Larry, thanks for the write up. i'v e also read your power timing article. I understand the using lighter springs will make it easier to get to advance when revving the engine. Then swapping them back out to normal for the distributor. The part where i am confused is, how do i know what my total timing should be at 2500-3000rpm? How do i know that 34* advance on my advance knob timing light is better than 24* advance or 36*? Im assuming that by dialing in my total timing, will set my initial timing at the same time in idle. thanks
Most Buick V8's run the best at 30-36* total timing. If you look at the factory distributors, they all spec out at 30-34* total timing. All that should be in at 2500 RPM for best performance. You know that because that is what I am telling you:grin: 32* is an excellent starting point. You can adjust from there if you like. I want you to completely forget about your initial timing right now. It will be whatever it will be once you set the total advance.
YES, the clouds have parted; I think i finally got it!!! All i needed was the spec for the engine. The manual reads 26-30 @ 4600rpm maximum centrifugal advance but i will go with your suggestion and set my light to 32* total (vacuum advance disconnected and plugged) while in park. From there should i be good to begin adjustments to the carburetor? Ideal rpm in park for idle would be 560prm? thanks again guys for helping me out here
I suggest setting the idle speed as low as you can with still having a strong idle in gear. I still suggest setting the idle mixture screws with the car in gear, it makes a difference.
what do you suggest for a 340 with 10.1 compression? 560 rpm is pretty low. im still getting used to the "feel" of the car. So for now i have to go by the numbers in order for me to be able to do it.
i attempted to re-time the car. I set my light to 32* and hooked up a vacuum gauge to the ported outlet on my carb. i think my tach may be messed up because i couldn't get the engine to rev up to 2500 rpm, the tach just would not get that high. So by using the vacuum gauge, i revved it until the gauge read all the way to 17 lbs of vacuum, after that the vacuum would drop back down to 10. So i figured that was WOT and turned the distributor accordingly to get the 32* to line up with the tab while keeping the vacuum as high as possible. i need to get a good, reliable tach so that im sure of the rpm's. The car sounds good, it sounds a tad bit high, but i cant tell for sure without a tach. Another thing i noticed, while attempting to remove the distributor cap to check its condition, one of the passenger side cables basically broke at the nipple. Really weird, so now im just going to replace all the wires, cap and rotor. Maybe its time after 5 years? thanks again, any pointers would be appreciated. ---------- Post added at 09:23 PM ---------- Previous post was at 08:54 PM ---------- i found an older tach but it only reads up to 2000 rpm, can i still get adequate total timing with this?
There is no specific RPM you have to rev the engine up to in order to set the timing, just rev it up untill the timing mark stops moving. With the stock springs in the dist. it might need to be revved to over 3000 to max out the timing. At least with the older tach you could set the idle speed. There is usually a switch on the tach. for 6 cylinder or 8 cylinders, make sure that switch is in the correct position. I would set the idle speed to 650 RPM in park and if it idles nice in gear that is fine.
Stop right there...you don't want to measure "ported" vacuum, but instead manifold vacuum. Are you aware of the difference? Also, when we're talking about vacuum (negative pressure, or pressure below our atmosphere) with a typical gauge used in the US, it will me measured in units of inches, not PSI (pounds per square inch). On top of that, look at the face of your vacuum gauge. Does it show inches of mercury, or inches of water (H2O)? I know this can be confusing, but those details matter a lot. Devon
" just rev it up untill the timing mark stops moving." So if i set my dial to 32*, i rev the car until the lines meet up, when does the rotation (adjustment) of the distributor come into play? F*** i thought i had it! ---------- Post added at 10:59 PM ---------- Previous post was at 10:55 PM ---------- Well from what i've researched, on my carter afb, the lower passenger port is manifold vacuum. (i mis wrote ported and meant manifold) Right, it's not pounds, it measures inches/mercury.
Like Devon says, find a vacuum port that gives a reading at idle. This will be a manifold vacuum source. No vacuum at idle equals ported. When you dial to 32 and rev the engine the mark should stop moving when it lines up with the timing tab. If the mark goes out of range of the timing tab then spin the dist. a bit so that the timing gets in that 32 range when reved up. To start with you need to find out what your total timing is and get it within the range that will work well. If you just rev it till it gets to 32 and stop there then you could have an extra 8 or 10 degrees on top of that at full throttle and you do not want that. To adjust the total timing just raise or lower the initial timing. Yes there are other ways to change the timing curve but lets keep it simple for now.
Now that i've thought about what you said in your previous post. I dialed my light to 32* and revved the engine pretty high. Some times the line would hang for a while and be too far in front or too far behind (once i adjusted the distributor) I finally turned the distributor slightly and was able to have the lines meet up perfectly when revving up and the lines would hang there for a while, if i kept opening the throttle the line would slowly separate but not that much. (i'm assuming this is where the vacuum advance would compensate, maybe that doesn't matter right now, im probably wrong) I'm assuming that is where i need to be, according to Larry and the 32* total timing. When i let the throttle back down and shot the light, i had to dial back down to 18* for the lines to meet. That seems a little off to me. From what i've read here im supposed to be 8-10* at idle. ---------- Post added at 11:41 PM ---------- Previous post was at 11:38 PM ---------- How do i know what total timing i need to be at? how do i know what will work well? just by sound and no pinging? Is it in my book? im going by what larry said and using 32* as my total timing.
Those are excellent questions, and they cannot be answered by following Larry's guidelines or those of anyone else. Your goal in adjusting your ignition timing and it's curve totally depends on how you drive your car, and what you expect to get from it, and to avoid detonation (pinging). There is no perfect recipe for initial or total timing, or the curve in between. You will have to discover all of this yourself. Trial and error will show you how the car performs when you change one thing at a time. Try not to change more than one thing at a time so you can realize the impact of each change. Devon
Devon is correct, A starting point should be 30-32 degrees, this should be safe. I have never tuned a 340, I will try to find that article where they were dyno testing a 340 cube engine. If I remember correctly they ran about 30 degrees timing. I have seen engines that have carbon build up and would not tolerate the timing that most engines would. carbon deposits make pre-ignition more likely. I was forced to run 26 degrees max timing on a carboned up engine, then after I cleaned it it ran best at 36. I know that most Buick 350s make the best power and fuel mileage at 32-36 degrees of timing and 10 degrees of vacuum advance on top of that. When at light cruise the engine will run cooler, get better fuel mileage and last longer with a bit more timing. This is why the vacuum advance is a great way to add this extra timing because when you floor the gas this extra timing goes away. The problem with the stock vacuum advance canisters is that they add about 20 degrees of timing which is too much if you are running lets say 32 degrees of timing. So, if you are running the stock canister then consider running a bit lower total timing so that you do not have too much timing when the vacuum canister adds timing.
Ah, i see. Basically, my car is a cruiser, i drive it around town in traffic, stop lights etc 30mph on average, occasionally on the freeway. So, considering the tach im going to use max's out at 2000rpm, 1. i would rev it up to 2000rpm 2. set my dial to 32* as a starting point and turn the distributor until the 32* line matches and hangs at the tab at 2000rpm? then clamp it down. 3. Adjust my carb to 560-650rpm at idle - plug the vacuum advance back in. 4. adjust mixture screws and drive it? 5. should i use my vacuum gauge (at manifold) to see that it reached max vaccum at 2000rpm? or is that doing too much? ---------- Post added at 09:37 AM ---------- Previous post was at 09:30 AM ---------- according to this manual for a 340 http://www.teambuick.com/reference/library/67_chassis/files/69-a.pdf i should have initial timing of 2.5* then 26-30* max mechanical timing the vacuum advance should only add 14-18* advance which makes a total timing of 48* so if i use 30 - 18 = 12* of timing at 0 on my dial. or can someone help me interpret this? i have a 4 barrel carb.
If your tachometer can't read above 2000 rpm, disconnect it and see how far you can throw it. Then get another. (1) Don't stop watching the ignition timing at 2000 rpm. Keep increasing engine speed until you see no changes in ignition advance. You may see 20 at 2000 rpm, but then you may see 25 at 2500 rpm and 30 at 3000 rpm. To really know what your total ignition advance is you need to know at what rpm the centrifugal advance mechanism is fully engaged, i.e. no longer continues to change with the increase in engine speed. (2) See above. Do not stop at 2000 rpm. (3) & (4) Yes. (5) For this situation there is no value in checking manifold vacuum at that rpm. NO. Regarding any timing advance due to the vacuum canister, forget about it when considering total timing as we're discussing here. When you're accelerating at wide open throttle, the vacuum advance canister has no effect on total timing. The vacuum canister changes advance at or near idle for part-throttle driving. We can get to that later. Devon
whoa (light went on in my head)! So im essentially chasing the marks on the balancer and tab? So rev it to 2000 or whatever number and turn the dial on my light to where they line up. Rev it higher, the marks will change, and adjust the dial again to where the marks line up. Rev it even higher, the marks will change, and adjust the dial again to where the marks line up (but they might not move, and at this point, is where i would set my distributor) and that would be optimal? But then, couldn't this happen at any point where the distributor it turned? How do i know the distributor is in the right location? Say if i put my dail at 60* ( i know this is wrong) then turned the distributor and revved the car until it reached 60* how would i know that is totally wrong?
Not exactly. at this point you can look at the dial on your timing light and see if it's around 30-35 or so. If you're seeing more or less than that, turn the distributor to get it into that range. This is just a starting point in the scheme of tuning. No, nothing has been optimized yet. Here's the deal...there's no way to know what total timing your car will like, you have to experiment. You will also have to experiment with the rpm at which the total timing is achieved (the springs and weights do this). On top of that you may find your car likes a total timing number but would run better with a different initial timing number. Modifying the amount of timing the centrifugal mechanism is allowed to add changes this. Just when you thought you were catching on... Devon
Damn man, i thought i was getting the hang of it. So forget all this hypothetical **** that's going through my head... I want my total timing to be 32* as Larry suggests Im going to rev the car high (past 2500rpm), and if the 32* doesn't line up ... im going to turn the distributor accordingly until it does line up and hangs there Then plug in the vacuum advance set the idle to 560-650 rpm and drive the damn car and see how it runs, listen for noise etc... if it runs like ass i will go with what the book says and bring the total down to 26-30* From that point What does the fine tuning entail? Yesterday, when i set the distributor to 32* and let the car back down to idle, it showed 18* initial timing. Is that right? thanks for the patience.. i dont know why i cant understand this, i get almost, everything else... :af:
Yes, you're on the right track! Don't worry about any fine tuning at this point. The above will keep you busy for the afternoon! Devon
what kind of tach should i use for this? http://www.oreillyauto.com/site/c/d...=Search_N0531_1319048_3100&pt=N0531&ppt=C0134 dash style hard wired or http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html digital, wireless any insight on this? Yesterday, when i set the distributor to 32* and let the car back down to idle, it showed 18* initial timing. Is that right?
