400 tuning
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Elder User
Joined: Aug 2004
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From: NE Wisconsin
400 tuning
Two problems:
1-dead spot in the power band at 2000- 2250 rpm
2-predet. only when towing above 2800 rpm
400 .40 over, valve timing straight up, xe 256, 600cfm holley 4160, 8.5 powervalve, 68 jets?, stock secondary, 12deg initial timing, med/med springs and 10L weight in dizzy, 1 5/8 primary long tubes into 2 1/4 duals with H pipe, magnaflow glasspacks.
1-dead spot in the power band at 2000- 2250 rpm
2-predet. only when towing above 2800 rpm
400 .40 over, valve timing straight up, xe 256, 600cfm holley 4160, 8.5 powervalve, 68 jets?, stock secondary, 12deg initial timing, med/med springs and 10L weight in dizzy, 1 5/8 primary long tubes into 2 1/4 duals with H pipe, magnaflow glasspacks.
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Joined: Mar 2008
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flat spot, and detonation issue
form your description, your timing sounds spot on, and I can relate to how frustrating this issue is from when you know what you have. From this combination of issues, it seems to me that you have a lean condition as the secondary curcuit begins to operate. I'd suggest installing a step lighter secondary diaphragm spring, and should that not totally fix the problem, investigate what secondary metering plate you have, and an enlargement to the main circuit port on the plate. remember that drilling the plate is permanent.
another approach would be increasing the nozzle size; you'll probably want a #28 (0.028") nozzle.
another approach would be increasing the nozzle size; you'll probably want a #28 (0.028") nozzle.
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Elder User
Joined: Aug 2004
Posts: 620
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From: NE Wisconsin
thought about a bigger secondary plate.
What nozzle are you refering to?
Primarys are 68, accel. shooters are 45 w/ red cam and hollow screw. Don't know what size secondarys I have.
Opening the secondarys earlier might help the dead spot. I'll have to hook the vacuum guage back up and go for a drive.
What nozzle are you refering to?
Primarys are 68, accel. shooters are 45 w/ red cam and hollow screw. Don't know what size secondarys I have.
Opening the secondarys earlier might help the dead spot. I'll have to hook the vacuum guage back up and go for a drive.
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Joined: Mar 2008
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400 tuning
nozzle means shooter.
couple of questions:
what size accelerator pump are you running? I'm sure a shooter size over 0.040 needs a 50cc so that the acc pump won't starve. The part number for the 50cc conversion kit is 20-11, and is a bolt on. the only accommodation that's needed is clearance when mounted to the intake(mock up to check for need of a spacer plate).
what position is your pump cam in?
The secondary plate will have a model number stamped on it that will cross reference to an main circuit size and idle circuit size, and will help you find the number should you want to try a different VS plate in your carb.
Example:
a '37' stamp is part number 134-37 that measures 0.073 main circuit hole and 0.031 idle circuit hole. the link below is a helpful reference for consideration.
Holley Performance Products Catalog
couple of questions:
what size accelerator pump are you running? I'm sure a shooter size over 0.040 needs a 50cc so that the acc pump won't starve. The part number for the 50cc conversion kit is 20-11, and is a bolt on. the only accommodation that's needed is clearance when mounted to the intake(mock up to check for need of a spacer plate).
what position is your pump cam in?
The secondary plate will have a model number stamped on it that will cross reference to an main circuit size and idle circuit size, and will help you find the number should you want to try a different VS plate in your carb.
Example:
a '37' stamp is part number 134-37 that measures 0.073 main circuit hole and 0.031 idle circuit hole. the link below is a helpful reference for consideration.
Holley Performance Products Catalog
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Elder User
Joined: Aug 2004
Posts: 620
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From: NE Wisconsin
Thanks for the info on the plate.
I have the 30cc pump that works fine. Remember, They rate the accel. pump for ten pumps, not one every now and again.
Hole two, I think. Now I have to look.
I have the 30cc pump that works fine. Remember, They rate the accel. pump for ten pumps, not one every now and again.
Hole two, I think. Now I have to look.
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Elder User
Joined: Aug 2004
Posts: 620
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From: NE Wisconsin
holley 600cfm 4160 68 jets, 45 shooter, red pump cam, stock secondary spring and metering plate, 8.5 powervalve
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