Series 1 Carburettor trouble

Hi, I have an 80 with a 2 ltr. engine in it, which I have owned for 51 years, rebuilt three times, so you’d think I’d know what I was doing by now. Used to run it on propane from a gas bottle in the back in the seventies through a home made conversion, then had it on an old SU off a mini on it for donkeys years. I’ve just put the original carb back on, with new diaphragms in the accelerator pump, it starts beautifully, idles beautifully, then stalls when I press the accelerator. I’ve cleaned the heck out of it, but to no avail. Any suggestions gratefully received.
Cheers
GGW

Set the float level?

Thanks for the thought. Apart from making sure the float and the chamber are clean I’ve done nothing to it. It worked when it came off, in 1986 I think, so I expected it to work now.

If the float level is right it sound like the idle jet is ok but the main jet or passageways are blocked

you did not mention whether it has a bias needle or fixed assuming fixed, check float needle the piston drop cleanly ,light oil in damper ,check for wear round throttle spindle