A little more pep for all of you Carburated folks Out there. |
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A little more pep for all of you Carburated folks Out there. |
pcdarks |
Mar 18 2021, 02:43 PM
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#1
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Member Group: Members Posts: 80 Joined: 22-June 13 Member No.: 16,037 Region Association: None |
This is something for you to try to get more pep when you first hit the gas. First of all read it through until you understand what I did. I switched over from FI to a center mount progressive two barrel carb but this would work with any carb configuration. I had the stock distributor with vacuum advance and retard. I hooked up the vacuum retard to ported vacuum on the carb. What this does it retards the timing at idle. I then timed the engine with the vacuum hooked up to factory specs. The engine idles as it should at around TDC. As I start to accelerate from a stop the vacuum drops and the retard in the distributor releases giving me a little timing advance and the engine takes off with more pep. This advance works until the engine catches up and vacuum increases causing the distributor to retard to stock timing. Now the mechanical advance works for the rest of the acceleration. If I am cruising in a higher gear and give it gas the distributor again advances when the retard losses vacuum when the pedal is pushed giving the car mare advance again until the engine increases vacuum where it then retards to factory timing. At cruise speeds. the distributor mechanically advances to 27 degrees and runs there until again acceleration causes the vacuum to drop and momentarily advances the timing. The car has very noticeably better take off from a stop and accelerates quicker at speed. try it.
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PlaysWithCars |
Mar 20 2021, 10:14 AM
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#2
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Senior Member Group: Members Posts: 524 Joined: 9-November 03 From: Southeast of Seattle Member No.: 1,323 Region Association: Pacific Northwest |
Be sure and check your total advance. Its been too long since I worked on a -4 to remember exactly what the timing curve looked like. But, if I understand what you've done correctly, you are getting more advance at low speed acceleration which will make it peppier but you might also be getting excessive advance at high rpm WOT acceleration that could lead to pre-ignition. Check your total advance at 4000 rpm with the vacuum line disconnected.
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Mark Henry |
Mar 20 2021, 11:20 AM
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#3
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Be sure and check your total advance. Its been too long since I worked on a -4 to remember exactly what the timing curve looked like. But, if I understand what you've done correctly, you are getting more advance at low speed acceleration which will make it peppier but you might also be getting excessive advance at high rpm WOT acceleration that could lead to pre-ignition. Check your total advance at 4000 rpm with the vacuum line disconnected. Agreed, 28 (27) degrees BTDC total advance is the most you want with carbs. IIRC 3500rpm. |
JamesM |
Mar 24 2021, 09:05 AM
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#4
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Senior Member Group: Members Posts: 1,915 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
Be sure and check your total advance. Its been too long since I worked on a -4 to remember exactly what the timing curve looked like. But, if I understand what you've done correctly, you are getting more advance at low speed acceleration which will make it peppier but you might also be getting excessive advance at high rpm WOT acceleration that could lead to pre-ignition. Check your total advance at 4000 rpm with the vacuum line disconnected. Agreed, 28 (27) degrees BTDC total advance is the most you want with carbs. IIRC 3500rpm. (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) Also though, I believe you may be misunderstanding how/when vacuum is occurring in your intake. First "Ported Vacuum" if that is what you attached your retard canister to, is above the throttle plate so it produces low vacuum at idle and increases when you open the throttle so this would not be retarding the timing at idle. If your timing is retarding at idle you most likely are connected to manifold vacuum. BUT Secondly, in either case (ported or manifold vacuum) engine vacuum only drops under load so just sitting there revving your engine to check the timing will still be retarding the timing via vacuum. The manifold vacuum is only going to drop if there is a load on the engine (revving in neutral does not produce a load), at which point you will see more advance than what you set it to. It sounds like all you have done is over advance your timing. If you want to achieve similar results in a safer manner you could get a programable distributor to dial in more advance though the low and midrange while still maintaining a safe max advance. Alternatively you could try connecting the advance side of the distributor to actual ported vacuum (if one exists on that carb) which would add advance off idle but then pull it back under load so you dont detonate your engine however if you set your timing properly in that case with no vacuum lines connected it may leave you over advanced at idle (depends on the mechanical advance curve in the distributor you are running). |
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