General Category > Quadrajet Carb Talk and Tips
HEI Distributor mechanical advance curve options
Cadman-iac:
Well, I have a problem that is stumping me, I need some advice.
Here's the situation. I have my test distributor set up just like the one in the picture on page 1 of this thread, and it works very well, my timing light is going off at a minimum rpm of 400, which I think is fine, that allows me to pinpoint the degree at which it fires.
Here's the problem, as I speed up the drill and it reaches 2500 rpm distributor speed, the light shows that the weights are deploying to maximum at around 1000 rpm, ( I have light springs on it just for initial testing).
However, the tip of my timing indicator that is substituting for the rotor shows that im only getting around 4 degrees of advance. And I was getting a strange second flash from the timing light, you could see it on the distributor shaft and weights, like a double image.
At first I thought I used the wrong pole piece, it was a 6 cylinder one with 5 of the points ground off, but it had some really odd shaped sections to it, so I switched to a standard 6 cylinder pole piece that looks identical to the 8 cylinder one, just 2 less points, then removed 5 of them. Works exactly the same, lights up the timing light at 400 rpm all the way up to 2500 rpm. This eliminated the second flash and double image, but I'm still not showing any more than 4 degrees of advance, even though you can clearly see the weights are extending completely.
The center plate is a #482, and the weights are a #105, with just the lightest springs I have.
I also thought that it might be the aluminum reinforcement plate I installed to keep the protractor steady, causing some weird interference with the pole piece somehow, so I removed it and checked again, same result.
I swapped the capacitor in the distributor as well, just in case, same as before.
I took an old plastic rotor and ground it off on the bottom to clear everything, marked where the firing point is, and it still only shows 4 degrees of advance.
Anyone have any ideas as to what would cause this? I'm at a loss now. I'll post pictures on the next post for reference.
Rick
Cadman-iac:
#1 is the 1st pole piece with the odd shapes.
#2 is the standard 6 cylinder pole piece with 5 removed points.
#3 is my pointer for the protractor.
Kenth:
The needle moves according to the speed of the centrifugal control turning, then you see the number of degrees on the scale per speed you are using.
Cadman-iac:
--- Quote from: Kenth on April 26, 2026, 01:21:35 AM ---The needle moves according to the speed of the centrifugal control turning, then you see the number of degrees on the scale per speed you are using.
--- End quote ---
Yes, I'm aware of how it works, and it does to a certain extent, but it's not giving the results that it should be yielding.
I can manually move the weights and watch the indicator move across the protractor the expected amount of degrees, which in this case is right at 20 degrees, yet when spun by mechanical means the indicator only shows an advance of about 4 degrees. It's this discrepancy that I'm trying to figure out. What is causing this?
Yes, I can do this by installing on the engine and seeing what the results are, but that's very time consuming, not to mention how difficult it is for me to reach the distributor.
This bench test was to save my back and the gas needed to test each combination of parts. The gas used I can live with, but I'll be 68 in a month and climbing into the engine bay is not what I want to be doing at this stage of my life if I can help it.
There's got to be something that I'm overlooking, but I can't think of what it might be, any help is greatly appreciated.
Thanks, Rick
Cadman-iac:
Alright, I couldn't find the reason why my timing was only showing up with about 4 degrees of distributor advance, even though you could clearly see it working like it's supposed to with the distributor cap removed and a remote coil.
So I've scrapped that method of testing, and I did some research online into building my own distributor machine and found one that looked like it would work for me. I think DJD OLDS mentioned it earlier but it sounded too complicated at the time.
So after building it and testing everything multiple times, making some improvements as I went along, I've finally got the information I wanted for the parts I've got on hand.
Here's a few pictures of what I built for a distributor machine, and one of the results of my testing the parts on hand.
I only tested with the center plates installed numbers up as the factory intended, because I had tried them numbers down during the last round of tests and found that most combinations showed they didn't work nearly as well. There were a couple that looked like they would work upside down, but the time involved in testing each one I felt wasn't worth the effort.
So I hope this will help someone down the road with making a decision on what to use if you have any of the pieces to choose from that I've tested.
Rick
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