Backfiring - should I be concerned?

[Royce]

I used to get flame out the tail pipe, just before I had to have the engine rebuilt because of trashed valve seats resulting in valve to piston contact, I think I should have used more lead substitute. That was 1989 when I had Rebello build me an L28 engine.

I have always been told it is still a "backfire" even if it occurs in the carbs. I think it is because of the point in time it occurs in the cycle of the engine!?

The "shut of the engine" backfire is a rich condition and occurs in the exhaust. It usualy results in a muffler exploding!

Have fun!

[2ManyZs]

Backfiring through the carbs is usaully caused by the timing being to far advanced. It is trying to fire while the intake valve is still partially open. This is the one that will cause the most damage to an engine, since you not only have the flash, but some of the compression is being released into the intake and back through the carbs.

The old trick of cutting the key off just pumps raw fuel mixture into the exhaust, no ignition, no fire, so it gets exhausted. Then when you re-fire it, it will ignite in the exhaust. Won't cause as much damage, but I have seen mufflers burst their seems if this is done too many times.

I ran a straight exhaust on my ITS car, and as fas as I know it didn't throw any fire out, if it had people wouldn't have been trying to push my slow car out of the way so much.:tapemouth

[jalexquijano]

Im having this same precise problem, My car is a 1972 240z with a Schneider 274F Camshaft and remanufactured SU Carbs by Ztherapy!!! Also have pertronix ignitor and have set the Distributor timing to 11 BTDC. Please note i have also removed all the emmissions crap including the antibackfire valve from the balance tube.  Should i lower the timing to 10 BTDC at idle to avoid the sudden gunshot when decelerating?

[Chickenman]

See reply at:

 

http://www.classiczcars.com/topic/52702-attempted-to-tune-su-carburetors-but-still-backfiring-on-intake/#entry482353

 

George. Stop making multiple threads on the same topic. People can't follow what you've done. It starts to get really annoying and multiple threads on the same problem are generally against most Forum rules.

Edited December 4, 2015 by Chickenman