After half-rebuild, engine still won't start

[geekeasy]

I'm still trying to get my A4 running after half a rebuild.

We now have compression, fuel, and a spark but it won't start.

After trying to start it for a few minutes, we got large backfire out the exhaust.

1) I'm not 100% sure that the Carb was put together correctly. There's an open screw hole on the bottom of it, but from the manual it seems that might be correct.

2) There didn't seem to be a bunch of fuel on the spark plugs, so it is possible it's not getting enough fuel.

3) But maybe the mostly likely problem is that the timing isn't right. Any advice on how to correctly set the timing?

Thanks for any advice and help!

[Sam]

My bet is on the timing due to the backfire. I had a similar problem one time after cleaning my distributor [points] thought I put back in the same position - was way off and getting a backfire. Just follow the TDC routine with the rotor pointing aft and that will be a good starting point.

[joe_db]

The carb does NOT have any open holes when installed correctly
You are likely missing the main jet plug or the scavenger tube. Please send a photo, either one of these would be very dangerous.

[CajunSpike]

Timing is probably off..but just because you see spark doesn't mean the spark is right.
I had a situation where you could see spark if you grounded the plug and crank.
However, it was a weak white/yellow spark, not a crisp blue spark.

Turns out the points were badly adjusted. It was close enough to spark but not close enough to run the engine.

[capnward]

Your report of an open screw hole on the bottom of the carb woke me right up. Joe is correct. Sounds like you need a scavenger tube fitting in that hole. Otherwise you'll be leaking gas into the bilge. If you were missing the main jet plug it probably would just make a puddle of gas under the engine. Either way, it's dangerous.
I'm pretty sure that in late model A4s, when doing initial timing from #1 TDC, the rotor needs to be pointing to starboard, (away from the head), not aft. The Moyer video on this is excellent.

[geekeasy]

Here's the open screw thread on the bottom. The hex screw fitting that could have gone here is now on the back (toward the back of the engine) top side of the carb.

Should I have put that screw on the bottom and left the one of the top/back open?

[CajunSpike]

There's supposed to be a metal line running from that hole to the intake manifold. Its purpose is to capture any fuel that leaked out the carb throat, and feed it back to the intake to be burned.