hi can any1 help me

The carb will often flood the engine after a hot run.
Caused by the high temps in the engine bay which
can vapourise fuel from the carb bowl or, worst case,
actually boil the fuel out.

A float needle valve not sealing tightly can also cause this.

Besides checking the carb, see that the engine bay is
tightly sealed around the engine.

"Backfire" as you describe is usually caused by small
leaks in the exhaust system.

reply

Hi thanks what do you mean by engine bay sealed? the tin wear isnt fittint that well would that do it? also only starts if i press throttle down cheers

Is the carb & dizzy correctly tuned?
Are all the bolts done up tightly - fannymould to heads, carb to fannymould
Also as Speedy Jim suggests, is the exhaust "A" ok?? - No holes??

I am in Sussex too & can look at these for you if you like??

If the engine tinware isn't perfectly sealed, the engine
will draw in extra hot air from the exhaust system underneath.
That will raise the engine bay temp above what it should be.