wet plug and slight missfire at 3/4 throttle

Skeltonsc

Member
Hi Guys I have an old Johnson 60hp 2 cylinder 2 stroke outboard motor, the motor runs and starts great however it has developed a small missfire at around 3/4 throttle and after long runs I find that the one plug is damp where the other is nice and dry.

what could possibly be the issue here? what do I need to check.

Thanx guys
 

Break Even

New member
Hi Skeltonsc. A friend of mine had the same problem with his outboard. He found a crack in the head next to the sparkplug. The head could also be corroded through.
 

Skeltonsc

Member
Hi I changed the plugs in December, made up new plug leads at the same time as the old ones where perished.

I'm also inclined to it being a carb problem, but I also think the thermostat has been removed as the motor just gets warm to the touch not hot.

I think I'm going to swop the coils and see if the problem moves up to the top cylinder or if it stays at the bottom.

anything else I can try?
 

Skeltonsc

Member
Good day guys,

I did a bit of fiddling over the weekend with the motor.

Both plugs are a nice tan color however the bottom one has a oily film layer on it.

The compression values are both 950 KPA or 135 PSI for both cylinders. Workshop manual says anything above 100PSI is still in spec.

I took out the thermostat only to find there is no thermostat, it had been removed by the previous owner.

So now I'm trying to find a thermostat as its pretty pointless to try tune anything up if the engine is not at operating temperature.

Will keep you guys posted.

Thanks
 

IWyk

Sealiner
Bottom Carb may be over fueling. The settings are quite fine on the screw so you should make 1/12(divide the screw up like a watch, for lack of a better way to explain this) turn adjustments and then run it a bit and try it.

Make very sure you know what it is adjusted at the moment(mark it and count how far you turn to get it too the bottom) so you can return to the exact same setting if needed.

Should be about 1 1/2 turn out from bottom but this may vary from carb to carb due to wear etc.

Key is to make small adjustments and then try it.

You may want to confirm that you have replaced the plugs with the correct ones. Sounds simple but if you use the incorrect plugs problems can arise.
 

Skeltonsc

Member
Howzit,

I'm still trying to find a thermostat for the motor that wont break the bank or have to wait 6 weeks for.

no body seems to stock them and I'm a little wary of getting a used one.

I had a look at the carbs and cannot find any adjustment screws on them, the carb has 3 jets and the only thing that can be adjusted is the IDLE speed and the float drop.

Any ideas while I try an source a thermostat.

Also looking for a skeg guard have phoned around but no luck
 

Skeltonsc

Member
So far so good, I couldn't source a thermostat locally and was not going to pay in excess of R600 for a simple thermostat.

I managed to find a motorcycle one the opens at 88 degrees that fits perfectly.

Ran the motor in a drum over the weekend and the thermostat is opening and the motor gets up to its operating temperature now.

Now I need to get my skeg repaired and find a skeg guard

as I damaged this on a rock in December while reversing near the edge of the vaal dam.
 

Skeltonsc

Member
Howzit Guys,

Just an update on my problem,

took the boat out this weekend for the first time in a few months.

engine now runs at the correct temperature with the modified motorcycle thermostat.

but the bottom plug still runs wet.

the miss fire that I was hoping to sort out has gotten worse

the boat will run perfectly for about a km then it will bog right down and miss, if you stop and rev the engine it revs fine then put it back into gear it will sometimes go then bog down again in a few seconds. I've checked the float levels both carbs are set the same

the top plug burns nice and brown the bottom one stays a black color

I've now swapped the coils to check if the problem moves to the other cylinder

will check again over Easter weekend.

Thank you
 

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trier

Senior Member
Are you sure there is no mixing screws on the carbs? (very strange). Have you tried a different heat range plug (hotter)? Had something similar where i trolled it fouled plugs and when i tried to accelerate it missfired. Went one one plug hotter and all fine (from B8HS to B7HS). You say you have a workshop manual, recheck the exact float measurement. Also is it autolube or premix??
 
its clear from the black plug mixture is not right.

plenty of aspects.
could be bottom crank seal.....
If I were you, change carbs, bottom to top.
then run it again. but place brown plug at the bottom, so if colour changes then its easier visible.

don't fiddle to much with settings for now.

do the simple stuff first.

2 stroke motors are brilliant, easy to maintain, operate and to understand.

Iwyk................

die laaste ding is kompressie toets.
die manne moet leer om die basics eerste te doen, die simple maklike goed.
ons moet net leer om die manne reg raad te gee!

dit help nie ons sit die manne op loop nie......hulle verllor hengel tyd.
 

Skeltonsc

Member
Hi Guys I'm still certain that its an electrical problem with the coils or CDI as the boat misses randomly.

When it does go it goes very well and gets on the plane easily since the new Prop was fitted.

I have changed the plugs and swapped coils around to see if the problem follows the coils.

Failing that I will swap the carbs around as its a simple job on an old engine.

I'm going to try take the boat out this weekend to see what she does.

Thanks for all the advise so far. I did do a compression test as the motor is 36 years old and I have only had it just over a year now.

I'm also leaning to crank seals being old and brittle because when I took the powerhead off the other day to modify the thermostat the gaskets all disintegrated, so maybe a bit of preventative maintenance is not a bad idea.

I'm also trying to find carb kits on this motor but the dealers that I have asked for quotes simply don't get back to me.
 
change the HT leads
If they are old they should be carbon and they do crack and cause a miss fire at revs
check the caps as well
 

colindt

New member
Fuel pump diaphragm has a crack or pin prick hole in it and excess fuel is getting into the cylinder via the pulse pipe.
 

Skeltonsc

Member
Hi, thanx for the advise,

I forgot to mention that I have fitted new HT leads as the old ones were leaking sparks everywhere.

I also repaired the fuel pump diaphragm because the fuel pump was leaking externally.

will try take the boat out on Sunday and see what the coil change does.

I'm leaning towards a coil issue or a float that is sticking however just seems difficult to get parts on this old outboard.

Thanks
 

Skeltonsc

Member
Howzit,

Havent had a chance to take the boat out yet but as promised here are some pics.

While I was taking some pics I noticed that the top crank seal is leaking under the stator/flywheel

here are the pics as promised.

Thanks
 

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Skeltonsc

Member
here is the top carb, I cannot find any adjustment screws on these,

the part number is 325343 stamped on them
 

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