[massey478]

My experience with these motors, especially the 478 in my Massey 1100 tractor, are that most of them are under-fueled. Now that we have the percentage of alcohol in fuels we have another problem different from the fuel these motors were designed to use. When pulling garden tractors on alcohol we had to increase jet sizes a lot to get the power from alcohol. The same is true here now; the alcohol in the fuel has a negative effect. More has to be put into the motor to get the power back. 'Back in the day', 1970's, when I worked at Meyer Motors GMC/Allis Chalmers dealership we would have complaints about these motors. We would drill out the main jets about .010" size increase and power would come up, run cooler, and mileage would actually increase because the driver did not have to have his 'foot in it' so much. When the weather conditions were right we would have motors 'backside' pistons, burning them. After repairing the damage we increased jet sizes and the problem never happened again. I suspect the industry's push for fuel mileage caused some of this leaning out from the factory to happen. For my Massey with the 478 (hence my name) I had several drilled jet sizes I tried until I got what I wanted. There is also an enrichment piston in the carb that drops dowm as engine vacuum decreases, opening an enrichment jet to give the motor more fuel. My 478 would drop more RPM than I wanted it to in a herd pull before the enrichment came in so I stretched the spring on the rod for the enrichment valve until I got it to come in at less RPM drop. When it let the RPM drop too far, when it came in the power boost would cause the tractor to spin out. I also throw away the timing light and 'power' time motors, moving the distributor and trying it until I get the proper performance. We also do that with out street/race motors then mark the distributor base so we know where to set it. I also find that the standard ignition system with a MSD 6 or MSD 6al and the associated MSD coil added will help tremendously. These units give five spark pulses per plug until they reach 3,000 RPM at which time they give one. Much better than Pertronix. The MSD 6al is different from the MSD 6 in that the 6al has chips that can be plugged into the side that limit the high end RPM the motor is allowed to reach. Made the motor run much better. I think the 5 sparks per plug help these motors light the fuel more efficiently in the large bore size they have. Believe me, you do not want to get shocked by one of these units! Big no-no! Just my experience here. Others may be different, but it has always worked for me on these motors.