Engine Tuning

I finally got the engine tuned up and running right. It has been about 25 years since I have built an engine, so all that experience is basically lost and needed to be re-learned. I had a book back then, but I have Google now, which is both good and bad. In the end, I learned some things and made it through.

The hodge-podge of parts for the front end of the motor continue to cause issues. With a lack of timing marker, I learned I could set the timing and carb with a vacuum meter. Well, I have one of those, so I tried it out. Basically, I set the idle for max vacuum per the Edelbrock directions that came with the carb, then I did the same with the distributor. Unfortunately, I didn’t know at that point that the distributor should be set 1-2 inches of vacuum off max, so my timing was pretty far off. It would start and idle, but it would miss a lot at higher RPMS.

Without a timing marker, the Top Dead Center mark on my harmonic balancer was showing something right of 12 o’clock. I didn’t put it all together until later, but with a 74 engine and timing chain cover, the timing marks on my 69 balancer are going to be wrong for where I need to put the TDC mark. With the later style water pump outlet on the driver side, I cant have a 2 o’clock timing marker since I can’t see it.

To solve this, I dug up the variable timing marker I picked up from Summit a few months ago. I ended up taking the center pulleys off again to get it installed. These are all things I should have done before the engine was in the car. Live and learn.

Summit adjustable timing marker

With a new timing marker, I needed to set TDC according to that mark. I used a piston stop to find clockwise and counter clockwise piston max up position on #1. From there, I split the difference and call that TDC. I had to take the pulley off so I could measure the ballancer’s diameter and use the right timing marker tape for re-zeroing the timing marks on the ballancer. The kit I got from Amazon had 4-5 different length tapes for various diameter balancers and I had to pick the right one.

New timing marks set. TDC is calculated via pistop stops

Once I got it all marked and re-assembled, I fired it up and got ready to figure out just what I had going on. On first check, I was running around 30 degrees before top dead center. I understand the target with the Pertronix ignition should be 10-12. That would explain the stumbling at higher RPM.

I found that when I dialed it back, idle dropped, and vacuum started dropping too. I thought I might have an issue as I heard a ticking from the back passenger side of the engine. Listening closer, I found an exhaust leak. The exhaust shop didn’t tighten down the pipe to the manifold. Before figuring out it was exhaust, I thought it was head related possibly, sending me on the wrong direction from dialing back the timing.

After some research, I learned I should be about 2 inches off max vacuum, which is what it dropped to when I dialed it back to 12 BTDC. I reset the idle and tweaked the throttle connecting rod which was binding a little. I took it for a test drive and everything went smooth. More power, no stumbling.

It was a learning experience, but that’s what this project is. I like that I can be self reliant to tune the car in the future, and keeping it running in top shape. I was starting to think I should take it to a speed shop to solve it, but knowing how it all works makes me feel much better about maintaining it.

UPDATE 8/1/19:

I spent some more time tuning the carburetor. It turns out this Edelbrock 1406 has a default lean setup. I read on the VMF about setting it up like a 1405 and tuning it from there. I ordered the metering rods and jets for the default 1405 off of Amazon and tried it out. It works much better. The flat spots on acceleration are gone, along with the stumbling at constant speed high RPM. If you find yourself with a 1406, I would recommend doing the same. The part numbers are listed in the tuning manual that comes with the carburetor.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s