More Engine Discovery... New Timing Numbers!

[Anonymous]

So I tweaked on the engine some today...

I installed the correct PCV valve, and put in a new set of plugs (BOSCH Platinum) without changing the gap on them. I had them set to .50 before... running MSD 6 and DII dizzy...

These two things did wonders for the idle... it idles much smoother with the plugs at a smaller gap.

But, I am still only pulling 12 inches of vacume with this 270 cam, and Schnieder says I should be getting 16 inches at 700 rpms... I am getting 12 inches at 900 rpms... drop it to 700 and I only get around 10 inches.

I did not have the timing light today, so I did not adjust the idle or timing at all?

I changed the intake gaskets and header gaskets and have no leaks that I can find, I hope not anyway, I have changed them twice now.
The gauge and the idle are steady at 900 now, no surging?


The engine still runs hot when warm and cold when cold?


I am going to start calling around looking for a mechanic who knows Holley carbs and see if I can get some help on this one, too long now with the exact same problem and no discoveries.

 

[Anonymous]

My aforementioned Pontiac had low engine vacuum and an overheating tendency, as well as deiseling. It was pulling only about 10" of vacuum at idle. Messing with the vacuum advance can, and placing it on a manifold source improved the vacuum to 15"+, and I was able to reduce the idle speed.

 

[Anonymous]

The problem I have with using manifold vacume as opposed to the ported source is on the highway I have no power and the car shudders if I am hooked to manifold vacume, and I also have no throttle response at low speeds, I tried this and it was in some ways better, and in others not so good...

it may be that I need to change the distributor to run with manifold vacume or I need to look into running with no vacume advance at all?

dazed and confused again?

 

[BIGREDRASA]

I know you've had initial timing all over the place. What is your current setting? You still exhibit the classic symptoms of retarded timing. One thing to look at is to advance the initial timing, while increasing the spring tension on the vacuum canister to reduce the advance, and increase the size of your centrifugal advance springs, to also delay advance. As always, change one thing at a time. Many parts stores carry the differnt springs. Mark them, take lots of notes, take pics.
If you can get your hands on a vacuum pump, you can see how many degrees advance you get at the different vacuum levels. For starters, try advancing a couple of degrees, and screwing in the vacuum advance adjuctment 1/2 turn at a time.

 

[Anonymous]

I have an old Vette with a stock dual point distributor and no vacuum advance, and it runs fine. But vacuum advance would offer the benefit of better part throttle acceleration, fuel economy and probably a lower idle speed. Lack of vacuum advance is a compromise, because you can dial in only that amount of advance just shy of detonation at a particular rpm. Vacuum advance is load sensitive and can be tuned to maximize economy and performance in conjunction with engine speed. The only reason I can see that manifold sources would not work better than ported sources is if the distributor is over-advancing the timing. Emission era Distributors used more vacuum advance and less centrifugal advance than non emission distributors. Combined with ported sources, this allowed them to retard timing at idle. While cruising steady, the ported source and the emisision distributor provides good advance for economy. But, when you step into the throttle, the vac advance falls. Since the emissions era distributors have less centrifugal advance, timing is even lower and acceleration is doggy. Your problem could be in the timing curves of the distributor.
Have you tried the ported vs manifold source since you replaced the gaskets?

 

[Anonymous]

As Tony S states, a vacuum pump is handy. I plug the vacuum hose to the distributor and hook up a mityvac pump. Then with the engine idling, start increasing the vacuum and see what effect it has on the timing. As he said, make notes.

 

[Junk-Falcon]

it sounds like

 

[Anonymous]

I do have a vacume pump... I can do that tomorrow, I will pick up the timing light in the morning, my brother has it.

I will go through this step by step...
plug the line on the carb, hook the pump up to the advance...
with the engine at idle, mark the timing, draw the vacume with the pump and see A. How much draws... B. How far the timing advances. Correct?

I do have Full Roller rockers, completely adjustable. I am changing the valve cover gasket this weekend, I need to shave it to fit the intake runners on the Aussie head.. I did not do that, and it is leaking into the runners... I need to pull it, cut it, install a new gasket and seal it.

I can check the valves when the cover is off.

 

[Lazy JW]

I agree with Tony, those are symptoms of slow timing. I would aproach this one in steps. First, temporarily unhook the vacuum advance, then recurve the mechanical advance for best performance. Do this by playing with the timing until it idles well at good vacuum. Then adjust the timing for full throttle, high speed timing. This will probably be a different setting than the best idle setting. Then find out how much advance the centrifugal advance is delivering, and at what rpm it is all the way advanced. After finding the best idle setting and the best power setting, you know how much advance you need, now modify the advance curve to give you that much advance, set it for the best idle timing, and it should run much better. Then you can add the vacuum advance back in to the system, and tailor it to give best part throttle/cruise economy. This will all take a while, as you have a non-stock setup and apparently need a custom timing curve. The mechanical advance may need to be limited to allow a more advanced idle timing without exceeding the maximum advance setting. This may require welding or brazing a physical stop inside the distributor, but isn't really all that difficult, then the springs can be altered to suit. Ah, this brings back old memories of my motorhead days in the Seventies 8)
Joe

 

[Anonymous]

Check the vacuum advance at 1/2" to 1" increments. It will start coming advancing the timing at maybe 5" and be fully advanced at 10". The numbers depend on the particular vacuum can and whether or not it is working properly. You might even find that your cannister is able to advance the timing at vacuum levels higher than what your engine is currently pulling, eg 13 or 14" before it is fully advanced. If this is the case, it leads to unstable idle problems. If you have a straight nipple into the vac can, you may be able to adjust the tension on the spring. It will change when the vacuum can begins and finishes the advance. On some cannisters, it will also change the amount of vac advance that it delivers. With the vac hose disconnected, read the total timing at increments of 500 rpm up to about 3000 rpm. All of the centrifugal timing should be advanced by then. At the 3000 rpm, you'll want something on the order of 35+ degrees of total mechanical timing (vac line plugged). If you don't get that much, check to see that the weights freely move and or replace the springs with lighter ones. At idle, with the vac line connected, you'll want 25 to 30 degrees of timing. You'll have to test drive to see how much your car can handle. You may be able to dial in more vac advance if you are not pinging.
Doug

 

[BIGREDRASA]

Doug and Joe have given you enough to chew on for a while.
I hope you have better luck than I did with my old Slant 6 '75 Dodge van. I could never get the timing where it ran well without pinging like heck. :x That's why we called her "Miss Piggy." Because pig and ping are close, and she sure was a pig when it came to performance.

 

[Anonymous]

OK, so here are the numbers I measured twice and put everything on paper so I would not mess this up.

I think my distributor needs some work.

I have a dial back timing light, I hooked the number one wire in and the battery. I hooked the tach to the MSD tach out and grounded to the block, and I ran the vacume off the intake.

Here are the initial numbers with everything plugged.
@900rpm = 10 degrees initial (off the mark on the engine, however to dial back to zero on my light only read 7 degrees not 10...)
@1500rpm = 13 degrees (dialed back to 0 on all the numbers)
@2000rpm = 16 degrees
@2500rpm = 20 degrees
I could not get a 3000rpm reading as this tach does not go beyond 2500.

here are the readings with the car in idle at 900 and pulling on the vac canister with the pump.
@2-3" inches(basically on the first mark) the reading was 12 degrees
@5" the reading was 30 degrees (jumps fast and far)
pulling till the advance stopped @10 degrees the advance was 35 total from the vacume, all numbers are minus 7 since there was 7 initial on the dial back light at zero.


Now I have not put it back together and taken the readings, it was getting really really hot, too hot to hang out over, so I am letting it sit for a bit I will get some more numbers in a while.

 

[Lazy JW]

Sounds like you have made a good start. It is important to know how far the advance goes, and at what rpm it stops advancing, so a different tach will be needed to finish mapping the distributor curve. I have always done this by marking the crank pulley as I don't own a dial-back timing light, just a basic one. I even did this on my 300. The stock timing curve turned out to be about right for my stock engine (Duh!) You want the advance to be pretty much all done by about 3000-3200rpm. If it is still advancing above that then you need some lighter advance springs. I don't like the way your vacuum can is working. Something is seriously wrong there. Hang in there, you'll get it yet
Joe

 

[MustangSix]

I'd try bumping it up a few more degrees, maybe start with an initial timing of about 14 degrees. Wouldn't hurt and the engine might run better at higher speeds. Under load, it looks like there is not enough advance at the 2000-2500 mark.

 

[gtm1086]

Hello Jimbo.

I have been following your quest to get your motor dialed in. I keep coming back to two items. a vacuum leak and timing. It sounds like your last go around you got everything sealed up nice and tight. That leaves timing. I agree with Jack. Crank that timing up to around 14 to 16 degrees to start with. Go run the car. if it doesn't ping you may want to give it a bit more. You may need to have some work done on your dizzy but you also need to make sure that the marks on your ballancer are correct. You maybe seeing 14 degrees but in reality it may only be at 10 degrees if the ballancer has slipped.

Gary

 

[Anonymous]

Those numbers sound like the numbers I was getting on my '66 Pontiac that had an emissions era HEI distributor. Too much of the advance is built into the vacuum side of things and there is not enough centrifugal advance. That explains a lot of your symptoms. At cruise above 2500 rpm, you are getting about 55 deg of total advance. The engine can usually handle that at the higher rpms. Something around 50+ is acceptable if you are not getting pinging on light throttle.

If I understand what you posted, at 2500 rpm with vacuum line plugged, you are only gettng about 20 degrees total, 13 degrees of centrifugal advance and 7 of degrees are initial timing. At cruising speed above 2500 rpm, if you stomp on the gas, the wide open throttle drops the engine vacuum, and your advance drops from 50+ deg to just 20 deg. Your engine will accelerate better with about 36 deg of advance at WOT. If you are only getting 20 deg at WOT, the engine will feel doggy. As Mustang Six notes, you can set the initial advance to 14 deg. This will give you about 27 deg at WOT and result in more zip. However, I suspect that since you have so much vacuum advance, the engine will ping under light throttle since the total advance at cruise will be over 60 deg. Maybe a ported source would correct that tendency.

I am not familiar with the Duraspark to know if the vacuum cannister is adjustable via the hex key in the nipple. I would imagine there may be different cans available just as there are for the GM products on the V-8's, but I do not know if they can be used on the 6 cyl distributors. The vacuum cans are rated in distributor degrees of advance. So a can rated at 8 deg will provide 16 deg of crankshaft advance. Your current can would have a rating of about 15 distributor deg. It took very little engine vacuum before your timing advanced. I guess that would make sense on a distributor intended to run on ported vacuum. But at anything above idle, ported vacuum and manifold vacuum are not going to be that different, at least not as far as that vacuum can is concerned since it takes very little vacuum to advance it. I do not know if it will be easy to recurve the distributor to your satisfaction without taking it to a professional or flat out replacing it. I didn't have any luck getting a new vacuum can for my Mustang's Loadamatic so I replaced the distributor. I bet if it was a Chevy, they would have the parts.

As you may have noticed when mapping the ignition with the vacuum line unplugged, the engine gets hot with retarded timing. Emissions distributors used ported vacuum to retard the spark at idle. This creates higher temps that can lead to deiseling. One of the patches they developed to combat the deiseling was the use of Anti-deiseling solenoids that made sure the throttle plates closed all of the way when the engine shut down. I remember my 73 Comet having all kinds of solenoids piled onto that little 1 BBL carb.
Doug

 

[Anonymous]

Sounds like I am closer to finding a solution.


It may also be possible the distributor is one tooth off, because right now as it sits the engine is set to 7 degrees initial, and the advance can is hitting the oil stick, I can move it closer to the engine, but I should probably either pull the distributor (which I do not want to do) or rotate the wires around one position so I can get more room to play.

which direction do I need to rotate the wires to bring the advance back away from the engine, do I move them closkwise or counterclockwise. I think they would all be moved counterclockwise. Am I correct?

I am going to advance it first to 14 and see if I can find some allen wrench adjustment on the advance.... this distributor is a new AutoZone DII dizzy that was pulled from a 79 Fairmont 3.3L so your ideas on the emissions distributor could be right on.

I also have all of the symptoms you described at highway speeds, on light throttle the car rocks... if you give it some gas it will go, but it feels like it is skipping a beat there, and under medium throttle once the engine passes 2500 things buck (too much advance coming in past that point). I have been limited by this engine since it went back in the car to a ceiling of 3000 rpms and I have to cruise around 2000-2200 rpms.

What I need to do is dial in more initial. And drop the vacume advance so it comes in more like 20-25 instead of 30-35.... if the initial was like 14-16 that would give me 25-30 plus the addes 20-25 for totals at 2500-3000 of 45-50 (instead of 50-55)... and try that.

Because what happened yesterday was bad, running on the highway it gets too warm, then when you come off the highway and sit it is retarded and gets even hotter... it cannot cool itself down unless you run just the right load at 1800-2000 rpms for five or more minutes. It was only 77 degrees yesterday, not the 98 it will be in two months.

 

[MustangSix]

One thing at a time. Just advance it first to see what effect that has. Then adjust the vacuum. Doing both at once might not tell you which is the correct adjustment.

The heat at speeds could be caused by too little advance. At part throttle the vacuum is only going to contribute a portion of its advance and the engine is relying on the centrifugal and initial settings. 20 degrees at 2000 is not enough; you need several more.

 

[Lazy JW]

As Mustang Six said, one thing at a time. If this were mine, I wouldn't even worry about highway performance until I got it to idle correctly. You gotta learn to walk before you can run. You have low vacuum at idle because the throttle is open too far. The throttle is open too far because it won't idle with the throttle closed further because the vacuum is too low for the idle circuit in the carb to work properly, and the vacuum is too low because the timing is too retarded. You may need even MORE than 14 degrees initial advance to be able to get the throttle closed enough for the idle circuits to work. I would verify the timing marks on the crank pulley first, then work up from there. Get it to idle well, then find out where the upper advance goes WITHOUT the vacuum, it can be added in later after the rest is taken care of. Have fun,
Joe

 

[Anonymous]

You are right about the idle situation, and I agree that I need to sort that out first... I am going to work with it this afternoon...

But 90% of my driving time with this car is on the highway at speeds of 75-85 mph... and I have to be concerned about my ability to run and walk.


For now I am going to work on advancing the engine, I think 14 is a good place to start... see if I can handle more.

I will post the results here later today!

Jimbo