Backfiring

[1969_Mach1 333]

My first thought is it sounds like unburned fuel igniting in the exhaust system.  I've lost track, has the extremely hot exhaust header issue been resolved?  Probably all related.  I think if you find out why the idle speed needs to be turned up so all the issues will be resolved.   

[ClubSport 29]

maybe the spark plug are too hot causing pre-ignition

[1969_Mach1 333]

I listened to that video a few more times.  Is it just me, before the pop, I faintly heard other exhaust noises that sound like engine run-on (dieseling) after the motor was shut off.  It takes a long time for the motor to come to a stop after it is shut off.  Is the motor running too hot?  Does it do this if the engine is shut off while the trans is in gear?

[barnett468 418]

3 hours ago, 1969_Mach1 said:

I listened to that video a few more times.  Is it just me, before the pop, I faintly heard other exhaust noises that sound like engine run-on (dieseling) after the motor was shut off.  It takes a long time for the motor to come to a stop after it is shut off.  Is the motor running too hot?  Does it do this if the engine is shut off while the trans is in gear?

From my post last night.

"ok, from what i can tell by the video, that after sound is likely either a timing issue or a throttle plate that is open too far or high compression, but it is definitely not jetting. It is sort of similar to "dieseling" that mach 1 mentioned, and deiseling is often caused by a throttle plate open to far, ignition timing, very hot engine, and/or high float level."

 

[Her69fastback 3]

I think I mite have it fixed. I put a new electric fan that  pulls 3000 cfm. I also adjusted the air fuel mixture. Set the timing at 10. Let it run in the garage for about 15 mins & the headers never got red & it never dieseled your ran on. Should I change the thermostat to a 180 degree? I’m wanting to replace the gauges to ones that will fit in the stock cluster any suggestions. Thanks again for all the help everyone gave me. Couldn’t have done it without all your guys  help. Going to take it out for a drive next weekend. 

[barnett468 418]

1 hour ago, Her69fastback said:

I think I mite have it fixed. I put a new electric fan that  pulls 3000 cfm. I also adjusted the air fuel mixture. Set the timing at 10. Let it run in the garage for about 15 mins & the headers never got red & it never dieseled your ran on. Should I change the thermostat to a 180 degree? I’m wanting to replace the gauges to ones that will fit in the stock cluster any suggestions. Thanks again for all the help everyone gave me. Couldn’t have done it without all your guys  help. Going to take it out for a drive next weekend. 

ok great, however, what was the engine temp under the same conditions before the fan installation?

what is the current t stat rating?

what was the timing set at before you changed it?

what fan did you install?

what fan was on it?

[Her69fastback 3]

I don’t know exactly what the temp was or is. The car has the factory gauges. So the gauge was setting in the middle of the gauge & never moved from there when it got up to temp. I took the radiator cap off & waited the the thermostat opened to see where the gauge was setting at. It stayed right there. The timing was around 12 I set it to 10. The fan was one I had. I put one that pulls 3000 cfm. I don’t know the cfm of the old fan. Both are 16inch fans. It’s from American volts 

[barnett468 418]

ok, well, the important thing is that it seems to be fixed. That's one more internet forum success!

[Her69fastback 3]

Thanks again for all the help.

[1969_Mach1 333]

Glad to hear it's fixed.  Thought it would be something simple.  And running too hot is one cause.  If you're not certain what thermostat is installed, it would be worth changing.  A 180 degree would be okay.  I use a 160 in mine and the motor run at about 175 degrees.  But that's just my preference.  Most people use a 180 degree thermostat.

[Her69fastback 3]

I’m going to change it out when I put new gauges in it. Thanks again for all the help