fuel flows only on pri. and vac. ports open on tank

[my90kat750]

fuel only flows on pri.when I turn it on nothing and of course off is nothing.is it good to keep it on pri?the vac. line from the carb to the petcock it hooked up but the port on the sender and bottom of tank is open.do those have to be plugged?
could this also be the reason I have a low rpm dead spot of is it cause I just need to jet it?

[Vandil]

Prime is gravity feed, and you shouldn't just park and leave the bike overnight with it set on Pri. Sounds like the fuel petcock valve needs a rebuild if it flows on Prime only and the vac line is hooked up and un clogged.(has suction?)

[my90kat750]

Prime is gravity feed, and you shouldn't just park and leave the bike overnight with it set on Pri. Sounds like the fuel petcock valve needs a rebuild if it flows on Prime only and the vac line is hooked up and un clogged.(has suction?)

doesnt seem like the vac. line has suction

[JayBell]

time to rebuild the petcock, and replace the vacuum line as a just in case.

[bob393]

There is no off on these bikes. Prime, on, and reserve. Fuel only flows by gravity in the prime position, you need vacuum for the on and reserve to flow fuel. If the vacuum line is hooked up to the port on the side of carb 4, that is correct. The hole in the bottom of the tank by the fuel gauge sensor has nothing hooked up to it but the one coming straight down behind the fuel cock should have a drain hose running out under the bike. That's not critical and will not effect the running of the bike but if you overfill the tank that's where it runs out of.
I would take the hose off carb 4, put the fuel cock to run and apply vacuum to the hose to see if fuel flows. I would just gently suck on it but I'm not going to recommend that here. If fuel doesn't flow and the tank has gas in it than it's time for a fuel cock rebuild.

[my90kat750]

There is no off on these bikes. Prime, on, and reserve. Fuel only flows by gravity in the prime position, you need vacuum for the on and reserve to flow fuel. If the vacuum line is hooked up to the port on the side of carb 4, that is correct. The hole in the bottom of the tank by the fuel gauge sensor has nothing hooked up to it but the one coming straight down behind the fuel cock should have a drain hose running out under the bike. That's not critical and will not effect the running of the bike but if you overfill the tank that's where it runs out of.
I would take the hose off carb 4, put the fuel cock to run and apply vacuum to the hose to see if fuel flows. I would just gently suck on it but I'm not going to recommend that here. If fuel doesn't flow and the tank has gas in it than it's time for a fuel cock rebuild.

no vac. line on carb 4.that port is open and the vac line for the petcock goes between 2 and 3 carb

[Kreylyn]

no vac. line on carb 4.that port is open and the vac line for the petcock goes between 2 and 3 carb

Not sure I understand that, but I don't think it's right...

Petcock must have vacuum to function in the on/reserve positions. The vacuum port is on the side of carb 4. No lines should be hooked to the tops of any of the carbs.

If the bike is not running to supply the vacuum to the petcock, fuel should not flow from it. You can manually test the petcock is working by applying suction to the vacuum line hooked to the petcock to see if fuel will flow then.

Krey