Backfire on Deceleration

[onefastmustang]

So I finally put my webers back on the car. Bear in mind I put in a new cam recommended by Keith Craft so I had my 4 barrel on there to reduce the variables until I was sure I did that right..

Now that the webers are on there it did mellow the cam out a little bit boy is it meaner now with the throttle.. I spun the tires a few times without even intending to. It seems to run really well from idle up to almost WOT. I don't want to get on it too hard yet since the cam has only been in the motor for about 400 miles. Ill give it another 100 first. However on decel if I leave the clutch out and pull off the throttle, sometimes I get a mild backfire. Could this be I am too lean or air getting into the exhaust? It only happens on the right side.

[vector1]

air into the exhaust, look for a leak.

[carmine]

What are you cam specs?

[Scufty]

Just curious ,,but why are you concerned about going easy on it for another 100 miles? Its either broke in or not and that is done in the first 15 min or so of run time. ?

[onefastmustang]

Originally Posted by carmine

What are you cam specs?

Here are my specs...

[onefastmustang]

Originally Posted by Scufty

Just curious ,,but why are you concerned about going easy on it for another 100 miles? Its either broke in or not and that is done in the first 15 min or so of run time. ?

I guess I am a little overprotective.. but I hear what you are saying..

[ray humbel]

try tightening headder, possible bad gasket

[carmine]

Cam looks good.

What kind of webers, 48ida or idf and what venturi size and jetting.

[onefastmustang]

Originally Posted by carmine

Cam looks good.

What kind of webers, 48ida or idf and what venturi size and jetting.

They are 48IDA carbs.. From memory here is what is in there now..

Main Venturi: 37
Aux Venturi: 4.5
Main Jet: 155
Emulsion Tube: F16
Air Corrector: 175
Idle Jet: 65F10
Idle Jet Holder: 120
Pump Jet: 50
Exhaust Valve: 000
Needle and Seat: 2.00

[carmine]

Looks good.

I would recomend changing your venturi size to say 38 or as high as 40.

But for now re-check your syncronization using a syncrometer with engine hot.

And get your self an air /fuel ratio meter. Very helpful with webers.

PS. remember that if you change venturi size that can affect making changes to jetting sizes and air correctors on idle circuit and main circuit.

[onefastmustang]

Yep.. that was it.. I tore apart the left side exhaust and re-did all the gaskets.. No more backfire.. Car runs great. I punched it a couple of times on a back road and quickly remembered "Respect the Cobra"

[carmine]

Good call Ray Humbel.