Stumped with backfire from carburator

[huero]

Thank you all that have responded.
Cap rotor and distributor are brand new

[sc2dave]

once warmed up, create a small vacuum leak to see if it revs up. If it does, too rich.

[huero]

Pulled the cap on the port at the carb base (manifold vacuum) and rpms increased slightly

[geraldtson]

From all the things you've checked i think i'd remove sparkplugs and vale covers and turn engine over manually or by starter and see if you can find a sticking intake valve. Could be shavings in valve guides if recently reworked or number of things. Burnt valve,bent valve.sticking lifter in bore and so on.Can't really tell by video but engine doesn't really sound right either, maybe to high on timing. Spark plugs don't reflect it but if you have vacuum brake booster make sure its plugged in? Don't think You have one on that application but just if. Engine sounds lean but looks rich? Recheck for true TDC mark on damper. Also check that you don't have any dripping boosters at idle?

[fdicrasto]

I just watched the first video and looking at the carb as it was running, noticed what looked like a small puffing shooting out from the front left lower portion of the carb. Possibly an uncovered vacuum port??

[MadBill]

I think that's a reflection from the fan blade..

[huero]

I just watched the first video and looking at the carb as it was running, noticed what looked like a small puffing shooting out from the front left lower portion of the carb. Possibly an uncovered vacuum port??

Fan Blade

[JoePorting]

Any time a Holley backfires, you have to replace the power valves. If they are blown, raw fuel will leak past them and go down the PV vacuum port causing a rich idle.

If it's an old 56 car/truck, did you replace all the wiring and not use chassis grounds? Old wiring will give you a weak ignition and all the old rusty body/frame metal will make for bad grounds. Use wired grounds.

[rp930]

Any time a Holley backfires, you have to replace the power valves. If they are blown, raw fuel will leak past them and go down the PV vacuum port causing a rich idle.

If it's an old 56 car/truck, did you replace all the wiring and not use chassis grounds? Old wiring will give you a weak ignition and all the old rusty body/frame metal will make for bad grounds. Use wired grounds.

Absolutely not true. Almost any newer Holley has a check valve to prevent this. Even before this it didn’t happen every time.

[sc2dave]

Any time a Holley backfires, you have to replace the power valves.

I've had many backfires on my carb and never had to change pv.

[sc2dave]

Huero, any updates?

[Tuner]

After a backfire you have to replace the whole carburetor. A backfire will rupture the diaphragm in the fuel pump and cause the gas tank to have a hernia. If it is an electric fuel pump it will spin the motor backwards and blow so much electricity back it will cause the battery to have a hernia. A strong backfire will blow the spark back and cause the plug wires to prolapse and the coil to have a hernia. Don't forget to re-torque the manifold bolts or maybe the lug nuts.

[huero]

Huero, any updates?

Sorry, for the delay and thank u to all that are helping. Unfortunately for me, the only update is that I admitted myself to the ER on Friday and today I am getting surgery to get a gall bladder delete.
https://flic.kr/p/GHGnFC

[cv67]

lol

[lg1969]

I suggest of trying a hotter heat range on the plugs. It look like the are a little cold. Running a carb without a choke sometime does not help either.