Vacuum petcock

[damachinist]

With lots of reading from this board I began working on a 1987 en450. It began as scrap parts and with the help of this board I managed to get a bike out of it. My question is can a petcock cause the carburetors to flood? With a dummy jug I can get it to run and spin up to  9500rpm slight hesitation about rid-range. As soon as I put the tank on with a new petcock it floods out.

[knoizy]

Sounds like one or both of the carb floats are stuck, I'd suggest you rebuild the carbs anyway if there's some midrange stutter.

[damachinist]

So why would it be running okay with the fuel jug and then issues with the tank? Just wondering if I'm not understanding. It seems like a float sticking would be constant regardless of whether it was a tank or jug. 

[knoizy]

Good point and I'd considered that myself then reasoned no matter tank or jug the float should be stopping a flood, but the physics always wins so there might be another explanation! I've never had a vacuum fuel tap, the 454 tank came with on/off/reserve and the carb vacuums are capped so I don't know if there's anything in that equation that could surprise you. I've had floats sticking on side stand but not centre and quirky things like that with intermittent faults but for me it all comes down to getting the carbs off and having a look, should tell you instantly if there's a problem. When you say "flood" do you mean running rich and stalling or is there actual fuel pouring out into the airbox?

[damachinist]

Fuel can be seen running from the air pods but only when I have the tank installed. on just a fuel jug they work fine with no issue doesn't seem to be running rich. 

[damachinist]

Okay figured out the problem. The petcock had a flaw in the diaphragm causing the vacuum to pull fuel into the throat.