15hp only runs good cold?

[ace420ace]

Hello all, I have a 1981 15hp johnson which when first started up will run wide open no problem for about 10min then i let off throttle and go to get back to wot and it wont go, the rest of the day it will only work up to about half throttle without missing and bogging.
I ran with a timing light to see what spark did at wot and bottom cylinder was not sparking great at wot. Replaced coil same result, wires look good.
Would bad reeds cause this to happen or thermastatÉ. Will troll great all day,starts good, carb rebuilt,new plugs, pumps water fine.

Any help greatly appreciated.
Ace.

 

[kbait]

Sounds like your CD ignition box is failing.. I'd first switch coils around, run until it fails, and see if the spark failure switched cylinders. If it followed the coil, bad coil or plug wire. If the other coil failed, cd box or wiring to it from under flywheel is likely faulty.

Good luck!

 

[ace420ace]

is the cd box also called the powerpackÉ and does it cause erratic spark or just fail.
THANKS

 

[kbait]

CD box, powerpack, brainbox etc.. all the same. Can fail intermittently. Perform test described in my earlier post to help determine if it's bad, or the wiring to it is bad.

 

[ace420ace]

hello i was just out on the water and have new symptom, ran great for first 10 min as usual then only about half power,missing and sputtering so i turned it off waited 5 min and starts first pull and runs full power for 5 min then gradually runs bad missing and sputtering until it stalls , 5 min later start up and full poewer. My question is does anything fail when warm besides coils{ just replaced} or powerpack {going to replace}??
thanks

 

[AlTn]

if it has spark to either cylinder then the electronics under the flywheel are working

 

[ace420ace]

cool thats what i thought.

 

[ace420ace]

hi guys i replaced the powerpack today took it for a run on the lake and worked great for first 15 min then died on me was not able to get it going again, pulled about 100 times and got it to idle badly then die. rowed home checked plugs, top plug looks like someone dripped hot metal on it full of stuff, maybe melted?
any help would be great.
thanks

 

[ace420ace]

upon further inspection top plug was fouled with so much grey carbon couldnt see electrode, fuel issue?

 

[AlTn]

suggest you do a "decarbon" treatment < look under the Top Secret files at the beginning of the forum >, but before you go for the wot run, is there any evidence of an overheat having occurred? < discolored head or block, melted insulation on wires, etc.? > if you can put your fingers on the head/block area for 3 or more secs. you're probably ok, if you have an IR Gun 160 degs F is good...are you running the correct plugs? The safest course would be to pull the head and inspect the cylinders and pistons, but if you're certain this was just carbon fouling the plug, do the decarb and check it out afterwards.

 

[nwcove]

hi guys i replaced the powerpack today took it for a run on the lake and worked great for first 15 min then died on me was not able to get it going again, pulled about 100 times and got it to idle badly then die. rowed home checked plugs, top plug looks like someone dripped hot metal on it full of stuff, maybe melted?
any help would be great.
thanks

that doesnt sound good. ive never seen " grey carbon" on a plug......grey is usually melted aluminum, upper crank seal maybe gone?

 

[ace420ace]

will check the head tomorrow, there is some black oil, grease substance on the inside of cowl got thrown off flywheel today maybe the wd 40 i sprayed on recoil starter a few weeks ago?

 

[ace420ace]

now instead of running on one cylinder it dies after 15 min

 

[AlTn]

ok..does the spark die?..is it running out of fuel?...can you pump the primer bulb and it will continue to run?...is it overheating?...if you pull the plugs immediately after it stops, do you see evidence of water on the plugs?..beads, etc.?...check these things and post back

 

[ace420ace]

spark jumps half inch,just rebuilt fuel pump should it be hard to blow through? primer dosnt do anything, dont think its overheating no discolored head and water always pumping, top plug has grey white clumps on it, bottom is good tan color, something is going on with top plug to make it foul.
today i put it on muffs idled like a champ for 10min, i shut her off. problems come after wot.
thx

 

[AlTn]

appears that pulling the head to inspect the piston and cylinder is in order, " grey white clumps " fouling just one plug is unusual on a 2 cylinder motor

 

[ace420ace]

compression is 105 on that cylinder and 115 on other had the head off a few weeks ago all looked good will pull it off again this weekend.

 

[AlTn]

did you surface the head and use a new head gasket when you reinstalled it? if so, do the decarb treatment as outlined in the Top Secret Files and recheck the compression. If the numbers remain the same pulling the head is next.With the head off check each piston for lateral play, there's gonna be some but does one seem to have a greater amount?...roll each piston up to TDC and take it past an inch or so. Hold the flywheel to prevent the crank from turning and push the piston with a wooden dowel, plastic screwdriver handle, etc. so as not to scratch the piston top, do you feel or hear a "click" which would indicate some wrist pin wear? With those compression numbers you are bordering on the 10% allowable difference before teardown and measurements are recommended.

 

[Robert Ellis]

do you think water might be getting into that cylinder?

 

[ace420ace]

will decarb and report back, i dont know about water, how could it get in and what would it do.{head was good and flat new head gaasket}