possible fuel petcock issue - 82 xj550

[maximnewb]

The fuel switch for my 4cyl 82 maxim 550 has 3 positions: on, res, and pri.

With the gas tank disconnected, I only get fuel flowing freely out the ports when the switch is turned to the "pri" position. In the other 2 positions "on" and "res", no fuel comes out (none at all). And there is quite a bit of fuel in the tank.

Also, when it is turned to "pri" the fuel comes out the main port (the oen which leads into the carb float bowls) not through the priming tube, which runs to the carb holder on the first cylendar.

Maybe I'm completely wrong on how this switch should function, but this definitely does not seem right. Could it have been re-assembled improperly in the past?

Thanks.

[kar_the_terrible]

your petcock is just fine. its a vacuum operated petcock.

The priming tube you speak of is actually the vacuum tube. when the engine is running, the a vacuum created in this tube will displace a diapraghm in the petcock thus making fuel flow in both the on and reserve positions.

when the engine is off, there is no vacuum, hence you need to turn it to "pri" to let fuel bypass the diapraghm and drain out of the tank. the only way fuel should come out of the tank is through the feeder tube leading into the carbs..

so as opposed to ordinary petcocks, which have a reserve, on and off position, this one stays off by default.

[Aggroton]

yeah it really messed with my head when i first got mine too...3 carb cleanings later it runs great.

[padedwalls]

If you are curious to see it work just detach tank and place a hose on smaller port and suck on it as to cause a negative pressure. BE PREPARED, this will cause fuel to spill out of larger port! This is the normal operation, if no fuel exits: your petcock is perhaps bad.