help with a 70 hp mercury

[todd281]

I recently bought a boat that came with a 70 hp 3 cylinder model 650 engine . The cowl says it has thunderbolt ignition . It has good compression but no spark on any of the cylinders .I have disconnected the tilt switch and it made no difference. My research so far has led me to believe that bench testing the switch box is not a option. Is there a way to bench test the trigger? Could the rectifier be the problem? Can it be bench tested? I suppose all three coils could be bad but that seems unlikely. I have checked all the wiring, and the ignition switch, they seem to be fine. Any insight would be appreciated. I will post some pictures as soon as I can . thanks

 

[Texasmark]

Does your control box have a kill switch that usually has a lanyard attached that you hook onto your body somewhere such that if you fall overboard it trips the switch and kills the triggers aka engine? Switch is usually on the rear of the control under the key or sometimes on the side toward the rear, aft of the throttle/shifter lever.

 

[todd281]

Thanks for the response There is no kill switch

 

[Faztbullet]

Download the CDI troubleshooting manual and test the stator......usually its a stator or switchbox.

 

[todd281]

I went to the CDI web site and downloaded the manual , however after looking at it, I do not believe that it applies to my system. My motor was made in 1979 and it appears that the parts,[switch bow. trigger, and stator, coils,] are original . The CDI switch box shown on there troubleshooting page has 6 wires, my switch box has ten. As far as testing the stator, could you give me a rundown on "how to" . Or perhaps point me to a web site that could walk me through it. Thanks again for all the help so far.

 

[todd281]

Ok I got spark today , After some more web searching I found a page that instructed me to disconnect the rectifier and low and behold , spark on two of the three cylinders . Weather permitting, I will check further tomorrow to see what the culprit is on the bad cylinder. thanks for all the help

 

[Texasmark]

Merc has problems with their CDIs per one of the mechanics that frequent the site and I had 2 go out on my 90 triple in 10 years. A quick check of your triggers is to swap a CDI with a different cylinder and see if the problem stays or follows the swap.