Tuning Question - Carb first or Timing First???
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 3,280
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From: Virginia Beach Virginia
Tuning Question - Carb first or Timing First???
I need to tune my engine and make it run more efficiently and more smoothly. To do this, I figure I need to adjust my carburetor and my timing. But since the systems work together and the performance of one alters the other, which comes first?
If I am making some poor mechanical assumptions, please forgive me and correct me. I am learning. :D
Thanks,
Stephen
If I am making some poor mechanical assumptions, please forgive me and correct me. I am learning. :D
Thanks,
Stephen
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Tuning Question - Carb first or Timing First??? (VolVette)
I highly recommend you start with the ignition system and timing. Faulty timing and timing advance curve will often give symptoms of carb trouble, and trying to tune a carb to fix an ignition problem is a pretty vain effort, as you can imagine.
I think you have copies of my timing papers. Utilizing this knowledge and your handy new adjustable timing light, hook the puppy up and verify that your centrifugal timing curve is working. Make sure the advance is coming in nice and smooth, and that your total timing, with the vac advance disconnected, is pegging out at about 36 degrees when you rev the engine a bit. If you're running points (non-HEI), make sure you set the dwell before you do anything to the timing, since each degree change in dwell will change the timing one degree. Set dwell for 30 - 31 degrees if you have points. Hook up your vacuum advance and verify that it is working properly. Make sure it's hooked up to a ported vacuum source and not directly to manifold vacuum. Once you have all this set up and verified, you can then move on to the carb and do the final tweaking and tuning.
It's a lot of fun to play with, and quite rewarding if you find a few issues to correct to make the car run a little better. Tag me back if you need any help.
[Modified by lars, 8:43 AM 10/3/2001]
I think you have copies of my timing papers. Utilizing this knowledge and your handy new adjustable timing light, hook the puppy up and verify that your centrifugal timing curve is working. Make sure the advance is coming in nice and smooth, and that your total timing, with the vac advance disconnected, is pegging out at about 36 degrees when you rev the engine a bit. If you're running points (non-HEI), make sure you set the dwell before you do anything to the timing, since each degree change in dwell will change the timing one degree. Set dwell for 30 - 31 degrees if you have points. Hook up your vacuum advance and verify that it is working properly. Make sure it's hooked up to a ported vacuum source and not directly to manifold vacuum. Once you have all this set up and verified, you can then move on to the carb and do the final tweaking and tuning.
It's a lot of fun to play with, and quite rewarding if you find a few issues to correct to make the car run a little better. Tag me back if you need any help.
[Modified by lars, 8:43 AM 10/3/2001]
Race Director
Joined: Jun 2000
Posts: 10,046
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From: FL
Re: Tuning Question - Carb first or Timing First??? (VolVette)
Do distributor first.
Get some light springs in, rev it to 3000, set timing at 36 BTDC with vacuum disconnected.
Let idle timing fall where it may (mines at 14 BTDC). Play with springs so curve comes in about 2800 rpm( I am using medium springs from a recurve kit).
Get an adjustable vacuum advance and set it so it adds about 16 degrees. I did this by attaching it to full time vacuum at idle. Can not connected 14 BTDC, can connected 30 BTDC. Then I reconnected it to a ported source.
Once that is done, you can adjust the carb idle, jets, rods, etc. Lars has some good info on carb troubleshooting. Do a search for a thread called "Quadrabog" for more info.
Good luck.
Get some light springs in, rev it to 3000, set timing at 36 BTDC with vacuum disconnected.
Let idle timing fall where it may (mines at 14 BTDC). Play with springs so curve comes in about 2800 rpm( I am using medium springs from a recurve kit).
Get an adjustable vacuum advance and set it so it adds about 16 degrees. I did this by attaching it to full time vacuum at idle. Can not connected 14 BTDC, can connected 30 BTDC. Then I reconnected it to a ported source.
Once that is done, you can adjust the carb idle, jets, rods, etc. Lars has some good info on carb troubleshooting. Do a search for a thread called "Quadrabog" for more info.
Good luck.
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 3,280
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From: Virginia Beach Virginia
Re: Tuning Question - Carb first or Timing First??? (VolVette)
Thanks Lars and Steve,
Lars, I bought myself a new adjustable timing light and was excited to use but just as I was about to use it, I drove my Vette and something terribly was wrong -- after a lot of troubleshooting, it turned out there was a very small, but significant leak in the small vacuum hose coming off my carb going to my vacuum advance. So, now that is fixed and I can begin to play! :D
First, information: I have a ZZZ crate engine with 20K, a 650CFM Holley carb
I started to play a little last night but had a couple of questions:
1) Where is the best place to hook up a timing light? I used jumper cables to go straight to the battery. I hope there is something more convenient than that?
2) Where can I get the spring sets? Sometimes I have difficulty getting parts for my ZZZ engine because no one knows what it is. Will I have problems finding these springs?
Thanks for your help!
Stephen
Lars, I bought myself a new adjustable timing light and was excited to use but just as I was about to use it, I drove my Vette and something terribly was wrong -- after a lot of troubleshooting, it turned out there was a very small, but significant leak in the small vacuum hose coming off my carb going to my vacuum advance. So, now that is fixed and I can begin to play! :D
First, information: I have a ZZZ crate engine with 20K, a 650CFM Holley carb
I started to play a little last night but had a couple of questions:
1) Where is the best place to hook up a timing light? I used jumper cables to go straight to the battery. I hope there is something more convenient than that?
2) Where can I get the spring sets? Sometimes I have difficulty getting parts for my ZZZ engine because no one knows what it is. Will I have problems finding these springs?
Thanks for your help!
Stephen
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Tuning Question - Carb first or Timing First??? (VolVette)
Light hookup is easy: just clip the positive onto the positive post on the back of the alternator and clip the negative to the ground lug that sticks out of the back of the alternator. That puts all your wires right by cylinder #1. Piece of cake.
You can buy springs at any parts store or speed shop. Pick up Mr. Gasket part number 928. This is a spring set for the early point-style distributors, but the springs work perfectly. Use the two gold springs in the kit to start with and see how your timing and advance behaves and take it from there.
You can buy springs at any parts store or speed shop. Pick up Mr. Gasket part number 928. This is a spring set for the early point-style distributors, but the springs work perfectly. Use the two gold springs in the kit to start with and see how your timing and advance behaves and take it from there.
