430 missfires tru carb

[hdtattoo]

Hi guys , me Fred from the old country the Netherlands !!
i instald a 1969 430 cu in my 1973 Regal.
block was rebuild,with a higher cam , edelbrock intake , Rochester 4 barrel and twin flowmaster exhaust.
after 14.000 mls I have a intake back fire.
engine starts, takes rpm and drive wreally fine...BUT flooring it from idle rpm it "pangs" almost like a gun shot ! smoke from under the hood....
NO vacuum leaks, plugs wires newly instald , compression s good Hei ignition, cheap china made so swaped the module for a OEM AC Delco...
Still the same FU problem...
What to do ?
Thanks
Fred

[telriv]

From the sound of it it's possible an exhaust lobe on the cam went "Flat". The harder you run it the worse it will get. Remove the valve covers, start the engine & look closely at the action of the rocker arms. If there is a flat one it will open less than the others.

[LARRY70GS]

Could also be going extremely lean. Look at the air valves on the secondary side(on top). With the engine off, tip in the air valves with your finger and make sure that the secondary metering rods are rising with air valve rotation. There is a small plastic cam that is responsible for raising the secondary metering rods, sometimes they break. That will produce a lean back fire through the carburetor when you floor the gas.

[hdtattoo]

Thanks guys

[hdtattoo]

Oeps, wrong button there whas not done yet...
anyhows, camshaft you say , well since it works oke every now and then I ruled that out. I keept on tinkering with the ingnition, when I changed the coil in that HEI I noticed the yellow wire coming out of the distrubitor was not lined up correctly next to the other two wires and makng grounth contact to the disstrubitor, fixed that and no more back fires tru the carb FOR NOW ! I had days before that it worked good....
I will floor it for a few more days
OKE so no more backfire but it does "hick " now and then
I did checked the carb. as sugested and think the primairy valves stick somewhat
will go from there....
thank so far guys

[telriv]

Glad to hear & that it was NOT a major problem. You NEVER mentioned it would run OK sometimes. It's hard enough to do diagnostics over the internet, BUT we need the proper facts/info to be able to help & do a proper diagnosis.
Just sayin'


Tom T.

[hdtattoo]

understand Tom, thanks
I wreally needed to tell more ,must have been the FU headage it gave me....
Owhwell I only need to figure out the other iseuw now , must be a minor thing also...thanks fo the help