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> 2500 RPM stumble partial throttle 2.0 -4
SVG223
post Mar 15 2025, 01:35 PM
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QUOTE(brant @ Mar 15 2025, 10:06 AM) *

Agree with Superhawk.

All of the basics first
Timing valves dwell? And plugs. Fuel pressure to stock. Check the cht (that is what they put the resistor on…. Not the MPs). I would not recommend a rheostat. As it changes the mixture across all rpm. Where as a MPS tune adjust for engine load and not at all rpm. I wouldn’t ever even try to mess with an MPS unless you have an AFR installed on the car

Thanks for the info, this all makes sense. I set the timing at 29 last year but I will soon need to reset it when I replace the distributor seal. I would love to get a CHT gauge and a AFR gauge sometime in the future. My analog clock in the center console no longer works and would like to put one in its spot.
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SVG223
post Mar 15 2025, 02:53 PM
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QUOTE(emerygt350 @ Mar 15 2025, 06:04 AM) *

I chased what I thought was a lean miss for months only to find the TPS was the problem. Try driving it with the TPS disconnected. Cracking open and adjusting the mps is not a job to take lightly. At 34 lbs you will be running significantly richer than before. If you are still missing I would look elsewhere for the moment.

Will do. I just started the car without the tps connected, it is odd to me that the car runs without it. I'll take it for test drive later, I'm curious.
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SVG223
post Mar 15 2025, 03:35 PM
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Well, I tried the suggestion from @emerygt350 about disconnecting the tps, and it has the same issue with it unplugged. It ran pretty strong actually with tps disconnected and air cleaner box removed for the short test trip. It is very rpm specific with light load something cuts-out at around 2600 or so, smash the pedal runs like a champ. Dirty distributor trigger points maybe. I will continue to dig.
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emerygt350
post Mar 15 2025, 04:04 PM
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Interesting. I would also check the coil too. Although I haven't experienced this symptom from a bad coil in a 914 I have on other cars. I only mention it because it is easy to check and one more thing to knock off the list before you tear into the distributor.

It's a 75/76? So you have the retard on the dizzy? Have you tried disconnecting that and going for a spin?
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brant
post Mar 15 2025, 05:06 PM
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Doubt it is the distributor points for fuel injection

Sounds like distributor plate for you ignition points
Set the dwell and re time. Next
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emerygt350
post Mar 16 2025, 05:32 AM
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I had another thought as well... Does your car have the EGR setup? If I remember correctly that would be plumbed to ported vacuum and kicks on during cruise under light throttle. You should make sure that (if you have it) and the retard are hooked up correctly. If they are, I would disconnect them and see if the problem persists.
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JeffBowlsby
post Mar 16 2025, 08:13 AM
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A better price on the Tech Tips book - Direct from AA

https://autoatlanta.com/Tech-Tips-700-For-P...PN-RBK7074.html
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SVG223
post Mar 16 2025, 02:03 PM
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QUOTE(emerygt350 @ Mar 16 2025, 05:32 AM) *

I had another thought as well... Does your car have the EGR setup? If I remember correctly that would be plumbed to ported vacuum and kicks on during cruise under light throttle. You should make sure that (if you have it) and the retard are hooked up correctly. If they are, I would disconnect them and see if the problem persists.

On my test drive, I didn't have the air cleaner box installed so the engine wouldn't have been receiving the exhaust gas and it still had the issue. I haven't tried driving without the retard vacuum hose removed yet. I may still need to test the tps because the car doesn't run worse without it except for idle.


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SVG223
post Mar 16 2025, 02:05 PM
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QUOTE(JeffBowlsby @ Mar 16 2025, 08:13 AM) *

A better price on the Tech Tips book - Direct from AA

https://autoatlanta.com/Tech-Tips-700-For-P...PN-RBK7074.html

That's a much better price, thanks!
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emerygt350
post Mar 16 2025, 03:55 PM
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The car will run fine without the TPS. It's only an accelerator pump. It does have a trigger that tells the ECU you are at idle, activating (supposedly) that mixture pot on top of the ECU. But that is it. When I am trying to figure out ignition issues first step is disconnect that and both the retard and advance (you have EGR).


Did you trace your hose coming off the advance port on your dizzy can?
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SVG223
post Mar 16 2025, 04:23 PM
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QUOTE(emerygt350 @ Mar 16 2025, 03:55 PM) *

The car will run fine without the TPS. It's only an accelerator pump. It does have a trigger that tells the ECU you are at idle, activating (supposedly) that mixture pot on top of the ECU. But that is it. When I am trying to figure out ignition issues first step is disconnect that and both the retard and advance (you have EGR).


Did you trace your hose coming off the advance port on your dizzy can?

The advance port hose isn't connected. I keep it loose like stock.
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emerygt350
post Mar 16 2025, 06:23 PM
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Excellent. Often that gets put on something...

Well.... I guess it's dizzy time?
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SVG223
post Mar 16 2025, 09:40 PM
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I found some play in the distributor shaft. I thought I would check the gap on the points before I took it apart to clean and I measured .007" then with thumb pressure .018". I'm thinking this could be my issue.
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emerygt350
post Mar 17 2025, 05:27 AM
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Don't forget your dwell. That can make a big difference too.

Check to make sure your advance/retard plate and weights are moving freely. Pull some vacuum on the advance and retard and see if the actuator moves back to the neutral position.

Do you mean lateral play? Like bad bearings?
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SVG223
post Mar 17 2025, 01:51 PM
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Now I'm thinking about buying a dwell meter and new bushings for the distributor or buy a Pertronix Ignition Ignitor Conversion Kit. The trouble with Pertronix is sometimes I like to leave the key on to listen to the radio and I have read they burn up within a minute of being left on. 123 distributor seems excessive for my stock tuned engine.
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SVG223
post Mar 17 2025, 02:04 PM
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QUOTE(emerygt350 @ Mar 17 2025, 06:27 AM) *

Don't forget your dwell. That can make a big difference too.

Check to make sure your advance/retard plate and weights are moving freely. Pull some vacuum on the advance and retard and see if the actuator moves back to the neutral position.

Do you mean lateral play? Like bad bearings?

Yes, lateral play. My points gap varies from .007 to .018. The high number seems close but .007 is that enough to register a spark? I'm not sure if I have the tools needed to press new bushings.
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emerygt350
post Mar 17 2025, 02:56 PM
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Bad bearings can do that. If I were you I would just go with the 123. It is an incredible product and the driveability improves immensely. That is if you go that route. You might be able to find a stock one dizzy locally to troubleshoot with, but they are all 50 years old.
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FlacaProductions
post Mar 17 2025, 07:25 PM
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The petronix issue with leaving your ignition on was "cured" with the igniter II (and beyond) versions, I believe. Give them a call to double-check or someone here will chime in.
https://pertronixbrands.com/products/pertro...stributor-4-cyl
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SVG223
post Mar 17 2025, 07:27 PM
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The vacuum retard diaphragm has a hole in it. That would have raised idle speed but not sure what else.
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SVG223
post Mar 17 2025, 07:28 PM
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QUOTE(FlacaProductions @ Mar 17 2025, 08:25 PM) *

The petronix issue with leaving your ignition on was "cured" with the igniter II (and beyond) versions, I believe. Give them a call to double-check or someone here will chime in.
https://pertronixbrands.com/products/pertro...stributor-4-cyl

Oh, that would be great!
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