Diagnosing a stumbling type 4 Engine

[telford dorr]

Coil resistance readings, unless way off, are generally a poor indicator of coil condition. Best diagnosis is to swap in a known good coil and see if the symptoms improve.

I assume you've checked the points and the points plate ground wire.

Might swap in a known good condenser (although "new" ones have been somewhat marginal lately...).
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'71 panel, now with FI
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[Whaanga]

Thank You - I've 'looked' at the points and cleaned them with some fine grit sand paper. I checked the connections on the condenser and didn't 'see' any anomalies. I have a new coil, condenser, and a new set of points standing by but want to test each component separately rather then just swap out parts without a logical approach.

From what I can see here, the connections look solid.

As I said in my earlier post, electronic diagnosis kicks my butt so am grateful for the help here. I'm trying to learn how to work through the components systematically track to down the problem rather than just swap out parts and 'hope ' for the best.
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Late 1973 Bay w/a transplanted 914 Engine

[telford dorr]

[Hoody]

It sounds to me that you are having intermittent spark issues causing the engine to miss on one or more cylinders. I know that some people here have had excellent results with NGK plugs and wires. I am a big fan of Genuine Japanese parts. Even if this does not solve your problem it will be money well spent. But I have a feeling that one or more of your spark plug ends is not continuously operating as it should which is why you are getting good to decent to bad back to good results. These engines vibrate quite a bit unless they are perfectly balanced. NGK plug wires do not have the issues that many of the other brands do in this regard. Just a thought.

[Whaanga]

Thanks Hoody,

Again, trying to learn to diagnose as opposed to swapping out parts and hoping for a change, how do we evaluate the health of the plugs? Obviously, they can be removed and inspected but if they 'look' to be in good health, how do you determine if they are firing properly?
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Late 1973 Bay w/a transplanted 914 Engine

[Whaanga]

I pulled the plugs and as you see, there is lots of buildup from my overly rich running carb. Might this have an effect on the intermittent issue I'm dealing with?

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Late 1973 Bay w/a transplanted 914 Engine

[Hoody]

Yes....those plugs will definitely cause issues. PM sent.