L36 Mixture Checking

[Skyguy007]

I have a '69 390hp 427 and TH400 that hesitates getting off the line with partial throttle then takes off OK. The engine sometimes backfires up the carb if I get on it quickly after a turn at slow rpm. The car runs great at high revs. Anyone have an idea how to check the mixture at idle to make sure its not too rich or too lean? If it's not mixture, I'm open to other ideas.

 

[warren s]

Sounds like a possible timing issue. Part throttle vaccume advance problem. Check timing not just at idle but at differnt RPMs. You can also hook up a vac pump to the advance canister and see if the timing changes the correct amount.

Could also be a mis / cross firing ignition wire, though that would happen more often.

Just some ideas of the top of my head.

Good luck.

 

[Skyguy007]

L36 Mixture Problem

Good ideas. I've checked the timing for total advance with the springs removed from the weights, but I haven't checked the vacuum advance mechanism itself. Since the ignition's all original - except for the plugs and wires of course - I'm thinking about sending the whole system, including the transistor module, to a fellow in Richmond, IN - I think it's TI Specialties - who will blueprint and rebuild the whole thing back to better than factory specs. I have a vacuum hand pump, so I'll take a look at the advance mechanism first. Thanks.