Tweaking a new Demon carb

[billschroeder5842]

I'm wondering what or if there is anything I can do to tweak my new carb.

I put a Demon 1901 on my 75 roadrunner with a 400. The carb is a 625 cfm on a stock intake, stock dual exhaust, stock dizzy and stock dual air cleaner.

I'm super happy with the carb; runs great, starts fast and idels smooth. The only thing that bothers me is the occasional back fire when I stab (totally stomp) on the gas at lower RPMs. If I accerate just short of a full on stomp, the car takes it all with no back fire and accerates well.

The timing is currently set at 10 and the vacuum guage reads 17.5-18. This is "down" from 14 and 19 hg (which seemed to run pretty good on the old) but I was worried about detonation, so I backed it off.

If I increase the timing, I know I'll get a bit more umph off the line, but will that help to eliminate the occasional back fire?

Also, I worry about the accuracy of the mechanical timing light. What is the best way to time the engine using a vacuum guage? I know the Chevy guys time by vacuum successfully.

Thanks!!

[A383Wing]

is it a lean backfire? Maybe it needs a little more accelerator pump squirt?

[billschroeder5842]

So, just messing around I bumped the timing up to about 12-14ish and a super steaady 19hg adn 750 idle.

The car just feels better at this setting. I have to reconcile that that a 40 year old car is a bit loose and might not confor to factory specs.

I took it for a quick drive it it feels good from a dead stop with a normal/agressive acceration.

I did not punch it---yet. I'm drivining to work tomorrow!

[c00nhunterjoe]

Sure sounds like a lean pop to me. Might try stepping up a size on the discharge nozzle. I assume the secondaries are vaccum? If so, some adjustment there may be needed

[Cooter]

Sure sounds like a lean pop to me. Might try stepping up a size on the discharge nozzle. I assume the secondaries are vaccum? If so, some adjustment there may be needed