Missing at 3500 RPM and Above

[drolston]

Originally Posted by oldbugger

Plugs?

Please elaborate. Will plugs that fire okay at 5,000 rpm no-load misfire at that RPM under load? Does the pressure on the compression stroke go up that much? I don't think so; just on the power stroke.

[cadillac512]

Originally Posted by drolston

Please elaborate. Will plugs that fire okay at 5,000 rpm no-load misfire at that RPM under load? Does the pressure on the compression stroke go up that much? I don't think so; just on the power stroke.

Yes, compression pressure does go up that much but it's throttle opening that does it rather than load per se'. 5000 no load takes very little throttle opening and the cylinders don't get a full air charge but full load wide open does for sure. Lots more resistance to the arc jumping the plug gap under load at high rpm.