Where to start with Mercury 8000

[Mercury800]

I pick up a 1978 Mercury 800. It has 140 psi on 3 cylinder and 130 on the last bottom cylinder. The motor does not have the spark. Where should I start to trouble shoot it. It has a new CDI box.

 

[fastjeff]

Buy/ borrow a DVA meter. A few minutes checking with one of these (my new favorite tool) will tell you what's wrong. If you already have an ohm meter, you can purchase an adapter for yours on Amazon for about 30 bucks.

Jeff

PS: First, try disconnecting the kill wire from the switch box (black/ yellow or orange).