455 Ignition Timing Issue!!??

kruiser52

New Member
Hello everyone, I have an interesting ignition timing issue.

First off, I am a mechanic of 20+ years. I have worked on lots of carbureted vehicles through the years, but this one of mine has got me stumped.

I have a 69 Skylark, with a 1970 455 in it. It has an HEI distributor, and a Holley double pumper carb. I built this engine 20 years ago, as a young apprentice in the trade. When its running and driving, it runs really strong with no apparent issues, lots of power and excellent throttle response.
My issue is starting and idling. The carb setup seems to be dialed in the best it can be, as far as idle mixture etc. But it does have the choke locked open. (Which I realize, makes it harder to start cold, but should be fine once its warned up)

The main issue I am concerned with is how my ignition timing seems to be operating. I have the vacuum advance disconnected and some lighter springs for the mechanical weights. I was told by an old guru, years ago, to just set the total timing at 2500 rpms. Which I set at 30 degrees at 2500 rpms. The car runs really strong at this setting, but at idle in gear, seems to be loading up, and stalls once in a while. And its really tricky to start, even warmed up. Sometimes backfires up the carb too. So I went and checked the ignition timing at idle, and with a digital timing light, it appears the at idle timing goes up to 46 degrees! That explains why the backfiring up the carb. My question is, why is this happening?
With the engine running at about 900 rpms idle, the timming seams way out. When I bring it up to 2500 rpms, the total timing is right at 30 degrees. So it seems like the mechanical weights are pulling it the wrong way? Everything in the distributer seems to work fine, the weights are nice and free, and the vacuum is disconnected. What am I doing wrong?
I have checked a lot of vehicle timing before, and usually when you check total timing at 2500, it always goes down to like 10 degrees or so at idle.


This one has stumped me for a while. Like I said, driving down the road, it runs excellent, with lots of power! Like a 455 should! Its just this idle/starting issue. I have had lots of cars with the choke locked open, so I know thats not the issue. Something is incorrect with the timing, and I haven’t figured it out. If anyone has any ideas, that would be great!
 
Hello everyone, I have an interesting ignition timing issue.

First off, I am a mechanic of 20+ years. I have worked on lots of carbureted vehicles through the years, but this one of mine has got me stumped.

I have a 69 Skylark, with a 1970 455 in it. It has an HEI distributor, and a Holley double pumper carb. I built this engine 20 years ago, as a young apprentice in the trade. When its running and driving, it runs really strong with no apparent issues, lots of power and excellent throttle response.
My issue is starting and idling. The carb setup seems to be dialed in the best it can be, as far as idle mixture etc. But it does have the choke locked open. (Which I realize, makes it harder to start cold, but should be fine once its warned up)

The main issue I am concerned with is how my ignition timing seems to be operating. I have the vacuum advance disconnected and some lighter springs for the mechanical weights. I was told by an old guru, years ago, to just set the total timing at 2500 rpms. Which I set at 30 degrees at 2500 rpms. The car runs really strong at this setting, but at idle in gear, seems to be loading up, and stalls once in a while. And its really tricky to start, even warmed up. Sometimes backfires up the carb too. So I went and checked the ignition timing at idle, and with a digital timing light, it appears the at idle timing goes up to 46 degrees! That explains why the backfiring up the carb. My question is, why is this happening?
With the engine running at about 900 rpms idle, the timming seams way out. When I bring it up to 2500 rpms, the total timing is right at 30 degrees. So it seems like the mechanical weights are pulling it the wrong way? Everything in the distributer seems to work fine, the weights are nice and free, and the vacuum is disconnected. What am I doing wrong?
I have checked a lot of vehicle timing before, and usually when you check total timing at 2500, it always goes down to like 10 degrees or so at idle.


This one has stumped me for a while. Like I said, driving down the road, it runs excellent, with lots of power! Like a 455 should! Its just this idle/starting issue. I have had lots of cars with the choke locked open, so I know thats not the issue. Something is incorrect with the timing, and I haven’t figured it out. If anyone has any ideas, that would be great!
This is a wild guess:
What car did the distributor come from? Buick-designed engines use CW distributor rotation. Others like Pontiac designs use CCW distibutor rotation.

A CCW distributor installed in a Buick would bias the timing in the wrong direction as the weights start to swing out. The movable pole piece that changes the timing would spin the wrong way and retard the timing as engine speed increases instead of advance it.
 
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kruiser52

New Member
This is a wild guess:
What car did the distributor come from? Buick-designed engines use CW distributor rotation. Others like Pontiac designs use CCW distibutor rotation.

A CCW distributor installed in a Buick would bias the timing in the wrong direction as the weights start to swing out. The movable pole piece that changes the timing would spin the wrong way and retard the timing as engine speed increases instead of advance it.
This is a wild guess:
What car did the distributor come from? Buick-designed engines use CW distributor rotation. Others like Pontiac designs use CCW distibutor rotation.

A CCW distributor installed in a Buick would bias the timing in the wrong direction as the weights start to swing out. The movable pole piece that changes the timing would spin the wrong way and retard the timing as engine speed increases instead of advance it.


Hey, thanks
The distributer definitely came out of a Buick. It was probably a 75 or 76. As those are the only year HEI Buicks. I thought about the CW and CCW differences, with the cap off and engine cranking, it all seems to be moving correctly.
 
It should not be possible to install an incorrect distributor in a Buick 455 even with changing out the drive gear. But somebody may have found a way to do it. Especially if they mixed parts from different distributors together.

Beginning in 1975 for several years, Buick installed some engines made by Olds or Pontiac which had CCW distributor rotation. If the part number can be located on the distributor, we can look it up to find the original usage.

The '76 Buick shop manual shows a 455 distributor to have full mechanical advance at 4400 rpm of 13.4 to 18.0 deg. This agrees well with your swing of 16 deg at 2500 rpm using the lighter springs. The travel is just in the wrong direction.

Attached is a picture from the '70 Buick shop manual (fig 68-29). This distributor has points, but it should be close to the HEI mech advance. Viewed from the vacuum hose connection, the vacuum advance unit is to the left of the main shaft. As the weights swing out, the weight base moves CW in relation to the to advance cam. This advances the timing at the rubbing block or the timer core as the shaft spins CW.

The other picture (fig 6E-53) is from the '66 Pontiac Tempest shop manual. This is a CCW distributor using transistorized ignition. The vacuum advance is on the right side. The weights and advance cam are sort of mirror images of the CW pieces. As the weights swing out, the weight base moves CCW in relation to the advance cam. This advances the timing as the shaft spins CCW.

If you can compare these pictures to your distributor maybe we can find out why the advance works backwards.
 

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The '69 wiring had a special resistance wire that fed power to the coil. This resistance wire was in the harness under the hood. The resistance has to be bypassed in the HEI system so that the distributor gets full battery voltage when the ignition switch is in START or RUN.

Attached are a couple of old Dealer Service Bulletins regarding problems with the early HEIs. Probably long shots, but they may be worth investigating.

One question which should have been asked earlier: Did it ever run right with the parts now in place?
 

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