15 hp 2 stroke intermitantly drops a cylinder.

[CJ_1080]

Hey all, I have a 1989 mercury 15 horse 2 stroke 2 cylinder tiller drive outboard. It is on the back of a 16 foot duck boat. We were motoring out to the duck pond this last weekend and everything was great, about half way you could feel a cylinder cut out, started loosing speed and running rough. We pulled the plugs and the both looked fine. We were dead in the water for about 10 minuets and then we fired it up and it ran great. On the way home same thing ran good, then dropped a cylinder and ran rough, but you could feel it trying to catch. I'm familiar with electrical problems and heat, so I took off the cover and ran it for a bit.... when I did this the engine picked right back up and ran fantastic!

when we got back, I checked the plugs and had spark at both when cold, also ohmed out the coils and they seemed fine. I might have to just run it until it acts up, and test it then???? Any suggestions on where to start or what to look for??

 

[flyingscott]

Check the switchbox.

 

[CJ_1080]

I was thinking it was either a trigger or the switch box...... is there a way to check it if I can get it to act up again? I tried to do a search on it but couldn't find any info on the style I have! Thanks for your timely response, trying to get this fixed before the weekend!!!

 

[flyingscott]

www.cdielectronics has the troubleshooting guide for your motor.

 

[CJ_1080]

Thank you Flyingscott... I do not have a DVA adapter, but I do have a high end fluke, and a analog multitester as well. I am a plant maintenance guy, so I have troubleshooting abilities, do you think I would be able to fix this with tools on hand, or do I absolutely need the DVA tools??

 

[racerone]

First run with a timing light to perhaps see which coil is acting up.-----Then switch coils to see if fault follows the coil.

 

[CJ_1080]

I will have to get the garbage can out tonight and run it until it acts up!!! Anything else you guys think I can check? I checked the fuel screen in the motor, it was clean, it has new fuel line/primer bulb, fresh premium non-ethanol fuel, I run synthetic 2 stroke oil in the gas, I put an ounce per gallon of seafoam in the fuel as well. Trying to do everything I can to take care of this thing! Sucks having problems on the water!

 

[CJ_1080]

Only reason I'm ruling out a fuel issue is when it acts up, it pukes fuel/oil out of the prop, so it is getting the fuel/oil mix.....must just not being ignited properly!!!

 

[CJ_1080]

Ok..... I officially know for sure there is no spark on the bottom cylinder. Swapped the wires on the coils and the bottom one started sparking. So it's not the coils. Ohmed out the triggers and they were within spec. Swapped the trigger wires and the spark didn't change, so in my mind that rules out the triggers. So I'm guessing the cdi switch box.....any one else have any other suggestions???

 

[Sea Rider]

It's very difficult to duplicate an electrical intermittent issue wihile engine is being tested on muffs, barrel. One thing is at idle-fast idle rpm, other at sea, lake when more throttle is in demand under load while powering a boat.

Check if someone can lend you a switch box before venturing buying a new one to rule that out.

Happy Boating

 

[CJ_1080]

Swapped the switch box with a known good one and still dead. So pretty sure it isn't the box. Is it possible that the triggers ohm out good but are bad??

 

[flyingscott]

Only one trigger on that motor highly doubtful it failed. Does spark jump 7/16" gap? What is your compression? When was the last time your carb was serviced?

 

[CJ_1080]

The spark on the top cylinder will jump a half inch gap with my adjustable spark tester. Compression is 110 on both cylinders cold. Carb was cleaned this spring. We don't leave fuel in it, we run it dry. We use premium fuel, non-ethanol fuel and we use seafoam every tank.

 

[w2much]

Run it in the dark to check for arcing. Those wires may have cracked somewhere. When it fails is when you may need to do your testing. Failure under load or heat is frustrating but it sounds like you know enough to know that. New spark plugs for certain. Primer diaphragm dumping fuel into lower cylinder? Water intrusion after warming up and under load ?