Rotax Hard Starting.

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BrianW

Active Member
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Jul 2, 2018
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39
Location
Altus SW Oklahoma
Rotax Hard Starting.

NGK resistor plug caps are used on many Rotax engines. Model LB05EZ is sold as a 5k ohm ( = 5000 ohms) spark plug resistor cap.

Older plug caps may go high resistance or open circuit. This makes for hard starting, and may overstress the ignition coil etc. A cheap meter with a resistance range can test these caps. A first easy check is the resistance path between the two plug cap clips at either end of an ignition coil. The resistances are additive: two plug caps at 5000 + 5000 ohms plus the coil resistance which is typically 7000 or 8000 ohms - total: 18000 ohms (18 k okm). Faulty values on hand are 40+ megohms (40000000 ohms) and too high to read.

To check the resistor cap on its own, unscrew the cap from the ignition cable. There is a 'wood' screw to capture the wire on the cap.

Resistor plugs are often used with these caps. NGK BR8ES is a 5000 ohm (5k ohm) spark plug often recommended for these engines. These can be checked between tip and central electrode. No failures have been noted.
 

pictsidhe

Well-Known Member
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Jul 15, 2014
Messages
7,426
Location
North Carolina
I've never had a resistor cap fail on me, yet. I have had several carbon leads fail open circuit. I also once had a set of 4 Bosch platinum tip plugs lose their centre electrodes after a few hours. Anything can and will break, sometime.
 

Dana

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Apr 3, 2007
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9,203
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CT, USA
My understanding is that you should never use a resistor plug with a resistor cap. One or the other, but not both. The excess resistance is hard on the ignition module.
 
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