Blowing gas out of the carbs

I advanced the cam and I had lots of compression ie 180 psi both sides. The engine is non interference so the valves will not hit the head. When I tried to start it it was real hard to kick and it kicked back but I think that that is because the ignition timing was all messed up and I didn't spend any real time trying to get it correct. It did fire however and it doesn't try to blow my hand out the back of the carb. I will play with it more and post more later..

swooshdave said:

Two ways to adjust the floats, one is you move the valve seat (not that easy to get it right) or buy the new adjustable floats from Amal.

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I've found a way to move the valve seats a predictable/repeatable way, so as to keep on using the old non-adjustable floats. I filed/sanded/lapped off a substantial amount of material from the bottom of the seats, then bought a sack of shims from McMaster-Carr.com to raise them back up with. All you do is pop out the seat (heating the bowl, of course) and add or remove shims, then press the seat back in all the way.

The shims I got are 0.8mm OD, 0.2mm ID, 0.2mm thick, 18-8 SS, item 98089A245, 25 for $6.48. That's a lot cheaper than a new set of Stay-Up floats, plus more precise than trial-and-error bending of the tabs on the latter. You can get thicker and thinner shims too, depending on how granular you want to be with each change.

From the geometry of the float, you can figure how much each shim will change the height of the float at the far end. There's a 1:4 ratio of shim thickness to float end height, and a roughly 3:4 ratio of shim thickness to float height at the centerline of the spray tube, so I can sorta guess - because I don't really know exactly where the center of buoyancy is - what the fuel level height change would be. I'm in back to basics mode with my bike, so I set the floats to the max height they can go without touching the carb body, and I'm doing road test-plug reading-pilot screw-seat shimming cycles to get them down to where they need to be.

"Carry on, and dread nought"

Change your float needles, new viton rubber tip of course.

I have encountered same troubles because of incorrect ignition timing. Have you checked this?
Dox

Echoing DOXFORD above and adding this, do you have a Boyer? And if so, do you have the black/yellow and black/white wires correctly connected? It wouldn't have anything to to with the gas blowing back, but could explain why it will run once you have it spinning fast enough. Reversing those wires will throw the timing off in a major way, and also keep the box fully advanced.

I figured out that the cam was marked incorrectly from the factory and now it is turned about a 1/4 of a turn off. The bike runs great now...no gas out of the carbs and compression is correct and the valves are all opening at the correct times thinks to a degree wheel.

Glad you found it...had to be something like that as the intake valve just had to be open instead of closed when the piston was coming up. Only way to explain the air blowing backwards out of the carb. If the valve is closed, it can't do that. Enjoy the bike!

zcarman said:

I figured out that the cam was marked incorrectly from the factory and now it is turned about a 1/4 of a turn off. The bike runs great now...no gas out of the carbs and compression is correct and the valves are all opening at the correct times thinks to a degree wheel.

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Zcarman
what cam are you using?
Curious
CNN

I figure that it is the stock cam. I doubt that the previous owners would have changed it.