3 cyl merc skip

[weaselnot]

I have a 1973 65hp merc. At times it runs well with no problems. When it fails it will sometimes shut off and not restart (no spark) when you start testing, it will on its own start firring, and will start. Most of the time running (at all speeds) it will have random missfire (skips on all 3 cylinders). Its hard to test when it is cranking. I have preformed a compression test (125lb) and a major tune-up when I got the motor, new coil (cracked housing), waterpump, foot oil, rebuilt carbs, plugs and wires. Will an ignition module (switch box) fail partilly? I have checked the wires on the distribitor where the bend they are good. Can anyone help!!!

 

[Faztbullet]

Re: 3 cyl merc skip

A rotten wiring harness,bad grounds,keyswitch,mercury switch and a defective/failing trigger will do this. Remove the mercury switch first unless the wiring insulation is falling apart then replace harness..

 

[weaselnot]

Re: 3 cyl merc skip

The wirring has been repaired the ign switch has been bypassed and the grounds have been ckecked by putting one probe one the neg batt post and touching all eng componets including switch box case.

 

[Faztbullet]

Re: 3 cyl merc skip

Try disconnecting the mercury switch(#29) from switchbox(white with blk stripes if I remember) and test , if skip goes away replace it as it is a safety feature..

http://www.mercruiserparts.com/Show...bdesc=CYLINDER+BLOCK+AND+CRANKCASE+COMPONENTS

 

[weaselnot]

Re: 3 cyl merc skip

Mercury switch was removed because of short not allowing it to fire. This was the first object repaired.