Goofy Coil Resistance

[bacon K5]

Havent seen a new thread on coil resistance in a while, so thought I'd share this for people searching in the future.

394xp running strong, but wouldnt turn off. Had good wire connections between switch and coil, and the switch was good. From reading, it seems the resistance of the primary should be in the ~100ohm range while the secondary is in the ~1000ohm range for a 1o:1 ratio.

I measured mine and found almost the inverse. Spark plug boot to ground was 238,000, kill tab to ground was 220,000, and the kill tab to the spark plug boot was 23,000.

All numbers seem to be way too high, and the resistance of the primary:secondary is almost 1:1. If the two windings are equal, it makes sense that the plug never stopped firing. Seems odd that it runs so well with a goofed up coil.

Anyone ever run into this before?

 

[albert]

Is your stop switch grounded? It should have a short jumper wire from the eye terminal on the switch to the left front carb box bolt, which threads into the crankcase.
If it runs good hot and cold I would not worry about the resistance of the coil.

 

[bacon K5]

Yes it's grounded and has good contact

 

[bacon K5]

In case anyone was following this, a coil fixed the issue. New coil was 10 ohms from kill tab to ground, plug to ground and kill tab was in the 11k range.

 

[C Dixon]

Kill switch to chassie or block ground should never read higher than 10 ohms. If higher switch is bad. There should be practically no resistance thru a killswitch.

 

[bacon K5]

Kill switch to chassie or block ground should never read higher than 10 ohms. If higher switch is bad. There should be practically no resistance thru a killswitch.

Switch to chassis was almost nothing. I was referring to the tab on the coil to the iron core

 

[C Dixon]

Switch to chassis was almost nothing. I was referring to the tab on the coil to the iron core[/

Switch to chassis was almost nothing. I was referring to the tab on the coil to the iron core

You got It right. But never test coil resistance thru kill switch. Test both seperatly. Use a good True RMS meter in the Ohm range. I use a Fluke 179.

 

[Agrarian]

You got It right. But never test coil resistance thru kill switch. Test both seperatly. Use a good True RMS meter in the Ohm range. I use a Fluke 179.

True RMS is used for measuring AC voltage and current. It has nothing to do with measuring resistance. Any half-way decent DMM should give you an accurate resistance value as long as it reads very close to 0 ohms when the test leads are put together.

 

[C Dixon]

I was wishing to point out the fact. That a quality meter is more trust worthy than a cheapo. You take a Northern Tool meter and compare it to a Fluke you will see a big difference in the readings. I'm a Commercial HVAC tech. I use meters everyday.