Stuttering under acceleration when warm

[bueller]

A little background first. I've done a lot of things to my car since I purchased it and within a few weeks of each other, I upgraded to a Spec 1 exhaust, installed new fuel lines, spark plugs, plug wires, rotor and cap. Sometime after that, I noticed a hesitation or stutter when accelerating after the car was warmed up (driving for about 10 mins or so). The stutter is most noticeable when accelerating in the 1800-3000 RPM range but once I'm above that range, the car seems to even out and accelerates fine. Car is rock solid at Idle when cold or warm and stays right at 750 or so.

I'd read somewhere that after installing a performance exhaust like the Spec 1, some sort of adjustments might need to be made, but for the life of me, I can't find where I read that anymore. If I should make adjustments, can anyone point me in the direction of what I should be adjusting? I'm assuming it's just the mixture, but I'm scared to touch that as I've read that should always be the last thing you touch.

I recently acquired a Dwell meter and the following video shows my results as the car heats up.


https://www.youtube.com/watch?v=L-u58xaQ8tM

TL;DWatch -- Cold, I get a steady 45 Dwell reading. 3 mins later the reading oscillates between 35 and 45. Approximately another 7 mins after that, dwell oscillates between 40-48 and another 10 minutes after that, dwell oscillates between 44-48. On both the last two readings, it seems like the dwell wants to stay at the higher end of the oscillation longer (hard to describe but video shows this). Disconnecting the O2 sensor or pressing the WOT switch gives me a steady reading around 48-50.

These readings seem to indicate issues when the engine is warmer, but seems to be correct when it's cold or just warming up.

Any recommendations given all of the above information?

Thanks,
Bueller

[David T]

Some things to check:
Injector spray patterns
Vacuum leaks
Vacuum, mechanical advance, and initial base timing.

[Bitsyncmaster]

Your dwell reading is a little high. You should be running around 35 deg with a hot engine. I would not think that dwell setting would cause the hesitation with the warmed up engine. You don't have to wait to adjust the mixture last. Any time you change things on the engine, just hook up your dwell meter and adjust it. Your new exhaust probably changed the dwell setting.

[NckT]

Set the primary fuel pressure from 5.2-5.3 bar to 5.3-5.4 bar (76-77 psi ish) then reset the fueling with the dwell meter.

I'm not sure if the US octane rating is the same as UK Octane rating, but we have 95ron as basic unleaded, so for us here, ignition timing can be advanced to 14-14.5 btdc no vac advance.

The above verified in a rolling road.

Good luck

[opethmike]

Set the primary fuel pressure from 5.2-5.3 bar to 5.3-5.4 bar (76-77 psi ish) then reset the fueling with the dwell meter.

I'm not sure if the US octane rating is the same as UK Octane rating, but we have 95ron as basic unleaded, so for us here, ignition timing can be advanced to 14-14.5 btdc no vac advance.

The above verified in a rolling road.

Good luck

Hello friend,

The U.S. uses different formulas to calculate octane ratings:

https://www.etuners.gr/fuel/

[bueller]

Thanks for the responses. I've checked for vacuum leaks but haven't checked spray patterns or timing yet.

I was leaning towards adjusting the dwell as my first step given the new exhaust, etc. Should I be checking the spray patterns and timing before that too or is it okay to try the Dwell first?

Also, I don't currently have anything that can test fuel pressure but if I need to go down that route, I'll definitely purchase what I need. How likely is it that I need to adjust the primary pressure too given the background on work that was performed? She's a low mileage car (under 20K) and she was running perfect as far as I could tell before the upgrades and updates.

Thanks!

[NckT]

Hello friend,

The U.S. uses different formulas to calculate octane ratings:

https://www.etuners.gr/fuel/

Thanks for that :)

[NckT]

Thanks for the responses. I've checked for vacuum leaks but haven't checked spray patterns or timing yet.

I was leaning towards adjusting the dwell as my first step given the new exhaust, etc. Should I be checking the spray patterns and timing before that too or is it okay to try the Dwell first?

Also, I don't currently have anything that can test fuel pressure but if I need to go down that route, I'll definitely purchase what I need. How likely is it that I need to adjust the primary pressure too given the background on work that was performed? She's a low mileage car (under 20K) and she was running perfect as far as I could tell before the upgrades and updates.

Thanks!

I'd test the fuel pressure as even if the car had low mileage, the primary fuel pasture spring weakens over time and needs additional shims to even bring it back from stock. Typical values noted over 30 plus cars have been only 4.7-4.8 bar where setting pressure should be 5.2-5.3 for stock engine.

If you've got a fuel pressure gauge on you can also test the control pressure regulator (CPR) also known as the warm up regulator (WUR) / accumulator capacitance and rest leak down rates too.

[bueller]

Thanks NickT. Makes sense.

I'm going to order some shims from DeloreanGO to have ready to go after I get the fuel pressure tester. It will be a bit before they get here from over the pond. I'll test and adjust these things and get back with the group with the results.

Thank you!!

[NckT]

Thanks NickT. Makes sense.

I'm going to order some shims from DeloreanGO to have ready to go after I get the fuel pressure tester. It will be a bit before they get here from over the pond. I'll test and adjust these things and get back with the group with the results.

Thank you!!

Good luck

I'm 'Admin-bloke' on www.deloreanclub.co.uk/forum in case you search there too.

NickT

[bueller]

Got my pressure tester and I'm getting right at 4.9 bar for Primary Pressure. This is certainly at the bottom of the 'Checking Value' per the manual so I'll be adding some shims once they arrive to get it to the 5.4 recommended number for the UK Performance exhuast (though mine is a DPI Spec 1).

Control Pressure was right at 30 psi or 2.1 bar when started cold (first thing in the morning) with vacuum and electrical disconnected from the WUR at approximately 80 degrees F outside temp so that looks to be pretty close to the range of the chart in the book. Control pressure slowly increased but didn't seem to want to go above about 42 PSI or 2.9 bar even after idling for 10-15 minutes. Rest pressure stayed above the 1.7 minimum (2.1 bar after 10 minute wait) so that looks reasonably solid.

Does the 42 PSI control pressure after 10+ minutes indicate any issues with the WUR? I understand that it is really just used during warmup and I don't really have any noticeable issues with a cold start or initial idle, but the lower number makes me a bit curious.

Thanks!

[Bitsyncmaster]

Did you have the vacuum and electrical heater back on the WUR when testing warmed up? I normally get about 50 PSI.

[bueller]

Did you have the vacuum and electrical heater back on the WUR when testing warmed up? I normally get about 50 PSI.

Yes, I did try attaching the Vacuum and Electrical back to the unit towards the end of my testing and it didn't seem to make much of a difference. I did notice that the electrical connections were a bit corroded so I'm not sure if that was possibly related. I've cleaned the contacts with some special cleaner that is electronics safe, but I haven't tested since then as I wanted to let the car cool back down.

[Bitsyncmaster]

Yes, I did try attaching the Vacuum and Electrical back to the unit towards the end of my testing and it didn't seem to make much of a difference. I did notice that the electrical connections were a bit corroded so I'm not sure if that was possibly related. I've cleaned the contacts with some special cleaner that is electronics safe, but I haven't tested since then as I wanted to let the car cool back down.

It should have voltage with the engine running. If the heater is not working the engine has poor cold running performance for a longer time. The voltage comes from the RPM relay.

[bueller]

It should have voltage with the engine running. If the heater is not working the engine has poor cold running performance for a longer time. The voltage comes from the RPM relay.

I'll check for voltage next time I'm in the shop. Should it be a standard 12v-ish that I'm seeing there? I run your RPM relay so I'm sure that part is all fine, but will verify no wiring issues.

[Bitsyncmaster]

I'll check for voltage next time I'm in the shop. Should it be a standard 12v-ish that I'm seeing there? I run your RPM relay so I'm sure that part is all fine, but will verify no wiring issues.

Yes one pin should have the normal 12+ volts with the engine running and the other pin is ground.

[bueller]

I just ran out to check things and the voltage on the electrical plug when running was right where it should be. Granted, I didn't get to see a full cold to warm cycle as I didn't let it sit overnight, but when I plugged the electrical back in while it was running, I'm getting a solid 50 PSI control pressure now when warm. My guess is that corrosion noted earlier on the electrical connection may have caused an issue with my previous tests.

I'll check again in the morning from cold to make sure the pressures are where they should be but if that checks out, then I'll continue to wait for my shims to bring up the Primary Pressure and then I'll set the dwell appropriately and see what happens.

Thank you all for the continued assistance!!

[NckT]

50 psi == 3.45 Bar so this is good warm control pressure.

Have you done the test to check the vac delay valve?
On warm engine with control pressure at 50psi (I keep having to convert from Bar) disconnect the vacuum pipe that comes from under the inlet manifold that goes to the T plastic piece at the control pressure vacuum piping.
Apply a vacuum to this part.
As soon as the vacuum is released, the control pressure should go down to between 1.2 and 1.8 Bar (17-26 psi) and stay there for approx 8 to 12 seconds, then return back to 3.4 bar (50 psi).

Keep up the good work, it's nice to see some diagnostics going on instead of part swapping

[bueller]

Have you done the test to check the vac delay valve?
On warm engine with control pressure at 50psi (I keep having to convert from Bar) disconnect the vacuum pipe that comes from under the inlet manifold that goes to the T plastic piece at the control pressure vacuum piping.
Apply a vacuum to this part.
As soon as the vacuum is released, the control pressure should go down to between 1.2 and 1.8 Bar (17-26 psi) and stay there for approx 8 to 12 seconds, then return back to 3.4 bar (50 psi).

Keep up the good work, it's nice to see some diagnostics going on instead of part swapping

I haven't done a vac delay valve test yet. Based on some reading I've done the last couple of days, it appears I would need a vacuum pump to test this which I don't currently have. Would something like the Mityvac MV8000 (http://www.mityvac.com/pages/products_hvpk.asp) be appropriate or can this test be done with something less precise like a shop vac or something else that can suck?

I am a big fan of understanding the inner-workings of things I own. The K-Jet is definitely more complex than I'm used to so I've done a lot of reading of manuals and online here. My knowledge has gotten better but I'm a far cry from where I'd like to be. Thanks again to you and the many others who help newbies like me!

[Bitsyncmaster]

You can use engine vacuum to run your test. You can make a T with a hose on the intake manifold or probably just use the ignition distributor advance hose (warm engine and not at idle).

[bueller]

You can use engine vacuum to run your test. You can make a T with a hose on the intake manifold or probably just use the ignition distributor advance hose (warm engine and not at idle).

Completed the test on the Vacuum Delay Valve and that tested out okay also. Dropped to just right below 1.2 bar mark and then slowly made it's way back to 3.4 bar.

Back to waiting for the USPS to get those shims to me.

Thanks!

[NckT]

In the meantime double check the ignition advance timing, especial the static mechanical advance vs engine speed and compare that to the manual. Is not unknown for an advance spring on a bob weight to come off and the timing gets too far advanced giving the engine the stuttering or pinking noise.

Also check that the vacuum pipes operates correct and that the ignition advance solenoid operates correct and had the vac pipes in the correct way around to the diagram and that the vacuum source is correct as in the thermo vac switch operates fine.

I'll assume you've checked the high tension leads and distributor cap/ rotor am, coil voltage etc

Good luck

[Soundkillr]

Thermo vacuum switch was bad on my car. Ran great cold but once warm had hesitation off idle up to 2k. You shouldn't have vacuum at the wur once warm. If you do, that could be your problem.

[bueller]

I just checked base timing and it was a bit off -- roughly around 10 so I adjusted that to be 13 dead on (that distributor nut is a PITA). With the help of my oldest child, I also tested the mechanical advance. Since that moved the mark off the gauge a bit, I had to guesstimate, but it looks to be accurate for both 2000 and 3000 rpm but didn't try 4000 because my child's patience was running thin by then :)

While I didn't test the vacuum advance specifically I did accidentally leave the vacuum hooked up the first couple of times I tried to test mechanical advance and it does look like the extra vacuum did make a bit of difference in the advance, but I don't have the proper tools to test that fully at the various vacuum levels.

For the vacuum lines, I found this article over on the UK forum by NickT/Admin-Bloke (http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619) and per these tests, my thermo vac switch appears to be working correctly and the proper hoses go to the proper locations.

As far as the other items, I did recently install new plugs, plug wires, distributor cap, rotor, and a new coil. I've checked at night to see if there were any issues with the wires sparking and didn't see any sparks so I believe these new pieces are working as expected.

Let me know if there's anything I'm missing.

Thank you!

[NckT]

........

For the vacuum lines, I found this article over on the UK forum by NickT/Admin-Bloke (http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619) ......
.

Thank you!

Admin-bloke is me ;)

[NckT]

Admin-bloke is me ;)

Oops, I said that already in Post No.10.

I've copied the test text here from the link in case moderators here don't allow back links etc.
http://www.deloreaneurotec.uk/viewtopic.php?f=17&t=4619

Vac pipes Vac pipes... the bain of DeLorean engines...
Incorrectly connected make the car run a bit rubbish......

To save time stripping the inlet manifold off and to save time, you can do the following to check that the vac pipes are connected the correct way around. There are 3 vacuum pipes come from the thermo-vacuum switch from under the inlet manofold.
1 to the T Piece on the Control Pressure Regulator
1 to the Distributor Solenoid (located between the Fuel Distributor and the fibreflass firewall/ bulkhead)
1 to the Inlet Manifold, on a small pipe stud on the Inlet Manifold nearest to the ceramic resistors

With a COLD enginer (i.e. one that has been left overnight), Blow down the pipes separately.
2 of the vacuum pipes should flow air through each other the other one feels blocked.
Label the blocked one as "Distributor Solenoid"

Run the engine until it is at normal running temperature ie coolant temp is +80c

You should be able to blow down the one marked distributor and out of one of the other pipes. Label this pipe "inlet manifold".
If you blow down the 3rd pipe it should feel blocked. Label this as the "Control Pressure Regulator".

Let the engine cool down (i.e. leave it left overnight),

Verification Test:

With a COLD enginer (i.e. one that has been left overnight),
Blow through the vacuum pipe labelled "Inlet manifold", Air should come out of the vacuum pipe labelled "Control Pressure Regulator".
The remaining vacuum pipe labelled "Distributor Solenoid" should be blocked.

Run the engine until it is at running temperature.
Blow through the vacuum pipe labelled "Inlet manifold", Air should come out of the vacuum pipe labelled "Distributor Solenoid"
The remaining vacuum pipe labelled "Control Pressure Regulator" should be blocked.

If your vacuum pipes pass the above test, connect them up, noting that the vacuum pipe from under the inlet manifold marked "Distributor Solenoid" connects to the CENTRAL Vacuum stub on the Distributor Solenoid. This too is also handed and affects the way the engine runs.

If test is NOT OK then but always follows the engine hot test, chances are your thermo vac switch is stuck in the "HOT" position.
Before you replace this, check that you are actually checking the correct vac pipes from under the inlet manifold.
I have noted on one car that the pipe from under the inlet manifold was actually connected to the hot water valve vacuum connection!

Enjoy !

Admin-bloke

Admin-bloke, "The D Whisperer"
Pie n Pint Northerner....
Vin #4068 - y'official "Mighty Auto" test car for Admin-bloke tuning.

https://www.justgiving.com/campnibble

Forum Founder [means I just installed it........] and Tech Help
DeLorean Club

The Future's Bright....
The Future's DeLorean Club

[David T]

There was a Service Bulletin covering how to check for proper vacuum hose routing. Refer to ST-32-12/81

[bueller]

Got my shims installed and after experimenting with a few different combinations, I've got the Primary Pressure set right at 5.4 bar now. I then tested Dwell from cold and initial readings are fixed at 45. After getting into closed loop, the dwell fluctuates between 36 and 44. If I press the WOT switch at this point, I get a fixed 46-47 or so. I did not adjust the mixture given that these values seem to be more or less where they should be.

I then drove her around for a little while and I can say that it is a massive difference compared to before. The stuttering when accelerating was gone as far as I could notice. Steady power throughout the RPM band!!

However, when I got back to the shop, I checked the dwell again, and the dwell is no longer fluctuating while idling. It shows a fixed 46-47 now just like the WOT was pressed or if I had my O2 sensor disconnected. I'm assuming this shouldn't be happening, but confused on why Dwell reads correctly early on but then acts like it's in open loop. Could this be a bad O2 sensor that works sometimes and doesn't others?

Thanks!

[Bitsyncmaster]

Got my shims installed and after experimenting with a few different combinations, I've got the Primary Pressure set right at 5.4 bar now. I then tested Dwell from cold and initial readings are fixed at 45. After getting into closed loop, the dwell fluctuates between 36 and 44. If I press the WOT switch at this point, I get a fixed 46-47 or so. I did not adjust the mixture given that these values seem to be more or less where they should be.

I then drove her around for a little while and I can say that it is a massive difference compared to before. The stuttering when accelerating was gone as far as I could notice. Steady power throughout the RPM band!!

However, when I got back to the shop, I checked the dwell again, and the dwell is no longer fluctuating while idling. It shows a fixed 46-47 now just like the WOT was pressed or if I had my O2 sensor disconnected. I'm assuming this shouldn't be happening, but confused on why Dwell reads correctly early on but then acts like it's in open loop. Could this be a bad O2 sensor that works sometimes and doesn't others?

Thanks!

It's great your making progress. I would suggest your WOT switch is intermittent. I've seen a few go bad. Just unplug one of the wires off the switch and see if that cures your problem.

[NckT]

I'd have said the same thing what Dave mentioned too re a sticking wide open throttle microswitch.

I'm glad the shims arrived ok and you've noted the difference it makes too.

[NckT]

I'd recommend to finish off with throttle plate adjustment as described in Post No. 19 onwards in:

http://dmctalk.org/showthread.php?15633-Attempting-to-destroy-my-idle-lumpiness/page2

Good luck

NickT

[Trstno1]

Got my shims installed and after experimenting with a few different combinations, I've got the Primary Pressure set right at 5.4 bar now. I then tested Dwell from cold and initial readings are fixed at 45. After getting into closed loop, the dwell fluctuates between 36 and 44. If I press the WOT switch at this point, I get a fixed 46-47 or so. I did not adjust the mixture given that these values seem to be more or less where they should be.

I then drove her around for a little while and I can say that it is a massive difference compared to before. The stuttering when accelerating was gone as far as I could notice. Steady power throughout the RPM band!!

However, when I got back to the shop, I checked the dwell again, and the dwell is no longer fluctuating while idling. It shows a fixed 46-47 now just like the WOT was pressed or if I had my O2 sensor disconnected. I'm assuming this shouldn't be happening, but confused on why Dwell reads correctly early on but then acts like it's in open loop. Could this be a bad O2 sensor that works sometimes and doesn't others?

Thanks!

Quick side question. Where do you install the shims you are talking about? My pressure seems to be about the same as yours prior to the shim installation.

Thanks

[bueller]

Quick side question. Where do you install the shims you are talking about? My pressure seems to be about the same as yours prior to the shim installation.

Thanks


There's a 16mm bolt on the passenger side of the fuel distributor that faces the rear of the car. When removed you will see something that looks like this pic:

53907

If you don't see the leftmost part, use something non-abrasive to reach in there to get the last part out. Shims can be found at https://www.deloreango.com/us/fuel-pressure-regulator-shims.html

[bueller]

I'll check the WOT switch tomorrow if I can. Hoping this can be cleaned so I don't have to drop $60+ if it's bad. I don't suppose anyone knows of a cheaper cross reference part?

I will also do those throttle plate adjustments that NckT when I get the chance. I saw those a while back and was curious if those would be helpful.

Thanks all!

[Trstno1]

There's a 16mm bolt on the passenger side of the fuel distributor that faces the rear of the car. When removed you will see something that looks like this pic:

53907

If you don't see the leftmost part, use something non-abrasive to reach in there to get the last part out. Shims can be found at https://www.deloreango.com/us/fuel-pressure-regulator-shims.html

So do you just replace the shims that are there or do you add to the ones that are there to get the desired pressure?

[bueller]

So do you just replace the shims that are there or do you add to the ones that are there to get the desired pressure?

I added to what was already there.

[MikeWard]

Out of curiosity, what size did you need to bring it back up to 5.4 bar? I would guess a .50mm or .75mm shim (those appear to be the norm)?

[bueller]

Out of curiosity, what size did you need to bring it back up to 5.4 bar? I would guess a .50mm or .75mm shim (those appear to be the norm)?

Wish I could remember :) If I recall correctly (and I don't really), I think it was the 2 middle size shims .. pretty sure the thickest and the thinnest were not used, but I tried a few combinations so I might be wrong.

[bueller]

It's great your making progress. I would suggest your WOT switch is intermittent. I've seen a few go bad. Just unplug one of the wires off the switch and see if that cures your problem.

I warmed her up today and went for a little ride. She's still running great and when I went to check the Dwell after getting back from the drive, and the dwell is swinging again as it should. I'll keep an eye out for the WOT switch and check again over the next several runs to see if I can duplicate the issue, but working fine for me this morning.


NckT -- On the Throttle Plate adjustments that you linked to. Can you clarify which 3 screws you're referring to? Is it the #1-3 screws mentioned on page D:01:13 of the DMC workshop manual or are there some other ones I'm not aware of? Just want to make sure I'm working through the right adjustments later this week when I'll have the time to work on it.

Is this it: 53908


Thank you everyone for the help!

[NckT]

Hello. Yes, I'm referring to those brass hex headed bolts as in the picture.

Don't forget the metric feeler gauge (or whatever the imperial equivalent would be)

Re the wot switch, try spreading electrical switch cleaner or wd40 at the point where the full load switch presses on it. Disconnecting it will prove if it is the wot causing it to go into a fixed dwell or not.

Good luck with it all.

NickT

[bueller]

Hello. Yes, I'm referring to those brass hex headed bolts as in the picture.

Don't forget the metric feeler gauge (or whatever the imperial equivalent would be)

Re the wot switch, try spreading electrical switch cleaner or wd40 at the point where the full load switch presses on it. Disconnecting it will prove if it is the wot causing it to go into a fixed dwell or not.

Good luck with it all.

NickT

Thanks for clarifying. I ordered the feeler gauge last night on good old amazon prime so will have it in a couple of days!

Good tip on cleaning the switch. I have a can of electrical cleaner that I'll run through it when I get the chance.

[bueller]

I've made the final adjustments to the curb idle/idle switch screws as well as the 3 brass hex screws. I didn't notice any particular difference when driving it, but it may just be that I was pretty close on those already.

After running for a bit though, I did have that bizarre Dwell issue again. During initial warm up the dwell measures like it should and RPMs are right around 850 at idle. Dwell is solid at first then swinging between 35-45 or so. After the car has been run for a while though (10 mins or so), that dwell reading starts moving higher but still swings a little bit but has a much smaller oscillation. Every so often, it would hold steady for several seconds around the 48-50 range and if I revved the engine a bit, the dwell would begin to swing but in the range of 45-50. It would do this over and over and while hot, would never really drop below 45 or so. Idle also seemed to be increased a bit to around 1000 - 1050 or so.

It definitely is not the WOT switch since if I press that, the dwell pegs closer to 60. Likewise, disconnecting the WOT switch doesn't affect the dwell.

Any ideas on why the dwell would change that much as the engine warms up? Is this something to be concerned with? Let me know if you need additional data points.

Thanks!

[Bitsyncmaster]

I've made the final adjustments to the curb idle/idle switch screws as well as the 3 brass hex screws. I didn't notice any particular difference when driving it, but it may just be that I was pretty close on those already.

After running for a bit though, I did have that bizarre Dwell issue again. During initial warm up the dwell measures like it should and RPMs are right around 850 at idle. Dwell is solid at first then swinging between 35-45 or so. After the car has been run for a while though (10 mins or so), that dwell reading starts moving higher but still swings a little bit but has a much smaller oscillation. Every so often, it would hold steady for several seconds around the 48-50 range and if I revved the engine a bit, the dwell would begin to swing but in the range of 45-50. It would do this over and over and while hot, would never really drop below 45 or so. Idle also seemed to be increased a bit to around 1000 - 1050 or so.

It definitely is not the WOT switch since if I press that, the dwell pegs closer to 60. Likewise, disconnecting the WOT switch doesn't affect the dwell.

Any ideas on why the dwell would change that much as the engine warms up? Is this something to be concerned with? Let me know if you need additional data points.

Thanks!

You set your dwell with the hot engine. What your seeing are pretty small changes. Are you reading dwell or duty cycle? I ask because WOT reads 60% duty cycle. I still think your dwell adjustment is set a little high.

[bueller]

You set your dwell with the hot engine. What your seeing are pretty small changes. Are you reading dwell or duty cycle? I ask because WOT reads 60% duty cycle. I still think your dwell adjustment is set a little high.

I haven't actually adjusted Dwell at all since I've owned it so this is still the default dwell from when I bought it and the tamper proof plug is still in place. I didn't change it after getting fuel pressures adjusted since the readings were dead on while warming up and after the 02 sensor kicked in -- Just seeing this oddness when the engine's fully warmed up.

As far as dwell vs. duty, I'm not really sure I understand the difference and I've probably been using the terms interchangeably. I'm using an Actron analog dwell meter (CP7605) set to Dwell and I've connected the green/positive to the diagnostic port per this video (https://www.youtube.com/watch?v=cpNB1eRktzM) and the negative to a ground on the engine itself. All my references throughout this string to dwell settings were with the above connections. However, as I think about it, now I'm not sure it wasn't a 50 reading vs. a 60 reading with WOT pressed -- the key takeaway for me with regards to the WOT switch was that pressing it did make a difference in the reading and disconnecting it didn't change any of the readings.

If it would help, I can definitely take some videos of the meter readings again so that everyone can see exactly what I'm describing.

[Bitsyncmaster]

I haven't actually adjusted Dwell at all since I've owned it so this is still the default dwell from when I bought it and the tamper proof plug is still in place. I didn't change it after getting fuel pressures adjusted since the readings were dead on while warming up and after the 02 sensor kicked in -- Just seeing this oddness when the engine's fully warmed up.

As far as dwell vs. duty, I'm not really sure I understand the difference and I've probably been using the terms interchangeably. I'm using an Actron analog dwell meter (CP7605) set to Dwell and I've connected the green/positive to the diagnostic port per this video (https://www.youtube.com/watch?v=cpNB1eRktzM) and the negative to a ground on the engine itself. All my references throughout this string to dwell settings were with the above connections. However, as I think about it, now I'm not sure it wasn't a 50 reading vs. a 60 reading with WOT pressed -- the key takeaway for me with regards to the WOT switch was that pressing it did make a difference in the reading and disconnecting it didn't change any of the readings.

If it would help, I can definitely take some videos of the meter readings again so that everyone can see exactly what I'm describing.

Your using dwell. So book number are correct. Duty cycle numbers are 10% higher than dwell numbers.

[bueller]

Got some time to work through adjusting the mixture screw and now I have everything dialed in with dwell centering on 40 when the engine is fully warmed up. I took her for a spin today and can say she is easily running better than she has since I got her. No trouble accelerating anymore -- all stuttering and hesitation is gone.

Many thanks to Dave M, NickT and others who've assisted in this thread!!

For those needing to adjust the mixture, I was pretty gun shy given all that I'd read here but once you get everything else buttoned up properly, it's not terribly difficult. The drilling out of the tamper proof plug is the hardest and most nerve wracking part. I followed the directions on this thread (http://dmctalk.org/showthread.php?8362-Removing-the-anti-tamper-plug-covering-the-mixture-adjustment-screw) and had no issues. For those who wondered what the tamper proof plug actually looks like when it's removed, here are a couple of pictures. I tried finding similar pics so I had an idea how deep to drill, etc. and couldn't find them. Hopefully this will be helpful to others also:

Note: The screw you see is not part of the tamper proof plug, but you probably knew that already :)
54090

You can see the steel disc in the bottom of the plug that is mentioned in the link above:
54091

Thanks again for everyone's help. Nick and Dave M, if you're ever in the Dallas area, please look me up as I owe you lots and lots of beer.

[NckT]

You're welcome. I'm glad it's sorted and that the shims made the difference to the performance exhaust.

NickT

Ps I love beer ;)