Holley Carburetor Backfiring

[Doobiemon]

I have a pre-magnum 360, stock cam, edelbrock rpm air gap intake, fresh set of low performance heads, headers, sock ignition with an orange box, with a holley 650 double pumper. I had the holley on a high performace 360, forged flat tops, j heads, eagle racing rods, 519 lift cam, etc...etc. I dropped a valve and trashed a piston and the block, but that is a different story. I was trying to get a motor together to get me by until I could build another h.p. 360. I had a low mileage stock bottom end, with a set of rebuilt heads. Put my air gap intake, carb and headers on it. I rejetted the carb and started with the stock jetting..67 primaries, 72 secondary. It is spitting back and occaisionally backfiring though the carb. In park, when I crack the throttle open, the initial accelerator shot seems ok, but once I get past the shot, holding the throttle at a steady rpm (2500 - 3000 rpm) is when the problem starts. I shined a light down the main body of the carb.I can see fuel dripping at a pretty good clip on the passenger side discharge nozzle/ booster venturi. The driver's side seems ok. The carb is only about a year old, sat for about 3 months with no fuel in it. I pulled the primary bowl and metering block and blew out all passages with compressed air. It did not help. Any Advice??

[dwc43]

Your carbs too small for botn engine sets to start with. Stock carb was 800 cfm Tq. You should at least run a 750. And your primaries are way too lean. Pull your plugs and check them for color. Oh, and since you backfired that crappy holley, you'll need a new power valve each time it backfires. A backfire will feed back into the power valve passage and bust the rubber diaphram every time.

[dave571]

Originally Posted by Doobiemon

I have a pre-magnum 360, stock cam, edelbrock rpm air gap intake, fresh set of low performance heads, headers, sock ignition with an orange box, with a holley 650 double pumper. I had the holley on a high performace 360, forged flat tops, j heads, eagle racing rods, 519 lift cam, etc...etc. I dropped a valve and trashed a piston and the block, but that is a different story. I was trying to get a motor together to get me by until I could build another h.p. 360. I had a low mileage stock bottom end, with a set of rebuilt heads. Put my air gap intake, carb and headers on it. I rejetted the carb and started with the stock jetting..67 primaries, 72 secondary. It is spitting back and occaisionally backfiring though the carb. In park, when I crack the throttle open, the initial accelerator shot seems ok, but once I get past the shot, holding the throttle at a steady rpm (2500 - 3000 rpm) is when the problem starts. I shined a light down the main body of the carb.I can see fuel dripping at a pretty good clip on the passenger side discharge nozzle/ booster venturi. The driver's side seems ok. The carb is only about a year old, sat for about 3 months with no fuel in it. I pulled the primary bowl and metering block and blew out all passages with compressed air. It did not help. Any Advice??

Before you get crazy on the carb, verify the timing..

a 650 holley is plenty big enough for that motor, despite the fiction posted here.

The power valve is a good thing to check.

If you can see fuel dripping, there must be something wring there. something leaking by in there somewhere.

It's not a complicated carb. Get a kit, and tear it down. Pay close attention to the stuff you find in the dripping area, (gaskets, floats, jet, etc)

[bbaspense]

SInce you have it apart.. add the kit that saves the power valve from backfires.. it's a ball and spring.. comes with a diagram to help with drilling... easy to install...

Then you never have to worry about blown power valves..

[70AARCuda]

Have you checked the float levels also?

Your 650 is just fine on your small block...