Here's a live update from the garage. i have everything back to normal, that is, no curve kit installed. Back to factory springs and weights. i removed the dash pot. rpm 1200 dwell 13* vacuum 20 going to adjust dwell now.
Okay, idle screw adjusted out. Rpms 800 dwell 30 vac 21 initial timing showing 12* engine doesn't seem to like this much! it doesn't die but the engine shakes a bit more than normal. car does restart fine. at this point the engine is too hot to check for vacuum leaks with carb cleaner so I'm gonna rest the brain for the night and pick this back up tomorrow. If you guys think of anything else in the meantime, let me know. thanks
Great job. Now adjust your two air/idle mixture screws on the front of the baseplate. Adjust one at a time. Turn it in until engine stumbles and back it out until you get highest vacuum reading, then adjust other died same way. Should smooth out your idle.
X2. Go slowly, and listen to the engine as you turn the screws. And it doesn't hurt to adjust them alternately a couple of times, as changing one can have a small effect on the other as the engine smooths out. And the lower you can coax that idle speed - at least while you're tuning it - the better. A well-tuned stock 350 ought to be able to idle smoothly as low as 400-500 rpm in neutral, and pull 18-20 inches of steady vacuum at that speed. At anything above 800 rpm, the centrifugal advance starts to come alive, so you really can't set the timing unless the idle is down below 800. For driving, bump it back up to the stock setting as indicated above.
Just so it's known, I could probably screw out the idle adjustment screw a little more but the engine was stumbling so much that I decided to leave it be at 800rpm. I can probably lower it once I get the air/fuel mixture screws adjusted more. When I rebuilt the carb last month, the spec for those screws was to screw them all the way in "finger tight" to where I just felt it seat and then back them out 2 full turns (I believe) and that was a good baseline to start from. I was going to just start off today with doing it that way but if you guys figure it's better to go from where I have it now. Is there anything wrong with adjusting them both at the same time? That's what I did originally, half turn right, half turn left...wait and listen, and then continue.... I pretty much turned them both to try to achieve the highest idle that I could hear (this was before I had a vac guage on it). So here's the plan, I'll bring the vacuum up as high as I can by adjusting the air/fuel mix screws and then turn down the idle adjustment screw on the throttle arm until I can get it a little lower. After I have determined that the engine is ideling the best that she can, I will take the necessary steps to start power-timing. Thanks again guys
Do the air/idle adjustments one side at a time. You can start from where you are now, that would be fine. You can do one side, then go to other, then back and forth again until best vacuum reached.
Update: I adjusted the carb tonight, it was fairly labor intensive...lots of back and forth..I had it pulling vacuum of 22Hg but the engine was gasping at this point...so I screwed the air/fuel screws in a tad and found a spot it liked at 21. I then double checked dwell at 30* at this point I'm still timed at 12 degrees so I bring it down to spec of ~4* at idle my rpms are ~650 at this point and I make a very small adjustment to the idle screw to get it to run its best. Still seems to fumble a bit with the rpms varying +\- 50 I believe it could possibly be a plug issue. I plan to check the plugs soon as well as their gaps. I forgot to check for more vacuum leaks, do you all feel that 21 is good? If not, where should I adjust to get more if there is indeed no leaks. I plan to take her for a spin tomorrow and see how it rides, if it's all good then I'll proceed to the next stage. thanks for reading and goodnight. edit: reading over this thread before bed I've noticed a mistake on my part. I set initial timing at 4* but I still had the vacuum advance plugged in....so it's all wrong. I'll have to fix that before my ride tomorrow. This could possibly help with the stumble.
Heck yeah, 21 inches of vacuum at 650 is great! Yup, getting an engine tune all dialed in is a labor-intensive thing, but the results are something to be proud of - I know of a lot of high-dollar cars that run in spite of the way they're tuned. Once you're done, it oughta start right off, especially when warm, and the throttle response should be nice and snappy. Yeah, disconnect and plug the vacuum advance, ten reset the initial/static/base timing, 4 is a good starting point - but as mentioned, I agree and will bet that it'll like 8-10 a LOT more. The idle fumble may well go away when you reset the timing, if not you might want to tweak the idle mix screws a tiny bit. You'll find that the idle mix, idle speed, and ignition timing settings can all have an effect on each other, even if it's a tiny one. With my old 350, whenever I changed one thing I'd tweak the others, and (not to brag too loudly) i had probably the most well-tuned 350 ever, lol (see my sig)
lol, nice. I did notice that all night after I had it dialed in a little that when I was going back and forth starting it, that I'd only need to reach in and turn the key. My car has been pretty hard to start since I got it and I really have had no problems the last two days tweaking it. Just tap the throttle arm under the hood and reach in on the first start and then only turning the key from there on out. I'll bring the timing up after work tonight, I'd assume with it showing 4degrees now with vaccum that it's actually more like 8 degrees BTDC without the help of vacuum advance. After I have all of this ironed out, I plan to "attempt" to limit vaccum advance with a plate as well as use the aftermarket bushing, springs and weights. Please let me know if there are any pitfalls for any of this, I have the powertiming idea down now after having done it so many times over the weekend, but if there is anything you guys think I should watch out for, please speak up. Thanks
The vacuum that my canister is hooked into appears to come from the caburator area, though I've not followed the line to see exactly where it's coming from, I assume it's manifold vac. I can get that timing light, though I have no problem using my basic one and the 30 degree line I've put on the balancer. Just to clarify, I had 4 degrees of timnig with the canister plugged in, so I can only assume if I'm getting roughly 12 degrees from the Vacuum advance that if I unplugged it, that it would drop to 8 degrees Below top dead center. (thats 12 degrees of total movement). I could be wrong on poossibly how I'm explaining this but it will be like -8 degrees ( 8 degrees below Zero).
You know what they say about the word assume, right? Why must you assume? Ported vacuum originates above the throttle blades, so at closed throttle, there is little or no vacuum at the port. As you open the throttle, vacuum rises rapidly. Manifold vacuum originates below the throttle blades. It is present at the port at closed throttle anytime the engine is running. As you open the throttle, manifold vacuum will decrease as the load on the engine increases. At part throttle cruise, ported vacuum will equal manifold vacuum. At wide open throttle, BOTH ported vacuum and manifold vacuum will go to 0. Want to know whether you have your VA hooked to manifold or ported? Just pull the hose off the source with the engine running at idle. If it hisses, it's manifold vacuum, and you have just initiated a leak. If it doesn't hiss, it is ported. Hold your finger over the port and slowly open the throttle. You will feel the suction as you open the throttle. In every VA canister, there is a spring that OPPOSES the vacuum pull. Engine vacuum must overcome the spring to advance the timing AT ALL. As vacuum drops, the spring wins out, and pulls, whatever advance was there, out. Most stock canisters are spec'd out at a maximum of 14-18* of advance at 16" of vacuum. At 6-8" of vacuum, the canister starts to advance the timing. The Crane adjustable canister offers 2 adjustments. One adjustment is to the spring tension inside the canister. That is done with an allen key through the canister port. The other adjustment is for the amount of advance in the canister. The problem is with the way Crane instructions tell you to do this. There is a small black stepped cam that comes in the kit. Crane tells you to mount that cam under the far side mounting screw for the VA canister. As you turn the cam, the steps contact the end of the canister link, and push it further into the canister as a starting point. There are 2 problems with this. One, it changes your initial timing. For each notch, it's 2*. Two, it compresses the spring inside the canister. Years ago, Dave Ray (The Ignitionman) came up with a better way to use that cam. He drilled and tapped a hole so that you could mount that little cam forward of the link. This restricted the amount that the link could pull in thereby limiting the amount of advance that way. Now, by turning the cam, you could restrict the amount of advance independent of the spring tension adjustment through the canister port. There are pictures of this in that very 1st post in the Power Timing thread. Then of course, you could use the same principle to attach a block off plate to a stock VA canister. You could also use the Crane cam to limit the stock canister and make it adjustable.
Well, here's how I figure I have manifold vac, my vac guage is directly in line with the hose that runs to my canister, so I'm getting 21 in-Hg of Vac going to that canister at idle. If it was ported then I wouldnt be getting little to no vac to that canister at idle, correct? Even with me dropping RPM's down to 650 last night, I had over 20in-Hg of Vacuum. Larry I've read the initial post in your power timing threat a half dozen times already, the one thing I wanted to make sure of is this.....you referenced a .080 and .10 spec (or something similar) of travel for that vac canister advance rod. Essentially if I remember correctly, it equaled 8 and 10 degrees of advance added. The block off plate is there to limit that movement to only 8 or 10 instead of 12-15 and I understand the plate is mounted inboard on the canister. If I get a feeler guage and line up a thickness of .080 (again that number or the correct one in your post) is that the measurement between the blockoff plate and the rod? In other words, when vacuum is added to that setup, the rod will close that .080 gap and be up against the blockoff plate? Thats the only thing I wasn't 100% sure on. Thanks guys
You got it, the link moves .086" for 8*, and .104" for 10*. All you are doing is restricting the distance that link can pull the advance plate. The stock canister should be 14-18*. With full manifold vacuum, it should advance the timing somewhere between 14 and 18*. You can't see or adjust the initial timing with the VA connected.
I plan to get everything correct before I try anything fancy. And rereading the posts above, I was explaining things incorrectly. The numbers above 0 are the "advance" so they are the positive numbers, by advancing the engine you are causing the spark to come in advance of the piston, the more advance the earlier the plug sparks.. so the numbers above 0 would be BTDC because the piston hasn't made it TDC yet. I know you already know this, I'm just spelling it out for myself, I had it backwards like you said. What I plan to do tonight, time permitting, is just get the initial timing (without vacuum advance) to around 4*. I already know the vacuum advance is working at idle so at that point I'll hit the road and see how it drives.... all stock. I'll deal with power timing it if I have some left over time, but that might be something better suited for this weekend.
I'm not sure where he is if he has the VA connected. With a stock distributor, he has to set his total to whatever he would like to run, and before he can do that, he has to disconnect and plug the hose to the VA. Once he sets the total, the initial will be where it needs to be for that distributor, and the total advance he has selected. Dave Ray was on this board long ago. He is the guy who modifies stock distributor to run as GM HEI's or plug into an aftermarket CD box. I have one of his distributors (MSD trigger option) in my engine, have for a long time. www.davessmallbodyheis.com
I understand. The canister delivers somewhere between 14 and 18*. Back in the day, that was manufacturing tolerances, so it could be 14, it could be as much as 18 or anywhere in between. Then there is the mechanical advance. If he is above 800 RPM, some of that might be in also. That's why I say, plug the VA. Put the really light springs in, power time it to 32* or whatever you choose to run, and you are done. Who cares what the initial is at that point, it is what it has to be. If you really want to know, put the stiffest springs back in, idle engine down until it just about runs, and see where the initial is. Subtract the initial from the total you set, and that's what's in the distributor (if you want to know) Then select a combination of springs that get all the advance in by 2500 RPM or so, restrict the VA canister, run it off ported or manifold, and that's that.:laugh: It never ceases to amaze me how guys can make something so simple into a major project that takes forever. :grin: Part of why I wrote the Power Timing thread.
Everybody here has provided me with more than enough info now to do everything I want to do, Thanks again guys.
It's frustrating for me. I scream at the screen sometimes:laugh: It's the same questions over and over. I have tried to make that Timing thread as comprehensive as possible, and guys link to it all the time. They beat me to the punch most times. The biggest problem I see is the guy who want to bypass basic automotive knowledge and work on his car. He has no idea what he is doing, or how things work in an engine, but he likes fast cars and he wants to work on his car. The worst part of that is you can't even advise some one like that because it's like you are speaking Chinese. They lack the basic understanding, so it takes pages of responses just to get them to understand basic ignition timing. Simply reading the ignition section in any Buick Chassis manual would remedy that, or even a Google search of 'Ignition Advance Basics". I agree that guys want to Power Time an engine that has other problems thinking that will fix things.
