MKIII build complete but trouble starting

As written dozens of times, ALL THE CIRCUITS, both fuel and air, must be visually confirmed using aerosol spray while "cleaning the carb", or it is all a guessing game.
Do it right, do it once.

concours said:

My experience has been the brass seat has corrosion/varnish deposits, (that keep the needle from sealing) to cure I use Mother's Mag (fine abrasive metal polish on the end of a wooden toothpick, or wooden match. A small pencil eraser ( like from a mechanical pencil) sanded to a point, will do the trick also to polish that seat.

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I like that pencil eraser and polish trick. I’ll try that next time …

This reads like you are having fun Anvill.
Keep your updates coming...

Fast Eddie said:

I like that pencil eraser and polish trick. I’ll try that next time …

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As alternative to wasting your stock of mech pencil rubbers, i've used some Autosol polish on a Q-Tip end, other end in a power drill and then gave the valve seat a nice polish in a few seconds. This was on a Mk1 Amal but sounds similar on the MK2.

Thanks for your advice guys. After another rebuild/cleaning and making sure the throttle cable was set correctly to allow the slide to fully close (thanks Greg) I have the air screw and idle screw functioning and the bike is idling much better.

But I'm still getting overflow from the lower vent tube on the Mikuni. I tried modifying the brass tab (pushed it about 1/8" lower) to lower the float level but it hasn't seemed to affect the overflow issue other than the overflow level is perhaps slightly lower. I have that lower vent tube running up under the seat so I can see that the overflow looks to be leveling out to about the fluid height of the bowl and doesn't ever collect any more than that. The needle/seat is new and I have a fresh set of jets incoming, but I'm not convinced those will resolve this problem. I guess maybe the next thing to try is blocking off one end of the vent tube and push some compressed air into the other side to see if it may have a crack or something? I will also try another electrolysis cleaning of the tank to try to eliminate tank silt--I am seeing a small bit and perhaps its blocking seals as suggested.

Thanks,
Anthony

I had the same, but on a mk2 Amal, so may not apply. It turned out to be a burr on the float spindle, causing the float to stick. Filed it down and all was well. It only happened when the bowl was tightened down, so took a few on/offs to realise.

Update on the overflow issue: the brass overflow tube in the bowl had a large crack running down its length, which I identified by filling the bowl with water, capping the top of the tube, and blowing into the hose at the other end. I lightly sanded, fluxed, and soldered the crack and the issue appears to be resolved. On to the next thing!

Anthony

Anvill said:

Update on the overflow issue: the brass overflow tube in the bowl had a large crack running down its length, which I identified by filling the bowl with water, capping the top of the tube, and blowing into the hose at the other end. I lightly sanded, fluxed, and soldered the crack and the issue appears to be resolved. On to the next thing!

Anthony

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Good find!