W7DC plugs are what's called for but I find they're too cold in all but the best engines. I use W9DC for almost everything around here and find they work better in engines that are a bit worn and run rich. I can get either plug by the box full of 10 and as many as you want.
These engines are very sensitive to ignition timing and even a small amount will make big a difference. If the vacuum switch over valve isn't working the engine won't run as well at higher speeds. It should kick in around 2,200 - 2,500 RPM's. It seems to hold longer as the RPM's are falling but comes on sooner as you pick up speed. This falls in nicely with some people reporting that their engine runs fine under 2,500 RPM.
If the engine pulls hard until you get above 3,000 RPM and then starts to cut out or misfire it's igntion related. Fuel injection problems or pump problems tend to have a constant misfire over a broad range and often with a very rich running engine. No amount of tuning or timing adjustments cure this.
If you run out of power at a certain speed and the engine just sits there no matter how hard you push the pedal or how long you hold it - that's timing. Too much retard.
If the engine looses power and seems to slow down, that's fuel. If it chugs a bit and then dies, you're out of gas.
If it starts hard like it has a dead battery, that's too much timing advance.
If it has a slight but steady miss at cruising speed, that's too much timing advance. A bad plug will have a steady miss especialy under load but you might not feel it as much at steady speed. Power loss will be very noticeable with a bad plug but with too much advance you will be loosing losts of power - you just can't feel it as much.
Dan Caron's
SL Barn
benzbarn@ebtech.net
slbarn.mbz.org
1 877 661 6061
