My '92 drs 350 has a leaky fuel petcock. it is a vacuum assist type. What would happen if I override the vacuum assist by just installing a solid gasket in place of the diaphram assembly? Flooding, leaking carb? or just epa stuff?

sticky float needle- run some seafoam through a tank of gas- also check for vacuum leaks as the petcock on bikes with a petcock are usually vacuum operated off engine vacuum.. if disconnected or leaky- that will starve the engine once the fuel in the float bowl is used up.

I'm going to guess that "pit ####" meant petcock :-) and yes they do "go bad" in a number of ways. There is a diaphragm inside which can crack over time. There is also a diaphragm return spring which may break (I've seen only one like that though). But most often, the use of fuel with ethanol in it will cause the breakdown of the plunger seal. When that happens, the petcock "leaks".... not externally but internally. The Maxim-X has a vacuum operated petcock which is supposed to only provide fuel to the carbs when set to PRI (prime) or when set to ON while the engine is running. When the engine is off, there should be no flow of fuel. But the damaged plunger seal allows fuel to flow from the gas tank to the carbs at all times, even when the engine isn't running. When you combine that leak with a leaky float valve, the result is usually a crankcase full of gasoline - clearly not good. If you'd like to know all there is to know about the XJ700X / XJ750X petcock, visit the following page on the Maximum Maxim-X web site:
Maximum MAXIM Resource for 1985 86 Yamaha 700 750 Maxim Models XJ700X...
There are also some helpful tips for rebuilding the petcock here:
http://www.maxim-x.com/pix/petcock/maxim-x_petcock_repair_tricks.txt
...with supporting pictures here:
Index of pix petcock
Hope that helps.

If you have a vacuum operated fuel petcock, it should also have a "prime" position. That should let the fuel flow without vacuum from the engine. If this solves your fuel starvation problem, I would double-check to see whether the the replacement petcock gasket(s) may have shifted just enough to block some little pinhole that's required for vacuum equalization. That has happened to me--the replacement gaskets aren't exactly the same as what was originally in there.
You can also test the vacuum release of the fuel petcock without taking anything apart. Put a mity-vac (a hand-pumped vacuum pump) on the vac line to the fuel petcock and see whether you can get the fuel to flow. Harbor Freight sells a cheap mity-vac type pump for under $20 when it goes on sale (which it does regularly).
Good luck!

First check to see if the oil level in your crankcase is too high. If you have a vacuum petcock malfunction (hole in the diaphragm) or if the fuel petcock is left in the prime position and a float needle sticks, then you get you get gas running into the cylinders, past the rings, and into the oil.
When you start your motorcycle the oil/gas mixture has no place to go, the crankcase is too full, and the mixture exits through the crankcase breather into the air box where it will ruin a paper air filter. Always turn your fuel petcocks off when not driving. If the petcock diaphragms are bad rebuild the petcock with K&L rebuild kits or replace the fuel petcocks with new ones. If the float needles in the carburetors are bad or sticking, take the carburetors apart, clean them, and replace any worn or damaged parts You will have to change your gasoline saturated oil for it will no longer properly lubricate your motor.Just a note: in 1983 brand new Honda's would fill there engines in gas. All the components were clean and new. This can happen to any machine in any condition at any time. When not riding always turn off the fuel vales never leave them in the prime position.

Answer #1 is spot on! Get the carbs professionally cleaned and set. They will inspect the needle/seat assemblies (or SHOULD) and replace as necessary.

It sounds like the carburetor is running out of gas. If you have the original petcock on the tank, you MUST have the vacuum line connected. When the engine starts up, vacuum from the carburetor is applied to the vacuum diaphragm in the petcock and opens the petcock. Without vacuum on the petcock, the only fuel you will get to the carb is if the needle valve in the petcock leaks.

Now, you said you had the tank painted. This is the clue. Painters pay a lot of attention to the outside of the tank but NONE to the inside. I would guess that the screen on the inside of your tank is completely blocked with small chips of paint or sanding material.

Replace the vacuum operated petcock. It's a "Motorhike" waiting to happen. A "motorhike" what you do when your bike quits and you wind up pushing it. I've seen too many of these things leave people stranded with a full tank of fuel but not a drop in the carb. Replace the OEM petcock with a high quality manually operated petcock like the old timers use. A Pingle is a very good choice. If you want to save a few bucks, check on the price of an OEM petcock for a 1995 or earlier model. Block the vacuum line off and I'd advise an inline fuel filter. Buy the sintered metal type filter that can be cleaned. These filters come in Chrome, and a few anodized colors as well.

See if this helps.
Steve

Check the fuel petcock to see if there's a similar-sized fitting.

Most carbureted motorcycles use vacuum lines for one thing only: To apply vacuum to the fuel petcock so it'll turn the fuel supply on ONLY when there is vacuum being applied.

Though the same bikes also typically have positions on them that override the vacuum safety system.

"Vacuum safety system"?

Yes.

Unlike a car, most bikes carry their fuel ABOVE the carb, and instead of a fuel pump, use gravity to feed the carbs. If you've got a petcock that's always open, only the float needles in the carbs hold back the fuel flow, and these are prone to being held at least partially open. The tiniest speck of debris can do it.

And the results can range from annoying to catastrophic.

If the fuel is flowing into a carb while the bike is parked, you can fill a cylinder and, when you hit the electric starter with good battery power, you can bend a connecting rod since liquids cannot be compressed. The piston will slam into the incompressible liquid and if the starter's stout enough, there goes a rod.

Or if the fuel leaks into a cylinder whose exhaust valve is open at the time, the bike will start but sometimes you're left wondering what that loud bang was and why are you feeling so warm and where on earth did that muffler go?

You should get this taken care of quickly because if I'm correct about this line, not only are you having to use manual override positions on the petcock (not a biggie -- the vacuum part is a frequent failure point -- just turn the petcock off when you park it), you have a vacuum leak which can result in at least poor running and though the leak is quite small, there's the possibility of running too lean and burning a hole through a piston, which kinda sucks.

your float is sticking or saturated or maybe just a little **** stuck between the needle and seat if it is the latter it might clear with some 4000 rpm reving if that clears it you need to find where its comming from bad petcock or even cheap fuel line if reving doesnt clear it (no offense)take it to a shop,inside a carb is no place for a carpenter

For the fuel pump portion you can go here - http://www.bikebandit.com/houseofmotorcycles/1992-yamaha-motorcycle-xj600sd-carburetor/o/m8199sch138373

Two hoses come from the intake area under the carburetors - the small hose on the left side (facing front) which is directly under #1 intake goes to the Fuel Petcock vacuum input. The hose under #2 intake goes to the Fuel Pump - vacuum intake (marked with P). The left side of the fuel pump is the input for fuel - the right side is the output for the fuel pump - the hose goes up to the small T input between carburetor 2 and 3. The input for the fuel pump has an inline fuel filter and that runs up to the Fuel Petcock fuel outlet.