Timing Question - Vintage Mustang Forums
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post #1 of 24 (permalink) Old 09-19-2019, 07:24 PM Thread Starter
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Timing Question

I'm in the middle of trying to tune this car (66,289,2bbl Holley,Pertronix Dist/Ign, 5 speed) and running into issues.

I'm setting the timing according to the manual (6 past TDC) with the vacuum port on the carb plugged/blocked and the distributors vacuum port open. I get it to the 6 and snug the bolt down to lock the distributor in place. I reattach the vacuum hose from the carb to the distributor and at idle the timing on balancer shoots to something wild like 30 past TDC. It doesn't stay at 6 and then move up to 21-24 with some juice.

Also the idle is no matter what 1000rpm. I cannot get it to 600-800 even with the idle speed screw almost completely out.

Any suggestions? Any way I can get some, "step 1. do such and such". Even if it requires starting completely fresh assuming everything is out of whack.
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post #2 of 24 (permalink) Old 09-19-2019, 07:47 PM
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Do you have your vacuum hose going to ported vacuum or constant vacuum? If it's constant, I would start by finding a ported vacuum source (should have one on your carb) and recheck results. If it's on ported vacuum it shouldn't change. That might also help with your idle. If it doesn't help with your idle, I would check for vacuum leaks first.
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post #3 of 24 (permalink) Old 09-19-2019, 08:02 PM Thread Starter
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Originally Posted by 1968inDenver View Post
Do you have your vacuum hose going to ported vacuum or constant vacuum? If it's constant, I would start by finding a ported vacuum source (should have one on your carb) and recheck results. If it's on ported vacuum it shouldn't change. That might also help with your idle. If it doesn't help with your idle, I would check for vacuum leaks first.
Hmmm, I'm pretty new and still learning so please bare with me. I have the hose going from the vacuum advanced port on the distributor to the timed spark vacuum port on the carburetor. Its the bottom port in the picture, as the top (most models) doesn't have a nozzle for a hose.

** no idea why this site always turn my pictures sideways? **
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post #4 of 24 (permalink) Old 09-19-2019, 08:51 PM
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Originally Posted by ipmaham View Post
Hmmm, I'm pretty new and still learning so please bare with me. I have the hose going from the vacuum advanced port on the distributor to the timed spark vacuum port on the carburetor. Its the bottom port in the picture, as the top (most models) doesn't have a nozzle for a hose.

** no idea why this site always turn my pictures sideways? **
Given its location, that's likely manifold vacuum port on the carb. That would explain why the timing moves from 6* when you hook up the vac advance canister. However, most vac canisters only advance 15* to 20* so how you end up with 30*, I don't know...except maybe with an idle at 1000RPM you're also getting some mech advance as well?? With the vac canister disconnected (and the port to the carb plugged) are you getting 6* and 1000RPM idle?
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post #5 of 24 (permalink) Old 09-19-2019, 09:05 PM
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It is quite confusing to see the Timed Spark Vacuum Port (some models) located that low in the carb base. The port above the idle mixture screw would be a more "traditional" location. It is clearly marked "Timed Spark Vacuum Port (most models)". You will need to verify that you are indeed hooked to a ported vacuum source.


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post #6 of 24 (permalink) Old 09-19-2019, 09:12 PM Thread Starter
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Originally Posted by P-51 View Post
Given its location, that's likely manifold vacuum port on the carb. That would explain why the timing moves from 6* when you hook up the vac advance canister. However, most vac canisters only advance 15* to 20* so how you end up with 30*, I don't know...except maybe with an idle at 1000RPM you're also getting some mech advance as well?? With the vac canister disconnected (and the port to the carb plugged) are you getting 6* and 1000RPM idle?
Hmm, I'm 99% positive it is the correct "timed spark vacuum port" and not the manifold vacuum port. As you can see in these pictures the manifold vacuum port is tucked even further under the carb (just wasn't visible in the other pictures).
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post #7 of 24 (permalink) Old 09-19-2019, 09:17 PM Thread Starter
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Originally Posted by rhutt View Post
It is quite confusing to see the Timed Spark Vacuum Port (some models) located that low in the carb base. The port above the idle mixture screw would be a more "traditional" location. It is clearly marked "Timed Spark Vacuum Port (most models)". You will need to verify that you are indeed hooked to a ported vacuum source.
I would buy an adapter to connect a hose on to and try that port, but unfortunately it is completely sealed. It's just a closed off and unused port
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post #8 of 24 (permalink) Old 09-19-2019, 09:20 PM
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Any way I can get some, "step 1. do such and such"...
Steps
(1) Make sure the timing mark on the balancer is correct. Best way to find if TDC is marked correctly is to get a piston stop. Unhook the battery. Put the piston stop in cylinder #1. Rotate clockwise by hand until stop. Mark balancer. Rotate counterclockwise by hand till stop. Mark the balancer. TDC should be midway between those two marks. Or you can get a quick idea if TDC is marked right by taking the spark plug out of the cylinder #1. Put a screwdriver in the spark plug hole and rotate by hand. Watch the screwdriver rise/fall... it will "dwell" at the TDC, so midway between the screwdriver stop rising and start falling should ~TDC on the balancer.
(2) Plug the vac port on the carb. Start the engine and set the initial timing (with the RPM ~750 or lower... you don't want the mech advance engaged at idle). Per the manual initial is 6* but, really, most people put it at 10* - 14* initial. Never understood why the manual says 6*... may have been an emissions thing(?)
(3) If you are getting a 1000RPM idle with the setup above, it is usually because of too much air (?). Could be the throttle butterflies are not closed enough. Or you may have a vacuum leak.
(4) Assuming you get #3 under control and the car idling ~750RPM, then hook up the vac advance canister (to manifold per your carb) to see how much more advance you get. At that point the idle RPM will increase and you should be able to close the butterflies some more to again get it down to ~750RPM where the mech advance is (usually) not engaged yet
(5) If the vac advance is advancing more than ~15* (which is sorta a standard setting) you can take an allen wrench, put it down the "snout" of the vac advance canister and turn it (which way?) to increase/decrease the amount of advance.
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post #9 of 24 (permalink) Old 09-19-2019, 09:27 PM
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Originally Posted by ipmaham View Post
Hmm, I'm 99% positive it is the correct "timed spark vacuum port" and not the manifold vacuum port. As you can see in these pictures the manifold vacuum port is tucked even further under the carb (just wasn't visible in the other pictures).
One way to tell... when the car is idling with the throttle completely closed, put you finger over the port. If you have suction it's manifold (below the throttle plates). If not it is likely "ported" (above the throttle plates). I am **assuming** that "timed" is the same thing as "ported" (??)
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post #10 of 24 (permalink) Old 09-19-2019, 09:36 PM Thread Starter
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Originally Posted by P-51 View Post
Steps
(1) Make sure the timing mark on the balancer is correct. Best way to find if TDC is marked correctly is to get a piston stop. Unhook the battery. Put the piston stop in cylinder #1. Rotate clockwise by hand until stop. Mark balancer. Rotate counterclockwise by hand till stop. Mark the balancer. TDC should be midway between those two marks. Or you can get a quick idea if TDC is marked right by taking the spark plug out of the cylinder #1. Put a screwdriver in the spark plug hole and rotate by hand. Watch the screwdriver rise/fall... it will "dwell" at the TDC, so midway between the screwdriver stop rising and start falling should ~TDC on the balancer.
(2) Plug the vac port on the carb. Start the engine and set the initial timing (with the RPM ~750 or lower... you don't want the mech advance engaged at idle). Per the manual initial is 6* but, really, most people put it at 10* - 14* initial. Never understood why the manual says 6*... may have been an emissions thing(?)
(3) If you are getting a 1000RPM idle with the setup above, it is usually because of too much air (?). Could be the throttle butterflies are not closed enough. Or you may have a vacuum leak.
(4) Assuming you get #3 under control and the car idling ~750RPM, then hook up the vac advance canister (to manifold per your carb) to see how much more advance you get. At that point the idle RPM will increase and you should be able to close the butterflies some more to again get it down to ~750RPM where the mech advance is (usually) not engaged yet
(5) If the vac advance is advancing more than ~15* (which is sorta a standard setting) you can take an allen wrench, put it down the "snout" of the vac advance canister and turn it (which way?) to increase/decrease the amount of advance.
1. As of right now I am sure TDC is correct. I was able to identify the piston was at it's highest position before coming down in cylinder 1
2. Got it, I'll shoot for 10-14.
3. Yeah, no matter what I cannot get the idle to go below 950rpm. I'll try to adjust the throttle butterflies a bit more. It's typically a #2 pencils diameter right? I'll also check for vacuum leaks (spraying carb cleaner around the carb and hoses will boost the rpm indicating a leak right?).
4. What do you mean by the vacuum advance canister? The "timed spark vacuum port" on the carburetor?
5. Didn't even know that is possible (if the "canister" is the timed spark vacuum port".

Thanks for the suggestions.
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post #11 of 24 (permalink) Old 09-19-2019, 09:40 PM Thread Starter
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Originally Posted by P-51 View Post
One way to tell... when the car is idling with the throttle completely closed, put you finger over the port. If you have suction it's manifold (below the throttle plates). If not it is likely "ported" (above the throttle plates). I am **assuming** that "timed" is the same thing as "ported" (??)
There is def. suction coming from that hose off of the carburetor when idling and the throttle is completely closed.
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post #12 of 24 (permalink) Old 09-19-2019, 10:28 PM
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1. As of right now I am sure TDC is correct. I was able to identify the piston was at it's highest position before coming down in cylinder 1
2. Got it, I'll shoot for 10-14.
3. Yeah, no matter what I cannot get the idle to go below 950rpm. I'll try to adjust the throttle butterflies a bit more. It's typically a #2 pencils diameter right? I'll also check for vacuum leaks (spraying carb cleaner around the carb and hoses will boost the rpm indicating a leak right?).
4. What do you mean by the vacuum advance canister? The "timed spark vacuum port" on the carburetor?
5. Didn't even know that is possible (if the "canister" is the timed spark vacuum port".

Thanks for the suggestions.
#3. I'm not sure what you mean by a #2 pencil diameter... is that the spacing between the butterfly and bore? At idle when looking down the throttle bore, the butterflies (I'm not talking about the choke plate) should basically "look" completely closed. There will be a just very slight crack between the throttle plates and the bore... nothing like a pencil diameter at all. Not even close. If you've got that much space between the butterflies and the bore at idle, that is probably your problem.
Yes spraying carb cleaner around does the trick most times (you can also use propane which is a bit safer). If you are using carb cleaner it is better if the engine is cold/cool... and have a fire extinguisher handy... carb cleaner is very flammable. Visual checking for cracks in hoses and plugs is also an easy way to find problems. Take the hose/plug (eg cap on a vacuum port of the carb) off, squeeze it with your fingers and if you see cracks in the rubber then replace it.

#4. The vacuum advance canister is that metal "thingy" on your distributor... the one the vacuum line from the carb hooks to. If this is hooked to manifold vac (which I think your's is), when you are idling or driving under very light load, the throttle plates are pretty much closed, the vacuum is high, and the "vacuum canister" on the distributor causes the spark from the distributor to advance (= fires earlier) which is what you want under light loads with a lean air/fuel mixture.

$5. #4 above probably clears up the confusion. The "snout" I'm talking about is the port where the vacuum line attaches on the canister, not the carb.

Last edited by P-51; 09-19-2019 at 10:32 PM.
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post #13 of 24 (permalink) Old 09-19-2019, 10:42 PM
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One other thought... when setting the idle speed the car ideally should be already warmed up and the choke should be fully opened. If you are doing all this analysis on a cold engine it could be that the "fast idle" is engaged and that *may* be why you're seeing ~1000RPM. The fast idle idles up at ~1200RPM or so. The idea is that when the car engine is cold you want to run the engine at a high idle speed to warm it up. Usually tapping on the accelerator will take it off of "fast idle" to normal idle even when the engine is cold.
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post #14 of 24 (permalink) Old 09-19-2019, 10:45 PM
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a. For a '66 289-2V without Thermactor emissions, factory timing spec was 6* BEFORE TDC, not after.

b. IIRC, curb idle for manual transmission, in neutral, is something like 625 rpm. If you can't adjust down to that figure, with timing set to spec, then look for binding of the throttle plates, sticking or maladjusted choke fast idle cam, or a vacuum leak.

Better yet, toss a vacuum gauge on a manifold vacuum source and tell us what the needle says...

FWIW, with the initial timing set to 6* BTDC, and with manifold vacuum for your vacuum advance, you'd be seeing the timing swing to around 28* BTDC.
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post #15 of 24 (permalink) Old 09-19-2019, 10:46 PM
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One more random thought... since you are using the "timed port", make sure the other "manifold port" is capped off. If not, that would be a big vacuum leak (sorry, if that's obvious).
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