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Timing and Tuning
#1
Hey guys,
After a month of troubleshooting my mustang is running again, but the problem I have now is my tinkering. I had tuned my carb. up previous to this whole fiasco, but since then I have adjusted my timing.

Now I'm looking at a power problem I am having. The first problem is the engine runs pretty terribly when it's cold. After 5ish minutes of driving it runs a whole lot better. The second problem is I feel I'm loosing low end power. There isn't much power when I launch compared to how it used to feel before playing with the timing and ignition, but I don't feel much power loss on the high end.

I guess what I'm asking is do any of you think this problem could be coming from either an incorrect timing adjustment or incorrect carb tuning? I used my Chilton manual to time the engine to exactly 6 BTDC, and the engine idles just under 600 rpms.
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#2
Valhallo;60952 Wrote:Hey guys,
After a month of troubleshooting my mustang is running again, but the problem I have now is my tinkering. I had tuned my carb. up previous to this whole fiasco, but since then I have adjusted my timing.

Now I'm looking at a power problem I am having. The first problem is the engine runs pretty terribly when it's cold. After 5ish minutes of driving it runs a whole lot better. The second problem is I feel I'm loosing low end power. There isn't much power when I launch compared to how it used to feel before playing with the timing and ignition, but I don't feel much power loss on the high end.

I guess what I'm asking is do any of you think this problem could be coming from either an incorrect timing adjustment or incorrect carb tuning? I used my Chilton manual to time the engine to exactly 6 BTDC, and the engine idles just under 600 rpms.

The factory initial timing setting and the distributor advance curve in general were set up with emissions and smooth operation in mind, not performance. IMO you should be running as much initial timing as your starter will allow without kicking back. That should be somewhere between 12 and 16 degrees initial timing. You must then modify the mechanical advance to allow total timing of no more than 36 degrees. The springs should be changed/adjusted so all the timing is in by 3000 rpm. It will also be necessary to limit the vacuum advance. This will restore the bottom end "punch" you feel you have lost and possible help the cold start operation.


73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#3
Set the initial timing to the highest manifold vacuum and then follow tommyk's advice about adjustments.

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#4
Another benefit of increased initial timing is that the engine runs much more efficiently. You know what that means? Better MPG!

Your cold-starting problems sounds like your choke isn't working correctly.

Let me check your shorts!
http://midlifeharness.com

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#5
Lol, while messing with the carb I disconnected my choke. Thanks Midlife. That solves one problem. And thanks for the info about the initial timing.
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#6
Engine Timing, Carb Jets, etc.

In my searches I have been unable to find a comprehensive guide regarding engine tuning in regards to Carb Jet selection, setting idle lean/rich mixture, setting mechanical timing, setting vacuum advance timing.

Could one of you guys write something up with specific information? For example, I would like to know if I run a 351W 262 cam with 1.6 rockers, what kind of idle vacuum pressure can I expect? How should I compensate my timing for this?

Even just a list of general rules, like set the timing WITH/WITHOUT timing to match your idle vacuum at 800 RPM.

These little things really make a difference in how an engine performs. Me, I don't give a crap how much my engine is shaking. As long as it is loud enough so I can't here the windows rattling and the yuppie wench in the BMW next to me complaining about how my car is stinking up the environment(actually had that happen once), it works for me.

But, when guys hop up their cars a little bit and want to know why their idle isn't smooth/consistent, it would be nice to prepare them for the task at hand: distributor springs, vacuum advance adjustment, and maybe carb jetting.


[Image: 11jmcuc.png]
351C Bold Manners, Brash Attitude
Favorite Teams: Michigan Wolverines and Whoever Is Playing Ohio State.

When I drive past a herd of cows, the cows MOO at me
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#7


TommyK;60965 Wrote:The factory initial timing setting and the distributor advance curve in general were set up with emissions and smooth operation in mind, not performance. IMO you should be running as much initial timing as your starter will allow without kicking back. That should be somewhere between 12 and 16 degrees initial timing. You must then modify the mechanical advance to allow total timing of no more than 36 degrees. The springs should be changed/adjusted so all the timing is in by 3000 rpm. It will also be necessary to limit the vacuum advance. This will restore the bottom end "punch" you feel you have lost and possible help the cold start operation.

Alright, I took my timing all the way up to 18, then back down to 14. Now I'm getting much better throttle response, but still lacking the power, and I still have backfiring. The problem might be that I'm just too far over, because I'm not 100% certain what I'm looking for when you say "Without the starter kicking back".

Also, when you say "total timing" and "all timing is in" are you saying that no matter how high it is revving it never advances past 36 degrees?

Sorry bout the rookie questions, but I really appreciate the help. Learning lots from you guys.
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#8
Valhallo;61388 Wrote:
TommyK;60965 Wrote:The factory initial timing setting and the distributor advance curve in general were set up with emissions and smooth operation in mind, not performance. IMO you should be running as much initial timing as your starter will allow without kicking back. That should be somewhere between 12 and 16 degrees initial timing. You must then modify the mechanical advance to allow total timing of no more than 36 degrees. The springs should be changed/adjusted so all the timing is in by 3000 rpm. It will also be necessary to limit the vacuum advance. This will restore the bottom end "punch" you feel you have lost and possible help the cold start operation.

Alright, I took my timing all the way up to 18, then back down to 14. Now I'm getting much better throttle response, but still lacking the power, and I still have backfiring. The problem might be that I'm just too far over, because I'm not 100% certain what I'm looking for when you say "Without the starter kicking back".

Also, when you say "total timing" and "all timing is in" are you saying that no matter how high it is revving it never advances past 36 degrees?

Sorry bout the rookie questions, but I really appreciate the help. Learning lots from you guys.

When increasing the initial timing you will reach a point where the starter will be unable to turn the engine over when it is fully heat soaked. This is what I mean by kick back. When this occurs you have too much initial timing because obviously you need the car to start reliably under all operating conditions. What I do is take the car for a drive on a warm day until it is fully warmed up, usually on the highway for at least 10 or 15 minutes. I then find a place to pull over and shut the car off and wait 2 or 3 minutes so that the engine becomes fully heat soaked. I try to re-start the car. If the starter kicks back (engine won't turn over) I reduce the initial timing to the point where the car will turn over. I have now determined the maximum amount of initial timing the engine will tolerate. Now I gingerly drive the car home because by advancing the initial timing I most likely have too much total advance for safe operation under "spirited" driving conditions. I make sure the vacuum advance is disconnected and plugged. THIS IS VERY IMPORTANT TO AVOID DAMAGING YOUR ENGINE!!

Once I am home I break out the dial back timing light to determine how many degrees of initial advance my new max setting gives me. For sake of argument let's say it is 16 degrees. Now using the curb idle screw I raise the idle in 500 rpm increments recording the timing reading at each setting until the timing stops increasing, usually somewhere between 3000 and 4000 rpm. When you reach that point lower the idle speed by 100-200 rpm and check the timing again. If it doesn't change lower it some more until you find the point it starts to go down. Record the timing reading and the rpm at which it occurs. That is your total timing reading. It will probably be well north of 36 degrees. It is now time to do some surgery on your distributor known as "re-curving". The procedure for this will vary depending on what type of distributor you have. Here is a link to instructions on re-curving a Duraspark. You can get a general idea what is involved.

http://www.reincarnation-automotive.com/...index.html

As far as the specific problems you are experiencing it would be helpful if you posted as much info on your combo as possible as well as details as to exactly what changes you made to the carb. I gather from your post that the car was running well, then you made some changes and now it does not?


73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#9
The fact that it is back firing may mean the distributor is installed one gear tooth off from where it is supposed to be. It will run but, not well. Just a thought. Chuck
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#10
1. Make sure you set the timing with the VACUUM ADVANCE on the distributor removed.
2. After setting the timing, Rev the engine a little. Your timing should advance (INCREASE BTD)a little otherwise your centrifugal advance plates are stuck. I don't know what the timing should advance, but if it advances measurably, you are probably ok.
3. Put on the Vacuum Advance hose. The timing should advance about 20 degrees more than in step 2.(spec will vary based on your engine/setup/etc.) If it doesn't your vacuum advance needs to be replaced.
4. I think if you jumped a tooth, you would be off by:

15 Teeth/ 360 Degrees= 1 tooth / 24 CAM degrees
1 Cam Degree = 2 Crankshaft Degrees(Cam rotates once every time Crankshaft rotates twice)
24 Cam Degrees = 48 Crankshaft Degrees

That is pretty serious, and can't really be fixed by adjusting the timing.


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351C Bold Manners, Brash Attitude
Favorite Teams: Michigan Wolverines and Whoever Is Playing Ohio State.

When I drive past a herd of cows, the cows MOO at me
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