73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: OldsFan on November 21, 2013, 10:17:48 pm
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I just joined, but I've already got a few hundred questions, lol.
First one that's really bothering me is the timing on my truck - it's waaaaay advanced. Looks like it is sitting at 27 degrees on mechanical only at idle (700 RPM) in park. Seems to only advance out to 34 or so at 3K. The previous owner has a vac cap over the line that goes to the advance canister, so I know that's not having any effect. It makes starting the truck pretty hard at times which is why it's bothering me - and the starter's only a couple of weeks old (as are the battery cables).
Yeah, I confirmed that the balancers original, not slipped and used a piston-stop to do it.... It's really that advanced.
It doesn't ping, it doesn't buck or do anything else strange - in fact, for a 305, it runs like a thief. Anyone have any ideas?
Oh yeah, with all the accessory drive and related stuff in the way, is there any better angle to see the timing tab on this engine? I have to sit up on the core support and look down over water pump to see it...
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34 degrees of total advance (once all the centrifugal advance is in) is about right. 36 would be no problem. Sounds like there is less than the normal range of centrifugal advance (20 degrees).
You should have the vacuum advance connected. Not sure what's up with that.
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Is this on your 85 C10, 305, 350C?
Check the advance weights, springs, bushings & pins under the rotor. Make sure the reluctor rotates freely on the distributor shaft and isn't sluggish or seizing in an advanced position. A broken or missing spring, sloppy weights and seized reluctor are common problems. Is the rotor installed correctly, so as not to bind the advance mechanism? Is it possible the PO changed the springs & weights to recurve the advance?
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Is this on your 85 C10, 305, 350C?
Check the advance weights, springs, bushings & pins under the rotor. Make sure the reluctor rotates freely on the distributor shaft and isn't sluggish or seizing in an advanced position. A broken or missing spring, sloppy weights and seized reluctor are common problems. Is the rotor installed correctly, so as not to bind the advance mechanism? Is it possible the PO changed the springs & weights to recurve the advance?
X2, the initial is commonly found@ 10- 12° hints the reason for such a hard start. I wonder if the previous owner tried to lock out the timing. 34- 36 @2500- 3000 rpm is where you want the mechanical to end up( it's why it runs like a thief :-)) now it's time to get that initial lower
What's under the hood??? If you have to ask maybe we shouldn't race...
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You should have the vacuum advance connected. Not sure what's up with that.
Heh... I hear you on that. Just for kicks, I started up the motor, put the timing light on the pointer and hooked up a vacuum tester to the canister. It holds vacuum, but no matter how much vac I put on it, it doesn't have any effect.
Is this on your 85 C10, 305, 350C?
Check the advance weights, springs, bushings & pins under the rotor. Make sure the reluctor rotates freely on the distributor shaft and isn't sluggish or seizing in an advanced position. A broken or missing spring, sloppy weights and seized reluctor are common problems. Is the rotor installed correctly, so as not to bind the advance mechanism? Is it possible the PO changed the springs & weights to recurve the advance?
Yup, my 85 LWB. I am going to pull the cap and rotor today (weather permitting) and I'll let you know what I find out. If it is screwed up, hilariously bubba-fied or whatever, I'll post pics. ;D
X2, the initial is commonly found@ 10- 12° hints the reason for such a hard start. I wonder if the previous owner tried to lock out the timing. 34- 36 @2500- 3000 rpm is where you want the mechanical to end up( it's why it runs like a thief :-)) now it's time to get that initial lower
What's under the hood??? If you have to ask maybe we shouldn't race...
Race??? Haha... This truck was a neighbor's grandpa's truck. His grandpa stopped driving years ago and when he passed away, the grandson couldn't sell it or scrap it - reminded him of his grandpa too much. So for years, it just sat. He sold it to me for a few bucks with the promise that I don't scrap it. No problem there, I like it way too much already. But for now, I think of it like I imagine his grandpa - old and a little stubborn, but full of character and happy to work half days in retirement. :)
Thanks for the suggestions - I am a little unfamiliar with it because this is the first time I've dealt with the 5 pin HEI module with knock sensor, etc. but hopefully it isn't too bad.
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Well, I did a bunch of work today just trying to figure out what's going on with the timing. I opened up the cap and rotor and found that there's nothing too rigged up and overall the cap and rotor look ok for now (though they could probably use to be replaced soon).
- First pic is just an overview of the engine bay which needs a cleaning. That's going to have to wait until I get these other issues worked out though.
- Second is the cap removed, rotor sitting in plain view. Doesn't look bad, moves around against the springs fine, no binding.
- Third is the rotor removed. You can see the 5 pin HEI module in all its glory.
- Fourth is me messing around with the weights to make sure things aren't bound up. Looks ok, but the springs seem a little heavy. I think I have some weight sets for Olds HEI's around in the basement. I'll probably put a lighter weight spring in there (assuming there's no difference between Olds and Chevy HEI advance mechanisms).
Read up in the next reply - I think I figured a few things out, but the next picture is important and I can't add it to this post.
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Ah, the fifth picture - you get to see my awesome graphic editing skills in Paint. This is the pin (red arrow) is the end of the vac advance canister. It is jammed or stuck. Completely. It doesn't move at all and I didn't want to try to force it. Ok, I did want to force it, but I held myself back.
So, here's what I know:
- The timing was set at 26 degrees. I timing tape to make sure I got semi-accurate results rather than just counting on my new-fangled timing gun (long story behind that one).
- At 3K RPM it was kicking out over 40 degrees.
- The vac line to the advance canister was steady at 20 inches Hg. No matter what. Revving or not, even when I turned the truck off it stayed at 20 inches. Yes, my vac gauge works fine, but I started to question my sanity. :o It took around 15 seconds for it to bleed all the way back down to zero after the engine was off.
- The truck was really hard to start. Took lots of attempts, cranking slowly and sounding like the battery was about to die.
Here's what I did:- Set the initial timing to 15 degrees. Beyond what it should be, I know, but read on.
- Set the all-in mechanical advance to 32 degrees (which caused 1 above).
- Saw the vac advance line suddenly start varying like it should. Dropping and rising with manifold vac.
- Started the truck 15 times or so over a few hours. It now starts like it should. For the first time since I've had it. :)
I am guessing that it will probably feel really unresponsive now. :( I am going to try to use some spring sets I have from Olds HEI's to try and get a little more timing advance capacity. Hopefully get the max to 34 and the initial down in the 10-12 region.
Now for the questions:- How could it not be pinging like crazy at 40 degrees? My Olds would not be happy with 40+ degrees under load...
- Did the vac advance jam up and the PO just try to get annoyed by crappy cruising gas mileage and then keep setting the timing more and more advanced? I mean 40+ degrees under vac advance for part-throttle cruise would be fine...
- Can I change the vac advance canister without removing the entire distributor?
- Does anyone have any idea why this would be setup this way???
Sorry for the long post, but I appreciate any advice... :)
Thanks,
Mark
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Well, I figured out why the distributor is so advanced. The HEI coil pack connections stick out far enough to prevent the air cleaner from sitting down onto the carb if the timing is set right. Advancing it a lot (twisting CCW) puts those connections right next to the cruise control vac motor and out of the way of the air cleaner. :-\
Any suggestions on what I can do from this point?
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There's a ton of headroom above the air cleaner. Put a spacer between the air cleaner and the carb. I had to do that to get my air cleaner to sit down on the Edelbrock carb because it is a different shape than the Qjet. Cement the spacer to the bottom of the carb with 3M Weatherstrip Adhesive and then mount the air cleaner on the carb until the adhesive sets up so you don't have to deal with the darn thing all the time.
You can get spacers in whatever height you need to clear:
http://www.jegs.com/webapp/wcs/stores/servlet/KeywordSearchCmd?storeId=10001&catalogId=10002&langId=-1&Ntk=all&Jnar=0&itemPerPage=90&Ne=1%2B2%2B3%2B13%2B1147708&searchTerm=air+cleaner+spacer
Of course the other thing you can do is index the distributor correctly. Sounds like the distributor was pulled out and put back several teeth out from the stock indexing, which is why you have the conflict now. It certainly didn't come out of the factory that way.
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Remove the cap and unbolt the distributor. Pull the distributor straight up just far enough to disengage the distributor gear from the camshaft. Rotate the complete distributor one tooth CCW then set it back into place and adjust the timing. Know that when you try to restab the distributor, the oil pump drive probably won't line up, so you'll need to bump the engine around until the distributor drops all the way down and seats.
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Note the relationship of the rotor to the distributor body before you pull it up, so you can be sure to have it in the same orientation when you restab it!
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There's a ton of headroom above the air cleaner. Put a spacer between the air cleaner and the carb. I had to do that to get my air cleaner to sit down on the Edelbrock carb because it is a different shape than the Qjet. Cement the spacer to the bottom of the carb with 3M Weatherstrip Adhesive and then mount the air cleaner on the carb until the adhesive sets up so you don't have to deal with the darn thing all the time.
Rich - great suggestion! It should've been my first thought. I was sure I was going to have to pull and reindex the distributor, but it is like 30 degrees outside today (was around 50 yesterday, cold snap :( ). After reading it, I just got a Mr. Gasket spacer kit from Advance Auto which they actually stock locally. Lo and behold, one of the kids at the counter actually knew what it was (said he races SBC cars with his dad). I had to dremel a couple of little notches into it to get the stock air cleaner to fit down on it properly. Regardless, the trucks's running again (minus the breather tube which doesn't reach) and has decent timing, too.
Note the relationship of the rotor to the distributor body before you pull it up, so you can be sure to have it in the same orientation when you restab it!
I probably wouldn't have forgotten this, but thank you for mentioning it.. Ask me how it feels when an Olds engine that some idiot (me :) ) setup way off backfires up through the carb at you. For anyone reading this in the future, make a mark on the distributor where the rotor is pointing so you don't forget later.
Remove the cap and unbolt the distributor. Pull the distributor straight up just far enough to disengage the distributor gear from the camshaft. Rotate the complete distributor one tooth CCW then set it back into place and adjust the timing. Know that when you try to restab the distributor, the oil pump drive probably won't line up, so you'll need to bump the engine around until the distributor drops all the way down and seats.
This is what I was planning on doing, but I have a couple of questions:
- The truck has vacuum based cruise control. Can the HEI cap even clear that module? Maybe it needs to be behind the cruise module? I guess it is trial and error.
- Can I line up the oil pump drive ahead of time somehow (screw driver or something)? I was thinking of setting the engine up to TDC on #1 when I do this and I'd want to drop it back in at the same point...
I haven't worked much on SBC's before, but it seems like things could get hairy if the oil pump shaft doesn't line up and I run the starter... Wouldn't the cam then be out of sync with the rotor? I mean, would the engine turn until the shaft lines up without turning the rotor? Then when things do line up, wouldn't the rotor be out of position? Maybe I don't understand what you meant...
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Take a look at the pic attached. Not sure if the terminals of the HEI coil will fit past the cruise module. The HEI coil terminals are what is preventing the air cleaner from just dropping back into place.
Glad I dug into this, though, because I found a bunch of rotted vac hoses and resulting vac leaks.
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If you pull the distributor all the way out, you can rotate the fuel pump shaft with a LONG blade screwdriver into the slot in which the distributor shaft tang fits.
I think on the HEI connector, you need someone on here with the same setup to take a look see where their connector comes out. Could you be far enough out on the distributor that the stock position for the HEI connector is between the cruise module and the firewall?
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If you pull the distributor all the way out, you can rotate the fuel pump shaft with a LONG blade screwdriver into the slot in which the distributor shaft tang fits.
I think on the HEI connector, you need someone on here with the same setup to take a look see where their connector comes out. Could you be far enough out on the distributor that the stock position for the HEI connector is between the cruise module and the firewall?
Did you mean to say "oil pump driveshaft?" :)
Take a look at the pic attached. Not sure if the terminals of the HEI coil will fit past the cruise module. The HEI coil terminals are what is preventing the air cleaner from just dropping back into place.
Glad I dug into this, though, because I found a bunch of rotted vac hoses and resulting vac leaks.
Why not measure the protrusion of the connector pod off the cap and compare the measurement to the available space between the cap and cruise module?
...I haven't worked much on SBC's before, but it seems like things could get hairy if the oil pump shaft doesn't line up and I run the starter... Wouldn't the cam then be out of sync with the rotor? I mean, would the engine turn until the shaft lines up without turning the rotor? Then when things do line up, wouldn't the rotor be out of position? Maybe I don't understand what you meant...
When stabbing a distributor on SBC & BBC engines, the distributor gear engages the cam gear before engaging the oil pump drive. As long as the distributor housing is within ~3/8" of seating on the intake manifold, the distributor is indexed with the cam gear. Bumping the starter repeatedly (1-3 times is typically all it takes) until the distributor drops the remaining ~3/8" is an accepted method; using a long standard blade screwdriver to align the oil pump drive is also an accepted method, as is using an old distributor drive shaft. Setting the engine on TDC compression before disassembly is the conservative approach that always works.... Use the method with which you are most comfortable.
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Did you mean to say "oil pump driveshaft?" :)
Uh, yup. My brain was right, my fingers mis-spelled oil. ;)
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Rich, bd - the explanation of the oil pump driveshaft, etc. was great. The gears of the rotor and cam will mesh before the oil pump driveshaft does... Makes sense now. A bit embarrassing to say I didn't know that, but hey, you learn something new every day, I guess. :-[
Either way, I'd much rather ask than break expensive engine parts. :)
Because it was so cold out today, I didn't bother with re-indexing the distributor. I need to get my truck into the warm garage to work on this further. Regardless, after your explanation, I wanted to see how it was setup. I found this link below with some pretty decent pics and a bit of description.
http://www.chevyhiperformance.com/techarticles/0609ch_installing_a_chevy_distributor/ (http://www.chevyhiperformance.com/techarticles/0609ch_installing_a_chevy_distributor/) So I am hoping to get my truck into the garage tomorrow and re-index that distributor.
In the meantime, I have a related question. The truck runs almost exactly the same as it did before. It idles well, runs well, accelerates without hesitation, etc. and yet, the max advance is set to 32 degrees right now when it was around 40 before. How can that be? I really expected it to be less responsive and "slower", but it (thankfully) seems just about the same as before... Do you think the knock sensor was "constantly" sensing knocking and retarding the timing, giving the impression that it was only reaching around 32 degrees?
Thanks again!
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Hey, none of us was born knowing this stuff. What's really stupid is not asking when you don't know, and dynamiting something expensive!
I think it could have been the knock sensor protecting the engine, but I don't have one of those so I don't know. Someone else on here will know for sure.
My base timing is 16*, with 36* of total timing, with no knock sensor, and it seems very happy with that.
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Hey guys - just FYI, I got a nasty cold probably from one of my family members (kids and teachers bring all that stuff home, :) )... Anyhow, I got the truck in the nice, warm garage and as soon as I am feeling better, I am going to re-index my distributor, so don't give up on this thread just yet.
I did a couple of things, despite being sick. I measured and realized that the HEI will fit past the cruise module. Just to make sure, I loosened it up and confirmed that it swings past. It is a pretty tight tolerance, but it does get past.
I also checked the timing with a new Craftsman timing gun (http://www.sears.com/craftsman-professional-digital-timing-light/p-00914066000P (http://www.sears.com/craftsman-professional-digital-timing-light/p-00914066000P))... I set the dial-back to 14 degrees, hoping to see the zero line up on the timing tab and tape. It did, but it was really jumpy (anywhere from 3 before to 3 after). When I set the gun back to zero, 14 lines up and pretty much just right. I double checked with my old gun (no dials, just a light) and things line up solidly. I am going to assume it is the electronics in the light and not the engine - but it would be really hard to actually rely on that feature...
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I got the chance to pull and re-index my distributor. When I pulled it, I decided "well why not just clean the whole thing up and put in a new vac advance can and...." The vac can wouldn't hold any vacuum, so I replaced it with a known good one that I had from an Oldsmobile.
Well, after putting the distributor back in, firing up the engine and setting the timing, I was pretty pleased. 12 degrees at idle, 32 at 3K. Seems to be happy with cleaned up setup. The air cleaner housing drops back onto the carb, no problem.
That's when I decided to hook the vac advance can up. So using full manifold vacuum, the advance goes from 12 to 40 degrees! That's 28 degrees of advance which seems like a lot. More importantly, I get a loud (enough to hear over the engine) "clatter" from the distributor. It isn't really grinding but very fast clicking. It varies with engine speed and is only present at high vacuum (> 18 degrees or so).
I think that the teeth of the advance plate on the HEI shaft are hitting the magnetic teeth on the pickup. You can kind of see it here: http://image.stockcarracing.com/f/images/12565867+w799+h499+cr1+ar0/scrp_0412_02_z%2Bstock_car_distributor_installation%2B.jpg (http://image.stockcarracing.com/f/images/12565867+w799+h499+cr1+ar0/scrp_0412_02_z%2Bstock_car_distributor_installation%2B.jpg)
and here:
http://www.chevythunder.com/ECM%20HEI.jpg (http://www.chevythunder.com/ECM%20HEI.jpg)
Have you guys ever had a noise from an HEI distributor before?
Does 28 degrees of vacuum advance difference sound like too much to you?
Thanks!
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GM HEI in stock trim should add about 15 degrees of vacuum advance at idle. Sounds to me like something's broke or been modified.
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BTW, the article in this thread has a great discussion of all these issues, as well as ported or manifold vacuum.
http://www.corvetteactioncenter.com/forums/c3-technical-performance/60830-ported-vs-manifold-source-vacuum-advance.html
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Hey Rich... That's a great link - covers a lot of different stuff as well as the eternal question of whether to use manifold or ported vac for the advance.
I realized you were right, something had to be broken or messed up. Take a look at the picture. The top canister is what I just pulled back out of the distributor and the one one the bottom is the broken original one. You can see the two part numbers (AS 5 and 691 20). Take a look at the actual advance "windows" that are cut, though. The AS 5 has a much larger stroke at full vacuum than the original. I think that's why it was giving such a ridiculous amount of advance.
Also, the orange arrow points out two tiny spot welds. I think there is probably a block off or plate or something that was originally welded on there. I am pretty sure the AS 5 one was off a friend's SBO from a few years ago.
Bottom line - I gotta get a new vacuum advance can. The only reason I grabbed the one I had was that no local stores even stock a vacuum advance can anymore. I can't get one before Monday. Sure, I could probably MacGyver something up to stop the advance on the AS 5, but c'mon - a working new part is better than a hacked up old one, right?
Well, I'll let you know how it goes. I appreciate your responses!
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I finally got a vacuum advance can that seems to work right (Echlin 1868 (http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Vacuum-Advance-Control/_/R-ECHVC1868_0168356281)) from Napa. I setup the timing again at 10 degrees and 30 degrees. All that went well.
I do have a couple questions, though and if you, Rich, or someone else knows - I'd really like to understand the answers:
1) The vacuum hose routing ("UHJ" is the label type) says I need 4 degrees BTDC, 550 RPM in Drive or 650 with the AC idle solenoid active.
Setting the initial timing I had the vacuum advance disconnected. To dial in the 550 RPM, though - do I connect the vac advance or not? Sounds like a stupid question, but I want to make sure I've got this setup right. :) If I set it to 550 without vac advance, it lands around 750 or so when vac advance is connected.
2) The vac line which was connected to the vac advance is kind of odd. I noticed that it runs through the "distributor delay valve" and when cold, appears to continuously hold 20 inches Hg, even under load. At some point after it warms up, it then switches to full manifold vacuum and rises and falls without the delay valve. That seems wrong - but - according to the vac diagram, it looks like the right hose. Any idea why this is the case? I included the vac diagram below if it helps...
Any info appreciated... Thanks!
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They did a lot of crazy stuff with ignition timing beginning on January 1, 1968 for emissions purposes. This was by law. My dad specified his 1968 Ford Country Squire wen he ordered it to be built prior to December 31, 1967, so his 390-4V wouldn't have any of that crap on it; that's why I remember the date.
They retarded the timing spec to 4* BTDC, and ran it on ported vacuum, which at idle (where pollutants are worst) ran so retarded with no vacuum advance that it exhausted the charge still burning into the manifold. They then used an AIR (Air Injection something or other) which ran on one of the fan belts to pump air into the manifold to use the still burning charge to burn up all the obnoxious stuff (mostly NOx) that got created when the charge was ignited under pressure. This made manifolds/heads/engines run hot when left idling, and was not friendly to exhaust valves. Some models used a selector valve that, when the engine started overheating, would switch from ported vacuum to manifold vacuum to give it a chance to cool down. The vacuum delay gizmo was to hold the spark advanced when the engine was cold because they were running the engine so retarded that you would open the throttle on a cold engine and it would stumble until the centrifugal advance came in.
And none of this will work right if you still don't have the AIR pump and all the other gizmos on the engine.
So, the solution to all this is to go back to the pre-1968 setup, which was optimized for performance and driveability, though not emissions:
1) rip all that vacuum stuff off (vacuum delay valve and vacuum selector, if you have them), and connect the carburetor manifold vacuum port (driver's side on your Edelbrock) directly to the vacuum advance cylinder on the distributor.
2) set the base timing to 14-16* BTDC with the vacuum advance disconnected and the carburetor port closed off. SBCs want 34-36* of total timing when all the centrifugal advance is in, and stock centrifugal advance on all Chevy HEIs of this period was 20*. I run mine with 36* of total timing with no problem; some people go even higher, up to about 40*. You can keep setting it higher until you get knocking, then back it off two degrees, but that will make you sensitive to the gas you buy -- if you get some marginal gas at a cheapo station, you may find you need to back it off more. 36* BTDC seems good no matter what kind of pump gas I'm running in it. You disconnect the vacuum advance to basically make it easier to set the timing right, because the vacuum advance hunts a little bit, so disconnecting it just gives you a stable image under the timing light. Otherwise you would set it to about 30* BTDC with the vacuum advance pulled in, which stock is 15*. Simpler to just disconnect it (and block the carb port) and get a rock solid image to set the timing with.
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Hey Rich. I know you are right - I should just tear off all of the emissions stuff - but I am trying to keep my vintage emissions system in place for the guys out there who realize that early 80's emissions controls with A.I.R. systems are just the ticket for the ultimate performance in racing applications. :o ;D
Just kidding. Truth is, I am thinking I may not pass the emissions test here in Delaware if I am missing the vacuum controls, etc. What I am considering doing is just hooking up the vac advance to manifold vac and capping the existing line. There are so many other vac-based things, though, I was not sure if it'd screw up some other stuff (like the tip-in valve whatever it is, etc.).
I gave it a shot yesterday, though. I have it set to factory settings (4 degrees BTDC, etc.) just to test and it actually doesn't run poorly. I am going to increase the base timing though, because it tops out at 25 degrees right now and I think it is leaving some gas mileage and a bit of power on the table that way.
Anyhow - Thanks for your help on this stuff! Much appreciated!