Ready to use 15hp johnson for boat anchor!

[billytewalt]

Please help! I have a 1995, 15hp johnson that wont run right. I pull the carb off, completely disassemble, clean with carb cleaner, re-assemble and motor runs and trolls fine for about 3 hours. after 3 hours engine dies while trolling and pukes out when given any throttle. i also notice a milky substance coming from the exhaust at the prop at this time. i have replaced everything from the tank to the motor. i have repeated this carburator cleaning process several times and always get the same results after 3-4 hours of trolling time. ??????what is happening and is the milky discharge related to my problem? Anyone please help!

 

[Davem3]

Re: Ready to use 15hp johnson for boat anchor!

i almost want to say head gasket, water is getting in the cylinders, but NOT 100% ??? (milky white substance)

the dying issues reeks of a electrical issue, when the coils / powerpacks get hot when bad, they carp out ( dying issue)

trolling is not always good, run it at WOT here and again to keep the cylinders clean ............ (dying issue)

hmmmmm, for now skip my first 2 recommendations and check the plugs and check for spark when hot? ????

let us see what that yields ????

 

[oldcatamount]

Re: Ready to use 15hp johnson for boat anchor!

Wrong plugs, or maybe the right plugs that are gapped wrong? Try opening the gap to .040.

 

[billytewalt]

Re: Ready to use 15hp johnson for boat anchor!

i almost want to say head gasket, water is getting in the cylinders, but NOT 100% ??? (milky white substance)

the dying issues reeks of a electrical issue, when the coils / powerpacks get hot when bad, they carp out ( dying issue)

trolling is not always good, run it at WOT here and again to keep the cylinders clean ............ (dying issue)

hmmmmm, for now skip my first 2 recommendations and check the plugs and check for spark when hot? ????

let us see what that yields ????

will check plugs as suggested tnx

 

[NovaNewfie]

Re: Ready to use 15hp johnson for boat anchor!

Is it smoking when you try to give it throttle? I guess on a thru prop exhaust it would be hard to tell. To me it would seem like you're oiling up by trolling that long and not burning the oil off by running at low rpms and that's what the discharge is. If you run it WOT for a bit here and there like every hour while trolling it might help. Check the plugs and see if they are fouled.

 

[Haffiman]

Re: Ready to use 15hp johnson for boat anchor!

Change impeller if you have not done it in the last year, check the thermostat function.(leaking membrane or stuck pin in vernatherm)
Check that the ground cable on the powerpack is attached to the UPPER screw and not the lower.
Use QL82C spark plugs.
Decarb the engine before adjusting the carb and idle.

 

[1946Zephyr]

Re: Ready to use 15hp johnson for boat anchor!

Do the plugs appear to get water on them? Is this a salt water motor? I have seen pinholes develope on the inner plate under the exhaust cover. These will tend to squirt water into the ports and into the cylinder.

 

[billytewalt]

Re: Ready to use 15hp johnson for boat anchor!

ok, not too scookum on how all this works, so i'll try to reply to everyones suggestions. this motor has been in the salt water but was always fresh water flushed afterwards. I did a compression test on it (cold) and got around 90lbs on each cylinder. then i warmed it up in a barrel of water and let it run in and out of gear for around 40 minutes, putting it in gear, neutral, and winding it up in between. after aprox 40 minutes, with it in gear and idling, it just died and would not restart. so, i then jerked the plugs and did another comp check on it while it was still hot. both cylinders only came up to 75lbs this time........is that normal? or is that a head gasket? also, can you go into a little more detail as far as the exhaust gasket that may be leaking? where is it? something that i can replace?

 

[Haffiman]

Re: Ready to use 15hp johnson for boat anchor!

I'm tempted to believe you may have some stuck rings.
Put the engine in the barrel, load it up with Engine Tuner and let it sit over night, run out the engine tuner and re test if any change in compression.

 

[Haffiman]

Re: Ready to use 15hp johnson for boat anchor!

If no change after de-carb, time to pull the head and check for a blow-by between cylinders. You will need a new head gasket.

 

[scipper77]

Re: Ready to use 15hp johnson for boat anchor!

I wonder if the head is overheating slowly due to barely inadequate flow from the impeller at trolling speeds? I guess what I'm really thinking is that if this does turn out to be a head gasket or warping head there may be another problem that is causing it.

Milky discharge is almost certainly oil and water and the only two sources of oil I know of is the 2 stroke oil and the lower unit gear lube. Is there milky discharge at all times or does it only happen after you have been running for a while.

 

[oldcatamount]

Re: Ready to use 15hp johnson for boat anchor!

I had a '88 15 hp and it ran like crap till I read the manual and re-gapped the plugs to .040.