1976 HEI distributor acting funcky

Moderator: Moderators

1976 HEI distributor acting funcky

Postby cliffsgt » Sat Apr 30, 2022 9:21 pm

My distributor in my original 140 Vega motor is acting funny. It’s a 1976 HEI distributor.
The motor is modified with a mild cam, I also have an after market intake and large two barrel carb on it with headers.
When I rev the engine up to about 3,000 RPM and put my timing light with the ‘advance’ on it, I’m not seeing any ‘advance’. I’ve ‘set’ the timing light at 32 degrees, I see the timing mark about 2-3" off the timing scale, it shows up under the water pump - when I’m adjusting the timing light, I see the timing mark on the harmonic balancer coming down to finally hit TDC on timing scale when I hit ‘zero’ on the timing light.
This puzzles me greatly.
Any advice or tips would be greatly appreciated.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm


Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Sat Apr 30, 2022 11:50 pm

ALSO: My basis timing is 12 degrees BTDC - not running vacuum advance on distributor.
No hook-up on carb for it - tried 'manifold vacuum' but early tests show motor didn't like it.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm

Re: 1976 HEI distributor acting funcky

Postby cosvega76 » Sun May 01, 2022 9:31 am

When I was a GM tech in the '70s I went to a GM training class about HEI. One of the things they touched upon is if your timing light showed an erroneous reading - I think 11 degrees - it's a problem with the timing light. Try another light.


Chuck
cosvega76
 
Posts: 2739
Joined: Mon Jul 03, 2006 8:36 am
Location: Moscow Mills, MO

1973 Chevrolet Vega GT

Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Sun May 01, 2022 11:43 am

Hmm . . . use a different timing light. Had not considered that.
I don't have a second light with advance but I've got friends that do - I'll see about finding another light.
Thanks for your input on this.
Anybody know what the max advance I can run on a Vega motor with stock pistons?
I've had the head worked and decked but I don't think it's enough to change the compression ratio drastically. Recently re-built the motor and the ring gap was at the minimum so I've probably got a little above the standard 8.5 to 1 compression.
I was thinking like 32-34 degrees total but just not sure.
Anybody have any thoughts on this?
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm

Re: 1976 HEI distributor acting funcky

Postby gt350fme » Sun May 01, 2022 12:11 pm

I have always used the old style timing light to manually find the magic 34-36 degrees at 3000 rpm, but of coarse your timing tab would need to go that high and stock one’s usually don’t, You could get a stick on timing tape for the size of your harmonic balancer.

Also for your engine to run well cruising around you will need that vacuum advance working, for example on my stock 73 smog equipped engine there is a vacuum switch on the fire wall that cut distributor vacuum in first and second gear and open for third and forth, in the lower gears the engine would surge and run crappy then in high gear run smooth, bypassed that sucker what a difference.

Good luck hope you get this figured out.

P.s. also do manually check to make sure the advance weights and springs are rotating and not stuck under the dist rotor cap?
In the end you may need to use the old Mallory mechanical dist.
Last edited by gt350fme on Mon May 02, 2022 10:15 pm, edited 1 time in total.
1964 Chevy panel K30
1973 GT Vega Hatchback
1977 Chevy K20
1984 944 porsche
1992 Lexus SC 400
User avatar
gt350fme
 
Posts: 626
Joined: Wed Jul 05, 2006 9:40 pm
Location: North coast California

1973 Chevrolet Vega GT

Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Sun May 01, 2022 7:15 pm

Thanks for the reply.
Yeah, I have a standard timing light which I used to set the timing at 12 degrees BTDC - considering bumping it to 14 degrees.
Lots of people say that the standard mechanical advance on the distributor is 20 degrees at 3,000 RPMs - and with the initial timing set at 14 that should get me to 34 degrees.
Unfortunately, I can not detect when the motor is starting to detonate - to many concerts I suppose. I killed the motor once by messing with the timing 'by-ear' and 'seat-of-the-pants', it was OK for awhile but when I really opened it up she busted some rings. I can hear other motors detonate while going down the road but the Vega motor with the solid lift head and a Dyno-Flow muffler is just to loud for me.
Anybody disagree with the statement 'standard mechanical advance on the 1976 HEI Vega distributor is 20 degrees at 3,000 RPMs' ?
Any advice would be welcome.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm

Re: 1976 HEI distributor acting funcky

Postby cjbiagi » Mon May 02, 2022 9:58 pm

Pretty much all stock HEI's have 20-21 degrees of timing. This assumes it has not been messed with. So, 14-16 degrees of initial puts you right in the 34-36 degree window. Vacuum advance will add another 10-14 degrees depending upon the can being used.
Clyde.........75 Monza 2+2
User avatar
cjbiagi
 
Posts: 8608
Joined: Sun Jun 25, 2006 2:37 pm
Location: Glenwood, Illinois

1975 Chevrolet Monza

Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Tue May 03, 2022 8:58 am

Thanks for getting back to me.
Ahh - 20-21 degrees of mechanical timing on a HEI distributor. Perfect!
So, I'll try setting the timing at 14 degrees BTDC and see how she likes it.
If I did create a 'timing tape' to put on the harmonic balancer, using a standard timing light, where should I look for the 'advance' at 3,000 RPMs - I would think at the TDC mark on the 'timing tab' but just wanted to confirm.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm

Re: 1976 HEI distributor acting funcky

Postby cjbiagi » Tue May 03, 2022 9:21 am

I believe that is correct. If you buy a tape make sure it is designed for the diameter of your harmonic balancer.
Clyde.........75 Monza 2+2
User avatar
cjbiagi
 
Posts: 8608
Joined: Sun Jun 25, 2006 2:37 pm
Location: Glenwood, Illinois

1975 Chevrolet Monza

Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Tue May 03, 2022 5:59 pm

Wonderful! Just what I thought.
I'm not sure what the diameter of the Vega's H-Balancer is - I suppose I could measure it. Do you think there is a 'timing tape' available for a Vega motor?
I was thinking of creating a 'timing tape' from the 'timing tab' - just copy it and duplicate a few times, then mark-off the increments and then taping onto the H-Balancer, and using TDC mark on 'timing tab' as the 'starting' point.
Seems like that'd work, wouldn't you think?
Maybe, I'm over simplifying it - any feed-back on this 'create a timing tape' would be appreciated.
Thanks for the response.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm

Re: 1976 HEI distributor acting funcky

Postby gt350fme » Tue May 03, 2022 6:50 pm

You could make up a timing tape that would be close, Or MSD and others has a tape kit pretty cheep from Summit, Amazon, etc, like $6.00
You do not have the required permissions to view the files attached to this post.
1964 Chevy panel K30
1973 GT Vega Hatchback
1977 Chevy K20
1984 944 porsche
1992 Lexus SC 400
User avatar
gt350fme
 
Posts: 626
Joined: Wed Jul 05, 2006 9:40 pm
Location: North coast California

1973 Chevrolet Vega GT

Re: 1976 HEI distributor acting funcky

Postby cliffsgt » Tue May 03, 2022 11:10 pm

Great! I'll check it out.
Thanks for the input.
User avatar
cliffsgt
 
Posts: 58
Joined: Fri Jan 18, 2013 5:25 pm


Return to Engine Tech

Who is online

Users browsing this forum: No registered users and 9 guests