Re: 69 Johnson 40hp can't keep running
100 is OK for that 40 hp. Basic timing on that engine is controlled by the flywheel key and the points setting. Points should be .020" at the most open they can be...at the high point of the cam.<br /><br />Beyond that, timing is controlled by the rotation of the armature plate, where the points are attached. This takes place when you move the throttle and continues as the throttle butterfly in the carb opens. The timing is advanced as the throttle is opened.<br /><br />You should check to see that the timing plate is moving as you advance the throttle. It's unlikely that it is not. There is also a link and synch operation in a complete tune-up, but that won't usually affect idling.<br /><br />Other reasons, fairly rare, for poor idling are bad reeds, a crankcase leak, poor carburetor base gaskets, and incorrect spark plugs.<br /><br />Most often, a poor idle is carburetion, especially if the engine can be made to run up at higher RPMs. I haven't worked on a Big Twin as late as yours, so I don't know the carburetor that well on that model. Mine's a few years older, and there were changes.<br /><br />Odds are that your problem is in the low speed fuel circuit, controlled by the low speed needle near the top of the carb. A bad packing nut is not an uncommon problem, causing an air leak. Also, there are small fuel passages and orifices on that engine that are easily clogged. That's the reason for the complete carb cleaning, including removing the plugs and blowing out all fuel passages.<br /><br />This engine should idle very well. The Big Twins were excellent idlers, because of their heavy flywheel. Mine will idle at under 400 RPM in gear, and quite smoothly, so don't be satisfied until the engine idles nicely.
