Backfiring out of a quadrajet carb?

[dasanii19]

1976 K5 blazer 350 5.7 4x4 (quadrajet carb)

Today I did a tune up and now im getting a back fire coming out of my quadrajet carb.

When I pulled the old plugs out they were very caked with black crud. I replaced those. I put new plug wires on and changed my air filter to a K&N filter. I also put a new rotor in. (HEI)

When I started the truck up after the tune up the motor seemed to be running very hard/rough (very shakey) when I gave it gas in a pumping motion this is when I got a back fire coming out of my carb. The truck does idle.

Should I check my timing? I do have a timing light but do I need to unplug anything before I time it?

Any other ideas? I was also thinking maybe the new filter might have something to do with the back firing? what do youi think?

Any ideas will be great.

 

[4X4HIGH]

Sounds like you got the plug wires crossed somewhere. Re-check your firing order and i'll bet you fix it.

Nothing to disconnect electrical wise to check timing but you do need to unhook the vacuum advance and plug it while you check timing.

 

[pauly383]

You unhook and plug the vacuum line going to the advance .Wouldn't hurt to time it . I have had the hold down loosen before , and the dizzy turn on motors .

 

[dasanii19]

Wow quick replies. Thanks

Yea, I mean the backfiring isnt pooping over and over or anything, its just one POP!! out of the carb when Im pumping on the gas.

I will check my plug wires and check the timing.

 

[BoondocK5]

Sounds like you got the plug wires crossed somewhere. Re-check your firing order and i'll bet you fix it.

Nothing to disconnect electrical wise to check timing but you do need to unhook the vacuum advance and plug it while you check timing.

4X hit it dead on! even us guys that been doing this for while still get them crossed now and again

 

[dasanii19]

But what would cause the very fouled plugs? I mean these things were caked with residue badly. I have never seen plugs like this before.

I dont know if this might be a cause but I do see an abnormal amount of smoke coming out of my exhaust. My father said it wouldnt hurt to re rack the heads. What do you think?

 

[BoondocK5]

Well, Not that I'm trying to brag, just convey my experience.I've been doing tune up work since 1993 professionally, and just running your engine with a carburator will cause plugs to foul, it's just a matter of time. so get those wires straight and have fun!

 

[dasanii19]

Sounds good, I hope its an easy fix. Ill post back either way. Thanks for your time guys.