Lots of initial timing necessary. Help?
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
Sounds to me that you have your vacuum advance connected to the wrong port. Should have full manifold vacuum. '73 may have had some emissions system that used ported vacuum, but most cars generally run better connected to full vacuum.
Time the engine with the vacuum disconnected and plugged to 8 degrees BTDC, then add in vacuum and it should idle nicely like that.
Time the engine with the vacuum disconnected and plugged to 8 degrees BTDC, then add in vacuum and it should idle nicely like that.
Race Director
Joined: Mar 2017
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From: Virginia
Sounds to me that you have your vacuum advance connected to the wrong port. Should have full manifold vacuum. '73 may have had some emissions system that used ported vacuum, but most cars generally run better connected to full vacuum.
Time the engine with the vacuum disconnected and plugged to 8 degrees BTDC, then add in vacuum and it should idle nicely like that.
Time the engine with the vacuum disconnected and plugged to 8 degrees BTDC, then add in vacuum and it should idle nicely like that.
As you said, you don't want more than 36 degrees of total mechanical advance.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
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From: Vail AZ
Nope. Vacuum advance is full manifold. But the timing is set with it disconnected and plugged. If I pull it down to less than 30° initial the engine dies. And yes, I’ve tried it with more throttle. I can barely keep it lit by feathering the throttle/accelerator pump, but without gymnastics, it’s 30° or more to keep running.
Race Director
Joined: Mar 2017
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From: Virginia
Nope. Vacuum advance is full manifold. But the timing is set with it disconnected and plugged. If I pull it down to less than 30° initial the engine dies. And yes, I’ve tried it with more throttle. I can barely keep it lit by feathering the throttle/accelerator pump, but without gymnastics, it’s 30° or more to keep running.
At idle, the engine shouldn't know the difference between a dist set to 30 degrees initial with no vacuum advance, and one set to 20 or so with a functioning vacuum can pulling another 10.
Last edited by Bikespace; Sep 22, 2020 at 07:42 PM. Reason: Changed image
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
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From: Vail AZ
Stock tach drive distributor and can-coil. It had been fitted with a Mallory Unilite module, but as one of the many steps to solve this issue I installed a set of points and a condenser, both AC Delco.
Last edited by any4xx; Sep 22, 2020 at 08:28 PM.
Race Director
Joined: Oct 2019
Posts: 10,735
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From: Deep in the Pisgah National Forest
Nope. Vacuum advance is full manifold. But the timing is set with it disconnected and plugged. If I pull it down to less than 30° initial the engine dies. And yes, I’ve tried it with more throttle. I can barely keep it lit by feathering the throttle/accelerator pump, but without gymnastics, it’s 30° or more to keep running.
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Melting Slicks
Joined: Apr 2019
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From: Northern Wisconsin
Not questioning your ability, but are you sure that you used the correct technique to find TDC with that piston stop (rotating one way until stop, then rotating the other way until stop, then find mid point)? That is about all I can come up with. There are videos on YouTube.
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
You are approaching numbers (30*) that destroys starters. If you are truly at that high of initial setting, you should be getting some serious kick-back.
You say you installed a new Timing Tape. I think its off considerably.
You say you installed a new Timing Tape. I think its off considerably.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
I’m not sure what to say.
TDC, as well as the new tape is marked properly.
Let’s forget all about vacuum advance please. All of my readings are taken with vacuum advance disconnected and the vacuum port plugged.
I DO appreciate anyone who takes the time to respond. But my issue is with how much initial mechanical advance is needed to keep the engine running. I may be able to mess with it some more and run it (barely) with 25ish degrees of initial mechanical advance. But 30° is where it will run reliably.
TDC, as well as the new tape is marked properly.
Let’s forget all about vacuum advance please. All of my readings are taken with vacuum advance disconnected and the vacuum port plugged.
I DO appreciate anyone who takes the time to respond. But my issue is with how much initial mechanical advance is needed to keep the engine running. I may be able to mess with it some more and run it (barely) with 25ish degrees of initial mechanical advance. But 30° is where it will run reliably.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I am not talking about Vac advance included. In your first post you mentioned idles nicely at 35 initial. Initial means no additional advance. Won't run below 30* initial.
Somethings not right here. Your tape is showing TDC. You believe that is correct. I do too. But beyond TDC something is off kilter.
Somethings not right here. Your tape is showing TDC. You believe that is correct. I do too. But beyond TDC something is off kilter.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
I am not talking about Vac advance included. In your first post you mentioned idles nicely at 35 initial. Initial means no additional advance. Won't run below 30* initial.
Somethings not right here. Your tape is showing TDC. You believe that is correct. I do too. But beyond TDC something is off kilter.
Somethings not right here. Your tape is showing TDC. You believe that is correct. I do too. But beyond TDC something is off kilter.
And that’s exactly why I’m asking the question here. I’m out of ideas. I guarantee you that my TDC mark is in the right place. That was one of my first ideas so I stripped the front of the engine and checked it, twice, with a piston stop. The mark is right on the money. But since I had no timing tape and the tab only reads to 12° I put the tape on today. I was previously guessing my initial to be around 30° based on measurements I took from my other 454 car that is parked right next to It.
I’m seriously stumped here. The only known quantity is that this engine won’t idle will less advance. I guess my question is really if that’s normal for this engine combination. My other 454 has a slightly milder cam and it runs best with about 20° of initial.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
Race Director
Joined: Oct 2019
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From: Deep in the Pisgah National Forest
Some engines barely run with initial timing set at 8 degrees and vacuum advance plugged. If yours won't run at all like that, find out how much your advance adds in then set your timing with the advance pulled in. Say that your vacuum advance adds in 18 degrees. Then you should set "initial plus vacuum" at 8 + 18.
Last edited by Yadkin; Sep 22, 2020 at 09:46 PM.
Safety Car
Joined: Apr 2006
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From: BC
My 69 427 runs best at around 19 to 20 initial and the original MS360 advance can adds an extra 12 degrees. Are you sure your vacuum advance can is working correctly and checked with a timing light? If your vacuum advance is frozen I can see how your engine would like 35 initial at idle but not if everything is working properly.
Race Director
Joined: Mar 2017
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From: Virginia
My 69 427 runs best at around 19 to 20 initial and the original MS360 advance can adds an extra 12 degrees. Are you sure your vacuum advance can is working correctly and checked with a timing light? If your vacuum advance is frozen I can see how your engine would like 35 initial at idle but not if everything is working properly.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
Race Director
Joined: Mar 2017
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From: Virginia
Do you have a vacuum gauge and/or pump? Can you tell us what your vacuum reading is at idle? My mostly stock L48, with 8.5:1 compression or whatever, will idle just fine at (effectively) 27 degrees initial advance. It is very rough and hard to start with less than that. Other than your hot engine, and three degrees, the only difference is that my initial advance is half mechanical, half vacuum.
Last edited by Bikespace; Sep 23, 2020 at 03:01 AM.