New to me 18 hp Evinrude.

[Bman2895]

Recently picked up a 1969-1972 18-25hp engine (still nailing down the specifics). But for sake or discussion we'll assume 18hp. I got a bit to mess with it after work. Seller said good compression and spark. Compression is good and even. And it did indeed have spark on both cylinders. It did fire up. Pumps water good. Though after a 30seconds or so it acts like it runs out of gas and putters out. Took the carb off. Someones been there before as it's had evidence of being recently " cleaned". Main jet and bowl where clean. Though the idle mixture adjustment is kinda gummy and the little oring on the needle is a damaged.

I noticed It would also go between running smoothly on 2 and occasionally it would miss. And intermittently run on 2. Then smooth back out. It does seem to do this worse as the engine begins to putter out. Checked spark and its nice and bright on one cylinder. And it's not as bright on the other. Ones a bright blue. And the others a dimmer purple ish color, but both seem consistent. On a points ignition whats more likely to cause the dimmer spark?

 

[Crosbyman]

bad - weak capacitor bad coil poor connection on the boot plug , overheating components etc.. etc....
why not just pull FW and service the ignition ... see utubes

Johnson

Maintaining Johnson E & FD Serie

 

[Nordin]

Checking for good spark you need to se if it can jump 3/8 in or more in atmosphere.
Checking for good spark with the spark plugs is not good enough.
Then as Crosby says pull the flywheel and check.
The coils at those old OMC are know as dry out over the years.
If good coils then clean the points and go from there.

 

[Mc Tool]

fuel pump or clogged filter ?

 

[Bman2895]

I'll end up pulling the flywheel. Someone changed both plug wires so connection to the coil is definitely suspect

 

[Bman2895]

Started with cleaning the carburetor. Replace some crappy looking lines. And it'll start and run in a bucket fairly decent. You still occasionally here the 1 cylinder dropping out. I fired it up on each cylinder independently and it does run on both independently however the top cylinder does the cutting out. Just like the Sparks coming and going oddly enough that was the cylinder with the brighter spark.

 

[Crosbyman]

you can try swappings parts to help find the problem child but condensers are frequently the problems. did you change them ??
try just swapping the 2 to see if the problem follows

clean the points with carb cleaner !!

 

[Bman2895]

So it seemed to clear up in the tank. So I ran it this evening out on the lake and it was doing well pushing my 14ft Crosby sled with 470lbs of people in it up to 19-20mph. Getting on plane easily. Then after a few runs it was dropping out that cylinder periodically then towards the end it wasn't firing well at all on the second cylinder. So I didn't run it anymore after that.

But I'm gonna pull the flywheel tomorrow and inspect.

 

[Crosbyman]

when it dies and while still HOT ... from plug boot .....measure HV side resistance to coil to engine body ground ...expect 4-8 KOhms

if open ... bad coil or wire wiggle things a bit incl boot did you replace plug wires yes-no ? with 7mm metallic strand wire (no CARBON wires!!)

if ok ..then back to pulling FW and checking condensers .....did you replace them ??? yes no ?

 

[cyclops222]

Any new correct sparkplugs ? Swap H V cables to spark plugs when problem occurs ? Does the bad cylinder have a slightly loose connection at either end ?

 

[Nordin]

Bman2895 have you pull the flywheel and check the points, cleaned them and set the gap and looked at the coils?

 

[Bman2895]

Okay update time. Pulled the flywheel. Found one of the condenser wires rubbed through along with the wires going into the back of each coil.

Replaced the condensers as I have some spares. Same results only really running on one. Tried to inspect the plug wires but I can't for the life of me figure out removing the timing base plate to look under it.

Pulled the coil for the top cylinder (the problem child). Snipped the wire end to make it fresh and swapped on an old coil I had spare from a 9.5. And go figure that fixed the cutting out. Tested and confirmed the kill wires weren't making continuity to ground to rule those out as well.

 

[Crosbyman]

ok looks like simple electrical problem and removing the plate is simple ...remove back corner coil long bolts and 2 base screws to lift out the assembly sorry can't posts pics now :-(


get this book it has all the info you need to service oldies...select & download store on your PC or USB or print double side and bound
https://watercraftmanuals.com/outboard/johnson/johnson-302231.htm[/URL]

 

[Crosbyman]

btw that book predates your model but... the mag is the same and so are lots of parts and concepts to service your "newer" engine

 

[Bman2895]

Yeah I'm familiar with servicing these ignitions. (How to set points, install parts etc). Though when a spark appears good when tested but cuts out when ran I don't have the experience to know what that indicates.

But it makes sense those two longer coil screws I always wondered why they were so long. Never had to remove the entire plate before.

 

[Mc Tool]

A .040" or 1mm spark on the plug while holding plug against the block is one thing but when put under 125-ish psi compression (thats at cranking speed but effectively even higher when engine is running ) makes it much harder for ignition to fire . This is why knowledgeable people will tell you the spark needs to be able to jump 3/8" or 10mm if holding the plug lead against the block. These old motors use a solid copper cored plug wire and dont like modern hi resistance plug wires or plug caps.
Im not sure of your set up but some of those old coils you can just stick a new HT lead into the coil but I think these also benefit from a bit of silicone goo to seal that lead into the coil .

 

[racerone]

But you have to remove the magneto plate in order to properly install new coils !

 

[Bman2895]

You do? I've always had luck just popping them out and if needed snipping the end of the plug wire and putting it back in. But then again. I've done say 6 of these older Johnson/Evinrudes with the points ignition so I may just be getting lucky.

Are those adjustable spark gap testers suitable? And where can i get ahold of wires with the solid copper core? It does infact have two much newer (guessing hi resistance) plug wires on it. And never knew about the goo. May need to do that.

 

[Bman2895]

Are all the old points coils the same regardless of hp? I'm fairly certain the coil i put in was from a 9.5hp. Obviously the same dimensionally. But would there be any difference in the spark?

 

[Mc Tool]

Are all the old points coils the same regardless of hp? I'm fairly certain the coil i put in was from a 9.5hp. Obviously the same dimensionally. But would there be any difference in the spark?

I would think the coils would be the same for a 9.5 and 18hp , within reason a spark is a spark . The solid copper plug wires are on ebay but I think any good auto sparkie should have some . The idea behind the goo is to provide a bit of dielectric strength just to stop sparks from leaking from that part of the coil to earth . The silicone can easily be removed later if needed , and I guess it might stop water getting in there , but if there is water getting that far inside your motor your probly to busy swimming for the shore to worry about it