32 replies to this topic

[Mr Piggy]

It sounds like your jets are not centred. That stops the pistons from dropping right to the bottom and upsets the mixture giving the problem you describe.
Wind the jets up as high as they will go. Loosen the jet clamping nut and push the piston down with a small screwdriver inserted through the damper hole. Tighten the nut. Now use the lift button to lift the piston and release it quickly. You should hear the piston clunk down. It should lift smoothly and not stick at the bottom. If it's not free and smooth, repeat till it is. This is vital! Once that's done, wind the jets down about 6 flats as a starting point. Fill the dampers just to the tops of the tubes, I prefer engine oil for this. Adjust the idle screws so that the butterflies are just open. Now start up and warm up. Adjust mixtures by lifting the button on each carb in turn. This should cause the idle speed to rise a little then faulter. Along with this you will need to balance the air intake on both carbs. It'll be a case of doing one then checking the other and going back and forth till it's all as close as you can achieve.
As for ignition timing,I'd Set it to 5 btdc static. Disconnect the vacuum advance and plug it. That should be close enough for it to run well and you can fettle it later.

[Mr Piggy]

Sorry, should have said when you lift the button.
If the idle speed increases and stays up then that's too rich so raise the jet.
If it just reduces it's weak so lower the jet.
Make adjust ments one flat at a time.

[Clip]

You don’t need the vacuum advance at all. Disconnect it and plug the carbie end. Where are you checking your timing from, flywheel or harmonic balancer/damper? I got caught using the HB marks on my 1275 which were way out. Used the marks on the flywheel, and got it perfect. But I’m not sure if that’s consistent with all A series engines.