trying to set timing
Thread Starter
Instructor
Joined: Mar 2003
Posts: 240
Likes: 3
From: Mt. Prospect Il
trying to set timing
Hi, while tuning my 327/350 this morning I ran into a problem.
Here is the setup. I installed a Breakerless SE to eliminate points, I know this is not necessary, and while tring to set the timing the timing mark keeps moving around. I can't keep it at 8 deg. The rpm jumps around from 800 - 1000 rpm. When the timing retards itself to far, the car dies. I've checked everything over twice, I'm stumped.
Here is the setup. I installed a Breakerless SE to eliminate points, I know this is not necessary, and while tring to set the timing the timing mark keeps moving around. I can't keep it at 8 deg. The rpm jumps around from 800 - 1000 rpm. When the timing retards itself to far, the car dies. I've checked everything over twice, I'm stumped.
Le Mans Master
Joined: Feb 1999
Posts: 5,844
Likes: 376
From: Mobile AL
Common causes of unstable idle speed.
Sometimes a past owner has installed very weak distributor advance springs or a vacuum advance canister that requires too much vacuum.
There's an Ironhead theory that a car will run better around town if the distributor mechanical advance is "all in" at low rpm. This same theory guides Do-it-ur-selfers to install "duel" points and a double-humper, 1,200 cfm Holley (with no choke, of course) on a street-driven 283. But I digress.....
Anyway, weak springs cause the mechanical advance to begin below idle speed. As the advance changes, the idle speed changes, so the timing never stabilizes. The fix is to re-install stock advance springs.
A similar unstable idle can be caused by a vacuum advance canister that requires more vacuum than the engine can generate at idle. This assumes that you're using full time vacuum to the distributor rather than a ported connection.
Here's a question for you: Did this problem first arise after installation of the electronic points, or has your enigne always had an unstable idle?
There's an Ironhead theory that a car will run better around town if the distributor mechanical advance is "all in" at low rpm. This same theory guides Do-it-ur-selfers to install "duel" points and a double-humper, 1,200 cfm Holley (with no choke, of course) on a street-driven 283. But I digress.....
Anyway, weak springs cause the mechanical advance to begin below idle speed. As the advance changes, the idle speed changes, so the timing never stabilizes. The fix is to re-install stock advance springs.
A similar unstable idle can be caused by a vacuum advance canister that requires more vacuum than the engine can generate at idle. This assumes that you're using full time vacuum to the distributor rather than a ported connection.
Here's a question for you: Did this problem first arise after installation of the electronic points, or has your enigne always had an unstable idle?
Thread Starter
Instructor
Joined: Mar 2003
Posts: 240
Likes: 3
From: Mt. Prospect Il
Yes I did. I put the points back in and it started right way.
When I checked the dwell, it was 40 and it won't adjust to 30 without killing the motor. Also, the timing can't be adjusted because it hits the coil.
I think I'm going to go back to the basics and start from the beginning.
1. set timing mark at 0 with rotor pointing to #1.
2. check dimple lines up
anything else?
When I checked the dwell, it was 40 and it won't adjust to 30 without killing the motor. Also, the timing can't be adjusted because it hits the coil.
I think I'm going to go back to the basics and start from the beginning.
1. set timing mark at 0 with rotor pointing to #1.
2. check dimple lines up
anything else?
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
Originally Posted by xsray
My vacume can has the following stamped on it:408 24. Does that mean 24 deg?
I have another distributor from a 300 hp car that has a vacume can that says: 469 14.
I have another distributor from a 300 hp car that has a vacume can that says: 469 14.
If you can't achieve the correct initial timing before the vacuum can interferes with something the drive gear is probably on backwards.
When setting initial timing get revs as low as possible, then after it's set increase revs and note the point that the centrifugal begins to advance the timing. If it advances immediately the centrifugal may have already started, which means your initial timing may not be valid.
Duke
Thread Starter
Instructor
Joined: Mar 2003
Posts: 240
Likes: 3
From: Mt. Prospect Il
Thanks SWCDuke. I've never pulled the base plate off a distributor. Would need some guidence on that. I have the balancer and the timing tag exactly at 0. The rotor is pointing to the second tower from the window. Just make sure I do this correctly, I have to reinstall the distributor so that the rotor is pointing to the first tower after the window?
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Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
You should be able to change the vacuum can without disassembling the dist. The disassembly/assembly procedure is in virtually any Chevrolet service manual.
Set the engine at 10 BTC #1. Install the distributor so that the rotor is about 20-25 degrees right of centerline when the base is seated. Rotate the dist until the points just begin to open. At this point the window should be near perpendicular to engine centerline and the vacuum can about halfway between the interference points. Start the engine and set the initial timing.
#1 wire is on the terminal that is closest to the RH edge of the window.
Duke
Set the engine at 10 BTC #1. Install the distributor so that the rotor is about 20-25 degrees right of centerline when the base is seated. Rotate the dist until the points just begin to open. At this point the window should be near perpendicular to engine centerline and the vacuum can about halfway between the interference points. Start the engine and set the initial timing.
#1 wire is on the terminal that is closest to the RH edge of the window.
Duke
Thread Starter
Instructor
Joined: Mar 2003
Posts: 240
Likes: 3
From: Mt. Prospect Il
Got the can swapped out, it pays to read the manual.
Got the distributor back in, set timing and idle speed with no problem.
The only thing is that the dwell angle is 43 deg? It only adjusts between 41 and 43. Bad meter?
Got the distributor back in, set timing and idle speed with no problem.
The only thing is that the dwell angle is 43 deg? It only adjusts between 41 and 43. Bad meter?
Thread Starter
Instructor
Joined: Mar 2003
Posts: 240
Likes: 3
From: Mt. Prospect Il
Yes, the drive gear was 180 out. I used the NAPA/Echlin VC1810. About 3 years ago I had a "corvette specialist" tune it for me since it was already in the shop to replace the rusted thru gas tank. Since that time I've been unable to tune it myself. I called him and he said I should bring it in, he would tune it. But I want to find out what he did and undo it. I really appreaciate the help here, thanks.
Last edited by xsray; Apr 3, 2005 at 11:17 AM.
