Thanks for allowing me to join, I have been using this forum for info for many years, now it is my turn to ask for advice.
I have a fury with a 383 mostly stock and an older rebuild, has never been on the road,Holley carb, Mallory unilite distributor.
Has been for many years going ok, but it developed a backfire through the carburettor under load, first it was only evident when cold but has become worse and is their all the time now.
I have been through the carburettor and found a few issues, float sinking, complete rebuild didn't change the problem, it is running rich so I don't think its leaning out!!
Have played around with timing, no change, have checked for manifold leaks none found, compression check came up all around 135psi.
Unilite module is working ok, coil seems to test up ok with ohm meter, carby mixture screws are all working, float level is right.
Still backfiring and running rich.....................What else can I check?????

 

Faulty power valve?

 

No tried that, carby has the backfire protection in it, and have tried a few different sizes, no change

 

kk -

If you checked everything correctly and your timing numbers are right (timing chain hasn't slipped), you're probably looking at a sticky or busted intake valve valve.

Archer

 

Thanks Archer, wouldn't the compression test show something if it was a valve????

 

135 For an old worn out motor.... Dam... That's a good engine if you ask me.....
Check the valve springs...

 

Low fuel pressure? Lean out backfire?