If I did not run with a little valve timing retard I had so much low-end torque that I was breaking my rear tires loose when I punched it to come out of the corner. By retarding the valve timing I lost a small amount of low-end power, but it was enough to keep the tires hooked up instead of breaking loose. If I could keep the RPM’s up at a decent level in the corner, then the retarded valve timing gave me more top end power which came in about one-third the way down the straightaway. From the corner to about half way down the straightaway always is the best, and sometimes the only place you are going to be to pass someone. There is also a lot more to this than just the valve timing; the car suspension has to be set to take you through the corners as fast as you can without dropping RPM.

When I ran the Cushman motor on the dynometer the motor would turn 7000 RPM, but this was well past its best torque point. It also loved ignition advance. But dynometer test only gives you guide lines as to what a motor can do in a controlled environment, not the track performance you need. Since we ran methanol alcohol for fuel we normally ran an ignition setting between 3 /16 and 1/4 inch before top dead center (BTDC). I had 2 sets of ignition points on my motor, one under the flywheel, and one on the camshaft. You can see both of these in the pictures. The flywheel points were set at .1875 BTDC, a mild setting to start the motor on, and the camshaft points were set to.250 BTDC, an extreme advance used while racing on the track. Remember that I used methyl alcohol in this engine and alcohol burns slower than gasoline so a little additional advance was necessary. Advance is necessary so that the fuel will ignite about the time the charge is fully compressed.

Photo of the Points on the Camshaft

We used what is called a battery ignition with a small motorcycle battery and a small motorcycle coil. In my case I used a double pole switch so I could change between the two ignition settings as needed. Since we had a water-cooled the motor, we had no use for a finned flywheel to cool it. Bob Sawyer cast a 4 to 5 pound cast iron flywheel that was used in place of the factory flywheel. You can see this flywheel in the engine picture. If you tried to use less that the 4 to 5 pound flywheel, your motor would surge and not run or accelerate well. When the water cooled Cushman first came into being, we ran 6-cylinder Ford ignition points under the flywheel. It worked, but we had a lot of point bounce at high RPM, plus broken points. When Bob Sawyer manufactured the new ignition point set up for the camshaft he used Honda motorcycle points, which were far better than the auto points.

Second set of Points on the Crankshaft

Now we will talk a little about what size carburetor we used. Over a 20-year period that the Cushman ran, the carburetor that was found to be the best was the 26 mm. In fact, the 26mm Bing carburetor that came on many German and Austrian motorcycles was the first choice of most Cushman racers. I know that there are those that think 28mm to 32mm is the best, but for our application, the 26mm worked better. Velocity, Velocity, Velocity, this is the key to a carburetor for the Cushman race motor. The 26mm will run great at high RPM'S, and will not load up at lower RPM'S. When you put the throttle pedal to the floor, the 26mm accelerated RIGHT NOW, and of course this is what you wanted in our type of racing. If I were going to run the Cushman motor at the dry lakes where you put the pedal to the metal, and never back off, I would use a 30 mm carburetor.

The intake manifold that you get with your Cushman motor leaves a lot to be desired in matching up with the intake port on your Cushman motor. Here again, for a scooter to putt putt around with it works fine. Bob Sawyer cast a new combination intake and exhaust manifold out of a good grade cast iron that almost all the Cushman racers used. This manifold allowed us to mount the Bing carburetor straight out about 3 inches from the block Whether you are just trying to make your scooter run a little bit better, or you are building a full race motor, this technique is used by most. Think about 2 funnels in your mind with the carburetor mounted to the large end of one funnel, the small necks of the two funnels simulating the intake port, and the large end of the other funnel is the intake valve. Don't grind a monster of a hole into the intake port of the block. Find the areas of the block that are in the path of the incoming fuel and grind a taper from the top to the bottom of the offending area. In doing this try and keep the hole in the block as small as the stock casting, grinding only enough to clean up the bore. This type of porting will give you a venturi in the block that will increase the velocity of the incoming fuel. Here again, as I said before Velocity, Velocity, Velocity is the key. The exhaust port needs only to be better matched to the exhaust manifold, grinding only enough to create good flow. I took out all the excess material under the bigger exhaust valve.

The Water-cooled head for the motor was a 2 piece casting, made of aluminum and it is pictured here. It has a water chamber inside that will hold about a cup of water. This water was pumped thru the block where the air-cooled fins were encased by a metal jacket welded around the fin area from the top fin down to the 8th fin. The water pumped through the block water chamber, then through a connection up into the aluminum head, from the head up thru a hose to a small tank with a 1-1/2 pound pressure radiator cap. The water, which ran about 180 degrees, would gravity flow down thru 1/2 inch copper tubing on the left side of the racecar to a small radiator in the front of the racecar. A small rubber impeller water pump mounted on the motor mount and run by a #35 chain to the rear axle pulled the water thru the radiator and to the pump through 1/2 copper tubing on the right side of the race car, and then pumped the radiator cooled water back up through the block, and the cooling cycle started all over again. Look closely at the picture of the combustion chamber on the water-cooled head. Bob Sawyer flowed the head to arrive at this design. The sharp edge dumps the fuel down the backside of the cylinder and fills it as completely as possible with fuel.

Photo of the Water Cooled Head

Water-cooling the Cushman block was not hard; it took a little time and effort but it was worth it. It has been many years since the modified the last motor so I don't remember the exact dimensions of the strip of 16 gauge steel that I wrapped around the fin area of the block, but each end was flush with flat area of the bolt holes for the intake, and exhaust. I used several large C clamps to pull the metal tight to the block.