timing
Thread Starter
Instructor
Joined: Jun 2010
Posts: 165
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From: concord ohio
timing
Need some help, I have read all of the Lars threads on timing and I think I am missing something. '78 383 initial is set at 15 degrees. All I can get for advance is 28 degrees at about 2,000 rpm with the vacuum advance disconnected. I revved the engine to 3,500 rpm and the light stayed right at 28 degrees. I did install the lightest springs form a Morosco kit. Any idea what I am missing? There is a number stamped on the weights, it is 42. Help
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
some times there are mechanical things that impact the advance.....holes need to be elongated some times and some times holes need to be welded closed.....look at the mechanism that is stopping the mechanical advance from moving.....also may not be a bad idea to make sure TDC is marked properly on balancer and timimng tab.
what kind of distributor is this? points or HEI
what kind of distributor is this? points or HEI
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
maybe the springs are too light ... fully-extended at low rpm ?
-add-
if ya do some drilling here ... you'll pass thru a sewer with alotta tripe about cam oil ... even a naked emperor or two ... but there's some gold a bit deeper ... including BarryK's timing thread; many think it's a nice adjunct to the good work of Lars.
http://forums.corvetteforum.com/c3-t...long-post.html
-add-
if ya do some drilling here ... you'll pass thru a sewer with alotta tripe about cam oil ... even a naked emperor or two ... but there's some gold a bit deeper ... including BarryK's timing thread; many think it's a nice adjunct to the good work of Lars.
http://forums.corvetteforum.com/c3-t...long-post.html
Last edited by jackson; Jul 5, 2011 at 01:02 PM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Le Mans Master
Joined: Apr 2005
Posts: 6,339
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From: Seattle Area WA
Its either shape of the weights that is limiting movement or something is in the way to keep them from moving any further. Some of those aftermarket weights are longer and cut different than stock.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
These are Mr Gasket weights that I had to reshape to get enough advance. Once the weights reacted properly, I had more than enough advance, so I brazed the slots to limit it to what I wanted.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
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From: McHenry Illinois
I reshimmed the distributor to .015". I also brazed up the slot in the top plate to limit the advance to 20 deg. While I was brazing, I brazed up the retard end of the slot also, my reason is because the springs are so soft that when I would accelerate, it would retard just for a second because the springs were holding the pins away from that end too. Now when the springs and weights are in place, as the weights are at rest the springs are holding it against the retarded end of the slot. I ended up using the aftermarket weights but modified them. The final is 16* initial at 750 rpm, 16* @800. 19* @900, 22* @ 1900, and goes up evenly till 36* all in at 2800.
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Thread Starter
Instructor
Joined: Jun 2010
Posts: 165
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From: concord ohio
I am using the original weights, the vacuum canister is stamped 626 and 10. The distributer is factory hei model number 1103337. Any idea of what the spec for advance are for this model distributer?
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
OK, your mechanical advance should be somewhere around 20*. Put the stock springs back in and see where idle timing is at. Don't be too shocked if it is around 8*.
If putting the stock springs back in doesn't reveal that the timing was advanced at idle, then something is keeping it from advancing. take the cap and rotor off and inspect the unit for burrs, casting flash, etc. that might be keeping the advance weights from moving thru their full range of motion.
You said you had read all of Lars's threads on timing, have you ever read any of his papers on timing? He advocates running the ignition with no springs, and setting timing at 36* as the first step in the process. Then put heavy springs in and observe where timing is at at idle. This way, when you put the lighter springs in, you can tell if the springs are advancing the timing at idle, and you aren't playing with the timing anymore, just the curve, because full advance is at 36 and will stay at 36. You are just playing with weights and springs to get the 36* where you want it, without any advance at idle. If you skip steps, you get poor results. Good luck,
Scott
Scott
If putting the stock springs back in doesn't reveal that the timing was advanced at idle, then something is keeping it from advancing. take the cap and rotor off and inspect the unit for burrs, casting flash, etc. that might be keeping the advance weights from moving thru their full range of motion.
You said you had read all of Lars's threads on timing, have you ever read any of his papers on timing? He advocates running the ignition with no springs, and setting timing at 36* as the first step in the process. Then put heavy springs in and observe where timing is at at idle. This way, when you put the lighter springs in, you can tell if the springs are advancing the timing at idle, and you aren't playing with the timing anymore, just the curve, because full advance is at 36 and will stay at 36. You are just playing with weights and springs to get the 36* where you want it, without any advance at idle. If you skip steps, you get poor results. Good luck,
Scott
Scott
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Don't feel bad about missing a little piece of info, Lars packs it in pretty good! The whole timing curve thing is pretty simple.........once you are on the other side of learning it! It can be really confusing until then. And there is still a chance that your problem could be some unrelated freak occurance.
Scott
Scott