hey Larry, I exchanged the distributor at Advance Auto and lo and behold, the car is running finally. Now I am trying to get the timing all set. I just wanted to clarify the initial base timing. If I set the engine to TDC on number one, do I need to set the distributor to fire at that point too. I was reading in another post on the board a suggestion to put the balancer at 8*BTDC and install the distributor so it is firing. This is what I initially did, and I could not get it started so I moved the distributor CCW a few degrees and it starts. Now my dialback timing light is showing I have 45* of advance at WOT, a high idle, 1500 rpms, and the engine begins to overheat. Obviously this is too much advance. I am using the method of the cam shaped bolt in my HEI and I am trying to set it lower to limit the advance more. I guess I am asking for a review on how to set the base timing (initial) and what I am doing wrong if anything? Thanks for all your help.
If 45* of total timing overheats the engine, you have other problems. As long as the engine runs, I would set the total timing without vacuum advance, to 32-34*. Wherever the initial timing is, it is. It's not like you have any choice. Unless you can adjust the amount of mechanical advance, the total advance dictates what your initial will be with a set amount of mechanical advance. Does the distributor have light springs in it?
Here is my scenario. This thread has been very helpful a long with emails to the wizard, cray, and a couple of phone calls to Mike Crippin to get it straight. Long story short, I had a low rpm stumble at cruising speeds. Swapped in a new adjustable vac can and added a block off plate to limit the amount of advance and this cured my stumble and still made my car start and idle better. I limited the amount of travel to about .104". Word for the wise, my vac can had a different length rod, or I bent mine when I drilled and tapped the holes in the vac arm. I only noticed this when I rechecked my timing and it was about 10 deg off (44 deg.) The rod must have been shorter moving the plate in the advanced direction? I backed the timing down to 34 with no vac, and measured around 39 with the vac hooked up. Anyway, thanks for everyones help, will keep this link updated.
Update. Notice some issues and bad idle and crappy throttle response so, Built and adjustable similar to Cray and installed that on the stock can. Timing all in at 2400, 34 total. Vac is set at additional 11 for 45. May be a little much under cruise but seems to be fine with no stumble. Don't hear any spark knock, of course the car is loud and the collecters have there own noise. Now I can play around a little more later. I believe I will learn more at the track. Thanks.
Sounds good Joe. 45* might be a little too much. If it is, you will hear some ping at light throttle in high gear while going up an incline. Or, the engine will surge under the same conditions on level ground. If not, you are OK.
After reading this post about 25 times, I decided to get a mech advance kit from the local Auto Parts mega store. I have a couple of questions. First let me start by saying it is a points distributor with no vacuum advance (I have a new one on order). I started with the "medium" springs that came with the kit which caused all my advance to come in at 1400rpm and made the valves clatter under acceleration. I shortly switched to the "heavy" ones in the kit which allowed all advance in at 2400rpm with no valve clatter. I made the 30* mark on my balancer and noticed that with all the advance in at 2400rpm I can get 30* total mech advance, but it brings my idle timing to 5-6* at 600rpm. I know factory timing should be around 2.5* at idle. Is it okay for the timing to be 5 or 6* at idle or do I need to order a bushing kit? If it is the bushing, is it safe to grind down the brass bushing that came with the kit to allow a greater range of mech advance?
First, there is nothing wrong with 5-6* of initial advance even if the stock spes say 2 1/2*. Also, be aware that there may be a small amount of mechanical advance in at idle speeds with the lower tension springs. You adjusted the total advance. That is more important. I believe in 66, the vacuum advance was hooked to manifold vacuum, so with the vacuum advance functional, your idle timing will be quite a bit higher. You will probably have to limit your vacuum advance to 8-10* because all your advance is in at 2400 RPM now. With the stock springs it wasn't in until 4000 RPM.
ok larry i need some input from you my 1970 sky with a 350 4v stock i think after reading you post about timming i decided to check mine i had 34 deg at idle and over 50 with the mechanical advance. so i set it up for 34 deg total installed a curve kit so its all in by 2500 give or take a hundred rpm the car now starts crappy i have to step on the throttle to get it started once started it runs ok but not to responsive. before i touched it it seems to have great throttle response but to top end typical of to much timming. now for my idea i want to add weld to the middle part of the dist where the wieghts sit at idle to limit my mechanical advance so i will have more initail with the same total i have checked everything on the motor seems ok i have no vacuum leaks idle mixture screws work ok choke ok it will idle at 500 rpms in and out of gear i have my vacuum advance hoked to manifold vacuum for better drivabilty if i power time the car at part throttle foot brake style i end up in the 50,s for timming i have been a gm guy for every and have never had a motor run like this kinda has me stumped larry one other thing that i thought maybe need to check is make sure the balancer mark is at tdc does this happen to these motors
I don't know how you could have 34* at idle. You did disconnect the vacuum advance when checking your total advance, right? If you had 34* at idle, the car would be hard to start hot. Are you sure of your timing light? Make a piston stop out of an old spark plug and check your balancer. It's rare, but they can slip.
vacuum advance was disconnected and used a second light to see if mine was bad that was my first thought. It did not start hard either thats why i am thinking the balancer may be my issue. i am going to try to get out there today and check tdc will take me longer to make a stop than check it be back in a few hrs with results
ok larry i checked everything balancer was correct with 34 deg total no vacuum car doesnt seem to run right ... i pulled the dist took it apart (hei gm) i welded up the mechanial advance so i could add 10 deg to my base timming and not add to the total so afer some welding measuring and grindind i now have 25 deg at idle and 9 mechanical advance to make my 34 total . the car now has a better idle more throttle response i did pull the plud they look ok the plugs the gap was 60 ??? so i regapped at 45 did not seem to change much but did it anyway i have never had a engine run like this seems to still be running behind itself if that makes any sense the only thing we did not do was a compression test we did pull the pcv line out just to see if we had anything blowing out the breather seems ok any thing i may have missed the car has 182000 miles not to sure about the motor though
I would check the vacuum reading at idle. I have seen vacuum leaks into the valley because of poor fitting intake manifolds (rebuild milling of block and heads). The result is it takes a lot of timing for them to run at idle. If you don't know the history of the engine, it may be the case. If you know what cam is in there, see if the vacuum level is as expected. If it is low, check for a vacuum leak.
hey larry i have been driving the car around a few cruise nights / shows ice cream ect to the tune of about 400 miles since i registered it. i will go out tomorrow and check it with a vacuum gage i dont think it has a vacuum leak but one thing i havnt done i will also reset the idle mixtures with the gage. the car still feels like it has no power or at least not as much as i am used to. when i am driving i think i can feel the vacuum advance add and pull timming ( i only have 10 deg ) cruising at 59 lets say come to a hill all i want to do is maintain my speed so i throttle it a very little bit as i do feels like it looses a little power and have have to step on the gas a little more as a let up on the gas it feels like the power comes back i did try to remove it totally but car doesnt run as good and i had to raise the idle speed a good amount just to get her to idle. maybe i am asking to much of my old girl or maybe just to used to driving fuel injected cars that are tune to a t once i get her really road worthy maybe a trip to the drags and just keep putting more timming in and see how she acts i would assume it should nose over or ping if it doesnt like it
I'd make sure your fuel pump is good, and that the float level in the carburetor is set right. Are you getting any hesitation/lean misfire? At the track, watch the trap speed. If it wants more timing, the trap speed will increase as you advance the timing. It will drop off if you add too much. I always add some Cam 2 at the track (2-3 gallons) for insurance against detonation.
Larry, This is the best post on the entire site! I can "see" the big picture now when it comes to timing. Something I cant read tho are the numbers on the timing tab of my 70 455. Long hash mark I assume is 0. but I cant read the other 2 numbers very well. 2-4? 4-8? Thanks for all the great information
Russ, Some timing covers have 0, 4, 8, others have 0, 4, 8, 12. There are lines every 2* I believe. If you are using a dial back light, all you need to see is the 0 line. Clean it up as best you can and mark the zero line.
Great thread! Thanks, Larry! I'm still trying to soak it all in, though. I bought the 928G Mr. Gasket kit to put in my stock 1972 Skylark 350 4B (with correct factory points distributor). My first question is in regard to the copper bushing in the Mr. Gasket kit: Does it limit the vacuum advance to the correct degrees (8-10*)? Or am I better off fabricating a block-off plate on my own? Unless I missed it somewhere, I don’t think anyone mentioned where the bushing actually limits the vacuum advance to. My second question is in regards to manifold vacuum: Where is the most common place to tap into it one these 350's if I want to make some comparisons to the factory ported source? The only place I can see one is where the brake booster connects. Should I tap into that or create a separate source (don't really want to drill into the manifold)? Thanks in "advance" for any help. :laugh:
Brent, The bushing limits the mechanical advance, not the vacuum advance. Those are 2 different things. If you look at post #3 on the 1st page, you will see a picture of where the bushing goes. There is a pin that rides in a slot under the advance plate, that determines how much mechanical advance is built into the distributor. The bushing goes on the pin, and limits the pin travel within the slot. Do not assume that you necessarily need to use the bushing. Depending on the distributor you are using, you may or may not need it. The 1972 350 distributors (if your's is original) have a smaller amount of mechanical advance built in, therefore, they do not need the bushing. Check the distributor number. It is stamped into the body circumference of the distributor. Post the number and I may be able to better advise you. If you plan on keeping the stock vacuum advance, make your own block off plate. There are plenty of pictures and instructions on how to do that in this thread. Keep reading until you understand. There should be a manifold vacuum source on your Q-jet. It is very simple to tell whether the source is ported or manifold. With the engine running and at idle, if you unhook a manifold source, it will hiss, and the engine will begin to run rough. If you unhook a ported source, it will not hiss, and idle will remain unchanged. There are 2 nipples below the air horn in front of the Q-jet. The passenger side one is usually manifold vacuum. Try ported and manifold vacuum. Decide which you like better and run with it. Good luck.
Awe! Now I get it. For some reason, I thought the bushing went on the rod that goes into the vacuum canister, thus limiting its travel. But thats no where it goes. OK, so I probably need to find me a bike chain link or something and make a block-off plate. . . thanks for clearing that up. Also, I seem to remember unplugging the hose from the factory air cleaner (when I switched to an aftermarket 4" chrome cleaner) and wondering why the engine didn't stumble when I did that (although I did put a plug on the carb afterwards). The line was hooked to the passenger side (manifold). Thanks again!
OK, I power tuned my distributor last night. And sorry, I forgot to get the number off of the side of it, but Id be surprised if it isnt the one that came with the car. Anyway, I replaced the points (set dwell to 30), replaced the spark plugs (Autolite platinum gapped at .40), and replaced the cap and rotor. I dont have a tachometer, but do have an RPM feature on my dwell meter. I installed the black springs (lightest resistance) from a Mr. Gasket kit and set the total advance to 30* at about 1,000 RPMs. I was surprised the mechanical advance was coming in so quickly, but the 1.76 mark on the balancer definitely would not move any further beyond that point. Does that sound right? At any rate, that put my initial timing at about 11* (idling at 500 RPMs). That means my distributor has 19* of mechanical advance in it, right? I took it for a test drive after that to see if there would be any pinging prior to any modifications to the vacuum canister (running from a ported source). Not a single ping at WOT or low-RPM loads. And the throttle response and seat-of-the pants performance are both greatly improved. Love it! But, still, my RPMs seem to be a little low compared to what others are posting in this thread. So, maybe my dwell meters RPM feature is not so accurate? o No: My idle screw is backed all the way out and the car idles pretty low, almost sounds like it has a hotter-than-stock cam in it, which I assume it doesnt. It never stalls on me either and comes off of idle without hesitation. Man, I sure wish I had known this stuff back in the 90s when my daily driver was running 11.1 compression in 100+* weather. That poor motor was either pinging or running hot. ou: Thanks again, Larry! :beers2:
