Outboard Engine Repair

mikefossl · #1 (**permalink**) 09-25-2011

I've got a 10yr old Nissan 5HP 2 stroke outboard that I have grown to hate. It was running reasonably well for the past few years with the ocasional hard start but now it decided to just stop in mid stride. The first time it happened I decided to do some overdue maintenance including cleaning the carb, changing the plug, replacing the water pump and overall spit and polish.

It started up and I ran it around for a bit without trouble. After about 10 minutes of steady 1/2 throttle running fine it suddenly stopped and would no longer start. I checked the vent, we had just fueled up and I checked for water in the carb all ok. I pulled the plug and could smell gas but it wasn't wet. I could only see a weak yellow spark on the plug.

I'm thinking I have a weak coil (and probably have for a while which caused the hard starting). The parts diagram says I have three coils: exciter coil, pulser coil and ignition coil. I'm assuming the exciter coil charges up the ignition coil and the pulser coil sends the signal to fire the ignition coil. Since I'm still getting some spark can I assume the ignition coil is the problem?

Lastly, I'm currently sailing in Japan and interestingly enough getting parts for my Japanese outboard is a problem. They do have some aftermarket coil/wire combos for scooters that look like they would work. Any problems giving that a try?

thanks,
Mike Fossl
S/V Second Jump

dabnis · #2 (**permalink**) 09-26-2011

Using a different ignition coil might be a challenge? If you are getting any spark at all the exciter and pulsing coils may be OK? A new ignition coil may be the answer assuming it is not a fuel related problem. I assume you have checked all connections and wires for chafing or breaking? Let us know what you find.

Dabnis

Ulladh · #3 (**permalink**) 09-26-2011

Before replacing coils check all connections as dabnis suggested, then spray the plug cap and cable with WD40, let sit for a few minutes then check the plug spark again. If the spark is better then you have moisture in the cable or cap rubber, replace plug, cable and cap.

INMA · #4 (**permalink**) 09-26-2011

Clost the plug gap a bit to reduce the voltage needed to get a spark.

Run the outboard on 75:1 oil mix to reduce any chance of a fouled plug.

Make sure you have an NGK plug, all the other brands are rubbish.

Check the fuel pickup and fuel lines for air leaks. If the tank is positioned very low try raising it to reduce the suction needed to get the fuel up. Is the fuel tank reasonably full and the petrol reasonably fresh?

Spilt fuel near the internal tank or any of the fuel lines will get sucked into the air inlet making the engine run rich and stall. If it runs ok with the engine cover off and poor with the cover on, look for fuel leaks or spilt fuel near the engine. I never let my internal tank get more than 1/2 full because any splash from the tank cap causes rough engine running.

Does fuel spill when you prime it.

mikefossl · #5 (**permalink**) 09-28-2011

The fuel tank is above the carb so no problem there. I'm not getting any spillage into the engine case. I am using NKG plugs and 50:1 fuel/oil mixture.

At this point the engine won't start and I'm investigating whether changing the coil is a good option. One other bit of info: when we changed the plug we went with a resistor model (which is an option for the engine). The motor wouldn't start with that plug nor could I see any spark when I checked. When I cleaned up the old plug (non-resistor version) and put that one in, the engine did start and ran for a while (see above).

I'll try closing the gap on the plug to see if I can coax a better spark.

dabnis · #6 (**permalink**) 09-28-2011

Quote:

Originally Posted by mikefossl

The fuel tank is above the carb so no problem there. I'm not getting any spillage into the engine case. I am using NKG plugs and 50:1 fuel/oil mixture.

At this point the engine won't start and I'm investigating whether changing the coil is a good option. One other bit of info: when we changed the plug we went with a resistor model (which is an option for the engine). The motor wouldn't start with that plug nor could I see any spark when I checked. When I cleaned up the old plug (non-resistor version) and put that one in, the engine did start and ran for a while (see above).

I'll try closing the gap on the plug to see if I can coax a better spark.

Sounds like the ignition coil is bad or going bad. If closing the gap works it probably won't be long before it fails completely. All this assumes all the wiring and connections are OK. Generally speaking electrical parts are not returnable so if it turns out not to be the coil at least you have a spare

Dabnis

tommays · #7 (**permalink**) 09-28-2011

I would do the service manual by mail order from a place like internet outboards as it will have a WAY to test the parts

dabnis · #8 (**permalink**) 09-28-2011

You can test the primary and secondary windings for continuity to ground with an ohm meter. Extremely high resistance or erratic readings may indicate trouble. As mentioned above a shop manual may give you what the values should be. Or you might try readings on another working motor to see if they are similar. If the coil is marginal it may start to fail after running for a while due to heat build up. I am guessing but I think a new coil wouldn't cost more than $75 or so? Parts changing is not very scientific but with all the solid state magic stuff it can be the easiest. Also, a shop may be able to test the parts for you?

Dabnis

mikefossl · #9 (**permalink**) 09-29-2011

I went back to the boat and after checking all the connections and reducing the gap a bit the motor started right up. I pulled the coil and found rust on the core as well as a gap between the insulation and the core where moisture might get in.

We also found a local Tohatsu dealer and I spoke to a mechanic. He suggested it may also be the exciter coil that was failing but we decided to order a new ignition coil and plug and see if that did the trick. I should get the coil next week and I'll post any further developments.

mikefossl · #10 (**permalink**) 10-07-2011

After installing the new coil the motor started up first try. Once I got everything set up on the dinghy for a test drive...nothing. Next morning I tried again and it started but again only once. I brought it to the shop where a couple of mechanics tried for 20 minutes to get it started with no luck. I have fuel, compression and spark. Looks like what's left is timing which means CDI unit? Anyway hopefully I'll know in a few days. Meanwhile I'm drooling over a brand new 5 HP Yamaha 2 stroke...hopefully the Canadian dollar rebounds soon.