Supercharger exhaust backfire

[KreagerM]

Time to address this issue I'm having with exhaust backfiring.

I'm running 5lbs of boost on my little 289 with a Pro-Flo Efi system. I'm running the stock paxton FMU 12:1. After doing the calculations I should be running a 8:1 FMU. I believe here lies my problem. It's definitely running rich with the 12:1 FMU.

It only backfires at high rpm's (near the rev limiter) as soon as I push the clutch in she lets out a hell of a boom out the exhaust. My buddy behind me said blue flames went shooting out my tail pipes. Sounds way to rich to me. Now this only happens at high rpm, when i press the clutch in.

My timing is right on as per Edelbrock recomendations, my plugs look good. so i'm thinking it's my FMU. Do you all Agree I'm going in the right direction?

Thanks

 

[10secgoal]

Do you have a wideband ? Couldn't tell you on the FMU honestly. If it's that rich a O2 would tell you right away. If you do a WOT pass and check the plugs, it's always easiest with a new set.

 

[Stanger007]

Look at what makes a backfire - if you believe your timing to be correct then you have unburned fuel in the exhaust.

Because this happens at higher RPMs you are likely blowing out the spark or having the spark cut (limiter).

Try gapping the plugs down or raising the limiter temporarily to see if the problem subsides.

Apart from that put a wideband on the car and see where it actually is.

You will find your answer.

Wes

 

[KreagerM]

Yes, The gap. I'll do that as well. I didn't think of that, I know the gap is stock, so that very well could be the problem. Thanks for the advice.

 

[iskwezm]

i used to keep my gap around 30 or less

 

[Stanger007]

i used to keep my gap around 30 or less

Agreed.

Wes

 

[KreagerM]

I definitely give that a try