Diagnosing Valve Train Clatter
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Laughing Gas
Joined: Aug 2010
Posts: 1,049
Likes: 230
From: Amarillo, TX
Got all the new valve springs installed on the other head. HUGE PITA with the head still on the motor in the truck. Had to make my own tool to compress them. But got it done & got the motor all put back together. Set the initial timing to 12* BTDC. Engine fired right off & ran very smooth. Only issue is it's bogging right off the line when I hammer the throttle. I'm sure a slight adjustment is required - do I need to add or pull timing to correct this? Rotate distributor clockwise to add more advance, right?
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 964
From: Tri Cities, TN
670 Holley
Got all the new valve springs installed on the other head. HUGE PITA with the head still on the motor in the truck. Had to make my own tool to compress them. But got it done & got the motor all put back together. Set the initial timing to 12* BTDC. Engine fired right off & ran very smooth. Only issue is it's bogging right off the line when I hammer the throttle. I'm sure a slight adjustment is required - do I need to add or pull timing to correct this? Rotate distributor clockwise to add more advance, right?
If that is a 670 Avenger make sure the accelerator pump is adjusted correctly, ie. the pump arm moves as soon as the linkage moves. You can get bigger squirters and different pump cams to change when and how much pump squirt you get.
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 964
From: Tri Cities, TN
I'm talking about the vacuum advance canister on the distributor. Ported vacuum is something that never existed until the Feds got involved with what was coming out the tailpipe.
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Laughing Gas
Joined: Aug 2010
Posts: 1,049
Likes: 230
From: Amarillo, TX
Ahh... You have no idea how many threads I've read about ported vs. manifold vacuum - with an equal number of proponents on each side. But I'll try full & see if it runs better. It has always been hooked up to ported, so maybe that was part of my problems all along.
Cargo Master
Joined: Dec 2015
Posts: 2,543
Likes: 322
From: Harned, Ky
Ported vacuum was used on cars and pickups dating back to the 50's or older, every 60's Ford, GM and Mopar vehicle I owned had the vacuum advance connected to ported vacuum
The first vehicle I remember having manifold vacuum was a late 60's GM with emissions
The first vehicle I remember having manifold vacuum was a late 60's GM with emissions
Hotshot
Joined: Jul 2020
Posts: 10,453
Likes: 2,630
From: Near Salt Lake City
Just drive the vehicle both ways using spark port and manifold and see which way works the best for you
When racing some guys do not want the vacuum advance dropping out as soon as they hit the throttle (manifold) and then having to wait a moment for it to build
When racing some guys do not want the vacuum advance dropping out as soon as they hit the throttle (manifold) and then having to wait a moment for it to build
Cargo Master
Joined: Oct 2020
Posts: 2,675
Likes: 784
Since you have a mild performance cam you should first move the vacuum line to the bottom port and use full manifold vacuum. Hooking the vacuum line to ported vacuum only gets you the 12 degrees initial at idle if you hook it to full vacuum assuming you have a 10 degree can that will get you 32 degrees at idle. That will get you a much more stable idle and higher vacuum. Then readjust the idle mixture. The idle mixture screws shouldn't be less than 3/4 to 1 turn out. This is important If they are in too far you may be to far into the transition slots this will cause all sorts of off idle drivability problems.
If that is a 670 Avenger make sure the accelerator pump is adjusted correctly, ie. the pump arm moves as soon as the linkage moves. You can get bigger squirters and different pump cams to change when and how much pump squirt you get.
If that is a 670 Avenger make sure the accelerator pump is adjusted correctly, ie. the pump arm moves as soon as the linkage moves. You can get bigger squirters and different pump cams to change when and how much pump squirt you get.
built a stock 1963 409 Chevy for a customer to run on the Hot Rod Power Tour one year. In '63 even the dual quad 425 horsepower 409 which this engine was had vacuum advance that was connected to a manifold and not a ported source. This was aggravating and made it difficult to get it to idle just right. What I ended up doing was installing a ported check valve in the line. Advance could go up quickly but went away slowly and this worked pretty well.
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 964
From: Tri Cities, TN
The real problem with using manifold instead of ported vacuum with an engine that has a cam is that it can be very unstable. Sure it'll sound better because there's more timing but the problem comes when something causes the engine to lose a little vacuum. It get's put in gear, clutch is let out a little bit etc. Manifold vacuum drops a little, timing drops a little, manifold vacuum then drops a little more etc.
built a stock 1963 409 Chevy for a customer to run on the Hot Rod Power Tour one year. In '63 even the dual quad 425 horsepower 409 which this engine was had vacuum advance that was connected to a manifold and not a ported source. This was aggravating and made it difficult to get it to idle just right. What I ended up doing was installing a ported check valve in the line. Advance could go up quickly but went away slowly and this worked pretty well.
built a stock 1963 409 Chevy for a customer to run on the Hot Rod Power Tour one year. In '63 even the dual quad 425 horsepower 409 which this engine was had vacuum advance that was connected to a manifold and not a ported source. This was aggravating and made it difficult to get it to idle just right. What I ended up doing was installing a ported check valve in the line. Advance could go up quickly but went away slowly and this worked pretty well.
I've ran into that on these Clevelands. Most of the time since the Ford cans are adjustable you can find an adjustment that keeps it from getting on the rocking chair but still maintains a decent amount of advance at idle even if it stumbles a little. I've had pretty good luck with the V391' 10 degree can in these Durasparks. Since these 351 Clevelands only came with points distributors I ended up with a box full of vacuum canisters before I found the magic one. But that's all part of the fun.
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 964
From: Tri Cities, TN
Thats a one size fits all distributor. The only way to know the advance curves, mechanical or vacuum is to use a dial back timing light and plot it on your engine or send it to someone with a distributor machine that will check it and recurve it. I use a hand vacuum pump to check and adjust the vacuum advance because an engine that's not under a load doesn't give you a good read on the vacuum advance.