Sderbyshire said:
The oil level does not go up with the bike standing and the petcock shut, it does go up on a test run.
So I'm thinking one or both of the float valves?
However there is nothing coming out of the overflows.
Guess I need to take the carbs off to investigate.
Was going to buy two new valves and try that, but genuine ones are quite pricey.
I've read that aftermarket jets are to be avoided, is this true for float valves as well?
If the float valves are leaking, you should see fuel out the overflow pipes with the bike sitting and not running with the petcock open. As a rule, the carbs should be able to empty the tank via the overflows and not introduce any fuel into the throttle bores, so none should get into the engine and the crankcase. If gasoline is indeed getting into the oil, suspect a problem with the overflow tubes. And instantly change the oil if you even remotely suspect any fuel has contaminated it - or you likely will have far greater problems than the carburetors. It takes very little gas to pretty much destroy the lubricating qualities of the oil, and severe damage is likely very quickly.
Yes, OEM carb parts ONLY! But I find it very rare that I need to actually replace a needle and seat assembly. Clean them like MBB suggests. Any fine polishing compound should work great - even toothpaste! (If you don't have any Brasso laying around!)
Put your carbs together on the bench without the needle and seat assemblies and supply them with fuel. Fuel should fill the bowls and pour out the overflow pipes. You should not see any fuel in the main bore because it should never get high enough reach it - it should only get as high as the top of the overflow pipe. Be sure that the bowl vents are not obstructed, otherwise it could be possible that even when the fuel gets higher than the overflow pipe, it can't get out fast enough because of the sealed chamber. There should be a hole in the top of the bowl in the main casting and it should lead to a port on the side directly to the atmosphere. You can see two vent holes in MBB's picture. Blow compressed air into the hole and it should exit the port with almost no restriction. If all seems well, put the carbs back together and bench check them by supplying them with fuel. Do this from an overhead supply with a hose so you mimic the actual line and tank. The vertical distance from the top of the fuel level in the supply has to be at least as high above the carbs as the level is in the tank when mounted on the bike. The bowls should fill up and no fuel should drip out anywhere. Be sure to angle the carbs like they would be on the bike too. My experience is the same as DD's as far as Mikuni (EDIT- not just Mikuni's, but they do seem to be worse) fuel valves sticking when first assembled. Even polished or new. Seems like just a few minutes of successful seating is all it takes to become trouble free, but they do tend to stick at first for some reason so you might have to fuss with them a bit at first.
I would add that I can not imagine it possible for fuel to somehow add to the crankcase oil volume while the engine is running even remotely well - as in cam timing is off substantially. Running it so rich that it hardly can be kept running at all would take many many hours of running to add enough fuel to be reasonably measured as added to the oil volume, so I have to think if it is indeed gasoline being added it has to be happening when the engine is not running. Seems like there would also have to be some sort of crankcase venting problem in order to create enough negative pressure in the crankcase to suck fuel down past the rings assuming there would ever be enough fuel to do so in the combustion chamber with the engine running.
