SC Backfire on start-up

[Jcon]

When I start my 1981 SC up from cold it stumbles and wants to backfire. Usually I start it and shut it down 2-3 times and it seems to work ok.

I noticed recently when I add techron to a tank of gas the problem disappears. Next tank of 94 octane without techron added it's back.

The WUR is new ( Problem existed before and after replacement)

I know that octane boost additives can have the affect of leaning the mixture, would the same be true of the techron type products. If so leaning out the air/fuel would likely help. Is the backfiring on a CIS SC caused by a rich or lean condition?

Any clarification would help.


Thanks

Jeff C

[BlueSkyJaunte]

I had a similar problem, stumble and near-backfire when starting cold. Once it actually blew the pop-off valve out of the airbox. I replaced my cap and rotor (as part of normal maintenance, not to fix this problem) and the problem disappeared. Looking closely, there was a slight hairline crack down the length of the old rotor. Any ideas how this could have changed only my startup behavior?

[RazorRacer]

I would check the timing and the advance/retard vacuum line.

Mine did the same thing. I leaned it out a bit and the backfire went away.

[Jcon]

Thanks

I'll try leaning it out a little on Sunday. It would be great if it worked

Jeff C