Carburettor air valve balancing

[James Wood]

Has anyone come across a sticky air valves in the carbs ? When revving lightly one of my air valves is not moving up and down at all, whereas the other one does (when pressing the throttle the air valves should move up I believe..............) Is this anything to do with the oil level in the dash pots ? Comments appreciated...............thanks

[Sheepdip]

Thats not good, presumably diaphram is ok? If its stuck then find out why. When I rebuilt another set one was sticky, polished the piston with autosolv until it fell under its own weight. With the damper out, oil level makes no difference.

[trunt]

Not oil, but it could be hanging up on the piston. Does it feel free if you lift it with your finger with piston out? With it in? If it feels ok then as sheepdip mentioned if the diaphragm is split it can’t develop a depression above the valve, so it will not raise..

[richardthestag]

when I build these up and find a sticky dash piston, I loosen the screws on the dashpot top and if then the piston rises and drops back to the bridge with a solid click I progressively tighten the dashpot screws until such point as it doesn't and back off a 1/4 of a turn. Works every time.

Unlike SU HIF type carbs the strom piston is not a machined fit into the carb body. however the piston does need to move freely in and out of the dashpot top. you can check this easily on the bench and use a find paper to get it all moving again.

Easy and effective fuelling for a Stag

[MikeParker]

Has anyone come across a sticky air valves in the carbs ? When revving lightly one of my air valves is not moving up and down at all, whereas the other one does (when pressing the throttle the air valves should move up I believe..............) Is this anything to do with the oil level in the dash pots ? Comments appreciated...............thanks

Definitely not correct. Unscrew the dash pot on the problem carb and pull to one side to jam the damper in the piston. You can then lift the piston. It should feel free. If it feels free and yet it doesn't lift when operating normally, the diaphragm is gone. If it feels a bit sticky, dismantle the piston/damper and you may find some light corrosion on the piston shaft. Polish it up with a cloth and oil and check it is completely free in the female part. Re-assemble and all should be fine.

I did not have quite your problem, but occasionally the car would stall, normally in traffic. You could not start it. On lifting the bonnet and removing a dash-pot there would be a clunk and the piston would fall. A similar problem of a sticky piston. Cured as above. I have not had that problem in 20 years now since polishing as above.
Mike.

[Wheelz]

I had a different cause. Rebuilt carbs, then found that one piston was very slow to drop. Put the old diaphragms back and problem solved. The diaphragms in the new kit were much too thick. I think this is avoided if you buy the quality rebuild kits from Burlens etc.

[James Wood]

Thanks very much to all , polishing of the pistons seems to have done the trick !