Webers spitting through fuel chamber breather

[dunclentdr1]

Ideas on causes gratefully received.

My 150bhp TC runs 40DCOE Webers with silver top fuel pump and fuel regulator set at 3psi.

At high revs fuel spits out through the fuel chamber breather holes on both carbs - see photo.

I have checked float heights (just over 8.5mm as they rest against needle valve, spec sheet says 8-8.5mm).

Any suggestions as to cause and solution?

Thanks

David

[mbell]

In theory the only way for fuel to get to that hole from the carb is via the top of the jet area. Either fuel splashing up from the fuel bowl or coming out of the jets(?).

I assume the engine is running well and the "spitting" you refer to is just the fuel coming from that hole? Or are you having engine running issues?

There a plate, that fill carbs between jet stack and body side, on the top of the carb body by where that hole enters. Is that fitted?

Do you have the paper gasket fitted between the top and body?

How are they mounted? is there enough flex in the mounting?

Have you checked the fuel level via the main jet stack method rather than the indirect float height to lid measurement?

[dunclentdr1]

Thanks - running very well - I think fuel splashing upwards is a plausible cause - paper gasket in place, fittings to manifold appear to spec, will try the dip method for fuel depth, was thinking at very high revs it was less likely to have full chambers so a bit baffled!

David

[nmauduit]

was thinking at very high revs it was less likely to have full chambers so a bit baffled!

if the fuel level with respect to the holes in the emulsion jet varies it will affect the running, so under normal operation the fuel level in the chamber should remain constant, even at full throttle (this can be checked indirectly by monitoring the fuel pressure at the carb while running WOT). The float/float valve is supposed to regulate a fuel level, provided that the incoming fuel pressure is both sufficient and not excessive (capability of the valve to shut off the incoming fuel from the pump).

[vstibbard]

Do you have the carburettors mounted with correct amount of flex, using MISAB or the original plates with two o rings per throat?

V