Ever used an air pump on the gas tank ?

If the tank is coated, there is a chance that the vent is plugged. Just opening the tank would break the vacuum and allow the gas to flow again. I have personally seen this happen and it starves the bike for fuel. It may have been the fact that you opened the tank, not because you pressurized it. Just a thought...

I think a properly vented tank with free flowing fuel lines and petcock will solve all your problems unless the problem is in the carbs

loudhvx wrote:

JimatMilkyWay wrote:

Well youse guys
When it, sort of "ran out of gas" I stopped, opened the cap and "sealed my mouth" on the fill hole such that I could pressurize it and help the fuel to fill the bowls.

Ha ha, I've had to do this a couple times over the summer myself until I replaced the filters.

My friend had to do it to his KZ400 when his filter suffered the same problems as mine.

... and yes, I've heard all of the "blowing the bike" jokes so let it go... :laugh: .

Man,,,
You _KNOW_ I had to think _REALLL_ long and _REALLL_ hard before I ever hit that send button.
I thought it would be ten times worse than it is.:whistle: Now,,,
Let's take a closer look at this gravity feed system and tell me where my math and/or logic is flawed.
Check your chemistry books and see how deep a column of gasoline is needed to produce 1psi pressure. Give up? 37in more or less. The distance, viz "depth" from the bottom of my tank to the top of my carb service level is a maximum of just under 6 in. So,,, 6/37=0.162
So at the bottom of my column of gas, from the tank outlet to the carb I have about 0.162psi or 2.6oz/in² . Yes, I admit the additional fuel depth inside the tank adds a little, and I do mean a little bit of pressure, so long as the tank is slap dab full, which is what I said in the first place.
Even a tiny air lock will dominate and stop fuel flow, and with my twisting turning lines to make everything fit, I need a little help.
One thing that might work for a while, while everything is connected, is to some how drop the lines or raise the tank till I can purge the lines. This might help for a while, but the air will creep, or possibly flood back in the first and every time I turn off the engine and let it sit.

Post edited by: JimatMilkyWay, at: 2007/12/12 19:34

79MKII wrote:

If the tank is coated, there is a chance that the vent is plugged....

Thanks for the idea MK2. I don't know if every tank vent uses the same scheme, but mine is beautiful in it's simplicity. I took the three screws out of the vent and disassembled it, just to see if it needed re-engineering you understand. The hole in the paper gasket is in the correct position and the channels are perfectly clean. I believe I have correctly diagnosed pressure/flow problems because of additional length and the twists, turns and extra resistance of the filters and air locks, viz bubbles in my lines.
But, keep the ideas coming.
Jim@MilkyWay

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I agree with the pressure calcs you did. 1 psi may be too much for the needle valve then.

Since you are running external filters, maybe you could try an old petcock and remove the screen on it. That way you know any restriction is in the external filter only.