Trying to get new engine running - backfires through carb

I've just installed a ZZ430 clone in my 80 Z28 and am having a hard time getting it started. I've a mechanical fuel pump that has not moved any fuel to the carb yet, so I'm pouring gas into the Edlebrock 750 carb. When I 'start' it, the car backfires through the carb and the fuel in the carb catches fire. My last attempt at starting the car caused fuel to erupt everywhere. Being that I've had a few minor fires, I'm now a little concerned about continuing.

How should I proceed?

Use the thumb over #1 spark plug hole method to confirm timing isn't off. Many times when a new engine won't start, it's off 180 degrees.

Ya sounds like you are 180 degrees off on the distributor. If you arent your timing is likely too advanced. Turn the engine to TDC #1 (put finger of the #1 sparkplug hole and make sure you get air pushing past, then continue to turn the engine till it is at 0degrees TDC) Then take the dist. cap off and look where the rotor is. It should be facing the #1 sparkplug contact. To get the timing close as possible without a timing light I take the engine TDC #1, Look in the distributor and line up the trigger (the pointy thing) then simply turn the distibutor body counter clockwise about 10 degrees.
Good Luck.
CoryM

9 times out of 10 back fire thru the carb indicates

180 out
firing order off
too far retarded

if it turns over hard or pops out the exhaust, that usually indicates to much advance.

Make sure the battery is charged, jack the rear of the car up (gravity :D ), take out all the plugs, and spin it over for a couple minutes.. shouldn't take long to prime the fuel pump. You can also use a small funnel to trickle fuel into the bowls thru the vent tubes.

Another thing is that your valves may be adjusted to tight and are not sealing. Check the ignition timing first though.
CoryM

I just finished a rebuild and I had that exact same problem. I had two issues: My distributor was 180 degrees off, and I had the rocker arms way too tight. Because my rocker arms were way too tight, I bent a pushrod which prevented a valve from opening, hence the popbacks through the carb. First check the distributor, and if it is all good, then definatly check the rocker arms. After I bent two pushrods I learned the proper way to adjust how tight the rocker arms should be, if you need help with that let me know.

It's all good, she's up and running. I just had the timing WAY off.

The same thing happened when I built my last motor. I even marked the distributor and everything and it was still 180 degs. off. :lol: Good thing you figured it out.