Okay it has come to me asking for help  By  george112 (Read 1,887 times)

Sounds to me like you might be facing more than a single issue...

1) Yes - having it accept WOT better after taping off the air snorkel inlet holes would indicate that it's too lean at full throttle... i.e - likely needs bigger main jet (as long as there are no other air leaks, such as caused by a split intake manifold, leaking manifold gasket, cracked vacuum hoses, etc...)..

2) The mixture screw is in reality an idle mixture adjustment screw, and is designed as a way to dial in the idle mix so as it idles smoothly, starts easily, and comes down from throttle into a smooth, consistent idle. It has little effect at high throttle openings, and playing around with it to address an issue at WOT will only serve to screw up that otherwise smooth, consistent idle. So once the idle is dialed in... don't mess with it - the WOT problems need to be be properly addressed elsewhere... and not with an idle mixture screw adjustment.

3) As long as it's not too restrictive and not capturing any large air pockets/bubbles, a larger fuel filter will be no problem at all (in fact, beneficial if anything - with it's larger surface area to catch more debris before plugging, as well as often using a paper filtering media, which is far more effective at catching small debris than the fine plastic screen that typically comes stock). Some visible bubbles inside the filter are normal, but fuel delivery can act a little "wonky" if they get sizeable. An air pocket can usually be cleared by tilting the filter - bubble up towards the fuel tank - whils sucking on the petcock vacuum hose, opening the petcock's valve and allowing the bubble to rise up into the tank.

I have a big John Deere paper filter on my ATM... works a treat.

4) The white smoke at idle... does the smoke itself smell more like fuel, or more like oil? I'm guessing that it may very well be oil, as if an engine is otherwise idling normally, the mixture would be close - certainly not rich enough to produce a cloud of smoke without stumbling/faltering/stalling. A tiny visible bit of smoke, maybe - but not any substantial amount (i.e. - cloud). If oil, then...

5) Check compression, if at all possible. Significant oil smoke out the exhaust could mean broken ring(s), which might be the cause of the difficulty in getting the engine started (low compression).

6) Do use feeler gauge on the valve adjustment - they're only a coupla' bucks, and should last many years/uses. These little GY6's can be a bit finicky when adjusting things... just as well get it right and avoid the possibility of improper clearance contributing to some other running or tuning issues, downstream.

7) Did you check/set float height when you replaced the float/needle/seat?? If incorrectly set, that could easily be a cause of the WOT troubles (as well as others).

8) You also mention replacing "the needle that goes into the diaphragm" - do you mean the slide needle? If so, that's normally not a regular replacement item (too risky matching it's taper profile from other than the original carb manufacturer), and should only be replaced if damaged or for more extreme (un-common) fine-tuning purposes. Also make sure it's installed correctly, with the needle's clip in the proper groove and the retaining cap right side up. And while buttoning up, make sure the delicate slide diaphragm and cover are installed correctly with the diaphragm's edge bead properly seated in the carb bodies' groove! A little tricky, but paramount!

9) And yes - flooding. With their auto enricheners - and often being a bit finicky to start in the first place - it seems that if these motors don't start on the first try, they tend to flood - as the enrichener continues to deliver too much fuel to an already "wet" combustion area. Holding the throttle wide open and continuing cranking to clear it is about the best (but still sucky) way to get 'em to fire, at that point, it seems.

FWIW... just some stuff to consider...

Bob