Dual carbs.backfiring

[Buick35]

Hi,New to this forum but trying to help my son out. He has a nice 69 Ghia with a 1776? cc,mild cam,new coil and dist.and dual Kadrons.New gas tank. When cold especially it backfires and runs rough under power shooting flames out of the exhaust.What could be a possible cause? New intake gaskets also.Thanks,Greg.

[mike6024]

way too rich or leaking carb diaphrams.

 

are these new carbs? or rebuilt with all new seals, etc? I don't think I understand your question very well. I am only familiar with sidedraft weber or dellorto anyway.

[Buick35]

Thanks,they are rebuilt with new seals.I also thought they were running too rich.Greg

[StillOutThere]

Are you using some sort of synchronization tool?  Like a Uni-Sync ?

 

[Buick35]

The vw shop we took it to did.I might have to bring it back to him. He replaced the distributor,coil,intake gaskets and cleaned the carbs.

[Buick35]

I just had a thought. Sometimes it takes a little bit of jiggling of the ignition key to get it to turn over.Could a bad switch cause backfiring?Greg.

[hchris]

I'm a little confused, you say backfire out the exhaust?  technically a backfire is through the carbs; afterfire is through the exhaust. 

 

Afterfire is pretty rare and is more likely to be a timing issue, wouldn't entirely discount carbs but more inclined to look at timing particularly when you mention cam,coil and distributor; assuming these have been newly installed  ?

[mike6024]

Timing is way off, or the carb mixture is way too rich.

 

Timing off is much more likely. Timing is probably retarded, meaning it needs to be advanced. Get a timing light and check it yourself, don't take it back to the shop.

 

 

[Buick35]

54 minutes ago, mike6024 said:

Timing is way off, or the carb mixture is way too rich.

 

Timing off is much more likely. Timing is probably retarded, meaning it needs to be advanced. Get a timing light and check it yourself, don't take it back to the shop.

 

 

Thanks,Greg.

[Eric Wahlberg]

I had a '73 Porsche 914 that had dual Weber carbs that would occasionally pop and sputter.  I found they would get dirt in the jets which caused this.  A good cleaning helped as did installing a good fuel filter.