Carb on fire

Well today was interesting. My distributor advance recurve kit arrived so I removed the distributor to swap the weights and springs. My first mistake was removing the distributor - I realise now I could have done this with it in the car but oh well.

The recurve kit was very badly made and when I put the rotor back on the distributor it wouldn't sit down properly and wouldn't snap back with the spring tension. Original weights and springs back in and the advance mechanism works as it should.

It all started going wrong when I refitted the distributor. I found TDC on cylinder 1 by removing all the spark plugs and turning the engine by hand with my finger over cylinder 1 spark plug hole. You can feel pressure on the compression stroke, I know my TDC mark is correct on the harmonic balancer so that was done. I adjusted the distributor so the rotor was at the cylinder #1 tower in the dizzy cap. Fine so far. I knew the timing wouldn't be perfect but I figured we would get it started then I was ready with the timing light to adjust it.

Started the car, it caught and ran for about 5 seconds then POP and a small flame out the top of the carb. Stopped the engine. I suspected perhaps the timing was too advanced so it was igniting the mixture when the intake valve is still open and blowing through the carb. Pulled all the plugs, rechecked TDC and set the dizzy conservatively retarded (read "most definitely retarded") from where it was.

Started the car again and it immediately went BANG again, this time a foot high flame roared out the top of the carb. I assumed this was bad.

I then went away and read the internet for a while and discovered if the timing is too far retarded you can also have a backfire.

Plugs out again to verify TDC and...... came to remove the plug on cylinder 2 and CRACK, the ceramic insulation shattered. No spare plugs. Early night then.

12 degrees BTDC? Check!

Verify its definitely on compression cylinder 1? Check!

Rotor lined up with wire #1 tower (white paint mark on machined dizzy body) Check! - yet still flames out the carb!

I eventually resolved this, it was just massively retarded. I failed to appreciate the fact that the spark comes when the rotor leaves the contact i.e. the trailing edge. Combine this with the fact that I underestimated how small a rotational adjustment of the distributor is required to start piling on the advance/retard and it's not difficult to be 10,15 or 20 degrees out. Now I know what I'm doing I won't fall in this trap again if I have the dizzy out in the future. I have to keep reminding myself that I've never really done any work on an engine before apart from changing spark plugs so this is all still a learning curve.