Misfire and backfire

[Polo62]

I got a 400 big block out of a 77 newport with lean burn I ditched the carburetor and distributor for a points distributor and a holley avenger 770cfm I set the timing around 8 to 10 btdc seems like that's where it ran the best which still is not smooth it misses and backfires threw carburetor and out exhaust I put a vaccum gauge on it it pulls from 17 to 20hg and vibrates back and forth from 17 to 20 my chart says points or carburetor both are new and came from other engines that worked good on it also has new timing set and balancer checks out ok any ideas

 

[lemondana]

Try putting a new condenser in the distributor. I almost bet that's it.

 

[khryslerkid]

Try putting a new condenser in the distributor. I almost bet that's it.

 

[HALIFAXHOPS]

New parts store Points and condensers are junk!

 

[66 Sat]

I'd double check your firing order, could be 2 plug leads mixed up.

 

[snakeoil24]

Look for leaky valve and also backfi re is likely lean condition or bent or burnt valve

 

[lemondana]

I have an old Echlin and Niehoff books. A lot of these old made in USA parts still available.

 

[DPeltz]

Compression, and/or leakdown tests. Condensor, and firing order double check also an excellent idea. You mentioned new timing set, did you degree your cam? New parts today must be scrutinized at every step.
Good Luck!!

 

[eldubb440]

vacuum advance on the correct port?

 

[moparedtn]

I have an old Echlin and Niehoff books. A lot of these old made in USA parts still available.

...and are about the only brands worth buying ignition parts from anymore.

 

[HALIFAXHOPS]

I have an old Echlin and Niehoff books. A lot of these old made in USA parts still available.

All I use in my rebuilds, new stuff is horrible and not worth my time at all.

 

[Polo62]

Look for leaky valve and also backfi re is likely lean condition or bent or burnt valve

Will a smoke machine tell me if valves are bent or leaking

 

[RemCharger]

Compression test.
Smoke test won't tell you much

 

[eldubb440]

I have screwed an air fitting into the spark plug hole on compression stroke and plugged in an air hose to find a burnt valve.......it obviously blew air out the tail pipe

 

[Polo62]

I have screwed an air fitting into the spark plug hole on compression stroke and plugged in an air hose to find a burnt valve.......it obviously blew air out the tail pipe

I'll try that next it runs missing but not a dead miss but when you try to go over half throttle it starts backfiring and won't rev it also goes dead every time you put it in gear so I crank it in gear no nuertal safety switch

 

[khryslerkid]

I'll try that next it runs missing but not a dead miss but when you try to go over half throttle it starts backfiring and won't rev it also goes dead every time you put it in gear so I crank it in gear no nuertal safety switch

Get yourself a new condenser. Don't over think it.

 

[lemondana]

Condenser-cheap, easy thing to try!

 

[snakeoil24]

Will a smoke machine tell me if valves are bent or leaking

No need compression and vacuum gauage

 

[Polo62]

I put another used carb on today quadrajet and it quit backfiring but still has a miss I'll try condenser next thanks everyone

 

[gtxrt]

what do the spark plugs look like. how about the coil