Backfire through carb HELP!

[BillySS]

A very good friend of mine rescently replaced his vacuum secondary carb with a new Holley 750 HP double pumper. We worked on tuning it for 2 days total now and no matter what we do it pops threw the carb and occasional backfires from the exhaust. I ritchened the Idle mixture screws 1/8 turn at a time till almost 3 turns out, Timing is good at 34* but it still has a miss. I'm getting very frustrated and need some advise. Car ran perfect with other carb on it, why he changed it is beyond me but we can't even put the old one back on cause he sold it. Please Help!

 

[slimbo]

are the mixture screws even doing anything? if the throttle blades are too far open your sucking in thru the transfer slots and the idle mix screws wil have little effect. is it a used carb? sounds like is is very lean at the tip in. takes a super lean condition to make it backfire. sure something else didnt happen....crosed plug wire maybe?

 

[Ed Cannon]

Does it pop when you nail it or just driving around part throttle? Could be a huge vacuum leak, floats set way too low, also a accelerator pump not working properly. Like was said by Slimbo lean condition causes back fire through carb.

 

[BillySS]

I feel like I'm friends with a chimp!!! He changed the plugs before the carb swap and a few plug wires were not on the plugs all the way. I wanted to kill him he is totally mechanically DEclined!!!! I'm sorry I bothered you guys.
Bill

 

[hevychevy567]

i know how you feel bro. My friend did the same thing to me

 

[brrymnvette]

I was going to say plug wires are crossed or not put on all the way, after I read the 1st post. I've had a friend just not put 3 of them on before b/c they didn't think they were necessary. I got the car for $500 with a blown motor shortly after.

 

[BillySS]

LOL Aren't the Mechanically declined easy?! Funny thing is I do most of the work on his car cause he is a very good friend of mine but the ignorance is overwhelming. I have to admit I was totally baffled. Car ran great before the swap, then I go to his house put the new one on and figured a few minor adjustments and he's off. NOPE never that easy.

 

[Malibu 361]

:-k And who was this.......?

 

[BillySS]

My friend Jimmy with the 79 Z28. You met him at the track rental.