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Fairbanks Morse 1.5 headless ignitor fouling

Reddog15

Registered
Hello,
Had my FM running at a show for the first time and had problems with the ignitor becoming fouled with carbon regularly. I would clean the contacts and it would run for about 5 minutes and then die. Lather, rinse, repeat. What is the most likely cause of this? The mix didn't seem overly rich since I didn't see any black smoke out the exhaust.
 
Last edited:

G.M.Johnson

Subscriber
Last Subscription Date
11/05/8018
I have a FM 3-hp z that sat for many years and once I got it running again the ignitor would foul out in a short time due to all the carbon build up coming off the head and the little pieces would get in the ignitor.
 

Kirk Taylor

Registered
Hello,
Had my FM running at a show for the first time and had problems with the ignitor becoming fouled with carbon regularly. I would clean the contacts and it would run for about 5 minutes and then die. Lather, rinse, repeat. What is the most likely cause of this? The mix didn't seem overly rich since I didn't see any black smoke out the exhaust.
Are you running the engine on magneto or battery and coil? If battery and coil, too much amperage can "burn" the contacts causing the engine to stop a few minutes after cleaning the ignitor. Also make sure that the ignitor shaft isn't getting sluggish from carbon/gum.
 

Reddog15

Registered
Kirk, I'm running a 12 volt battery and coil. I'm a bit rusty on Ohm's law, if I went to a 6 volt would that cut down on the potential burning?
 

MColopy

Subscriber
Last Subscription Date
11/03/2019
Ohms law tell us that watts(power) = volts x amps.
If you cut voltage in half the power to the contact would be cut in half. All the old cars with points used a ballast resistor to keep from burning up the points, you might try one on it and see if that helps.
 

Reddog15

Registered
Ohms law tell us that watts(power) = volts x amps.
If you cut voltage in half the power to the contact would be cut in half. All the old cars with points used a ballast resistor to keep from burning up the points, you might try one on it and see if that helps.

Thanks! I'll give that a try.
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
Fry gray carbon? Wet black? Oily black? For oil, you need SAE 30, about 6 to 8 drips a minute. As long as the piston is wet with oil, you are good. Too much oil or multigrade will foul the ignitor. Ignitor wet with gas is self explanetory - it is running too rich. Dry gray deposits mean too rich and too cool. These engine were not meant to idle with no load for long periods, they need to work!
 

Reddog15

Registered
Fry gray carbon? Wet black? Oily black? For oil, you need SAE 30, about 6 to 8 drips a minute. As long as the piston is wet with oil, you are good. Too much oil or multigrade will foul the ignitor. Ignitor wet with gas is self explanetory - it is running too rich. Dry gray deposits mean too rich and too cool. These engine were not meant to idle with no load for long periods, they need to work!
Dry black carbon and some pitting on the points. I'm going to figure out how to make my coil less hot and also figure out how to provide a load. I don't currently have anything to run with it. Are there good ways to provide a load without anything to run?
 

Old Iron Dave

Subscriber
Last Subscription Date
02/18/2019
halfing the voltage will result in halfing the current which will then result in one fourth the power. P=ExE/R, P=IxIxR, P=IxE.
 

Reddog15

Registered
Update; tested the ignitor today while out of the engine with a ballast resistor and it looks to have tamed the spark fairly well. Still blue but not as intense. I'll give it a try once I get my fuel feed ironed out.
 
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