Author Topic: Fuel petcock, possible blockage? (Read 3252 times)

Cruisecontrol · « **on:** October 21, 2005, 12:39:49 AM »

I got my '03 b12 up and running this week after it was written off last year and had not been started for about 10 months. It started perfectly first go and runs well, but only if the petcock is on prime. As soon as I turn it to on it drops cylinders and eventually stalls.
I rode up the freeway for about 40mins yesterday and as I got into town I switched from prime to on and within a minute it was running poorly until I just switched back.

Any ideas?

Red01 · « **Reply #1 on:** October 21, 2005, 01:29:29 AM »

Sounds like you're loosing vacuum singnal to the fuel petcock... loose or cracked vacuum line (should run from carb #4 to the petcock) or a damaged diaphragm in the petcock itself.

If it runs OK in Prime and Reserve, but not in On, then I'd say it's a problem with the petcock pickup getting clogged at the upper pickup point.

Cruisecontrol · « **Reply #2 on:** October 21, 2005, 01:50:27 AM »

I shall have to recheck the vaccuum line connections again. I would rather eliminate the obvious before pulling anything apart.

Thanks for the reply.

Farre · « **Reply #3 on:** October 21, 2005, 03:57:14 AM »

While we are busy in this topic, what should i check for if I have this problem with Res?

And a noob question: I recently bought a B4. i didn't look good yet, but i only saw an On and Res, no Prime... is this normal?

todius · « **Reply #4 on:** October 21, 2005, 12:52:25 PM »

Quote from: "Farre"

While we are busy in this topic, what should i check for if I have this problem with Res?

And a noob question: I recently bought a B4. i didn't look good yet, but i only saw an On and Res, no Prime... is this normal?

It does have a prime, but you have to remove that little phillips head screw to turn the petcock to prime (fully up position). I have no idea why they have that little screw.

Farre · « **Reply #5 on:** October 21, 2005, 06:01:31 PM »

I see, what's so special about Prime? is it 'better' than On?

rider123 · « **Reply #6 on:** November 06, 2005, 11:19:34 PM »

Prime allows the fuel to flow freely to the carbs through gravity. If your bike is not running and it's set to prine eventually it will start leaking out gas as the floats are not strong enough to hold back the tide of gas for long. If you've stored your bike for a long time and the floats are empty this "primes" them so that you can start the bike.