80 GS450 petcock, starving engine?

[ahmet]

I am almost done rebuilding my GS450. I have cleaned the carbs three times in a row, changed the plugs (they fire fine) and cleaned the petcock (new orings and seals installed also) and I still cannot get the bike perform at high RPM's. It starts fine with choke and in a couple of mins I can drop the choke off and it idles fine at 1100RPMs but when I give gas it hesitates big time and the RPM does not rev up. Very rarely it does and increases rapidly, then it drops down to idle. I am thinking maybe the petcock is not functioning properly. It does this in all settings (run, res, pri). Any ideas?
Also when the bike is idling if I pull the plug wire off the right cylinder the bike dies, but if I pull it off the left cyl it keeps going. I wonder if there are problems with the left cyl burning or starving. I know the plug fires fine because I visually tested it, nice strong spark is visible.
Thanks for all your input

[spots25]

how hot is the left exhaust pipe?

[xDUKEx]

do you have the stock airbox on it or have you replaced it with pods ???

[ahmet]

I have the stock airbox. I did not change it to pods.
One thing happened recently was I left the petcock on prime setting overnight. I started the bike in the morning and the left exhaust pipe sprayed raw fuel out from a small hole at its bottom.

[GS550joe]

leaky intakes??

it culd be a leak in the intake tube to the head.. vacuum will be low and excess air will get in the mix... try the spray method.. to see if the rpms rise slightly...

could be a leak on the exhaust it also affects the vacuum some what..

maybe the valves out of adjustment..

some thoughts on what caused no high end power..

Joe

[sf-nathan]

I am almost done rebuilding my GS450. I have cleaned the carbs three times in a row, changed the plugs (they fire fine) and cleaned the petcock (new orings and seals installed also) and I still cannot get the bike perform at high RPM's. It starts fine with choke and in a couple of mins I can drop the choke off and it idles fine at 1100RPMs but when I give gas it hesitates big time and the RPM does not rev up. Very rarely it does and increases rapidly, then it drops down to idle. I am thinking maybe the petcock is not functioning properly. It does this in all settings (run, res, pri). Any ideas?
Also when the bike is idling if I pull the plug wire off the right cylinder the bike dies, but if I pull it off the left cyl it keeps going. I wonder if there are problems with the left cyl burning or starving. I know the plug fires fine because I visually tested it, nice strong spark is visible.
Thanks for all your input

my 2 cents:

1. To check the petcock operation with the engine off remove the vacume hose that runs from the left side carb to the petcock. Remove it from the carb end of the hose. Next pull the gas hose the goes from the petcock to the "T" that provides fuel to the carbs. ( Pull this one from the petcock, cause its easier). Now to test the petcokc apply vacume presure to the vacume hose. I do this by mouth. It should not take much before the vacume actuated valve in the petcock moves and fuel should start to poor out of the supply side. Warning: if the vacume valve/ diaphram in the petcock is broken fuel will come out and into your mouth. If that happens replace the diaphram:-)

The petcock is only vacume actuated in run and reserve. This is so that fuel is only supplied while the engine is running. Prime is there to bypass that shut-off and dumps fuel into the bowls after they have been emptied (for cleaning or something). Leaving it on prime overnight will eventually dump fuel into the cylinders and into the airbox. THus your raw fuel. I'm surprised it even started.

2. Does it rev up with the choke left on? If so that might help you isolate this as either a fuel delivery problem or electrical.

3. Not sure why pulling one plug wire would shut it off and not the other.

Good luck!

[bgmart450]

If this just started after leaving it on prime you could have killed your spark plug after flooding the cyl leaving it on prime. Try switching them and see if the other spark plug runs OK in the problem cyl.

I rode home on one cyl this year and it SUCKED...

[ahmet]

I swapped the plugs and it is still the same cylinder. Funny thing is I injected some gas inside to the deal cylinder and the bike started on a single cylinder, the plug cable was unplugged from the good cylinder. Perhaps I have an issue with the carb to that cylinder? I tought I cleaned the heck out of them, maybe not. I will pull them out again and clean them one more time.