Backfire

[dlong70elcamino]

Cliff I just got my 17057213 carb back on my Chevy 350 in my Elcamino and it runs really good except somtimes it will backfire when the secondary opens then its ok runs fine after that does not seem to run out of fuel. Once it gets that pop out of the way its ok and runs like a scalded dog. It defiantly launches a lot harder than when it had that 600 Holley on it.And it runs great on the primary side like just regular driving.I got the secondary air flap spring set at 3/4 turn and pull off is at 2 sec.If i snap throttle it while i,m under the hood it don,t backfire and the air valve looks like its opening ok.  Got any ideas?......thanks Dan

[Cliff Ruggles]

Is the linkage holding the flap tightly shut.  Backfire in that situation is usually a momentary lean condition, flap opening too quickly or pull-off allowing it to open to fast and getting too much air and not enough fuel at the onset of the secondaries.....Cliff

[dlong70elcamino]

Cliff yes the linkage is tight. You set the vacuum break to 2 sec when I snap it open when i,m under the hood it don,t seem that the air valves flop right open.It has .041 sec rods in it primary's are 38-68 I haven't done the tip in procedure yet but it runs great in the prim side.Do you think I need to do something with the air valve spring?....Dan

[Cliff Ruggles]

Yes, the spring controls the airflaps, sounds like you need just a tad more tension so it's not coming it quite as fast......Cliff