ignition woes
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
ignition woes
Decided to check the distributor today with my new dial back timing light.
With vac. advance off and plugged, I read 10 degrees @ 850 rpm. Then:
24 @ 1500
28 @ 2000
29 @ 2500
29 @ 3000
Other then a slightly rough idle, my car (stock '76 L-48), runs OK, poor mileage (10-12). New plugs, wires, and cap.
I'm thinking of pulling the distributor, and going thru the top end, checking for binding on the weights. Anything else I should look at? Will my 29 total degrees of advance cause the poor mileage?
With vac. advance off and plugged, I read 10 degrees @ 850 rpm. Then:
24 @ 1500
28 @ 2000
29 @ 2500
29 @ 3000
Other then a slightly rough idle, my car (stock '76 L-48), runs OK, poor mileage (10-12). New plugs, wires, and cap.
I'm thinking of pulling the distributor, and going thru the top end, checking for binding on the weights. Anything else I should look at? Will my 29 total degrees of advance cause the poor mileage?
Race Director
Joined: May 2006
Posts: 18,690
Likes: 2,572
Yes it will, loosen the distributor, set the dial back to 36 and turn the distributor till the mark on the balancer lines up with the zero on the timing tab when you are at 3000 rpm. Lock the distributor and recheck.
Race Director
Joined: May 2006
Posts: 18,690
Likes: 2,572
That is what we are telling you to do, advance your centrifugal via adjusting initial for an additional 7 degrees to obtain the 36 total. Afterwards reconnect the vacuum hose to the vacuum advance. If you have problems starting hot then you can pull the distributor and check the advance limit bushing to see if it's shot.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
I agree with your first assessment: that the advance weights in the dizzy are somewhat stuck/binding. This could be due to the weights or the advance plate binding somehow. Disassemble it, investigate, and free up what is binding the mechanism up.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Thanks 7T1, I think that's what I'll do. Pull it, put it on the bench, and fix it.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Here's a follow-up. I pulled the cover and rotor, lots of rust on centrifugal advance system, not much movement. Pulled distributor for a complete upper side rebuild. It's amazing that it ran as well as it did, might account for the crappy fuel mileage.
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Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
So I started to disassemble the distributor. When I removed the advance weights and springs (both very rusty) , I found that the advance plate that sits on top of the rotor bracket has very restricted movement. It is a very tight fit, and does not have free movement thru it's range of travel. Should it be this tight?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
It should be free- especially with the springs removed. THe idea is that as the RPM goes up, (or down) the springs slow down the rate of the advance or retard.
When you get the shaft out I'll bet the shaft where it passes thru the reluctor wheel is rusty. Polish the shaft and the inner diameter of the reluctor and all will be smooth again. While it's apart, it's a good time to set the endplay on the shaft and check the bushings. Remember- there is a dimple on the distributor gear that needs to align with the rotor tip when you put it all back together.
When you get the shaft out I'll bet the shaft where it passes thru the reluctor wheel is rusty. Polish the shaft and the inner diameter of the reluctor and all will be smooth again. While it's apart, it's a good time to set the endplay on the shaft and check the bushings. Remember- there is a dimple on the distributor gear that needs to align with the rotor tip when you put it all back together.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Thanks Tim. I'm not sure that I explained the problem clearly. The main shaft itself turns freely. The main shaft also turns the rotor and the centrifugal weight attaching plate. The problem is that the centrifugal weight plate does not move freely in relation to the rotor. Since it doesn't separate from the main shaft, should I try to loosen it up with penetrating oil? I'm trying to find out just how easy it's supposed to move. As it is now, the advance weights do very little, since the plate doesn't rotate in it's slot to advance the timing. Sorry if I'm not explaining it clearly.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
It is apart and cleaned up. Took plenty of penetrating oil to free up the advance plate. I also found out that the vacuum advance was shot. I will pick up new weights and springs and put it all back together. I can't believe how bad it was. I forgot lars' mantra: Most carb problems are distributor problems! Can't wait to see how it runs.
Drifting
Joined: Aug 2005
Posts: 1,443
Likes: 65
From: Wauconda IL
Only 3000 RPM?
A lot of the OEM advance curves didn't fully 'come in' until 4K or above.
Once you get it all cleaned-up, I'd check it again and run it up to 4500 to see where your total ends up.
Just my .02
A lot of the OEM advance curves didn't fully 'come in' until 4K or above.
Once you get it all cleaned-up, I'd check it again and run it up to 4500 to see where your total ends up.
Just my .02
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
While you have it out, check the bushings and end play. Now is the time.
IF you drive out the pin at the drive gear it pulls off, the shaft pulls out of the housing, and the reluctor/centrifugal advance pulls off the shaft..
Google "GM HEI parts diagram" That brings up a bunch of pictures- there is a great exploded view in the top right corner of the pictures. Oddly enough, it's from this forum, but I couldn't find it here.
IF you drive out the pin at the drive gear it pulls off, the shaft pulls out of the housing, and the reluctor/centrifugal advance pulls off the shaft..
Google "GM HEI parts diagram" That brings up a bunch of pictures- there is a great exploded view in the top right corner of the pictures. Oddly enough, it's from this forum, but I couldn't find it here.
Last edited by TimAT; Dec 6, 2012 at 08:23 PM.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Well u did have a somewhat of a "curve". At least u had it all in by 3000 rpm - though u could use more adv. Best performance is something like 35 degrees at nearly 3000rpm but hey, not every timing curve is the same. Without road test or dyno verification your just guessing.
Found my weights frozen from lack of use - not rusty but just stuck together. I cleaned mine and used the teflon based spray lube - not messy like graphoils or even petrol lubes.
Good luck,
cardo0
Found my weights frozen from lack of use - not rusty but just stuck together. I cleaned mine and used the teflon based spray lube - not messy like graphoils or even petrol lubes.
Good luck,
cardo0
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
While you have it out, check the bushings and end play. Now is the time.
IF you drive out the pin at the drive gear it pulls off, the shaft pulls out of the housing, and the reluctor/centrifugal advance pulls off the shaft..
Google "GM HEI parts diagram" That brings up a bunch of pictures- there is a great exploded view in the top right corner of the pictures. Oddly enough, it's from this forum, but I couldn't find it here.
IF you drive out the pin at the drive gear it pulls off, the shaft pulls out of the housing, and the reluctor/centrifugal advance pulls off the shaft..
Google "GM HEI parts diagram" That brings up a bunch of pictures- there is a great exploded view in the top right corner of the pictures. Oddly enough, it's from this forum, but I couldn't find it here.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Well u did have a somewhat of a "curve". At least u had it all in by 3000 rpm - though u could use more adv. Best performance is something like 35 degrees at nearly 3000rpm but hey, not every timing curve is the same. Without road test or dyno verification your just guessing.
Found my weights frozen from lack of use - not rusty but just stuck together. I cleaned mine and used the teflon based spray lube - not messy like graphoils or even petrol lubes.
Good luck,
cardo0
Found my weights frozen from lack of use - not rusty but just stuck together. I cleaned mine and used the teflon based spray lube - not messy like graphoils or even petrol lubes.
Good luck,
cardo0
