Notes and references to this specific engine.

There is a wealth of information on Black Devil motors at Links are listed here for convenience.

See also the Chapter 12 article on Getting Parts.

Carburetor | Redrive Bearing Replacement | Overall List

Other articles specific to the Black Devil 172:

Black Devil Pull Starter Rebuild

My Black Devil 172 won’t start and I’m in the field. I Can’t Start My Black Devil 172.

Assuming your wing is laid out and you’ve found this on your smart phone. If you have a someone who can help, have them brace the motor.

This situation, where a motor is being recalcitrant, is among most likely times to have it 
surge to power and cut your arm off. Be careful! Be braced and be ready on every pull!

1. Try starting it withOUT priming. It’s probably too late because you’re reading this. But, in the future, do this first. Take the spark plug out, if it’s wet, dry it, then try starting.

2. Prime. Make sure you see some fuel go into the carb with no more than a few small air bubbles. Any air bubbles indicate a problem but just a few shouldn’t prevent it from working.

3. After priming, try holding some throttle in a way that will *NOT* increase throttle if the motor goes to power. It’s still dangerous and, if you have to start it with the throttle open, the motor needs work.

4. Let it sit. After priming, the motor frequently is easier to start after it sits for 2 minutes, possibly because the fuel vaporizes and is easier to ignite.

5. If you have the manual decompressor, try *NOT* using it (if you can pull against the compression). This will be hard if the compression is really good and it will always be harder on your pull starter.

Spark Plug Selection

Thanks Dave Moore and Brian Del Campo with this information.

The NGK BR9ES works but numerous pilots have found the following spark plugs to improve starting characteristics of the Black Devil motor. Namely, it may allow starting if it gets flooded. These are both resister plugs which reduces radio problems.

  • Denso W27ESR-U, recommended by the motor’s importer, Alex Varv.
  • Denso W24ESR-U, a hotter plug that was the one cross referenced to the NGK.
  • The “U” designation mean it employs their special U groove that is what helps starting when the motor is flooded. It is less likely to foul even if you overprime.
  • Both plugs are available at Autozone.


Two bearings go on large pulley. You don’t want to do this operation often, so get good bearings. #6004 c3 bearings are recommended. Here are two that work according to Alex Varv, the U.S. Importer. They carry the SKF sealed bearing. You want . Whatever you get, the numbers should have an s on them to indicate that they’re sealed.

  • SKF  6004 2RSJEM. These are available from Motion Industries, formerly many outlets were called Berry Bearing. Motion Industries does not, as of Sept, 2007
  • NSK 6004DDUCM.


Most Black Devils come with a Walbro WB37c carburetor. The membrane kit is D10-WB and you can buy the springs and other replacement parts for the carb here. MojosGear sells the complete carb which is great to have on hand. If you ever suspect carb problems, just swap them out. If the problem goes away, enjoy flying that day and rebuild the old carb when time permits. Then reinstall it to make sure the problem does not return and you now are back to having two airworthy carburetors.

When installing the kit, there are two identical membranes that come with it. Use the light colored translucent one.

Reduction Drive & Belts

For example, he found Jason belts for the Black Devil (and they only cost $11.00 vs. $48.00 from the manufacturer). That motor is now using Opti-belts which can be had for $13.00 each. At least one pilot is using a Goodyear belt which seems to work fine and is under $20.00

Decompressor Valve

The automatic valve that comes with the motor is prone to sticking in the open position. If that happens the motor will be extremely difficult to start. It must be cleaned frequently with carb cleaner or gasoline, maybe every 10 hours.  A solution is to install a manual button decompressor. You press the button to open the valve for starting. When the engine fires it closes, popping the button out. To restart, you press the button again. You won’t be able to reach it in flight so airborne restarts will be difficult at best.

The correct valve is available from Alex Varv. Another valve that works is available from as of Apr 14, 2008. Ask for the manual decompressor. It’s not quite tall enough to reach as easy as OEM but does work.

Be careful removing the automatic valve, the small hex ring on the nipple wasn’t designed to torque the whole valve out. You must have a real thin walled socket to get it out. Alex sells a special tool that comes in handy for the purpose. You can also grind down a regular socket but that takes a lot of grinding.