Re: frank & john... i need help !
The ignition systems on these engines are completely separate from the charging system. The alternator segment of the stator and the rectifier simply recharge the battery to replace starting power used.
The rectifier will therefore have no effect on the speed and power the engine is producing. It can, however affect the tachometer but your speed is more or less agreeing with the tachometer readings.
Losing power and gaining it back is a thankless and frustrating job to diagnose; it could be so many things, and the problem NEVER occurs while you are testing for it.
So start with the simplest, the fuel system, and be sure everything is performing properly from the tank pick-up to the carbs. As John said, change the diaphragm on general principles.
If fuel system corrections do not solve the problem, then go to electronics. Here, an intermittent short or intermittent bad ground will cause much tooth gnashing. So just do what you can. Check all wiring for corroded connections, broken wires, and grounds. If the problem is due to an intemittent problem with a coil, CD box, or trigger, it is going to be very difficult to find. And the parts are so expensive that you can't go replacing them willy-nilly to check.
