Scott
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Carb rebuild kit ordered, new gaskets and valves. Will rebuild carb again and see what happens.
Carb is definitely getting fuel. Float needle valves aren’t the issue as they allow fuel IN to the bowl when the level is low when the bike is running. They should be shut and not allowing any fuel in when the bike isn’t running. The problem is that the fuel that is in the bowl when the engine stops is draining somewhere… After examining the carbs and parts diagrams and following the flow of fuel through the carb the obvious thing to check is the slide needles but I have checked these and they are both seating correctly.
I just don’t know where to look next.
When you say float needles do you mean the needles in the slide valve assembly? I was running the bike with no air box/filter so I could see the slide assembly opening and it’s not sticking at all but then I know the needles have been lowered a notch to tune 3/4 throttle response so there’s a chance they might not be closing… Is it the needles that would control fuel flow to the Venturi when throttle is closed? I thought that was pilot jet? But then I suppose on thinking about it that if those needles weren’t seating that fuel could bypass the pilot jets and drain the bowl? But is it likely this would happen on both sides of the carb for both cylinders? If it was happening on one but not the other should the engine start running on one cylinder only? I’m going to record the starting procedure tomorrow and upload so you can see what is happening
If you stick with the standard air filter and end can then no. The stock downpipes are sleeved to half the diameter of the outer pipes and the standard can is too, which would maintain back pressure. But if you’re using a different end can, or have changed the intake system in any way you’ll need to up both jets to next size. You might find you need to fit a baffle too if you’re using an aftermarket can as loss of back pressure means you’ll get zero power at full open throttle.
I don’t think that’s the issue as when I got the bike back I completely stripped everything down, right down to the frame and the tank was drained and rinsed with fuel then dried with compressed air before being put back on. Its only had 5l of fuel put in since then and it hasn’t actually been out of the garage yet. I checked today and the float bowls are definitely emptying somewhere (I opened the drain valves on either side and not a drop came out) but there is no fuel around the carb, under the bike or anywhere like that. If that quantity of fuel (I reckon both bowls hold about 50ml between them) was leaking into my garage and evaporating I’d definitely smell it.
It just seems strange that I have to crank the engine for a good few minutes to start the bike each day, but once its started once it’ll fire first time if you kill it, or even if you go back a few hours later it only takes a couple of turns to go. When I’m cranking the engine to start I can even hear the engine getting closer as it’ll do nothing for a bit, then it’ll stutter when its starting to get fuel but not enough, then eventually it fires no problem. I’m ready to pull my hair out with it!
