Using vac adv at idle.
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From: Living in the Hartland
Using vac adv at idle.
Trying to use the vac adv at idle to smooth it out, works well in my Formula 16 to 20 degrees with a touch less cam and more compression. Can't seem to get the vette tuned right, have a hest/bog problem. Want some input from those that are/have done it. Any special tuning requirements, hints? I am at 8 deg int, 14 vac for 22 idle and also have 26 mech adv at 2800 rpm's for a total of 48. I show lean on the O2 sensor when giving part throttle before the sec open but have immediate squirt and a 13.5 pv ( up from 8.5 which seemed to help some) with 15 to 16 vac at idle. I am unsure of the sec pv rating but think it is either 6.5 or 4.5. Also show 13 to 13.5 to 1 on the 02 sensor at cruise.
Thanks
Thanks
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Re: Using vac adv at idle. (Fevre)
My opinion is not to use vacuum advance at idle.
Sometimes it's best to set the idle up by setting the total advance (without vacuum) and then seeing where the base timing is. In other words set the mechanical advance to about the right setting (32- 36 degrees at 3200 rpm) and then letting the initial timing be where it falls.
After that plug the vacuum advance to the correct port on the carb (no advance at idle) and then you should get 44 - 54 degrees total advance at around 3200 - 3600 rpm. If your getting too much vacuum advance then get an adjustable advance can and set that correctly.
Sometimes you can end up with an idle advance around 12-14 (without vacuum advance), a mechanical advance of around 20 degrees (so that's 32 - 34 at 3200 RPM) and another 10-16 vacuum (44-50 total advance).
Sometimes it's best to set the idle up by setting the total advance (without vacuum) and then seeing where the base timing is. In other words set the mechanical advance to about the right setting (32- 36 degrees at 3200 rpm) and then letting the initial timing be where it falls.
After that plug the vacuum advance to the correct port on the carb (no advance at idle) and then you should get 44 - 54 degrees total advance at around 3200 - 3600 rpm. If your getting too much vacuum advance then get an adjustable advance can and set that correctly.
Sometimes you can end up with an idle advance around 12-14 (without vacuum advance), a mechanical advance of around 20 degrees (so that's 32 - 34 at 3200 RPM) and another 10-16 vacuum (44-50 total advance).
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Re: Using vac adv at idle. (Fevre)
I would buy an adjustable vacuum advance. I have the Crane can on the side of my Unilite.
Your better off running the vacuum advance off of the ported vacuum. You don't want much if any VA below 1200 1400 rpm. The reason is. You end up fighting off idle bog etc. What happens is your able to tune a very smooth properly jetted idle with your 20 something advance. Then when you put the motor under load and blip the throttle your down at 8 degrees when the VA goes away.
Your solution with 26 mechanical I would run 12-14 initial for for a total of 38-40 degrees then dial in the vacuum can to 8 or so degrees to get the higher total.
Your better off running the vacuum advance off of the ported vacuum. You don't want much if any VA below 1200 1400 rpm. The reason is. You end up fighting off idle bog etc. What happens is your able to tune a very smooth properly jetted idle with your 20 something advance. Then when you put the motor under load and blip the throttle your down at 8 degrees when the VA goes away.
Your solution with 26 mechanical I would run 12-14 initial for for a total of 38-40 degrees then dial in the vacuum can to 8 or so degrees to get the higher total.
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From: Living in the Hartland
Re: Using vac adv at idle. (gkull)
Trying to get it to run as good as I can without dumping any more $ into or taking anything apart before I switch to FI. I had it running good last year except at idle where it was somewhat choppy. I might take the dist off and re adj the timing curve, but I have no idea where the adv stops are. Guess I could order some with an adj vac adv can. It does get much better gas mielage now that I am using the vac adv again, was getting occassional pinging with it last year. Thanks for the input.
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From: Severna Park Md
Re: Using vac adv at idle. (Fevre)
I wanted to run ported vacuum to my dist but for some reason my carb was registering vacuum from the ported connection even at idle(750). I canceled the signal by adjusting the secondary plates open a tad to allow more air in which raised the idle speed and allowed me to back off the primary idle screw which canceled the vacuum signal at idle. Now I have correct ported connection which has no vacuum at idle, but gives instant vacuum as soon as you crack the throttle. The car used to have a slight hesitation off a light. But since I fixed it as described above the hesitation is gone and the car runs much better.
The motor will be more relaxed if it can idle at a lower timing setting. Anytime you change the timing setting at idle make sure you go back and adjust the idle mixture screws on the carb.
The motor will be more relaxed if it can idle at a lower timing setting. Anytime you change the timing setting at idle make sure you go back and adjust the idle mixture screws on the carb.
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From: Living in the Hartland
Re: Using vac adv at idle. (Jvette73)
Been fiddlin' with it for the last few weeks, my neighbors can verify that. Nothing like a couple flowmaster 40's running for hours at a time to wreck your quiet weekend. Guess they should be happy the Formula is not running. :) Think I'll go back to ported vac adv and see how the car likes it, might have to run higher than 87 oct to keep it from pinging. :cry
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Re: Using vac adv at idle. (Fevre)
Yeah Fevre, give it a shot. It wont cost you a dime to try it. Switch the hose over to ported and reset the timing to 12-14 initial at idle. The lower timing setting at idle will slow the enging down so you'll probably have to turn up yur curb idle to compensate for the lower timing. The re-adjust the mixture screws. If you can set it up for no vacuum advance at idle then a big shot of advance as soon as you open the throttle, that should cover yur advance issues anyway. What about yur total mechanical timing? Will you be able to achieve the required 36 mechanical with an initial setting of 12 to 14 with vac unhooked?
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From: Living in the Hartland
Re: Using vac adv at idle. (Jvette73)
Pretty sure I set the timing curve for 12 initial and 36 at 2800 rpm's, msd probillet has different mech adv bushing stops to adj total mech adv. I wanted to get more adv at idle without a hard start with no choke.
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From: Severna Park Md
Re: Using vac adv at idle. (Fevre)
Pretty sure I set the timing curve for 12 initial and 36 at 2800 rpm's, msd probillet has different mech adv bushing stops to adj total mech adv. I wanted to get more adv at idle without a hard start with no choke.
:lurk:
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Re: Using vac adv at idle. (Fevre)
Fevre -
You can use the manifold vacuum on your vac advance as an effective tuning tool if you need more advance at idle. The only thing you need to verify is that the vacuum advance you are using pulls in its FULL RANGE of advance at the manifold vacuum level you're pulling at idle. In other words, if you're pulling 12 inches of vac at idle, you don't want to use a vac advance control unit that doesn't pull in the full advance until it hits 18 inches. I have a full list of vac advance control units with their specs if you need to select a unit that will work for your application. Contact me if you need info.
You can use the manifold vacuum on your vac advance as an effective tuning tool if you need more advance at idle. The only thing you need to verify is that the vacuum advance you are using pulls in its FULL RANGE of advance at the manifold vacuum level you're pulling at idle. In other words, if you're pulling 12 inches of vac at idle, you don't want to use a vac advance control unit that doesn't pull in the full advance until it hits 18 inches. I have a full list of vac advance control units with their specs if you need to select a unit that will work for your application. Contact me if you need info.
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Re: Using vac adv at idle. (lars)
Other than what Lars had to say. I looked in the Jeg's Cat. and Crane makes and adjustable for GM HEI it comes with 3 sets of advance springs and it's only @ $24 bucks.
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Re: Using vac adv at idle. (Fevre)
Well, Lars helped me with the same type problem. I went back to original specs on the carb/timing. The fix was to make sure the primary and secondary butterfly's were adjusted the same. Then just opening the secondaries 1/8th turn put it perfect. Sure spent lotsa time changing PV's, jets, timing, pump cams, etc. Thanks Lars.
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From: Living in the Hartland
Re: Using vac adv at idle. (gkull)
Other than what Lars had to say. I looked in the Jeg's Cat. and Crane makes and adjustable for GM HEI it comes with 3 sets of advance springs and it's only @ $24 bucks.
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From: Living in the Hartland
Re: Using vac adv at idle. (Fevre)
Well it runs better for the most part, no more bog/hest but now I have a little surging at certain rpm's and horrible deiseling/run on when you shut it down. Fix one problem and create another. :)
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Re: Using vac adv at idle. (Fevre)
Fevre - try a Ford vacuum delay inline with the distributor. They made several different ones identified by different colors. They used them in the late 70's for sure. It may cure your bog and still let you use vacuum advance at idle. It worked for me on a Mustang.
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Re: Using vac adv at idle. (Racer16k)
Hey Chris still fooling with the vaccum can, just toss it in the garbo, you'll feel much better. The MSD Probillet is a great distributor has a lockout plate when you toss the can and lets you put in springs bushings etc. so you can adjust it to idle at different advances.
I think I have the 18 drgree bushing in their so my intial timing is about 18 degrees. I have been runniing without the can for eight years now, I also get a little more torque down low for some reason :D
I think I have the 18 drgree bushing in their so my intial timing is about 18 degrees. I have been runniing without the can for eight years now, I also get a little more torque down low for some reason :D
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Re: Using vac adv at idle. (MotorHead)
Wayne
I noticed a increase in gas mileage which I like but the hest I did not. With it back in the normal config the exhaust seems to be hotter. I was working on the idle and others things over the eng on Tues and forgot to turn on the fans. Didn't notice till I heard it boiling over. :eek: I took it for a ride last night and when I got home I popped the hood to fiddle some more and heat was unbareable. Not sure if it is a direct correlation with the drop from 22 to 12 degress adv at idle. The deiseling is horrible, did you get your's fixed? I was hoping to get my cars running good for the summer and neither is cooperating. :cry
I noticed a increase in gas mileage which I like but the hest I did not. With it back in the normal config the exhaust seems to be hotter. I was working on the idle and others things over the eng on Tues and forgot to turn on the fans. Didn't notice till I heard it boiling over. :eek: I took it for a ride last night and when I got home I popped the hood to fiddle some more and heat was unbareable. Not sure if it is a direct correlation with the drop from 22 to 12 degress adv at idle. The deiseling is horrible, did you get your's fixed? I was hoping to get my cars running good for the summer and neither is cooperating. :cry
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From: Living in the Hartland
Re: Using vac adv at idle. (Racer16k)
Fevre - try a Ford vacuum delay inline with the distributor. They made several different ones identified by different colors. They used them in the late 70's for sure. It may cure your bog and still let you use vacuum advance at idle. It worked for me on a Mustang.
Thanks!
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Re: Using vac adv at idle. (Fevre)
Yea I fixed the deiseling, let the clutch out in gear when I shut it off :lol:
As for temperature don't forget the weather is much warmer now, I could not put my hand near the motor yesterday and my gauge was only reading 180, I shut it off and 2 hours later it was still 160 degrees :eek:
[Modified by MotorHead, 11:41 AM 6/26/2003]
As for temperature don't forget the weather is much warmer now, I could not put my hand near the motor yesterday and my gauge was only reading 180, I shut it off and 2 hours later it was still 160 degrees :eek:
[Modified by MotorHead, 11:41 AM 6/26/2003]
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Re: Using vac adv at idle. (MotorHead)
The deiseling is usually caused by hot spots in the combustion chamber. Mainly its caused when there is carbon buildup. WHn you shut down the ignition the carbon deposits can still be glowing red hot and provide and ignition source which is needed for it to run on after the key is shut off. Also other things can cause excessive cylinder temps like an air/fuel mixture that is too lean. also the timing chain could be stretched causing late valve timing which can lead to excessive heat. Or it could be dirty plugs that are still glowing after shutdown. To check for timing chain stretch you can remove the distributor cap, then rotate the crank clockwiseto take up the slack, then rotate the crank counter clockwise and see how far it moves before the rotor begins to turn the other way. if the crank moves alot back and forth without the rotor moving the timing chain is loose. By having further advanced timing at idle like 20 you may be helping cool things down a bit, but that doesnt solve the problem thats causing the run on in the first place. Iv everything else is right, having the timing set to 12 has nothing to do with run on.