The rotating mass of a stock flywheel absorbs horsepower. Installing an aluminum flywheel on a Honda GX160, GX200, GX340, GX390 or a clone engine will free up some rear wheel horsepower.

The stock flywheel and fan on the left weighs in at 5.8 lbs. The aluminum flywheel on the right weighs 3.4 lbs.

Remove the recoil starter and fan shroud. Remove the flywheel nut and thread it back on just a few turns. You are using the nut to protect the threads on the end of the crank so make sure the threads are not exposed.

Use a big screw driver to put pressure on the flywheel in the direction it needs to go in order to slide off the crank. We slide the screw driver between the flywheel and engine block, using it as a pry bar. While applying gentle pressure against the flywheel, hit the end of the crank with a hammer. I know this sounds like a caveman method of removing a flywheel, but this is a very commonly used method. You're going to give the end of the crank a hit with a hammer, right on the flywheel nut which is protecting the threads. This will jar the flywheel loose, off of its tapered shaft.

After the flywheel has been removed you need to take out the flywheel key. The bottom of the key is shaped like a half moon. Use a punch with a small flat tip to tap the flywheel key out of the crank. If you tap one end of the key down, into the crank, the other end will rotate up, out of the crank. Then you will be able to grab the key with a pair of pliers and pull it completely out.

Put the key in a vice and file down a step into the key. Every 0.006" you remove from the key is equal to 1 degree advance. So if you remove 0.048" you will have 8 degrees advance. A set of digital calipers will work great for determining how much material you have removed from the key.

If you don't have calipers or a file you can purchase an advanced timing key.

When you are finished, you can install the key back into the crank. Note the correct position of the filed key in the picture. Slide your new aluminum flywheel onto the shaft, making sure the mating surface of the flywheel and shaft is very clean. Once the flywheel is on the shaft and over the key, rotate the flywheel clockwise until it stops against the key. With the flywheel in place, install the starter cup and flywheel nut. Tighten the nut to 60ft.-lbs.

With the new flywheel installed you need to set the air gap on the coil. Loosen the two 10mm bolts holding the coil in place. With a feeler gauge, set the gap between the coil and flywheel to 0.020". Tighten the coil bolts and re-check the gap. Then rotate the flywheel just to make sure it's on straight and it does not come into contact with the coil.

When everything looks good, re-install the fan shroud and recoil starter. Now you are ready to go!