backfiring 283

I just finished building a 283 with double hump 202's, a big bump stick, and a 3x2. I'm trying to start it, well I got it started but it backfires through the exhaust and once in a while through the center carb, Vintage Speed built the carbs and I bolted them on. I'm running a new distributor. Any ideas on the problem? What do you suggest for time? Thanks

 

Usually it turns out to be that the plug wires are out of order, or the distributor is installed 180 degrees off.

 

Timing off, plug wires not in the right order, points not set right, bad connection in ignition circuit, leaking valve, poorly adjusted rocker arms .... to name a few.

 

I'm building the exact same combo; ( with Rochester 2GC's) Check your timing. If your timing is correct, then keep turning the distributor until the engine develops it's idle, (about 900 RPM's) If it's where it should be, it'll stop backfiring and the throttle response should be quick when you pull back on the throttle linkage. If there's a problem with the deuces, it'll most likely be the air/fuel mix. I would think Vintage Speed would have that adjustment already dialed in. If not, use a small standard (flat) screwdriver and "back" the air jets off on the carbs. That should take care of the problem. To me, it sounds like a simple matter of timing. It probably is too far in advance. Good luck! Be patient.

 

Sounds lean. Check that the outboard carbs are fully closed. Check for vacuum leaks. If all is ok then try fattening up the idle circuit on the primary carb. Does it backfire at idle or when you try to rev it?

 

I had the same problem after i tuned up a sbc,tried everything,turned out to be the condenser.

 

Had a SBC do the same after a cam swap. I could get it to idle good and would pop out the exhaust occasionaly, but give it gas and it would backfire through the carb. Turns out I had crossed 2 plug wires at the cap. Swapped them and she ran great. I also had to eat crow as I assured my helper for three hours that the order was correct and I new what I was doing. (oh to be young again)

 

i wouldnt assume that the carbs are ok as i and many others have found that altho they look pretty the carb setups from vintage speed are pretty hit or miss as far as the quality of the rebuild and matching of the parts such as jets and power valves// but i would first go thru the timing and igniton setup

 

Thanks to everyone for the quick suggestions. I will work on it tonight and let you know what happened.

 

Sounds 180 out to me.vacum advance shoud be pointed to #5 cyl. for appox.timeing.Did you change the timing cover.pointer location is different on some.

 

Thank you again for the suggestions. It turned out that I had the linkage messed up and that left the front carb open partially causing a severe vacuum leak. It now sounds great. I had forgotten what three deuces sound like when you open them up. Wow! Thanks again for the help.........