That would be very helpful. I won't have my Crane kit until next week. I need to tune the carburetor. The idle jumped way up once I re-timed it. Any tips on how to best tune my quadrajet?
If you think the timing discussion is complicated, wait till you get into carburetors! There is one screw to lower your idle, but choke and fast idle parts are often missing and make setting things up harder. The best thing that you can do for your Q-jet is to make sure it's the right one for your combo. Q-Jets were scienced out by Rochester Products and had a ton of R&D for each application. Jets, metering rods, idle air passages, float levels, accelerator pump parts, adjustments and settings all matter. The worst thing you can do is to start with an unknown junkyard unit and slap it on a big block. If you have a mismatched carb you're in for a lot of "fun". If you are lucky and have the stocker, buy one of the two good books out there for about $20 (I have Doug Roe's, other folks like Cliff Ruggle's) to help you tune and while you're at it keep modifications to a minimum. You can remove one or both springs on the mechanical advance and run the car briefly to check full centrifugal advance. You won't even need to rev it up!. Limiting the vacuum advance involves adding a mechanical stop so the vacuum diaphragm can't pull in all the way. I used a piece of sheet aluminum and cleverly mounted it, then by trial and error cut it to sneak up on the vacuum advance I wanted. The mounting was so clever that I cant remember just how I did it.
it has it's original carburetor. I was planning to try and tune it with a vacuum gauge and was interested in some pointers on what to shoot for, what order to adjust things. Mainly looking for info related to mixture and idle screws.
Here is my quadrajet basic adjustment sheet. hope this helps. Let me know if you have any other carb questions. View attachment Quadrajet Power Adjustments.pdf
Absolutely correct... and always the last thing to be found. Almost certain that this problem will exist on one or both aged original down pipes, or any dual wall replacement pipes. Get new solid tubing installed at your local muffler shop.
Print yourself of a copy of the tune up section and specs as well trouble shooting from the chassis manual - there are some GM extracts with that and a ton of Quadrajet stuff info also. temp libraries login is good till 3 may - you can browse and will asked for login when you open first book. http://buick-libraries.boattail-riviera-by-buick.com/ login id goodtill3004 passwrod garystctrim or select login in header http://buick-libraries.boattail-riviera-by-buick.com/login.php
Braze, MIG weld, or drill and tap for a screw. The Crane part sold for this purpose is nicely adjustable, this way is fast and cheap. Yes, the added metal can be trimmed to adjust the maximum vacuum advance, but "measure twice, cut once". It's hard to add material back on once you trim it off.
I want to keep the car completely stock appearing. I don't want to use the vacuum advance unit that comes with the crane kit I want to use the original. With that said, I'm a little confused about the original vacuum advance in combination with the new springs from the crane kit. Do I simply need to replace the springs with the right combo for my application (yellow to find initial all in timing at 1600, silver for 2200) and be done or do I need to do something additional with the vacuum advance unit as well? I know the crane kit comes with a stop plate and I'm sure I'll get a better understanding when it arrives as to what to do or not do with it, but I would really like to understand as best as I can now so I can be fully prepared. I've also read something about a bushing that is not included in the crane kit. Do I need to purchase or fabricate something else to make everything right?
You do not need to modify the stock vacuum advance UNLESS you plan to use lighter springs to bring the mechanical advance in earlier. The mechanical advance and vacuum advance work together. The point to remember, is that vacuum advance only works when there is vacuum. You'd be surprised how many don't understand that. The canister includes a spring that opposes the vacuum pull. Engine vacuum is an excellent indicator of engine load. At small throttle openings, vacuum is high, like at a steady state cruise, and that is light load. When you open the throttle wide, vacuum drops off, and goes close to, if not 0. Consequently, when you mat the gas pedal, the vacuum drops out and the spring in the canister pulls out whatever vacuum advance there was. You say you have a 1970 Buick Chassis Manual. Go to the ignition section, page 68-27. Have a look at the distributor specs for your 1111984 distributor. With 3.42 gears, your RPM at a steady 60 MPH will be around 2700. At 1800 RPM, the mechanical advance is only partially in. There is 19-23* + 6* initial. At a steady state cruise, vacuum will be high, at least 16", and the vacuum advance will add another 14-18*. Your total cruise timing will be in the area of 40-45*. Now you floor the gas pedal. The vacuum drops towards 0, and that 14-18* of vacuum advance drops out leaving you with initial + mechanical advance. As the RPM increases, the mechanical advance increases to it's maximum value at 4600 RPM (30-34*). This gives you 36-40* W.O.T. timing. Bringing all the mechanical advance in at lower RPM will boost the low end performance of the engine. You do that with lighter springs. For a street car, getting all the mechanical advance in by 2500 RPM is a good target. Now lets say you do that. Let's go back to our steady state cruise example. Here you are at 60 MPH at 2700 RPM. Now, instead of just 19-23* of mechanical advance, you have it all, 30-34* + your initial of 6*, AND, the vacuum advance adds it's 14-18*. Now you are cruising along, and your timing could be as much as 58*, and you are wondering why the car is surging on the highway. It is because you now have too much advance. What you need to do is make a block off plate for your vacuum advance to limit it to 8-10* maximum, which brings you back to the optimal cruise timing of 40-45*. That is what you want to shoot for. The best wide open throttle performance will result with 30-34* of timing. The best fuel economy will be achieved with a cruise timing of 40-45*. The snappiest around town light to light performance will result from getting all the Mechanical advance in early. So what is your choice? As I said before, that 1111984 distributor may have more advance in it than you need. I'm not really sure why Buick specd that distributor that way. If I was you, I'd use those yellow Crane springs and set the total advance (without vacuum) to a maximum of 34*. Depending on the exact amount of mechanical advance in YOUR 1111984, your initial timing may be lower than 6*, you will have to see. In any case, once you set the total to 34*, you can then re install your stock springs, and you don't have to touch your vacuum advance. IF you choose to use springs to bring in your mechanical advance in earlier, then you will need to modify the vacuum advance canister. The bushing that comes with some advance spring kits is made to limit the mechanical advance. This let's you run more initial advance, yet keeping the total advance the same. There is a pin that rides in a slot under the advance plate. The size of that slot determines the amount of mechanical advance built into a distributor. By installing the bushing on that pin, you limit the travel of the pin in the slot, and therefore, the amount of mechanical advance. See the Power Timing thread, post #3. There is this picture. http://www.v8buick.com/attachment.php?attachmentid=40145&d=1080945596 Running more initial advance comes into play with some larger cams. Reducing the mechanical advance is a must in this case as advancing the initial timing without removing mechanical advance increases the total advance by that amount. If I may make a suggestion, read the entire ignition section of the Chassis manual. Page 68-29, paragraph d deals with spark advance basics. Hope that helps
Helps a lot. If I want the best all around performance, I will have to do something with the vacuum advance. The crane kit comes with the plate and no bushing. Kits like the mr gasket 928 come with a bushing and no plate. No kit comes with both so often times people buy both kits or end up making their own bushing or plate to make a complete kit. Is the plate in the crane kit for limiting vacuum advance and the bushing in the other kit for mechanical and that's why if the crane kit (with the best springs) came with a bushing it would be the perfect kit or ? I've read a lot about plates, bushings, bicycle chain links, etc but not completely sure of what accomplishes what.
Yes, the plate in the Crane kit limits the vacuum advance, and the bushing is for the mechanical advance. Look at the pictures in post 1 of the timing thread. The plate is used in a different way than what Crane says to do in the instructions. Not sure why you are confused about what accomplishes what at this point. Different ways to do the same thing.
It all depends on what you have to work with and what you want. Even a stock engine will like around 12* of initial timing. The Buick 455 will usually like about 32-34* of timing at wide open throttle. At wide open throttle, there will be NO vacuum advance so you are looking at your initial timing plus your mechanical timing. That distributor you have has between 30 and 34* of mechanical timing. Do the math, you won't be able to run more than 4* of initial timing, and maybe not even that much. A bushing can cut down on the mechanical timing so you can run more initial timing. Some distributors already have a bushing installed from the factory. In that case, another bushing won't do much if anything for you. You have to look at your distributor, and see if you have a bushing. Then you need to set the total timing without vacuum advance, and then check to see where your initial timing ends up. Use the yellow Crane springs to set the total to 34*. Then shut the engine off, and reinstall the stock springs. Start the engine and lower the idle speed as much as possible. See where your initial timing is. Then simply subtract your initial advance from the total (34). That will tell you how much mechanical advance there is in your particular 1111984 distributor. You can then decide if you want more initial advance. If you do, you can see if you can use the bushing to lower the amount of mechanical advance so that you can run more initial advance. Once you get that set, decide whether you want the mechanical advance in quicker. If not, you can stick with the stock springs, and run the vacuum advance as stock. If you decide to to use lighter springs to speed the mechanical advance, then you will have to shorten the amount of vacuum advance. Either make a block off plate for the stock vacuum advance, or use the Crane canister and use their plate. Your choice.
Any idea how much the bushing will limit or affect mechanical advance? Haven't found the answer so far. I'm up to page 20 of the power timing thread yay! For a quick reference for myself with my "stock" car here's what I think I have learned or gathered from reading so far (and please correct me where wrong or if I missed something important): -set total timing to 30*-34* -initial will be what it is but ideally it should be 12* -use lighter springs to bring in advance earlier (hopefully 2500 rpm or less) -use a bushing to limit mechanical to allow higher initial if needed (especially with bigger cams) -fashion a plate to limit vacuum advance to 8*-10* (restrict pin movement to 0.086" for 8* 0.104" for 10*) I assumed mine was a 1111984, but my car was built later and although it has it's original distributor it's a 1112027 casting instead. Any difference between the specs on the two distributors?
I don't have any specs on the 1112027. Could be the same, might be different. None of my reference books have it listed. The easiest way to find out how much mechanical advance is in a distributor is to compare full advance to initial advance. Then just do the math. When you use the light springs, it is easy to see what full advance is at a relatively low RPM. Once you have measured that, shut the engine down. Install the heavy stock springs, start the engine, and turn the idle down as much as possible. Then measure initial advance. Subtract initial from full mechanical advance and you have the amount of mechanical advance in the distributor. Install the bushing and repeat the above. That's how you do that. Because the cam turns at half the crankshaft speed, 1* of distributor rotation = 2* at the crank. These are very small distances so the best way is to measure. You frequently can't get an accurate initial advance with very light springs because some of the mechanical advance is in at idle speeds. Turning the idle down is an attempt to ensure the same thing, that the weights are fully retracted. Most stock springs don't allow any mechanical advance below 1000-1200 RPM. What you have listed is correct. You are learning Grasshopper.:grin:
Thanks sensei. I had a little time to fool with it this morning. I put in the yellow springs and set total to 34 (vacuum hose off and plugged). It really liked the yellow springs at idle initial had to be around 12 which it loved but of course that was with partial mechanical since it had the light springs. Idle vacuum was 17" and it idled and took fuel well. I removed those springs and put the stock ones back in. Initial timing at 600 rpm was 4. I retuned the carb but it doesn't seem to like 4 at all and I can't get the splutter out of it. I could do so at 6 but can't at 4. If I go back to 6 that would put me at 36 since my 1112027 has 30 mechanical. Would that be ok? I can't find any specs anywhere either on the difference between the 984 and 2027 but I'm going to assume after my findings the only difference is the casting numbers. I believe they are otherwise identical. My Crane kit came with 2 yellow, 1 silver and 3 blue ou:
That sounds about right. See if there is a bushing on the pin. You can use a small mirror to peek under the weight assembly/advance plate. If there is no bushing there, get the Mr. Gasket spring set with the brass bushing and throw that on. Then total time it again and see where the initial goes. 36* total might be OK. You don't want it to ping at full throttle. Listen for that. Strange about the springs, but you can mix and match them. A Blue and yellow works pretty good for instance.
Anyone know how much the bushing affects total advance? Any reason why I couldn't use the block off plate that camewith the crane kit on my stock advance canister? What size drill bit in that picture on the power timing thread is being used to measure the length of travel on the arm? How is the best way to measure the 0.086 or 0.104"? My feeler gauge doesn't have anything that thick. Crane is sending me the missing spring.
