Another Timing Question
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Mountain Pass
Joined: Nov 2016
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Another Timing Question
Working a 400 and trying to get it running good. I set initial timing at 10 BTDC and when I run it up to 3500 rpms with vacuum advanced disconnected I’m only getting 23-25 degrees. If I adjust it to 30 degrees at 3500 rpms my initial is up at 16 degrees at 750 rpms at idle. The truck runs great at the 16/30 setting but will not start hot. I have to back it down to 12/26 to get it to start hot. Does this sound reasonable or is my mechanical advance too limited. Distributor is a reman’d motor craft that was on the old 351M that took out of the truck. The 400 is factory with a Edelbrock intake manifold, 1406 carb, and a comp 256DEH cam. Thanks in advance. I’m new at this and have tons hours of reading but not quite sure where to go.
Laughing Gas
Joined: Aug 2010
Posts: 896
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From: Bothell
It’s entirely possible that the mech advance cam in the distributor may be only 14 deg. Best way to find out is take apart the distributor and see what number is stamped on the mech advance.
have you revd it up past 3500? Sometimes they keep advancing due to springs that are too heavy. If that’s the case you’ll need a re-curve spring kit.
Here is some good reading about how the duraspark works inside and what to adjust.
Duraspark_distributor_recurve_instructions_index
have you revd it up past 3500? Sometimes they keep advancing due to springs that are too heavy. If that’s the case you’ll need a re-curve spring kit.
Here is some good reading about how the duraspark works inside and what to adjust.
Duraspark_distributor_recurve_instructions_index
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Mountain Pass
Joined: Nov 2016
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Thank you. That makes sense. I guess I expected to see more like 20 degree advance since I’ve read so much about how these things like 34 degrees of timing. Also it does seem to level off at 3500 rpms. Even with vacuum advance active I didn’t see over 30 degrees. I’ll tell you it’s a bit scary standing that close to a 400 with a timing light with a mechanical fan turning that fast so I’m not in any hurry to do that again. It’s actually my BIL’s truck and he drove it all afternoon and said it’s running great and starting good so I may leave well enough alone for now.
Logistics Pro
Joined: May 2015
Posts: 4,462
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From: Tri Cities, TN
Working a 400 and trying to get it running good. I set initial timing at 10 BTDC and when I run it up to 3500 rpms with vacuum advanced disconnected I’m only getting 23-25 degrees. If I adjust it to 30 degrees at 3500 rpms my initial is up at 16 degrees at 750 rpms at idle. The truck runs great at the 16/30 setting but will not start hot. I have to back it down to 12/26 to get it to start hot. Does this sound reasonable or is my mechanical advance too limited. Distributor is a reman’d motor craft that was on the old 351M that took out of the truck. The 400 is factory with a Edelbrock intake manifold, 1406 carb, and a comp 256DEH cam. Thanks in advance. I’m new at this and have tons hours of reading but not quite sure where to go.
You can get a little more advance without taking the distributor apart by removing the plastic bumper from the advance plate stop. That will get you another 2 to 4 crank degrees depending on how thick that bumper is on your distributor. I need to add that the numbers represented in the manual are for camshaft degrees and distributor RPM so need to be doubled for crank numbers.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
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Mountain Pass
Joined: Nov 2016
Posts: 148
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Thanks Crop Duster. This all makes sense and gives me some confidence that I got it set up correctly. We are just looking for a good running setup that is reliable. Willing to leave some hp on the table in order to have a safe setup. Also we are only seeing 15” of vacuum I think due to the more aggressive cam. That will affect/decrease the vacuum advance. My BIL drove it to run errands all day so it was a good test. He said it started easily after each short stop and didn’t get too got even sitting in traffic. It was about 90F ambient yesterday so I’m pretty happy right now. He seems satisfied so I may just leave well enough alone. He is wanting to go EFI at some point so that will probably be my next challenge. I really appreciate the input guys.
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