Plug Wire Clamp

I have a question for you more experienced builders or engine gurus out there. I am testing my engine and trying to iron out a plug fouling issue. I have Bendix mags (75 hrs since overhaul) and UREM40E tempest plugs with new harnesses. I have read extensively about all the plug fouling cures so I'm not really looking for advice there but I am curious about what might have caused the blackish look on my plug wires next to the edge of this adel clamp!



I used all the white silicone clamps that came with my new harnesses but needed to secure the wires to a few more places on the motor mount with regular adel clamps like the one seen here. After running the engine the first time, the blackish color appeared. I ran the engine a very short time just warm enough to do a mag check so I know it didn't get that hot there. I have two wires clamped together at four spots with the black clamps. Two spots have this blackish color on them and two do not.

I have run the engine several times since and seem to have a plug fouling issue that skips around to different cylinders at different times despite aggressive leaning and I'm wondering if clamping these wires together with the ordinary adel clamps have anything to do with it. Thanks in advance!

I used the black Adel clamps in various places firewall forward, and they seemed to outgas and put similar dark stains on the engine mount, etc. No problems or issues, but it's just somewhat unsightly. I think the orange ones are better based on looking at a friend's -8 (he used only those and no discolorations).

That said, it does look like they're clamped awfully tight...

Mike - I've got Adel clamps on my ignitions wires on my build, and they are stained like that also - and I haven't even had first engine start yet. It's a symptom of the Adel clamps apparently.

I think clamping those wires together is your problem.

Doing so could cause them to inductively couple or cause EMI.

Try to separate them.

SmilingJack said:

I think clamping those wires together is your problem.

Doing so could cause them to inductively couple or cause EMI.

Try to separate them.

Click to expand...

I agree and I would sleeve each with some old fuel line and use a larger adel clamp, or adel clamp them individually.

airguy said:

Mike - I've got Adel clamps on my ignitions wires on my build, and they are stained like that also - and I haven't even had first engine start yet. It's a symptom of the Adel clamps apparently.

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+1

This staining is likely from the rubber, not arcing. Arching based deposits tend to be very narrow and take quite a bit of time to develop. Induction from one wire to the other won't cause plug fouling. Fouling, if related to ignition, would be from a weak spark or no spark. You are looking for resistance, not inductance to cause this. Inductance from one wire to the other doesn't steal from the source power, but can induce power where you don't want it; Also, not a cause of fouling. You want to check the resistance of all high voltage paths. If all are fouling, look at your mag.

Larry

SmilingJack said:

I think clamping those wires together is your problem.

Doing so could cause them to inductively couple or cause EMI.

Try to separate them.

Click to expand...

I don't think so, that is completely industry standard. They are both shielded, and there is no way they could arc over next to each other.

Happy to say I believe I have solved the fouling issue. My idle mixture was very rich. I leaned it out to a point where I gained 30 rpm from full rich to leaned idle. I set the idle to 700 rpm. Cleaned the two plugs again and used a magnifying glass and found tiny clinkers that I wasn't seeing before. Then I ran the engine several times with no fouling. Thank goodness it wasn't the clamps or the mags.