Petcock Positions -Prime?

[Alan_nc]

O.K., I've been reading the posts on petcock position (ran out of gas yesterday).  Understand that when set to Prime the needle seat is the only thing stopping the gas from flooding all over.

What I haven't been able to figure out:  When on Prime are you pulling gas from the lower Reserve setting or the standard On setting?

[Atesz792]

Reserve it is
So you can 'prime' it even if you barely have any gas left.

[weedahoe]

I always left mine on prime and never any issues. How many lawn mower have fuel petcocks to shut off fuel?

[RossLH]

I don't recommend leaving it on prime. It just takes a grain of dirt for the needle to get stuck open, not at all an uncommon problem.

[gsJack]

I left my old 97 GS parked in prime on the center stand unintentionally for a few weeks once and when I went back to use it again it was a quart of gas smelling oil too full.  Only carb needle valve problem I've had in all my GS miles and the spec of dirt or whatever caused it washed thru without further problems.

On the other hand the four old Hondas I had before the GSs didn't have vacuum shut offs and I left them parked in the on position for years without a leaker.  Never bothered to turn them to off like your supposed too.   

[Atesz792]

Well, if your valve needle is in good condition, I guess you can leave it parking on prime, but I wouldn't intentionally ride it that way. You wouldn't know you're low on fuel unless your tank is bone dry.

[Alan_nc]

Thanks for the responses.  You answered my question.

So why is there both Prime and Reserve?

[Old Mechanic]

Vacuum is required for main and reserve. No vacuum necessary for prime. I only use prime if I have removed and drained the tank. Now I just clamp off the fuel line and pull the tank. I don't even mess with the valve at the tank. Clamp the hose, pull it off the petcock and stick a golf tee in the hose.

regards
Mech

[Janx101]

errr.... yes what mech said... but perhaps....

reserve is there (of course) to let you run after the main part of the tank ... with a safety margin

prime is there to let you err... prime! or fill the carb bowls when/if they are empty .. it operates without vacuum and reasonably quick! .. so i believe ...

... it seems to be the general consenus that you can run the bike while on prime also... but that its not a good idea to leave it on prime if the bike is just sitting there with engine not running..

similarly you can fill the bowls and get the bike running on reserve (or main if there is enough in the tank) .. by keep on cranking it till the  parasitic vacuum (small amount while only cranking) lets the fuel run in...  .. thats an untidy description though .. but anyway .. doing it this way means you are putting a lot more energy drain and load on the battery .. which you dont want if you are having low fuel issues when the bike wont start ... you gonna end up with fuel in the carbs .. but possibly no battery power left...

so .. use prime to let the fuel flow into the bowls quickly ... but dont leave it on prime forever!