New 390 Timing Mark Bouncing Around....
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Junior User
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New 390 Timing Mark Bouncing Around....
Hi Guys,
I just got through with breaking in the cam and lifters on my fresh 390 build. the only mods I have done to the engine are the addition of the Edelbrock 2105 intake, 1406 carb and Edelbrock 2106 camshaft with lifters.
I am trying to fine tune after break in. The TDC timing mark seems to be jumping around to set timing and makes it somewhat difficult to set timing. Also, the engine seems to not have a consistent idle. any ideas on what could be causing this? FYI....the harmonic balancer is the original from 1973. I have copied links to videos below.
Thanks!
I just got through with breaking in the cam and lifters on my fresh 390 build. the only mods I have done to the engine are the addition of the Edelbrock 2105 intake, 1406 carb and Edelbrock 2106 camshaft with lifters.
I am trying to fine tune after break in. The TDC timing mark seems to be jumping around to set timing and makes it somewhat difficult to set timing. Also, the engine seems to not have a consistent idle. any ideas on what could be causing this? FYI....the harmonic balancer is the original from 1973. I have copied links to videos below.
Thanks!
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Joined: Jul 2002
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From: Long Island USA
Make sure the damper ring isn't spinning on the damper either.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
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From: Long Island USA
Points? With the cap off, grab the rotor and push/pull it in the direction of the points cam, I bet it's got enough slop in it the points will actually open or close when you push/pull on it.
Go electronic, or a rebuilt dizzy or replace the bushing if you're capable.
It's not even about the timing jumping around, it's about the dwell and what that does to the coil voltage. Also, the vacuum advance will make it dance around even more.
Go electronic, or a rebuilt dizzy or replace the bushing if you're capable.
It's not even about the timing jumping around, it's about the dwell and what that does to the coil voltage. Also, the vacuum advance will make it dance around even more.
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Thanks Krewat....what do you think about the Pertronix stuff? Even if I do buy something like the Pertronix I still need to address the issue of slop in the dizzy shaft correct?
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Hi 69cj...thanks for the input. It was just a thought. The engine is really stock for the most part and I have read that many recommend to get away from the points based ignition. In reality i wouldn't mind keeping the stock ignition unless there is something to be gained on a stock engine with something like the Pertronix.
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Joined: Jul 2002
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From: Long Island USA
The Pertronix will alleviate the problem, and you could buy one now, install it, and see if that's really the problem. You're going to want to do it anyway 
Once you find that really is the cure, then either rebuild your existing distributor, or find a replacement. Because you changed the cam, you're probably going to want to dial-in the distributor mechanical and vacuum advance curve anyway.
If you want the original look, go with the stock distributor and the Pertronix, otherwise, you could go for the GM HEI, or Duraspark setup.
I still want to see what happens when you turn the engine over to where the flat side of the distributor cam is against the points, and push/pull the rotor in the direction of the points. I bet they open and close
Once you find that really is the cure, then either rebuild your existing distributor, or find a replacement. Because you changed the cam, you're probably going to want to dial-in the distributor mechanical and vacuum advance curve anyway.
If you want the original look, go with the stock distributor and the Pertronix, otherwise, you could go for the GM HEI, or Duraspark setup.
I still want to see what happens when you turn the engine over to where the flat side of the distributor cam is against the points, and push/pull the rotor in the direction of the points. I bet they open and close
Cargo Master
Joined: Apr 2004
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From: Golden, CO
A couple other things inside the distributor that can be roached, are the nylon (?) bushings that the centrifugal advance weights ride on, and the advance springs themselves. Time to bone up on distributor overhaul. 
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Thanks guys! I just ordered the original Pertronix Ignitor with the Flame thrower coil for $100.00 on ebay. I will let you guys know what I find once I install it.
I will also check the dizzy for play and see if the points are opening and closing when i push/pull on the rotor.
I would like to rebuild mine for the experience and also to have another notch on my belt for bragging rights with my buddies.....
I will also check the dizzy for play and see if the points are opening and closing when i push/pull on the rotor.
I would like to rebuild mine for the experience and also to have another notch on my belt for bragging rights with my buddies.....