Jump to content

engine timing and tuning


Recommended Posts

All,

 

recently, I noticed the engine was developing some significant pinging under heavy load (like when you go WOT because you like that kind of thing). Some background: I have points/condenser ignition 302 2bbl. I have ported vacuum which has generally worked pretty well - car has generally run pretty great. I have had one nagging issue where I have to run with the distributor rotated as far as it will go towards water pump. In general it was fine there, but it has bothered me that I couldn't get to zero initial timing. Against water pump was 12-13 deg of timing if I recall. It would generally pull about 15in vacuum at 800 rpm idle.

 

I went around the engine to check the cylinders and plugs. All cylinders produce between 125 & 135 psi, and all plugs were generally clean and the ceramic was a nice tan color, and gaps were all good at .034.

 

Since pinging usually has something to do with timing advance, I was curious if I had developed vacuum leak somewhere, so I looked for one. Everything seemed ok (hoses have been replaced in the past year or two). but I checked the vacuum advance module with a vacuum brake bleeder, and found that the line coming off the side of the module (not the axial port) could not hold vacuum.

 

I changed the vacuum advance module out, and still couldn't get it to run very well. It was rough and irregular. I was frustrated by the inability to get to 6deg initial timing, so I re-stabbed the distributor one cog over. I also put in new points and condenser. The new points actually improved things some too.

 

With the distributor re-stabbed, the car starts and runs great up to 2k rpm. Now it runs ok with the dist rotation in the mid range, and all the way over to the water pump is too far. Initial timing is around 6degs, and it idles real well, and generally seems normal. Pulls around 15in vacuum (15 seems low to me - should be 18-20 right?). But, when I really put the gas to it, I get a lot of hesitation, and it generally runs badly. it's the 2500+ rpm range that I have the problem.

 

timing at ~3K rpm is high 20's (thats with both vacuum hoses on vac advance). Seems low... should be over 30 but not more than 36 right? How do I get it there? I remembered I had not adjusted the hex nut inside the vacuum module axial port, so I went out and played with that some, maybe some improvements, but nothing at the high end.

 

All that to ask, how do i hold the good situation at low RPM, and adjust the high speed advance up to where it needs to be? Seems like I'm almost there, but Im kinda stuck at this point.

Pics of The Car

Link to comment
Share on other sites

  • Replies 37
  • Created
  • Last Reply

Top Posters In This Topic

.

plug the distributor vacuum hose and leave it plugged.

 

rev engine until max timing is reached and tell us what it is.

 

if you have a tach, tell us what rpm it reaches max timing at.

 

at idle, advance the distributor 4 degrees and see if the rpm changes and if it still runs smoothly.

 

retard distributor 4 degrees.

 

rev engine to 2000 - 2200 rpm or 1.4 throttle then advance timing 4 degrees and check rpm change and if it still runs smoothly.

 

if the rpms increased with both tests and it still ran smooth, leave it there then set idle then test drive.

.

Link to comment
Share on other sites

plug the distributor vacuum hose and leave it plugged.

 

I'm assuming you mean the axial vacuum port? Should I leave the vacuum port on the side attached?


Any chance you got some really bad fuel?

 

I can't rule that out, but I think it's unlikely. Car runs good until I really get into the gas pedal - or perhaps the high RPMS right before transmission shift (I have a C4 auto). When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother. Hate to say it, but better chance I screwed something up here

Pics of The Car

Link to comment
Share on other sites

*****When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother.*****

 

That sounds like fuel starvation.

 

The pinging is a different issue.

 

Paul

73 Grande

351C 2v

Now 4v Carb/Cam/headers/T5

 

Gasoline is for washing parts.

Alcohol is for drinking.

Nitomethane is for racing!

 

 

Work in Progress photos here:

Last Update: 4/23/16

 

http://s1270.photobucket.com/user/therocket366/library/?sort=3&page=1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Link to comment
Share on other sites

*****When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother.*****

That sounds like fuel starvation.

The pinging is a different issue.

Paul

 

oh. that's an interesting thought... Let me run the tests Barnett468 recommends, get those results, and then if it's not clear from that, I'll check into this. I guess that could be a fuel filter? or a fuel pump? I've had to replace the fuel pump in this thing twice and last time was just last year.

 

The bad pinging I had before does seem to be gone. At least when I'm taking off from a dead start I don't hear the pinging. And when RPMs are up, I get this shuddering...

 

Thanks for the advice though, I will keep it on the list of things to checkout.

Pics of The Car

Link to comment
Share on other sites

Results to Barnett468 tests below:

 

initial conditions

both vac hoses un-hooked and plugged (no vac advance anywhere - all mechanical)

Idles well at 850 rpm, timing ~10deg

 

Rev to max mechanical timing test:

Reaches about 32 deg timing at 5500rpm

during this test I noticed something that I think is a root cause of the issues. When I get up around 5k RPMs, I noticed that the timing light had SIGNIFICANT gaps in flashing. flashes get faster & faster with revving the engine, until this high speed, then I get erratic drops in flashes - meaning spark dropout. I don't know what the problem is here. I suspect this either is a problem with the capacitor, or I have something shorting the spark out when the distributor gets advanced (either mechanically or via vacuum). Any thoughts on this problem?

 

Idle tests:

13-15 in mg vacuum (needle stable)

advance timing 4 deg, engine idles just fine at 900-950 rpm

Cannot retard timing 4 deg because the vacuum advance module hits the Air conditioner compressor bracket.

Currently, my min timing is 8-10deg.

 

RPM's at 2000 test:

Engine runs fine in this RPM range. it's hard to hold there, as a little more fuel and the RPMs quickly get to 3-4k RPMs. I didn't have enough hands to hold the timing light, hold the throttle and and rotate the distributor to advance/retard timing. What I able to do tho was hold RPMs at ~2000, and measure timing. It's very close to 20deg timing in this condition. Seems to run quite smooth at this condition. Spark is regular at this condition (timing light flashes are quick and bright)

 

So, here are some thoughts:

- I believe something is causing the spark to drop out at high engine RPMs. No idea why. This is consistent with shuddering right before transmission shifts etc. I suspect the condenser as I have had to replace these units multiple times in this car, and they typically create symptoms like this shuddering when they go out. it's not always at high RPMs though.

 

- I wonder if PO put a performance CAM in this car when it was "rebuilt" I believe 30K miles ago. That might explain why I only have 13-15 in vacuum at idle. It doesn't "lope" though like a harley or anything, it generally idles relatively smoothly.

 

- My mechanical advance seems to be functioning. I don't know if "the curve" is right. I've only got 3 points from these tests (idle, 2k and 5k). Is 20 deg timing at 2k and 32 deg timing at 5k about right? I'll have to look this up...

 

Any more thoughts on the issues?

Any suggestions on what might cause my high speed spark to drop out/short out?

 

Thanks for any suggestions!

Pics of The Car

Link to comment
Share on other sites

improperly adjusted points, bad condensor, bad coil, old plug wires that are breaking down, cracked cap, moisture in cap, rotor covered in carbon, bad plugs-even one will be enough to cause problems.

 

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore.

 

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes :) (It only hurts for a moment until you go to HEI)

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

Link to comment
Share on other sites

improperly adjusted points, bad condensor, bad coil, old plug wires that are breaking down, cracked cap, moisture in cap, rotor covered in carbon, bad plugs-even one will be enough to cause problems.

 

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore.

 

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes :) (It only hurts for a moment until you go to HEI)

 

Yep what he said.

Link to comment
Share on other sites

Well, here is my take on each of these:

 

improperly adjusted points:

brand new and gapped per the book

 

bad condenser:

2nd new one this week. This is my highest suspicion, but it is a brand new part

 

bad coil:

New within last year

 

old plug wires that are breaking down:

Wires are 2 years old. I just pulled each and every one, cleaned & inspected them.

 

cracked cap:

Cap seems fine. I've had it off multiple times, clean and no visible signs of cracks.

 

moisture in cap:

cap is clean as a whistle.

 

rotor covered in carbon:

Clean, has been handled many times thru this process.

 

bad plugs-even one will be enough to cause problems:

Inspected and gapped each one, have verified strong spark at idle for every cylinder via timing light test.

 

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore:

Call me stubborn, but that's a $120 option, forces a mod from ported vacuum, and I can't help but feel it's not needed.

 

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes :) (It only hurts for a moment until you go to HEI)

i've learned this lesson already. More dollars to get to HEI, forces more mods in other places in the engine.

 

HEI and pertronix are "shotgun fixes" (combined in excess of $200)... I'd much rather find the root cause in the original systems here.

Pics of The Car

Link to comment
Share on other sites

Make sure that little ground wire that connects the breaker plate to the distributor body is in place. If it is missing or broken it can cause numerous problems.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

Link to comment
Share on other sites

Results to Barnett468 tests below:

 

initial conditions

both vac hoses un-hooked and plugged (no vac advance anywhere - all mechanical)

Idles well at 850 rpm, timing ~10deg

 

Rev to max mechanical timing test:

Reaches about 32 deg timing at 5500rpm

during this test I noticed something that I think is a root cause of the issues. When I get up around 5k RPMs, I noticed that the timing light had SIGNIFICANT gaps in flashing. flashes get faster & faster with revving the engine, until this high speed, then I get erratic drops in flashes - meaning spark dropout. I don't know what the problem is here. I suspect this either is a problem with the capacitor, or I have something shorting the spark out when the distributor gets advanced (either mechanically or via vacuum). Any thoughts on this problem?

 

Idle tests:

13-15 in mg vacuum (needle stable)

advance timing 4 deg, engine idles just fine at 900-950 rpm

Cannot retard timing 4 deg because the vacuum advance module hits the Air conditioner compressor bracket.

Currently, my min timing is 8-10deg.

 

RPM's at 2000 test:

Engine runs fine in this RPM range. it's hard to hold there, as a little more fuel and the RPMs quickly get to 3-4k RPMs. I didn't have enough hands to hold the timing light, hold the throttle and and rotate the distributor to advance/retard timing. What I able to do tho was hold RPMs at ~2000, and measure timing. It's very close to 20deg timing in this condition. Seems to run quite smooth at this condition. Spark is regular at this condition (timing light flashes are quick and bright)

 

So, here are some thoughts:

- I believe something is causing the spark to drop out at high engine RPMs. No idea why. This is consistent with shuddering right before transmission shifts etc. I suspect the condenser as I have had to replace these units multiple times in this car, and they typically create symptoms like this shuddering when they go out. it's not always at high RPMs though.

 

- I wonder if PO put a performance CAM in this car when it was "rebuilt" I believe 30K miles ago. That might explain why I only have 13-15 in vacuum at idle. It doesn't "lope" though like a harley or anything, it generally idles relatively smoothly.

 

- My mechanical advance seems to be functioning. I don't know if "the curve" is right. I've only got 3 points from these tests (idle, 2k and 5k). Is 20 deg timing at 2k and 32 deg timing at 5k about right? I'll have to look this up...

 

Any more thoughts on the issues?

Any suggestions on what might cause my high speed spark to drop out/short out?

 

Thanks for any suggestions!

 

Initial timing should be 6* at 800 rpm with no vacuum.

For your distributor:

At idle centrifugal advance is 0-4*

At 2000rpm 12-16*

At 3000 rpm 16-19.0*

At 4000 rpm 16.5 -21.6*

 

With ported vac you should have 0 advance at idle.

0-3* at 5" vac

0-6* at 6.5" vac

5-10* at 9.5" vac

5-10* at 20" vac

 

IRT missing at high rpm's the China made parts are of poor quality and I think that the point spring pressure may be low and your points may be floating at that upper rpm range.

-john

(jbojo)

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

 

Some Mod pictures can be seen at: [button=http://www.7173mustangs.com/forum-garage?filterxt_uid=2026]Bojo's Garage[/button]

 

 

Link to comment
Share on other sites

ok, unfortunately your description does not answer any of my questions . either the rpm increased a noticeable amount when you increased the timing 4 degrees or it did not.

 

either it continued to run smoothly when you increased the timing or it did not.

 

if you increased it 4 degrees, you can obviously retard it 4 degrees back to where it previously was . i did not say to retard it 4 degrees from where you started.

 

if the engine was not missing when your timing lite became erratic, don't worry about it.

Link to comment
Share on other sites

ok, unfortunately your description does not answer any of my questions . either the rpm increased a noticeable amount when you increased the timing 4 degrees or it did not.

the idle did increase a noticiable amount (from 850 to 950), and continued to run smoothly.

 

either it continued to run smoothly when you increased the timing or it did not.

it did continue to run smoothly.

 

if you increased it 4 degrees, you can obviously retard it 4 degrees back to where it previously was . i did not say to retard it 4 degrees from where you started.

ok. I mis interpreted the instructions then. In any case, it runs smooth at 10deg & @14deg, it runs smoothly if I advance or retard the distributor.

 

if the engine was not missing when your timing lite became erratic, don't worry about it.

The engine *does* begin to falter when the flashes begin to become erratic.

 

Make sure that little ground wire that connects the breaker plate to the distributor body is in place. If it is missing or broken it can cause numerous problems.

 

I double checked that tonight and both ends are tight and the wire looks healthy. I did readjust the wire a bit in case the connections had gotten corroded. No change. (Excellent idea though)

 

Initial timing should be 6* at 600 rpm with no vacuum.

For your distributor:

At idle centrifugal advance is 0-4*

At 2000rpm 12-16*

At 3000 rpm 16-20.6*

I can't get to these low levels at the current distributor config. I may need to restab the dizzy another one to the left to get there.

 

With ported vac you should have 0 advance at idle.

0-3* at 8" vac

0-6* at 11" vac

7-13* at 15" vac

14-20* at 20" vac

once i get the mechanical advance working like it is supposed to, I'll double check these vac advance numbers.

 

 

IRT missing at high rpm's the China made parts are of poor quality and I think that the point spring pressure may be low and your points may be floating at that upper rpm range.

I agree with the potentially crap parts issue. As far as I know there is not a vendor that makes truly good quality points/condenser. If you know of anyone, please send me the link.

Pics of The Car

Link to comment
Share on other sites

ok, jbojos info is not applicable to your engine so do not use it.

 

remove the distributor cap and rotate the rotor to see if it has spring tension on it and moves freely.

 

if you have points, set them to .016" - .017".

 

make sure the points are clean and not pitted.

 

 

did the engine rpm increase noticeably when you increased the timing 4 degrees at 2000 rpm?

 

did it still tun smoothly?

 

if it increased in rpm and still ran smoothly, leave it advanced 4 degrees and test drive it

 

do not connect the distributor vacuum hoses.

 

hard to say why it runs erratic at high rpm but the plug wires could be bad or the points could be chinese and have a weak spring . use ford points only.

 

if you have an electric choke and it is not connected to the back of the alternator, disconnect it then hold the choke open and rev it and see if it still runs erratic and the timing lite is intermittent.

Link to comment
Share on other sites

"timing at ~3K rpm is high 20's (thats with both vacuum hoses on vac advance). Seems low... should be over 30 but not more than 36 right? How do I get it there? I remembered I had not adjusted the hex nut inside the vacuum module axial port, so I went out and played with that some, maybe some improvements, but nothing at the high end."

 

I suggest inspecting the breaker plate for mechanical binding or the small round plastic glides being damaged or missing (I'm assuming OEM distributor). If those are good, carefully remove the breaker plate and inspect the mechanical advance, checking for binding of the weights. Look to see what numbers are stamped on the advance limit stops. The one being used will have a stop pin covered with black "rubber" in the slot. If it is stamped 13L that means 26 degrees of mechanical advance at the crank, when it is all in. 15L means 30 degrees etc.. Just my thoughts on the matter.

 

Chuck

  • Like 1
Link to comment
Share on other sites

Well, I had a buddy come over and we spent a long time on this problem. I have a dwell meter, and we spent some time trying to figure out why the dwell meter reads 40-42deg (spec is 27 for my 302 engine). Unless I have it connected wrong, or it is out of calibration I can't figure that out.

 

I assumed that setting the points gap wider would increase the dwell, and points gap tighter would decrease dwell, but the readings did not correlate. We opened the points gap up and never saw the dwell go above 45, and we took it down to .016 but there was negligible change in dwell reading.

 

We took 2 sets of timing readings one with vacuum advance OFF (and connecting lines plugged):

RPM Timing (deg)

800 10

1200 8

2000 16

3000 20

4000 22

5000 25

 

Then we did same with vacuum advance connected:

RPM Timing

850 8 (idles at 850 instead of 800 with vacuum advance attached)

1200 10

2000 16

3000 20

4000 20

5000 26

 

This data tells me that vac advance isn't "doing much" to change the timing. The engine generates plenty of vacuum, and I know the vacuum advance is brand new, so I don't understand the issue. I am beginning to wonder if the breaker plate and mechanical advance have worn out as Chuck suggests. They do look relatively new, but perhaps some plastic parts on them have broken off like he says. its a relatively easy check..

 

Car seems to run fine at low RPM's still. We took it out and drove it and at high RPM's it still got major hesitations and sputtering.

 

I am beginning to wonder if perhaps the fuel pump is not providing enough fuel (just like response #1in this thread mentioned!) . I know the pump is less than 1 year, but it is an autozone cheapie, and so these chinese parts can fail really fast - especially in the ethanol laden gasoline we get.

 

I'm gonna go vacuum check the fuel pump, and see if that tells anything. I'm also gonna inspect the distributor parts more closely. If anyone has any more ideas on timing or otherwise, I would appreciate it.

Pics of The Car

Link to comment
Share on other sites

Your stock distributor should provide a maximum of 10* vac advance and 21.5* centrifugal. So total should be 10* + 21.5* + initial Adv*. Tuning spec says 6* BTDC so the max you should see would be 37.5*. This is design but optimal for a motor is usually 34 to 36*.

 

What is your initial timing set at and your idle rpm?

 

When you replaced the vacuum adv did you adjust it to provide the correct adv?

-john

(jbojo)

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

 

Some Mod pictures can be seen at: [button=http://www.7173mustangs.com/forum-garage?filterxt_uid=2026]Bojo's Garage[/button]

 

 

Link to comment
Share on other sites

Ok, Did you do what I suggested?

 

If so what were the results when you drove it?

 

Don't worry about your vacuum advance . Leave it plugged until your car runs properly.

 

Rev the engine until it misses then move the distributor in both directions and see if it smooths out.

 

I mentioned it could be plug wires or weak points spring or bad advance or the electric choke . Try some other plug wires from another car and disconnect the choke as I suggested then post the results after you do these tests . You will likely not find the prob unless you simply start changing parts.

 

If your spark plugs are black they can cause the same prob.

 

Here's your numbers

 

800 10

1200 8

2000 16

3000 20

4000 22

5000 25

 

 

The numbers below are far more common unless the compression is extremely high.

 

650 .... 10

2000 .. 20

3000 .. 32

Link to comment
Share on other sites

Ok, Did you do what I suggested?

If so what were the results when you drove it?

 

It seems to run fine at various timing settings as long as the RPMs are below 3-4K RPMs. Adjusting the timing a little at any RPMs below 4k doesn't make much difference.

 

Rev the engine until it misses then move the distributor in both directions and see if it smooths out.

it misses at very high RPMs (5K RPMs) without load on the engine, so it is difficult to perform this test.

 

I mentioned it could be plug wires or weak points spring or bad advance or the electric choke . Try some other plug wires from another car and disconnect the choke as I suggested then post the results after you do these tests . You will likely not find the prob unless you simply start changing parts.

 

If your spark plugs are black they can cause the same prob.

Spark plugs are all in good shape. As I said they were all a nice tan color, and properly gapped. Compression tests were all nominal and generally consistent for all 8 cylinders.

 

Here's your numbers

800 10

1200 8

2000 16

3000 20

4000 22

5000 25

 

The numbers below are far more common unless the compression is extremely high.

650 .... 10

2000 .. 20

3000 .. 32

 

This seems like the key issue. timing is off at the high end. So far, I can't find any malfunction in the mechanical or vac advance systems that are causing my timing to be off at the high end..


Your stock distributor should provide a maximum of 10* vac advance and 21.5* centrifugal. So total should be 10* + 21.5* + initial Adv*. Tuning spec says 6* BTDC so the max you should see would be 37.5*. This is design but optimal for a motor is usually 34 to 36*.

Understand. If you review my previous post, you can see the initial timing is about 10.

Right now, I can't get the initial timing below about 10 due to vac advance module hitting the air conditioner bracket....

 

What is your initial timing set at and your idle rpm?

again: initial timing is 10deg at idle of about 800-850. 15 in-mg vacuum.

 

When you replaced the vacuum adv did you adjust it to provide the correct adv?

I tried. I don't have any instructions for how to adjust this device, and it didn't seem to make much difference with the hex screw tightened down or loosened.


I'm posting some pics of the distributor. I disassembled it tonight to inspect, clean. it looks fine to me. If anyone sees something in the pics out of whack, let me know - I don't see it.


I suggest inspecting the breaker plate for mechanical binding or the small round plastic glides being damaged or missing (I'm assuming OEM distributor). If those are good, carefully remove the breaker plate and inspect the mechanical advance, checking for binding of the weights. Look to see what numbers are stamped on the advance limit stops. The one being used will have a stop pin covered with black "rubber" in the slot. If it is stamped 13L that means 26 degrees of mechanical advance at the crank, when it is all in. 15L means 30 degrees etc.. Just my thoughts on the matter.

Chuck

 

very helpful thoughts here. I did this and when I look at the weights, they seem to be stamped with 13L (although the "3" is backwards???) implying 26 degs advance. I posted pics and I can't find any "rubber in the slot". Can you elaborate on this? this mechanism seems to move freely and the weights are free to move as designed. I can't find any problems looking at it. I noted that one of the weights is stamped with "62" and the other with "64". The springs holding each look a little different, but both seem to work fine.

IMG_7400.thumb.JPG.6bee46008b23a07aaf1b55a1f87456f9.JPG

IMG_7399.thumb.JPG.6bc1de0c7f202922cef4a8d3a75ec4f3.JPG

IMG_7398.thumb.JPG.2a6c07607e4eb667418cdfe4f3c2c66c.JPG

IMG_7397.thumb.JPG.b78c579849b181d1498d5ac0674affa4.JPG

IMG_7396.thumb.JPG.8ffae89a93e3d3ee2a5d51404a01a5f1.JPG

IMG_7395.thumb.JPG.a88e9a0038e8fdfc10ae0093a519b980.JPG

IMG_7394.thumb.JPG.54c07d3f05bfe637af358073680e43b6.JPG

IMG_7393.thumb.JPG.a0b2b3f1a0efb0159b57862eb93fe8d2.JPG

IMG_7392.thumb.JPG.8a93faea8e103264f03b306b45d68817.JPG

IMG_7391.thumb.JPG.e73b81d700b55f78e12e31422b69e862.JPG

Pics of The Car

Link to comment
Share on other sites

i can see the rubber is installed over the arm in the 13 slot

 

you said earlier that the rpms went up a lot when you advanced the timing 4 degrees . . you are now saying that advancing the timing 4 degrees had little effect . which one is it?

 

the low amount of timing will have ZERO affect on your miss . it seems electrical.

 

try the things i suggested then post the results.

Link to comment
Share on other sites

I'm assuming the vacuum advance is the correct part and working properly. I would double check that the vacuum unit is indeed correct. Try bending the vertical tab that is connected to the spring that has tension on it to decrease the tension. This should increase the amount of mechanical advance. The springs look like the wire gauge is a bit large but it is hard to say. You could also try these springs. http://www.autozone.com/1/products/46984-advance-curve-kit-ford-1965-includes-set-of-springs-mr-gasket-925d.html

You may have to mix and match with the stock springs to get the advance curve you want. Given the 13L slot and 10 initial you should see 36 total by 3500 RPM even with the vacuum advance disconnected and plugged.

As rpm increases more advance is needed because the speed of flame propagation is constant and the time it has to burn decreases as RPM increases. The thing that is confusing is that it seemed to run OK before any changes were made. That brings me back to rechecking the vacuum module. Especially the length and shape of the arm that connects to the breaker plate. Let us know what you find.

 

Chuck

Link to comment
Share on other sites

When you checked the breaker plate did you check the pivot bushing for play? If it is worn it will allow the breaker plate to move around, changing the gap/dwell, especially when the vacuum advance moves.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

Link to comment
Share on other sites

Thanks guys. Working these things.

 

One of the things I am curious about is this: Could the PO have rebuilt the engine, put in a hipo CAM, and "recurved" the distributor? I have no information about the engine rebuild that was done (but I am virtually certain one was done). The engine only pulls about 14-15 in mg vacuum at 800 rpm idle. I can't adjust anything to get it higher than that.

 

If it DOES have a performance CAM in it, and I go messing with the distributor curve without knowing what was originally intended, could I make the situation even worse?

 

Just curious...


When you checked the breaker plate did you check the pivot bushing for play? If it is worn it will allow the breaker plate to move around, changing the gap/dwell, especially when the vacuum advance moves.

 

that's a good question. I really tried to check this well (because I was concerned about this), and I have to say that I am not sure. I didn't dissemble the upper plate from the lower plate, but I moved them around alot (and added some lube) The two plates don't rotate concentrically, so it seems hard to know if there is slop. When installed in the car, I noticed that there were some movements of the plate that would affect gap. So, I don't have a good answer for this....


there is a light spring and a heavy one on your dist, if you buy the springs, remove the heavy one only and install one of the 925 springs . summit also sells those.

the heavy spring is the one to the right in this photo.

 

Got it. Thanks!

Pics of The Car

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.

×
×
  • Create New...