petcock on PRI --> loss of gas

[Cero]

Today I was drying the tank of my Gpz550. As from manual instruction i turned the petcock on PRI and then I turned out 2 carb drain screw. In a few seconds some gasoline was falling on the ground from the center of the bike...

why's that?! as soon as i turn the petcock on another setting gas cease to fall...

[steell]

Because "PRI" stands for "Prime" and is used to fill the float bowls with fuel when the motor is not running. All other positions require vacuum (engine running) in order for fuel to flow.

[Cero]

so it's right that the gasoline fall on the floor, because the engine stopped and the fuel continue to flow until it goes outside...is it right?!

thanks

[kawpaul]

Why did you open two drain screws? Sounds like that is where your fuel is coming from.

[zoro]

Originally Posted by Cero

so it's right that the gasoline fall on the floor, because the engine stopped and the fuel continue to flow until it goes outside...is it right?!

thanks

NO! If the "float bowl needle valves" are seating correctly and the "float bowl fuel levels" are set correctly, NO fuel should leak no matter where the petcock position is set. The vacuum operated petcock was adopted into use for "safety" reasons stemming from from two important causes! First, most riders are not mechanically inclined to maintain "float bowl" maintenance! Secondly, for the reason you described, gasoline has dripped overnight on many home garages and shop floors leading to many deaths and loss of property due to fire!

[Cero]

I'm restoring an '83 Gpz550 unitrack. I need to empty the tank and the carb from old fuel. Tomorrow I'll fill it with new gasoline, change engine oil and then I'll try a kick start. If it's going to start I'll then change/clean air and oil filters.

[zoro]

Originally Posted by kawpaul

Why did you open two drain screws? Sounds like that is where your fuel is coming from.

+1, Why did you remove the drain screws?

[zoro]

Originally Posted by Cero

I'm restoring an '83 Gpz550 unitrack. I need to empty the tank and the carb from old fuel. Tomorrow I'll fill it with new gasoline, change engine oil and then I'll try a kick start. If it's going to start I'll then change/clean air and oil filters.

Why not remove the tank and drain it into a gas can?

[Cero]

I did not removed them, i just loosen the screw to allow the carb drying.

(do I explain myself? I hope so, sorry for the worst english ever)

[Cero]

Originally Posted by zoro

Why not remove the tank and drain it into a gas can?

I guess it's faster and safer the method I used...isn't it?!
anyway I didn't dried it at all, as soon as I saw gasoline falling down I stopped.

[Cero]

Originally Posted by zoro

NO! If the "float bowl needle valves" are seating correctly and the "float bowl fuel levels" are set correctly, NO fuel should leak no matter where the petcock position is set. The vacuum operated petcock was adopted into use for "safety" reasons stemming from from two important causes! First, most riders are not mechanically inclined to maintain "float bowl" maintenance! Secondly, for the reason you described, gasoline has dripped overnight on many home garages and shop floors leading to many deaths and loss of property due to fire!

I've just ridden that post (there's a little bit of chaos).
Tomorrow I'll remove and dry the tank, remove & clean carb, check if some tube loose fuel (+ the works i wrote on the post above) and then I'll try to start the gpz.

The fuel did fall from both the carbs (it's right, I wanted it) and from the middle of the motorbike (i did not understand from where precisely)

[zoro]

Originally Posted by Cero

I did not removed them, i just loosen the screw to allow the carb drying.

(do I explain myself? I hope so, sorry for the worst english ever)

Vacuum operated petcocks can be confusing because they require vacuum to open the flow of fuel while they are in the "ON" position. However, if the engine is "not running" NO fuel should flow when the petcock is in the "ON" position! "ON" is "OFF" when the engine is off and not running! If fuel leaks from the petcock when in the ON position with no vacuum to the petcock, then the petcock is faulty and needs cleaning or rebuilt! Fuel will "always" flow when the petcock is in the "PRI" position because "PRI" bypasses the vacuum operated valve inside the petcock itself.

[Cero]

Originally Posted by zoro

Fuel will "always" flow when the petcock is in the "PRI" position because "PRI" bypasses the vacuum operated valve inside the petcock itself.

but not outside of bike's component, only inside carb and engine

[zoro]

Originally Posted by Cero

but not outside of bike's component, only inside carb and engine

Yes that is correct, Ill say again, If the float bowls and the needle valves are functioning and set correctly, NO fuel should drip from anywhere! Even on "PRI"(prime)!

[Cero]

Originally Posted by zoro

Yes that is correct, Ill say again, If the float bowls and the needle valves are functioning and set correctly, NO fuel should drip from anywhere! Even on "PRI"(prime)!

Thanks once again for your patience! I'll ask the Pope to sanctify you

[zoro]

Originally Posted by Cero

Thanks once again for your patience! I'll ask the Pope to sanctify you

No problem Cero, glad to help! As for the pope, hes a man like like you and I and does not have the authority to sanctify me or any other human! Only Jesus has that power!

[Cero]

I'll tell you in the next days if i manage to solve that problem.

thanks again

[fastpakr]

I'm not clear on what problem you're trying to solve. It sounds like everything is working correctly as it's designed. With the petcock on Prime, fuel flows through it unrestricted. By opening the drain screws (with the valve on Prime), the carbs continued to drain out the bottom. If you're trying to drain the tank and carbs, just attach a hose to the base of one carb before you open the drain screw, and put the other end of the hose into a container for the drained fuel, then open the drain screw.

[zoro]

Originally Posted by fastpakr

I'm not clear on what problem you're trying to solve. It sounds like everything is working correctly as it's designed. With the petcock on Prime, fuel flows through it unrestricted. By opening the drain screws (with the valve on Prime), the carbs continued to drain out the bottom. If you're trying to drain the tank and carbs, just attach a hose to the base of one carb before you open the drain screw, and put the other end of the hose into a container for the drained fuel, then open the drain screw.

Better and (safer) yet, remove the tank (with petcock "ON") and drain the fuel into a gas can through the petcock now set on "PRI"! Never drain a tank through the carbs! Diconnect the fuel line and divert the flow into a gas can!

[fastpakr]

Why would that be any safer? My way attaches a hose to the drain connection on the carb and runs into a gas can. Yours uses the fuel hose into a gas can. Neither spills a drop.

Unclear on the concept. I'm not saying mine is better, just not seeing why it would matter either way.