Backfire during burnout?

[cbodybob]

Finally got back to the track this weekend after 7 weeks. Car ran very good in both time trials. Round 1 was a little off, but close. Round 2 As I start my burnout car pops loud from the carb & shuts off. It started back up. Car was off the dial again this time by 27 hundredths. Flat out as my opp. Was on my door. 60 ft good 330 good. Car has never in 8 years of racing backfired through the carb. The next round I cleaned it out & the darn thing went back up 4 numbers causing me to break out when I had my opp treed Only thing I have changed is I added a 4 hole 1 inch spacer & a heat shield. Sucks cause I don't get out much here lately & this car has always run well. What's the deal?

 

[Cranky]

You increase the plenum volume with the spacer and probably leaned out the fuel mixture some. Were you already running on the lean side before the change?

 

[cbodybob]

You increase the plenum volume with the spacer and probably leaned out the fuel mixture some. Were you already running on the lean side before the change?

No it's been a bit rich. I think it has something to do with that spacer

 

[Budnicks]

IMHFO I doubt it has anything to do with the 4 hole 1" spacer,
unless you have a massive vacuum leak or something, after installing it...
even if it was a little lean or fat {rich you say} in your case...
I'd look at the ignition timing {something in the ignition system} or more likely some carb setting...
what kind of carb ??

 

[snakeoil24]

Did it stumble just before the back fire? if so it could be accelerator ran dry and leaned out.

 

[cbodybob]

Backfire

IMHFO I doubt it has anything to do with the 4 hole 1" spacer,
unless you have a massive vacuum leak or something, after installing it...
even if it was a little lean or fat {rich you say} in your case...
I'd look at the ignition timing {something in the ignition system} or more likely some carb setting...
what kind of carb ??

It's an Eddy 600 I pulled the plugs this afternoon & they looked like they always do. It didn't stumble. I rolled through water did a quick spin to get the tires wet. Waited 5-10 seconds for the signal to burnout. Steped on the gas like always & POW. The engine temp was about 145 & I usually stage at 155. Just don't have my rythem down from lack of driving time

- - - Updated - - -

The car was running great. Only a tenth off its best ever & it was 30 degrees warmer. Could it have just been a freak thing?

 

[70bigblockdodge]

Sure the timing hasn't creeped off a bit chain stretch and/or wear.

 

[daredevil]

How fresh is the motor? Maybe a piece of carbon or gasket trash or something got between the intake valve and seat. When that cylinder fired it ignited the fuel in the plenum.

 

[cbodybob]

Sure the timing hasn't creeped off a bit chain stretch and/or wear.

I doubt it Big. The motor is 30 years old & I drove it on the street for a few years. Has less the a thousand miles on it. I got busy with career & moved 3 times during the 90's so it sat in storage for all that time. I just started racing it 8 years ago. And like I said it was running great. On that last pass it went back to what I had originally dialed in round 1. But I had dialed down after 2 straight rounds of it slowing.

 

[70bigblockdodge]

Just throwing stuff at the wall to see what sticks. I fixed my ign problem with my Challenger at Norwalk, ground was loose, so at least it runs good on hwy, only ran a 15.6 letting it shift itself at 4800 I want to keep my 45 year old pistons right where they are. good talking to you Bob and good luck.

 

[cbodybob]

Backfire

Just throwing stuff at the wall to see what sticks. I fixed my ign problem with my Challenger at Norwalk, ground was loose, so at least it runs good on hwy, only ran a 15.6 letting it shift itself at 4800 I want to keep my 45 year old pistons right where they are. good talking to you Bob and good luck.

Thanks Big!

 

[Cornpatch MO]

Just a thought to throw out there. Do you have a rev limiter or something that could cut your ignition for a moment? If you have a good charge of gas in the cylinders and the ignition stops and then starts right up again. it will ignite the raw gas causing a backfire. .........................MO

 

[cbodybob]

Just a thought to throw out there. Do you have a rev limiter or something that could cut your ignition for a moment? If you have a good charge of gas in the cylinders and the ignition stops and then starts right up again. it will ignite the raw gas causing a backfire. .........................MO

Yes it's got an MSD6AL on it, but it backfired as soon as I hit the gas