Classic FAST backfire/tuning help

[jks67ss396]

hey guys

I have a classic fast on my NA healthy bbc. i started playing with adding timing and leaning out the mixture at cruise. The engine really seemed to like the increased timing. But, after about 10 minutes of driving, i came to a red light up ahead , so i let off the gas and got 2 big backfires and the car died. had to cost to the side of the road.

any ideas if the lean mix or the added timing could cause backfire on decelleration?

Is there a set of example VE, timing and AFR maps anywhere for these classic FASTs (BBC preferred)?

thanks

 

[HighPSI]

Since you mention VE, I assume you are tuning in speed density mode. How much vacuum do you have at idle? I would expect to see VE numbers around 40 at idle and around 80 at WOT. In an earlier post you were trying to use an FJO WBO2 on your FAST. Is that what you are tuning with? I would shoot for around 12.8 to 13.0 A/F at WOT and idle it as lean as you can get away with.

 

[jks67ss396]

Nah, my idle map kpa is around 65-70. cruing map kpa was i believe 50 or so..

I do still have my FJO in one header to act as a verification to the L1H1 sensor/FAST in the other header. Im tuning soley off the FAST AFR though.

idle is right around 14.0. Idles good there.

WOT is around 12.5-13.0, but i didnt even go there last night. i was just cruising, trying to play with cruising AFR and timing...

The car seemed to like cruise timing around 45 degrees and i think i leaned it out to 14.5, and it seemed ok. But, on deceleration, it backfired and killed the car.

Do you think thats because it was too lean or too much timing?

So, im wondering where are the deceleration ranges (rpm/map) on the tables and what AFR/timing should i be shooting for on decel?

thanks