1985 50 hp Cylinder dropping

[srussell28]

I have read the Cylinder drop test and need help. I have a 50 hp that I get the spark and have a timing gun, the gun lights up on 1,2,3 but doesn't light on 4. When I pull off the plug wire it DOES drop down and almost cut off. I also have a spark jumper and can see the spark, but it must be weak because the gun will NOT light on the 4th cyl. Have changed everything, New stator, trigger, switch box, coils, plugs and wires, rectifier. I have checked all the wiring many times and can't find whats wrong. I have good compression I get 135,135,130,135. Where do I go now? please help.

 

[Laddies]

Re: 1985 50 hp Cylinder dropping

Start by telling us what the engine is doing or not doing, what prompted all the parts changing, as you have learned, at this point throwing parts at a engine is costly and won't repair it so lets start at the begining with the basis problem

 

[srussell28]

Re: 1985 50 hp Cylinder dropping

It started end of last year, on the way back on a trip out the boat would only go 7-10 mph. Got home took out the carbs, rebult them with a full kit on both. Had a mercury man make sure they were perfect, they were. Change out the fuel filter and the gas lines, gas tank. No CHANGE. Ohm out everything, the stator was bad. Replaced it. Same issue only 7-10 mph. Changed out the rectifier it was not charging the battery after changing the stator also install a RPM Gauge. check spark, was getting a weak stark on 1 and 2 nothing on 3 and 4. Change the SWITCH box and ran better was able to get up to 16 mph, but was missing bad the 4th cyl will not light the timing gun, but I can pull the plug wire off and the motor will drop and almost cut off. Changed all the plugs (gapless) and plug wires. cHECKED every wire looking for a short found that the wires on the trigger were breaking down, but it would ohm out. Changed it out and still the same. The motor is only getting 3000 - 3500 rmps IN THE WATER out of the water it will rev past 5000 rpms. The prop is not spun. Timing is set. Thanks for any help you can give.

 

[Laddies]

Re: 1985 50 hp Cylinder dropping

Well I guess things that I would look at, did you repair the fuel pump, is the timing right 30 degrees, the primary pickup arm should just touch be touching the primary cam on the distributor, are both carbs. going wide open at full throttle. With all of this right we must go back to the ign. system, as you may have guessed by now an OHM meter to test a ADI system don't work well, you really need a DVA and espeically in a problem repair. At this point I would beleive you have a low voltage problem, it could be cause by a bad component that was installed or a bad connection in the system, start by swapping coils on 3 and 4 cyls and see if the problem moves.The next advice is see if someone you know has a DVA and will lend it to you or test the system for you. Stator voltage should be,-- blue/white=180v. or more,--red/white=25v. or more, trigger wires 4v. or more connected to the switch box, if 1 fails cross 2 of the wire to see if the problem move a shorted switch box don't, 180 on each of the green leads to the coils.

Here are some rules of thumb for the ADI system on your engine and may help you to understand the working of it.
No spark disconnect the black/yellow wie at the switch box and retry
The systems power comes from 2 winding a low (blue) and high (red) speed winding if the engine only idles well and don't run at high speed it's usally the high speed winding, test by connecting a DVA to the blue wire and runnig the RPM up it should read well above 200v. if there is a voltage drop just before the engine level off the stator is bad.
The trigger is 2 windings so a bad trigger always effects 2 cyls, 1 and 2 or 3 and 4 as each winding fire 2 cyls and if it is broken it will effect both cyls.
If the engine is losing spark on only 1 cyl. it must be a coil or wire on that cyl. or the switch box. hope this helps--Bob