Please explain the "pri" setting

[Anonymous]

What exactly is the "pri" setting for on the petcock? I don't have an owners manual but I have heard and read a problem with gas draining into the crankcase.

Thanks for clearing me up on the pri setting.

[satchmo]

Pri is the prime setting on the petcock. It allows gas to flow freely into the carbs without any vaccum action. Sort of like turning the tap on.

Normally most petcocks work by having the vacuum action from the carbs operate the diaphragm in the petcock which allows fuel into the carb bowls.

So when there's no vaccum there's no fuel.

Prime however allows the fuel to flow freely regardless of what the rest of the system is doing. This could get fuel into the crankcase, because it fills the carb bowls, and possibly overflowing into your engine, etc.

At least that's how I understand it.

Satch

[saaz]

Prime is like putting the tap on to manual . Fuel will flow regardless of the engine running. It is not a position for normal use.

[Anonymous]

Thanks for that info.

Which setting should I use when the engine is running and I'm ready to ride?

Which setting when I park the bike and shut down the engine?

[saaz]

I am assuming you have a similar petcock to me (78GS1000). Normally you just leave it on "On", the petrol can only flow whe the bike is running. This uses the main tank while the bike is running. "Reserve" is the last part of the tank, and you can leave it on this while running or when stopped as the vacuum shutoff should control this.

Prime is useful if you have not used the bike for a while and want to get petrol in the carbs before starting. Always put it on "on" in normal use as this prevents flooding when the bike is not running.