TB42 Backfires and Runs Rough until warm

[gilly81]

I've just ordered the Pertronix Ignitor 2 and Flamethrower coil. Hopefully this will help.

[Ben-e-boy]

if all else fails try putting a vacuum gauge on as a diagnostic. I cant remember exactly what each reading means Im sure its online.

[Ben-e-boy]

[gilly81]

Thanks - I'll be replacing all the vac lines this weekend so I'll give that a go!

[gilly81]

Ok guys problem solved! Thought I should report back with the fix.

Checked Vac lines, a few had perished right at the ends where they are stretched over the flared ends of the pipe, fixed those, - still rough.
Carby was looking dirty internally so gave it a decent hit of carby cleaner - still rough.
Triple checked points - looked a bit wide so regapped to 0.45mm - still rough

Drove to a mates place and borrowed his timing light - miles off!? It was running sweet a couple of weeks ago and i didn't touch the timing so I never thought that this could have changed itself. Turns out the bolt holding the distributor in correct timing is buggered and allowed the dizzy to move. Set it at 10deg with a new bolt and it's running as sweet as ever! The joys of buying an old car - at least I'm learning what can go wrong as I go.

Thanks to all for your suggestions! Appreciated. Pertronix II and Flamethrower Coil are on their way, that'll be next job!

[gilly81]

I just wanted to follow up on this because it may help someone one day...

The problem came back, although not as bad, no backfiring, idled fine and would actually drive the first few streets like a dream, and then start breaking down BADLY for 3-4 mins, before running perfect at full operating temp.

Tearing my hair out, today I made two more changes. Replaced the distributor cap (which really didn't look that bad anyway) and disconnected the noise suppressor. This one I'm sure is the culprit. The Mav has never run so smooth! From 2 cold starts since - absolutely no problems. Never so much as missed a beat since I disconnected that prick of a thing! Radio has no noise without it connected - yet to try the UHF though, may need to replace it if that's a problem.

So here it is for a search engine to pick up: If your TB42 Carby breaks down or misses and you've replaced points, leads, plugs, condenser, checked vac lines and all the usual, DISCONNECT THE NOISE SUPPRESSOR! It's a 2 second job I really wish I did first. I didn't think it would have any effect on spark delivery but it obviously does. Little bastard! LMAO.

cheers
Gilly