Ignition Timing Advance Problem
Thread Starter
Intermediate
Joined: May 2007
Posts: 48
Likes: 2
From: Reading PA
Ignition Timing Advance Problem
I have a 73 L48 with an all original engine at 71K miles. The engine was running rough and a tune up helped but didn't bring her back to good running condition. I rebuilt the distributor using instructions on this forum. I found the ground wire broken, a damaged lead wire and wear on the main shaft at the tach drive. I replaced all of these. There is no play between the shaft and bushings. End play set to .10 with a new Delco drive gear. After I installed the distributor and fired the engine I timed it to 12 degrees BTC. When looking at total advance by fring the engine to 2500 RPM I noticed that the timing didn't advance and in fact sometimes moved in the retard direction. It's a little better with Vac advance connected, but I still can't get more than about 14 degrees total advance. I'm using Mr Gasket springs, one black, one silver for the weights. Changing springs doesn't seem to make a difference. Weights move freely. Any ideas out there. Could this be something outside the distributor? Timing Chain?
Thanks, Dean
Thanks, Dean
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Interesting post.......very nicely worded....hmmm.....(Lars?).....you found just the right combo of old style weights and hypo shaft with the advance spacer limit missing and then put the weights on backwards.Just an idea."I've" never seen a timing chain that bad enough to offset all the advance in a dist.without jumping some teeth.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Interesting post.......very nicely worded....hmmm.....(Lars?).....you found just the right combo of old style weights and hypo shaft with the advance spacer limit missing and then put the weights on backwards.Just an idea."I've" never seen a timing chain that bad enough to offset all the advance in a dist.without jumping some teeth.
Thread Starter
Intermediate
Joined: May 2007
Posts: 48
Likes: 2
From: Reading PA
I bought the shaft from Last Detail Corvette. It is supposed to be a direct replacement for the L48 (non-SHP) engine. I thought about the weights and have checked them. They're the original weights and are in according to the GM service manual. In fact I tried to put them in backwards and you really cant get them to fit that way without the obstructing each other. The shaft advance bushing is the plastic type and was already installed on the replacement shaft. One other interesting fact. It idles well but it does occasionally backfire through the carb during acceleration at about 2500-2600 RPM. I was attributing this to lack of advance. I suppose I should have the distributor tested on a machine. I have to find someone in the Reading, Pa area that does this. Dean
Here's the link to the shaft I used: http://www.tld-corvette.com/prodinfo.asp?number=612700
Here's the link to the shaft I used: http://www.tld-corvette.com/prodinfo.asp?number=612700
Last edited by mrhurk; Jul 2, 2007 at 10:41 AM. Reason: adding information
