Originally Posted by amk
I cannot pinpoint you to the exact cause of the problem, but the theory of problem solving is simple enough. DR does not have a gas pump, i.e. gas flows free to the carb by its weight and atmospheric pressure.
So the first one is to make sure the carb's inlet is below the petcock. The last usually has a pipe of 5 cm. height inside the tank, so everything under the the pipe is stayed there forever and cannot be used.
Second, make sure the gas inside is under the atmospheric pressure, the breather is not blocked etc. Just take the gas cap off and depress start button again.
Third, remove all barriers between tank and carb's inlet, i.e. filters, here I am not sure, but there probably is a small oem one right in the tank petcock or in the carb. Take the petcock out, open it, disconnect the hose from inlet and blow into petcock, should be no resistance to the air flow.
It is one of three reasons, which one is yours? It actually may be all 3 of them simultaneously.
Originally Posted by Kommando
Not quite right. The DR and other carbed bikes are primarily fed by gravity. There's a bit of suction/siphon going on too, but the primary method of getting gas into the carb from the tank is by gravity feed. As long as there is no kink or blockage in the line, you basically just want the fuel to NOT have to flow uphill to get into the carb. Suction will overcome a little bit, but it can also allow air-bubbles to get into the line and affect fuel flow. The flow from my petcock to my carb is all either down or sideways. There is no uphill flow. As long as my tank is venting ok, I have no flow issues. I can run my tank pretty dry. Route your fuel lines so that there is NO uphill flow. If you can't do that, you may want to install a fuelpump.
Up hill is OK as long as its to the carb or a fuel tap. This gives any air the chance to escape. If its just a loop/siphon in the fuel line, then that when its a problem.
I got rid of the internal filters from the taps, and the one to the carb. I still have a servicable in line filter, which is also positioned vertically to no air traps in it either.
Having a swivelling inlet on the FCR helps for sure too.
On the BST, I cut off the original pipe and threaded in a straight fitting. When I tried to turn it, I thought it might break the carb.