HELP: Yet another Timing problem / Question
Thread Starter
Team Owner
Joined: Mar 2002
Posts: 44,629
Likes: 1,827
From: Huntsville AL
HELP: Yet another Timing problem / Question
I’m in the fine tuning stage of my 69 project and am having problems with the engine popping thru the driver side exhaust at 1900 RPM. The passenger side exhaust is fine. Below are the engine details and numbers I have pulled.
427 / Tri-Power
030 over w/ .140 domes
Mechanical cam / 108CL / 112 Lobe Separation
Intake .534 Lift / 239 Duration @ .050
Exhaust .539 Lift / 246 Duration @.050
Edelbrock Performer Alum heads, 100CC
Chambered Exhaust
Vacuum advance is hooked up at the Carb base
Dist is stock OEM, overall condition ??????
Idle RPM Numbers
RPM: 500
Initial Timing: 12 deg
Vacuum at the Vacuum advance: 0 in hg
Temp: 170 deg
1500 RPM Numbers
Total Timing: 41 deg
Vacuum at the Vacuum advance: 21 in hg
Temp: 170 deg
Total Timing seems to jump around +/- 4-8 deg
1900 RPM
Popping starts coming on thru the driver side exhaust.
Thanks in advance for any help or thoughts on this.
427 / Tri-Power
030 over w/ .140 domes
Mechanical cam / 108CL / 112 Lobe Separation
Intake .534 Lift / 239 Duration @ .050
Exhaust .539 Lift / 246 Duration @.050
Edelbrock Performer Alum heads, 100CC
Chambered Exhaust
Vacuum advance is hooked up at the Carb base
Dist is stock OEM, overall condition ??????
Idle RPM Numbers
RPM: 500
Initial Timing: 12 deg
Vacuum at the Vacuum advance: 0 in hg
Temp: 170 deg
1500 RPM Numbers
Total Timing: 41 deg
Vacuum at the Vacuum advance: 21 in hg
Temp: 170 deg
Total Timing seems to jump around +/- 4-8 deg
1900 RPM
Popping starts coming on thru the driver side exhaust.
Thanks in advance for any help or thoughts on this.
Tech Contributor
Joined: Aug 1999
Posts: 14,371
Likes: 6,365
From: At my Bar drinking and wrenching in Lafayette Colorado
Your timing numbers look funny.... I assume these numbers are with the vacuum advance unit hooked up, and that makes it difficult to tell what's going on. I recommend you do this:
Pull the hose off your vacuum advance and see how much total timing you're getting and at what rpm it occurs. You should get 36 degrees at 2500-3000 rpm, and it should be pegged out at this rpm.
Once you're set up for 36 degrees total max advance with the vacuum disconnected, hook up the vacuum and verify that it does not pull in any more than an additional 16 degrees for a combined maximum total of 52.
If you're outside these specs, you will see performance problems.
Once this is verified and set, issues with popping in the exhaust will be confined to valve issues and carb lean/rich conditions.
Pull the hose off your vacuum advance and see how much total timing you're getting and at what rpm it occurs. You should get 36 degrees at 2500-3000 rpm, and it should be pegged out at this rpm.
Once you're set up for 36 degrees total max advance with the vacuum disconnected, hook up the vacuum and verify that it does not pull in any more than an additional 16 degrees for a combined maximum total of 52.
If you're outside these specs, you will see performance problems.
Once this is verified and set, issues with popping in the exhaust will be confined to valve issues and carb lean/rich conditions.
