching the carbs and would know it has something to do with the petcock.

 

Or, not to be an ass, when you put the tank on you pinched off one of the lines, just sayin, it could happen.

 

none taken

So I looked a little bit into that but did not see anything pinched!

 

I'll admit that I've done this. Its a possibility so you're definitely not an ass for suggesting it.

 

Do you have the vacuum line conected to the petcock?Hehehehe....petcock.

 

yeah I have it all setup right. I discovered this morning that If I tilt the gas tank to the right side it starts and runs great.Now if I recall right the hose at the front of the tank is suppose to blow air out of it into the tank. its the hose that hides up front of the tank and runs down under the front of the engine and to the canister up front?. Any who its not blowing any air out of it at all. So Im thinking thats the problem. let me know if you have had this problem. I would put some pictures up if someone would let me know how to do it.

 

Debris in the tank?

 

No. The hose does nothing except equalize the pressure between atmosphere and the inside of your tank.

-Jake

 

So I got it running with the tank on for a little bit but it boggs down after about 3 mins. So I took the petcock out and it looks fine no debries in it.and when the bike dies out if I take the tank and tilt it it starts right up again for a few minutes then dies out

 

so have you run it with the tank lid open?

 

Yes I have

 

Float bowl vent line. Float bowl cannot fill because air can not escape.

Or the float bowl vent line hooked to the charcoal cannister, and the cannister has water in it? So the float bowls cannot vent.


Take a screw driver and empty the float bowl drain. Then turn on the gas from the tank and wait a minute. then check the float bowl and see if it filled.

ALSO Just hold the tank up and turn on the gas. Does fuel run out ?
Then hook up the vent line with an extension tube. Does the gas run out now?

 

Ok is there any kind of photo for that. Don't were it is located to take off.

 

Ok I found out that the tank was pinching the fuel line when I would mount it right .the reson for this is because last summer I had the bike worked on and the shop couldent get the orginal fuelline so the found something close.so i have to figure out how get an orginal fuel line. On the good side I did take it out for a ride and it runs like a champ.