Last year, I noticed that if I left the petcock on PRI, the fuel would leak out and drip on the ground. I cleaned the carbs, and found a blackish obstruction in one of the float needle valves. I blew it out with canned air from both directions, and cleared it. Then I added an in-line fuel filter to keep it that way.
I didn't have any problems leaving the bike parked on PRI... until today. I parked it in a parking ramp this morning; the attendant warned me that they didn't usually let motorcycles park there, because they leaked oil too often. I managed to look hurt, and they let me park there. Later, I parked in a different ramp after a lunch errand, and when I came back, I had a small puddle of fuel underneath the bike :x . The timing seems funny, since I had just assured the attendant at the other ramp that I had no leaks.
I'm at a loss how the float/valve could get clogged again. I guess the bike was parked once for 6 weeks last winter, but otherwise I've ridden pretty consistently. Also, I didn't notice any problems all this season until today. Very odd.
A question and a statement for you.
Statement: With the petcock on PRI, it is gravity-fed instead of vacuum-fed, and will therefore leak if it sits long enough on PRI.
Question: Why leave the petcock on PRI? Why not just leave it ON?
Quote from: gobstopperA question and a statement for you.
Statement: With the petcock on PRI, it is gravity-fed instead of vacuum-fed, and will therefore leak if it sits long enough on PRI.
PRI will basically allow the tank to fill the carbs' float bowls. The float bowls are very similar to a toilet tank: as the level rises, a plastic "float" rises. When the float gets high enough, then a stopper blocks the flow of fuel to the float bowl (in a toilet, this is a "flapper valve"; on a bike, it's a "needle valve").
So even with the petcock on PRI, the float _should_ cause the needle valve to close, causing the bowl to stop filling... and there is no problem. Having the petcock on "ON" also prevents the float bowl from filling if there is no engine vacuum. This is sort of a "belt AND suspenders" approach, since either lack of vacuum, or a full float bowl, should cause the bowl to quit filling.
Unfortunately, many bikes over time get crud in the needle valve, preventing it from completely closing, and a little fuel leaks out. This is similar to a toilet that keeps on running (slowly) forever.
So I would say that with a properly funcitioning carburetor float & valve, leaving the petcock on PRI _should_ have zero effect versus leaving on RES.
QuoteQuestion: Why leave the petcock on PRI? Why not just leave it ON?
In my case, the bike seemed to be losing power during a rainy ride today, which is sometimes caused by fuel starvation, and may be corrercted by switching to PRI. I was in heavy traffic, so just switched to PRI (and unforrtunately forgot about it when I parked).
In hindsight, I'm thinking that the float or needle valve may have just been "stuck". I've seen where I reassemble the carbs, and put them on the bike, but the float level is too high, as if the float needle is not closing. Then I tap the side of the float bowls with a mallet, and then the float height comes back down to where it should be. It seems like every now and then, the float or needle just don't seal, and need a little whack.