Vintage Mustang Forums banner
1 - 20 of 26 Posts

·
Registered
Joined
·
834 Posts
Discussion Starter · #1 ·
Hi friends

I achieved the following results ::::


I set my Initial back to 6 degrees. But I could not set the initial with the Diizy vac advance hose plugged it would just stall. I ran a curve test on the timing. The numbers are a bit shaky. Cuz RPMS that high scared me.

750 .... 6 D

1000 ... 26 D

1500.... 30 D

2000 ... 40 D

2500....42 D

3000.....50 D



My hand vac pump seal failed,..... its useless. I used the human suction method and could get the hose end in my mouth to seal heavy against my inner lip and stay there indefinitely.

So is a high advance such as the 50 degrees..... an example of a great deal of travel in the distributor plate? Should I change the small spring to a harder spring ...and that would drop the vac advance degrees to a guess of 30 degrees @ 3000 rpms.? I searching for better than current MPG of 10 mpg careful urban driving.

Much thanks
 

·
Premium Member
Joined
·
14,237 Posts
“……. But I could not set the initial with the Diizy vac advance hose plugged it would just stall.
^^^^^^ this is where you should stop and not proceed until resolved. Once a proper initial timing can be set as per the usual procedure, ie with the advance line plugged, then you can determine how much advance is too much with certainty.

Is 50 degrees too much on highway with low or no load engine ? No it is not, as long there is no pinging.

Z
 

·
Premium Member
Joined
·
5,479 Posts
50 sounds a bit high. Have you confirmed that your balancer has not rotated and that your pointer is at 0 degrees with you engine at TDC.
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #4 ·
50 sounds a bit high. Have you confirmed that your balancer has not rotated and that your pointer is at 0 degrees with you engine at TDC.
The timing marks engraved on the Crank show me my timing cover pointer sits at 6 degrees TDC . My rotor points to No 1 spark wire at cap. Yah its fine,
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #5 ·
^^^^^^ this is where you should stop and not proceed until resolved. Once a proper initial timing can be set as per the usual procedure, ie with the advance line plugged, then you can determine how much advance is too much with certainty.

Is 50 degrees too much on highway with low or no load engine ? No it is not, as long there is no pinging.

Z
hi Z Im pulling vacuum from the holley. Can you send a net link to try to troubleshoot?

thx
LAwrence
 

·
Premium Member
Joined
·
14,237 Posts
hi Z Im pulling vacuum from the holley. Can you send a net link to try to troubleshoot?

thx
LAwrence
Are you caping off the carb vacuum port ?

Alternatively you should be able to put a vacuum gauge on the manifold vacuum and roughy time the car for highest achieved vacuum reading. If the engine pings under a load then retard the timing .

In my opinion, the rotor pointing at the number 1 distributor wire is not really a precise measurement. You’ll need a piston stop to get a good idea of the exact TDC.

Z
 

·
Registered
Joined
·
1,656 Posts
Here are the factory specs for a 289 4V and a Boss 302. The graph of the left shows the total advance of mechanical and 10" of vacuum. The one on the right the advance as a function of vacuum. In other words, the curve on the left for the 289 4V would advance another ~9 deg if the vacuum increased to 20" Hg. Note that there's quite a bit of tolerance on these factory specs.

As you can see, 50 deg advance is not remarkable, as long as the vacuum is high and consequently the engine load is low.

If your engine doesn't run with the vacuum advance removed, something is wrong. Maybe the mechanical ignition timing is retarded and the vacuum advance compensates for it. You could take of the distributor cap, set the crank at 10 deg BTDC and check if the points just open or (in case of electronic ignition), if the sensor aligns with the toothed wheel. Then check again.

Also, I understand you revved it up with the vacuum advance attached? That is really not a good method, since vacuum will be really high when just revving it up. My advice: gett the engine to run with mechanical advance only, check the advance at various engine speeds, get your vacuum pump to work (or get another one) and check the advance at various vacuum settings (remember to distract the mechanical advance at the engine speed you're checking the vacuum advance). Then plot the results in a graph like below.

803535
803536
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #8 ·
Are you caping off the carb vacuum port ?

Alternatively you should be able to put a vacuum gauge on the manifold vacuum and roughy time the car for highest achieved vacuum reading. If the engine pings under a load then retard the timing .

In my opinion, the rotor pointing at the number 1 distributor wire is not really a precise measurement. You’ll need a piston stop to get a good idea of the exact TDC.

Z
No cap on carb port. Car stalls immediately when pulled from carb. I just gave up. What do you think?
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #9 ·
Here are the factory specs for a 289 4V and a Boss 302. The graph of the left shows the total advance of mechanical and 10" of vacuum. The one on the right the advance as a function of vacuum. In other words, the curve on the left for the 289 4V would advance another ~9 deg if the vacuum increased to 20" Hg. Note that there's quite a bit of tolerance on these factory specs.

As you can see, 50 deg advance is not remarkable, as long as the vacuum is high and consequently the engine load is low.

If your engine doesn't run with the vacuum advance removed, something is wrong. Maybe the mechanical ignition timing is retarded and the vacuum advance compensates for it. You could take of the distributor cap, set the crank at 10 deg BTDC and check if the points just open or (in case of electronic ignition), if the sensor aligns with the toothed wheel. Then check again.

Also, I understand you revved it up with the vacuum advance attached? That is really not a good method, since vacuum will be really high when just revving it up. My advice: gett the engine to run with mechanical advance only, check the advance at various engine speeds, get your vacuum pump to work (or get another one) and check the advance at various vacuum settings (remember to distract the mechanical advance at the engine speed you're checking the vacuum advance). Then plot the results in a graph like below.

View attachment 803535 View attachment 803536


Thanks I posted my results in my first post. as above. Vac advance pump works to hold with no leaks.
 

·
Premium Member
Joined
·
14,237 Posts
No cap on carb port. Car stalls immediately when pulled from carb. I just gave up. What do you think?
you need to cap the vacuum port on the carb before trying to time the engine. It sounds like you are not doing that.

ie, the vacuum advance unit is disconnected when setting the initial timing.

Z
 

·
Registered
Joined
·
79 Posts
Hi friends

I achieved the following results ::::


I set my Initial back to 6 degrees. This is typically too low, 12-16 is typical, ported vacuum provides 0 degrees advance at idle. But I could not set the initial with the Diizy vac advance hose plugged it would just stall. Check to see if your running ported vacuum or manifold vacuum. As others suggested attach a vacuum gauge to a manifold vacuum source and let us know what you get at idle after you fix the ported/manifold vacuum issue. I ran a curve test on the timing. The numbers are a bit shaky. Cuz RPMS that high scared me.

750 .... 6 D

1000 ... 26 D

1500.... 30 D

2000 ... 40 D

2500....42 D

3000.....50 D

As others have stated these numbers are not necessarily bad we dont know that much about your engine either.
My hand vac pump seal failed,..... its useless. Is it broken or not you say it is but then state in a previous comment that its working. This doesn’t make sense. Or maybe im just confused. I used the human suction method and could get the hose end in my mouth to seal heavy against my inner lip and stay there indefinitely.

So is a high advance such as the 50 degrees..... an example of a great deal of travel in the distributor plate? Should I change the small spring to a harder spring ...and that would drop the vac advance degrees to a guess of 30 degrees @ 3000 rpms.? I searching for better than current MPG of 10 mpg careful urban driving.

Much thanks
Additionally I agree that you should get a piston stop and verify TDC. Assuming you have an OEM timing chain cover the pointer should be in the correct spot to meet with a balancer where the TDC mark is in the right spot. The harmonic balancer needs to be checked. To do this insert a piston stop into the #1 spark plug cylinder and rotate the crank BY HAND until the piston touches the piston stop. Draw a line on the balancer where the pointer lines up. Then turn the crank the other way BY HAND until the piston touches the piston stop. Once again draw a line on the balancer where the pointer lines up. Directly in the middle of the two lines you drew is actually TDC assuming that you always look at the pointer from the same angle. If this lines up with the TDC mark on the balancer then you are go to go. If it doesn’t id take a closer look at the rubber holding the balancer together if its cracked and worn buy a new one and repeat the process. A new balancer isn’t always marked correctly out of the box. But as long as the rubber is good you could add a new permanent TDC mark.
Additionally its a good check (assuming your TDC mark is in the right spot) to line the balacer up for the initial timing that you want, say 6 deg with the pointer and see where the rotor is in relation to the #1 spark plug however this is not optimal reading due to tolerance stack up. A timing light is required to REPORT timing properly. To set timing use a vacuum gage. Additionally if your worried about MPG then you should tune the carb as well. Note that before adjusting initial timing your points should be gaped properly.
Hope this helps.
 

·
Registered
Joined
·
79 Posts
since the engine doesn’t run with the vacuum disconnected, it’s possible that the throttle blades are too far open to block the ported vacuum port, maybe to compensate for the late ignition timing
This is true but im also thinking that he’s running manifold vacuum not ported. The idle speed should be checked and so should the position of the throttle blades. I typically try to role out the easy stuff first before the more time consuming things. It’s easier to determine what type of vacuum source he’s pulling from first. Additionally this is a better route to go as it teaches you how to diagnose problems in a logical order. He might as well check for vacuum leaks, check the use a dwell meter, tune the carb and ensure the choke is working properly these things all play a role in good gas mileage.
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #14 ·
you need to cap the vacuum port on the carb before trying to time the engine. It sounds like you are not doing that.

ie, the vacuum advance unit is disconnected when setting the initial timing.

Z
Maybe I have the Vac line hooked up with a advance position that is to low, so when the hose is pulled it stalls. Not sure I completely understand yet. But I will leave it hooked up. Advance the timing while running to about 18 tdc, then pull the hose to see if a higher idle will keep me running. If so I will plug both and tune to max Rpms/ Vacuum on the vac gauge. will try this weekend

then as I read other blogs ... looks like you set max timing with the hose disconnected also.
 

·
Registered
Joined
·
79 Posts
Maybe I have the Vac line hooked up with a advance position that is to low, so when the hose is pulled it stalls. This is true. The issue is that ported vacuum provides no advance at idle vacuum is 0. This assumes that the idle speed is slow enough such that the throttle blades are in the correct position. A manifold vacuum source will provide vacuum at idle adding timing. Not sure I completely understand yet. But I will leave it hooked up. You need to solve this first before to continue. Advance the timing while running to about 18 tdc, then pull the hose to see if a higher idle will keep me running. You can try this but it’s really beneficial to understand your setup first. If so I will plug both and tune to max Rpms/ Vacuum on the vac gauge. will try this weekend

then as I read other blogs ... looks like you set max timing with the hose disconnected also. You set the idle advance with vacuum disconnected if is a auto you also put it in drive then set initial. From there you can determine what the timing is set at various points with in your engines RPM range. Then you can use a vacuum gun to apply controlled vacuum to the distributor at various RPM’s to see how the vacuum modulator is working in conjunction with mechanical advance. At the same time with a vacuum gage connected to the engine you determine how much vacuum your engine produces at various RPM with this information you can proceed with making changes.
 

·
Premium Member
Joined
·
14,237 Posts
Maybe I have the Vac line hooked up with a advance position that is to low, so when the hose is pulled it stalls. Not sure I completely understand yet…….”
You need to disconnect the line to the vacuum advance unit & plug the vacuum port on the carb before starting the engine.

Then you can start the timing procedure.

If the engine won’t start in that configuration then find out why. Usually a non start condition will be either be a vacuum leak or poor timing. Or both.

Z
 

·
Registered
Joined
·
79 Posts
You need to disconnect the line to the vacuum advance unit & plug the vacuum port on the carb before starting the engine.

Then you can start the timing procedure.

If the engine won’t start in that configuration then find out why. Usually a non start condition will be either be a vacuum leak or poor timing. Or both.

Z
Agreed but we still don’t know if he’s running ported or manifold vacuum…
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #18 ·
You need to disconnect the line to the vacuum advance unit & plug the vacuum port on the carb before starting the engine.

Then you can start the timing procedure.

If the engine won’t start in that configuration then find out why. Usually a non start condition will be either be a vacuum leak or poor timing. Or both.

Z
Thanks Z

I will try to do the start with out the hose to the carb. BuT i don't think it will start. / catch.

Do I set max timing using my light with the hose disconnected and plugged?

for others commenting. Its An all original engine. 289 4v holley.
 

·
Registered
Joined
·
834 Posts
Discussion Starter · #19 ·
You need to disconnect the line to the vacuum advance unit & plug the vacuum port on the carb before starting the engine.

Then you can start the timing procedure.

If the engine won’t start in that configuration then find out why. Usually a non start condition will be either be a vacuum leak or poor timing. Or both.

Z
Okay one big point. If I set the intial at 10 ish and plug the hose. no blog on the internet tell me how to set the STOP POINT on the high end of the degrees. The engine will take as much advance rotation at it wants.............. my only control i is crack the dizzy and change those little springs? wait the allen wrench in the nipple . ..........?
 

·
Registered
Joined
·
79 Posts
Okay one big point. If I set the intial at 10 ish and plug the hose. no blog on the internet tell me how to set the STOP POINT on the high end of the degrees. The engine will take as much advance rotation at it wants.............. my only control i is crack the dizzy and change those little springs? wait the allen wrench in the nipple . ..........?
Are you reading what we posted here or just other forms on the internet? Additionally yes changing the springs for the mechanical advance limits your timing on the high end additionally it effects how fast the timing changes due to an increase in RPM. The allen in the vacuum advance only works for some of the new vacuum advance canisters. The old ones are set differently I believe. If the engine is stock your timing should not change no matter if the vacuum line is connected to the distributor or not. If you unplug if from the distributor you should plug the line do you don’t have a vacuum leak. This vacuum leak also shouldn’t occur at idle because it should be connected to a ported vacuum source.
 
1 - 20 of 26 Posts
Top