cljolley

I have a 1971 Cutlass with a 350 in it. It has had an HEI distributor installed on it. I checked the timing with a timing light and followed the tune up procedure. The initial timing at 1100 RPM is reading at nearly 50 degrees advanced. I thought this was super crazy so tried backing it off closer to spec and the engine started running awfully. I'm not sure what to do about it and am completely stumped. I wanted to try and adjust the carb on it to remedy an off idle/part throttle cruise stumble it has, but figured I ought to check the timing first. Any ideas what may be going on? I already thought maybe the dampener had slipped, but that's the only thing I can think of...

oldcutlass

What HEI do you have, stock GM or ?? What timing light are you using? Why are you checking timing at 1100 rpm? Was the vacuum advance disconnected? What carb is on the engine? You might as well find TDC for #1 cylinders compression stroke and determine if in fact your harmonic balancer actually slipped.

joe_padavano

The engine won't run at 50 deg advanced, so obviously something is wrong. I assume you are checking timing with the vac advance disconnected and plugged. It's easy to verify if the mark on the balancer is correct or not. Remove the No. 1 plug and use a dial indicator or other device to place the piston at TDC and check the balancer scribe mark.

cljolley

I believe it is a stock GM unit. I was checking the timing at 1100 RPM per the tune up procedure in the repair manual. Vacuum advance was disconnected. Timing light used was just a standard Sears timing light, nothing fancy. It has an Edelbrock 750 CFM carb and a Performer RPM manifold among other modifications. It's got a Lunati cam too. Unfortunately the cars history is pretty unknown. It's been pretty molested I'm afraid. I do plan on checking the balancer, just haven't yet. I just wanted to see if anyone thought it could be something else. I am aware that the engine wouldn't run at 50 degrees advanced. I'm just wondering why it reading 50.

cljolley

There is no single scribe mark on the balancer, but a scale ranging from 0-60. It's faded and very hard to read but i scrubbed it clean and tried to mark it better with a paint marker.

And should I plug the vacuum nipple on just the carb (as I did), or does the advance module nipple need capped too? I just figured disconnecting it and plugging the vacuum source on the carburetor was sufficient.

oldcutlass

There was no HEI in 71 so the stock timing setting are N/A. When you declined the timing did you also increase the idle speed setting so the engine can stay running? Try setting your timing at 16 degrees BTDC @ 750-800 rpm. Your timing light was hooked to the #1 spark plug (front drivers side)?

cljolley

I did try and set it as close to 12 degrees as I could. Even if I increased the idle it would stay running until around 20, but ran like complete garbage. It responded terribly to any throttle input and would surge and sputter. When you say the factory timing settings are out the window with the HEI what do you mean? Certainly the engine should still require similar timing settings, no? And yes. Timing light was hooked to #1. I double checked the procedure time and time again and made sure I wasn't doing anything wrong. I played with the settings for nearly an hour but could not get it anywhere close to a typical timing setting.
Does an aftermarket camshaft affect the timing requirements for the engine?

oldcutlass

Your distributor is a large cap HEI right? Your car came originally with points and a points distributor has a different timing curve and amount of mechanical advance than an HEI. Therefore the original settings don't apply anymore unless the HEI had been modified to points type settings which is highly doubtful. After setting it to 16-18* BTDC @ 750-800 rpm, you'll need to readjust your carb a/f mixture screws.

Give this a read:
http://www.73-87.com/7387garage/drivetrain/hei.htm

Fun71

Kind of. As said, the HEI has a different amount of mechanical advance built into it, so the initial has to be higher than a points distributor in order for the total timing to be the same. So if you set the HEI to 10 initial, the total will be way low. The engine should still run, but performance will be degraded and it will run warmer. The HEI needs to be set to 16-20 initial.

It kinda depends upon the cam. Tailoring the timing curve can optimize performance, and increasing the initial can smooth out a rough idle due to a radical camshaft.

Fun71

So you have regular non-dial back timing light, an aftermarket balancer with degree markings, and the factory timing tab. Are you using the "0" mark on the timing tab when measuring the initial?



edit: Another thing I just thought of is someone may have installed the lightest springs in the advance mechanism. If so, there is likely mechanical advance coming in at 1100 RPM, and it could be a significant amount. Try checking the initial timing at a much lower RPM, or try checking the total at ~3000RPM.

cljolley

I did try and set it at a lower RPM last night. I got it set using the 0 mark on the tab. Set it to about 22. Hooked the vacuum advance back up to manifold after and it brought it up to around 46 at idle. I still feel like it's not running right, but I also know the carb needs cleaned and re-adjusted. But I figured timing was needed for a baseline. Is there anything else that could be wrong? The number one plug wire is at the terminal closest to the driver side at the firewall. So lookin at the front of the car it is at the rear just right of the centerline. Has the distributor been installed improperly? Would that even affect the timing? I'm so stumped right now.

cjsdad

Factory balancer, aftermarket timing tape, and it is way off. Sounds a lot like the balancer has slipped so best bet would be to make sure where the balancer hub lines up with the piston at verified TDC. If it is way off with everything verified, get a new one and start over. Tune it by ear for now because anything else is useless if the parts are not performing correctly.

don71

You asked if "anything else could be wrong"?

Are you sure the weights in the distributor are not rusted and sticking? They should move freely.

cljolley

They do move freely and are not damaged. I did however order a new ignition tune up kit with new springs and weights. I'm going to check TDC marks for accuracy, install the new components, and try to set the timing one last time. I also double checked the firing order as well just to be sure. I can't find anything wrong. I will keep you all posted.

oldcutlass

If your timing is as you say, first thing you need to check is if #1 tdc vs timing mark on the balancer is correct. If the balancer slips you have no way of stting your timing correctly and your chancing it coming apart and damaging things.

RandyS

If your balancer has slipped, you can create your own mark for TDC if you can accurately determine true TDC. Just use a permanent marker to draw a new line across the balancer.
(I'm surprised at how many times folks mention a balancer slipping, how often does this actually happen??)

oldcutlass

About the same as oil pickup tubes falling off...

jpc647

read through this thread I started a couple years back.


https://classicoldsmobile.com/forums...-mild-cam.html




You'll want to make sure you balancer hasn't slipped(there's a inner and outer ring, and the grooves should line up. Make sure your timing tab looks right(I should end at 14 or 16 degrees, and make sure the bolt on the balancer is tight ( I had this problem when I thought I had 50* timing initially).


Also, when you unplug the vacuum advance, plug the line! There's also photo's of my stock timing tab, it's dirty, but does yours look like that? Cause it should. If it doesn't, someone might have swapped tabs and it might not be reading right.