Played around with the distributor/carb/vacuum lines the past 2 days. My vacuum hoses were routed as in the 71 Chassis Manual pg 67-12. Went to pull the hose off the distributor to set the timing and there wasn't enough vacuum to lift a tissue. Based on what I've read on this forum, not good. Then took the hose off the left side of the fuel filter (facing the engine) and what a difference. Used that to the distrubutor, set the timing at 10 BTDC. Took the car for a spin and after all these years it felt like a different car! Went out later in the day and it gave me some grief starting. Went to a car show last night and it would not start! Hard to rely on the old screwdriver in the carb to get it running. Today again it will not start unless I route the vacuum hoses to their original paths... What the heck is going on??? I'm no expert with this which is why I always left well enough alone. But that burst yesterday was great...
sounds like your vac advance was on the ported vacuum side (drivers side) originally, and thus would not see any vacuum at idle. When you moved it to the passenger side of the carb you put it on manifold vacuum, ie vacuum all the time. The ported vacuum side would only see vacuum when youre slightly off idle, enough to expose the port to vacuum. It may be a bit more responsive when on the manifold vacuum side, but I dont think as much as youre indicating, normally. you hooked to the left side of the filter but high side or low? The lower has to go to the vacuum break. If you disconnect that your car will feel snappier because the air flaps fly open in no time. But it aint right. Youll get bog issues etc.
It was on the high side and really had a snappy feel to it, but not wanting to start made me switch everything back...
hi side is good. but if you had the hose hooked there while the motor was running and THEN set your timing to 10 BTDC then your timing without vac advance will be waay off. That could cause your hard start. I would disconnect the vacuum advance. cap the vacuum ports. reset timing to 10 deg BTDC with the vacuum advance disconnected. reconnect the vac advance to the Manifold vacuum port, hi side passenger side. adjust idle rpm.
I take my 71 350-4 off the upper passenger side, no starting issues what so ever. Factory timing was 6*BTC not 10* in 71 fyi. I think I have mine set at 7.5* and all in by 31*, maybe 32*.ou:
Factory was 4* BTDC for an auto, 6* for manual, however, you'll notice an impressive improvement in throttle response and low end power at about 12* BTDC. 10 works ok, but mine always runs best at 12 to 14. These engines are low on compression and can handle a lot of timing. With the dist. giving 14 to 18 degrees centifugal advance ( the stock spec for '71), and 14* initial you'd be at most 32* total, which could actually be a little higher. Try it, you'll like it.:TU:
I have a theory that your "cranking vacuum" may be enough to advance the dist. so much that the timing is too advanced to start well. To test this remove the vacuum line from the canister and plug it then try starting it... I think that is your issue here. Second I am not surprised that the car feels better with manifold vacuum since it adds timing from idle and this helps your engine get revving up quick. I do not like having extra timing at idle. In my opinion running the vaccum advance off a "ported" source is the way to go. However I get all my mechanical avdance to come in nice and quick which will give you back the power you now have. I do this by changing to lighter springs in the mechanical advance so that I can set dist for 12 degrees initial and all the 20 degrees of mechanical is all in by 2200 rpms. On top of my 32-34 degrees of total timing I also have 10 degrees of vacuum advance using a customized crane adjustable vacuum advance. When I floor the gas the vacuum advance goes away and I have the perfect amount of timing to make max power without over timing the engine. I REALLY strongly suggest getting a "crane cams" vacuum advance canister that can be adjusted for sensitivity using an allen key. Read the "power timing" thread in the FAQ section and you will be filled in on the details: http://www.v8buick.com/showthread.php?t=63475 Also read this so you understand a bit about the different types of vacuum.
The only real difference between using a manifold vacuum source vs a ported source is that timing is added at idle and on decelleration using a source below the throttle plates (full manifold), and added only at light throttle cruise with a source above the throttle plates (ported). The Q-jet uses a very accurately positioned ported vacuum source, which supplies FULL engine vacuum to the advance right off idle. Keep in mind that the amount of vacuum under the throttle plates is the same at any given location, so there is no performance improvement anyplace choosing a manifold vacuum source over a ported one. Also keep in mind here that many carburetors have ported sources designed for EGR operation, that have a late/weak signal, and even a bleed off port to limit the amount of vacuum at increased throttle openings. IF you choose to use a ported source to the vacuum advance unit, it MUST be designed for that purpose, and supply FULL engine vacuum at the slightest movement of the throttle off idle. With all the good information out there, folks still believe that using a manifold source helps power, throttle response, fuel economy, etc. I've even read posts where folks claim that going from idle instantly to FULL throttle is greatly improved once they switched from a ported to manifold vacuum source.....even though the engine vacuum is at ZERO when this occurs!ou: This topic gets kicked around frequently on several Forums. There is even a pretty long read from a "guru" that keeps getting regurgitated again and again. The info in that read is OK, but has several MAJOR flaws and is somewhat miss-leading, etc. In any case, for this particular thread, I would recomend using the correct factory located ported source to operate your distributors vacuum advance unit. If you want to try to improve engine performance/efficiency with spark timing, try moving the base setting ahead a few degrees, and maybe a slightly faster mechanical advance curve. The engine will tell you when it doesn't like the changes, be either difficult hard restarts (too much base timing), or detonation (pinging under load). Detonation at very light throttle openings indicates too much total advance from the base timing plus mechanical timing plus vacuum advance. Detonation at heavy/full throttle openings indicates too much timing from the base setting plus mechanical advance only. As mentioned above, the vacuum unit adds NOTHING at heavy/full throttle openings, as this basically equalizes the pressure(s) above and below the throttle plates. A word of caution with light distributor springs and aftermarket distributor recurve "kits". Most are pure JUNK, and will allow some timing in at idle speed, which causes a HUGE drop in engine rpms when the trans is placed in gear, or slight load placed on the engine. With the HEI distributor, they can and will add MORE timing at high rpm's with aftermarket kits/springs, so welding in a positive stop for the advance is highly recomended (manditory IMHO). FWIW, at least 8 out of ten tech calls to my shop for idle problems are DIRECTLY related to the distributor adding timing at idle speed, then some of it falling out when the trans is placed in gear. For those of you that think you need a really quick advance curve, my Ventura uses a pump gas 455 engine with a stock HEI distributor, stock center cam, weights, springs, etc. The only mods to it are welding in a positive stop for the mechanical advance at 10 degrees (20 at the crank), and MIG welding up the vacuum unit to supply 10 additional degrees at part throttle via a ported vacuum source.:TU: I continue to see folks with relatively "mild" engine combo's trying to get all the mechanical timing in at 1500-2000rpm's. Superficially this may "feel" like an improvement, but 19 out of 20 times a curve that light adds timing at idle, that falls out when the trans is placed in gear, cause terrible idle troubles, engine slowing down, stalling, etc (sound familiar?). It is better to add timing via the vacuum unit for "normal" driving, and use a slower mechanical advance curve, all in by 2800-3500rpm's is sufficient for most "high performance" street or street/strip engine combinations. Some basic numbers that we have used over the years that most iron V-8 engines respond well to. Base timing about 8 to 14 degrees. 10-12 degrees (20-24 at the crank) from the mechanical advance, all in by about 2800 rpm's or so. 10-14 degrees additional advance from the vacuum advance unit. This provides about 40-50 degrees timing at cruise. Going beyond that with a well thought out engine combination typically results in some light spark knock, or slight missing at very light engine load. As to which source to use for the vacuum advance, in almost all cases I'll use a ported source (correctly located). Some engine combo's do OK with a manifold vacuum source, but if you know how to tune a carburetor to delivery enough fuel at idle, in almost all cases running 20, 30 or 40 degrees timing at idle is not necessary.......hope this helps some?.....Cliff
Actually , what you have discovered is the difference between the timing on a pollution engine and a non- pollution engine... ''back in the day'' the optimum factory set up was to use direct manifold vacume straight to the vac canister on the dist... basic timing was set with the vac disconnected and blocked... set up like that , the response is crisp and positive, plus the engine gets the best gas mileage that way....but the government got envolved and things went to pot.... the 3 way vac/temp switch that controlls the advance used to be laying all over the shops where mechanics had taken them off...off their personal cars...
I agree with everything Cliff R said. There will be no difference between ported and manifold vacuum sources for the vacuum advance when it comes to power and gas mileage, all else being equal. Manifold vacuum will add advance at idle and small throttle openings, and that can make a significant difference in coolant temperatures during stop and go traffic in warm weather. I always advise trying both vacuum sources to see what you like best, then go with it. The important thing to remember is that the factory used relatively heavy springs in the mechanical advance that did not allow full mechanical advance until 4000 RPM or higher. At typical cruising RPM, only part of the mecanical advance was in. The vacuum advance added another 16-20*, and the car cruised down the highway at about 40* give or take a few degrees. That resulted in the best gas mileage. When you nailed it, tyhe vacuum advance would go away, and mechanical advance would go to maximum, and you ended up with the optimal 30-34* for best WOT power. When you start modifying the mechanical advance springs, you upset all of that. You now have all your mechanical advance in at cruising RPM, and the vacuum advance results in over advance. You need to reduce the amount of vacuum advance that the canister delivers. All this is discussed in my Power Timing thread.
Gents, I certainly appreciate all the comments and input. I will try a few more things today. For all the years I've been fooling with cars nothing is more confusing to me personally than this topic. I wish I could get a better grip on this! Thanks! Jeff
Well, I wrote the Power Timing thread just for guys like you:grin: Between that and the Ignition system section in the Chassis manual, you should be able to understand it. I think what happened here is that you connected the vacuum advance unit up to manifold vacuum. This immediately advanced the timing 16* or so. You then set your timing to 10*BTDC. When you shut the engine down, vacuum went to 0, the 16* went away, which left your timing while cranking at 6* ATDC. The engine will not want to start easily with ignition timing 6* retarded.
Here's what I did Sunday. Set the timing back to the stock specs, 4* BTDC and changed all the vacuum hoses back to the factory placements as well. Car started fine and drove like it always had. Went back in again added 2* to be at 6* BTDC and changed the cannister vacuum back to manifold vacuum. I don't know what it is but this really makes the car livelier. It starts fine and runs great. Maybe it just didn't like the 10* BTDC I had it at but for now I'll leave it here. Thanks for the help! :TU:
If you have the original distributor (1112080) you can easily bump the initial timing up to 10-14*, and still have a total advance between 28 and 32*. The 350 distributors in 1971 and 72 had only 16-18* of mechanical advance. When you set your initial advance, just make sure you disconnect and plug the hose to the vacuum advance. The reason the car feels so much better is because the manifold vacuum is immediately advancing the timing. You can Power Time the car and bring the advance in sooner, and you can make an even bigger improvement. You just need to modify the vacuum advance canister.
The distributor in the car is 11120661E3... When I initially set the timing at 10* BTDC she didn't want to start, hence the start of this thread. These are all baby steps for me. Later today I will make the mark on the balancer and see what RPM all the mechanical advance is in by. So if I read your PT correctly... Set the timing to factory spec. Since I don't have a dialback, make the mark at 1 3/4", at the RPM all the mechanical advance is in (1 3/4" mark stops moving) reset the dist to 0* on the timing tab to have 30* total timing or at 2* to have 32* total timing. I think I have that right. It appears the key here is what RPM the 30* mark stops moving. If it's above 2500 RPM I need the advance kit to swap the springs. I wonder how much those 39 year old spring may have loosenend?? We'll see. Thanks Again.
I have no idea what a 1112066 distributor is. I can't find it in any of my books. Some of the 350 distributors had lighter springs from the factory, others did not. Some had all the timing in by 2900, others, at 4600. If you have the heavier springs, you will not want to rev it to 4600 RPM in your driveway. I don't recommend doing that. You must be certain that the 30* mark has stopped moving up. The only way you can be sure of that is with light springs. Another thing, be AS ACCURATE AS YOU CAN when you measure that 1 3/4" clockwise of the original mark on the balancer. Even a small error will affect your results. Make the line as thin as possible.
I got it, buy the kit and install the weakest spring to avoid revving the daylights out of it. Then work my way up from the weakest spring to something that brings it all in below 2500 RPM. Scary, I'm starting to get it. ou:
Cliff & Larry, Since reading this thread, I have gone back and installed the stiffest springs in the Mr. gasket kit (gold) in my engine, and watched my idle (in DRIVE) smooth out considerably- the idle drop from PARK to DRIVE is not as bad as it used to be, and the engine seems a lot happier. Still running 32* at WOT. Oddly, or maybe not so oddly, I decided to set the idle mixture this time while the car was in gear, and achieved a much smoother idle than I did setting the mixture while the car was in PARK (but I have an Edelbrock, and this may not apply to the Q-jet?). Maybe this is how I was supposed to be doing it??? Anyway, great thread.
