78 Black Max 1500 only firing on one cylinder

jd0g255

Recruit
Joined
Feb 21, 2012
Messages
5
this whole week i've been out on the water on my boat. i'm going to add this just in case it has anything to do with the main problem: about two days ago i lost the power trip gauge. the trim still works, just the gauge will read all the way down, and won't change. the real problem is that i was cruising along perfectly fine, slowed down for a slow no wake passage, and then the motor sounded much more quiet and less shakey, like i lost a couple cylinders. tried to punch it coming out of the slow no wake and have no power, moving maybe 5mph faster. i slowly made it back to dock which was only about 100yrds away. pulled the cover off, started the motor, running really rough, started pulling the spark plug wires off the top of the spark plugs and only one is sparking.

so i dont think it has to deal with the plugs themselves, they are brand new, only 3 mont]hs old. boat has been running great all summer so far since may. what exactly should i be looking for to be the problem? or what should i replace first to see if thats it?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 78 Black Max 1500 only firing on one cylinder

It is doubtful that motor would run on 1 cylinder. Take a compression test and a spark test and report results.
 

jd0g255

Recruit
Joined
Feb 21, 2012
Messages
5
Re: 78 Black Max 1500 only firing on one cylinder

the boat fires on 2 cylinders, 2 and 6. but only those two. compression good.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 78 Black Max 1500 only firing on one cylinder

OK, look on the CDI Electronice we page for the ignition troubleshooting guide for that motor.
 
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