engine only runs in prime

[fj1100turbo]

Only way my 84 1100 will run when petcock is on prime..is that BC  canisters are bad or petcock

[Pat Conlon]

Petcock's not opening. Don't leave your faulty petcock in prime.
You will flood your engine, fill your crankcase with fuel and dump (a lot of) fuel on your garage floor.

Not a good thing to happen if you happen to have your water heater in your garage...

[balky1]

Only way my 84 1100 will run when petcock is on prime..is that BC  canisters are bad or petcock

Petcock. Stuck or torn diaphragm. Disassemble it and remove the diaphragm gently! Reassemble, try the suction test. Diaphragm tends to stick if your bike sits for months.

[fj1100turbo]

I took apart petcock...before when I sucked on vacuum line it did nothing...now I can hear the valve moving/opening but idk if its enough as I currently have clutch cover plate off and can't start it at the moment...don't judge me but how exactly do I perform the  suck test in case I'm not doing right or missing a step.

[FJmonkey]

I took apart petcock...before when I sucked on vacuum line it did nothing...now I can hear the valve moving/opening but idk if its enough as I currently have clutch cover plate off and can't start it at the moment...don't judge me but how exactly do I perform the  suck test in case I'm not doing right or missing a step.

Suck Test
Pull the vacuum line from the carb intake. Suck on it. If you suck and it feels like a plugged up straw/hose and and you cannot keep sucking air then your good to go. But if you suck and can keep pulling air, you have a leak that will affect fuel flow.

More on the suck test. http://www.fjowners.com/index.php?topic=14031.15

[Pat Conlon]

You want to know 2 things:

1) Does it open under vacuum? Here's where the suck test comes in. With the petcock on the tank and fuel in the tank, lightly suck on the vacuum hose. You should hear a click and fuel should freely flow....not dribble, but flow copiously.

2) Does the petcock hold a vacuum? You need a vacuum pump with a gauge for this test. I use my MityVac which every tool box needs one. Hook up the vacuum pump to the petcock vacuum line. *carefully* pump up the vacuum to where the petcock opens. Note on the gauge the needle position. Check back in 15 minutes to see if the needle has dropped indicating a loss of vacuum, most often due to a leaking diaphragm.
If the petcock looses vacuum it's just a matter of time until the loss gets bad enough to where the diaphragm can no longer hold the petcock open. It gets worse, never better, and soon Bingo....you're out of fuel.

If (when) this happens in the middle of a ride....no worries, the prime position will get you home.

This prime feature is a major reason I recommend folks who need new petcocks on the '86/87 FJ's convert over to the '84/85 petcocks (plug n play) which do have the prime setting, and are considerably less expensive than the 86/87 electric reserve petcocks.