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Loss of power/speed at full throttle

J

jrile005

New member
I have a 1985 15sk that I bought a few years ago and had it worked on because it was stuck in the forward gear. When I got it back I took it to the lake and ran it to see how well it would perform. It ran fine for a few minutes but then I had a loss in power/speed at full throttle. It runs great at half throttle but immediately has the loss at full throttle. I spoke to the shop that worked on it and they wanted me to bring it back to them (after an argument about a seal kit that may or may not have been installed) but I do not like the way I was treated and they were VERY expensive. I am trying to run it on a 1448 flat bottom jon boat and my father seems to think that the problem is cavitation, but I know nothing about this. The prop is a little worn but nothing serious and I have checked the splines inside the prop, and on the drive shaft. Ive also checked all the bearings and there appears to be no problem with any of them. Does anyone have any insight as to what the problem may be?
 
jrile005 said:
I have a 1985 15sk that I bought a few years ago and had it worked on because it was stuck in the forward gear. When I got it back I took it to the lake and ran it to see how well it would perform. It ran fine for a few minutes but then I had a loss in power/speed at full throttle. It runs great at half throttle but immediately has the loss at full throttle. I spoke to the shop that worked on it and they wanted me to bring it back to them (after an argument about a seal kit that may or may not have been installed) but I do not like the way I was treated and they were VERY expensive. I am trying to run it on a 1448 flat bottom jon boat and my father seems to think that the problem is cavitation, but I know nothing about this. The prop is a little worn but nothing serious and I have checked the splines inside the prop, and on the drive shaft. Ive also checked all the bearings and there appears to be no problem with any of them. Does anyone have any insight as to what the problem may be?
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Hi,
If it runs fine at half throttle, and loses power at full tap, you may find that you have a fuel starvation problem. I suggest you check for fuel line leaks or it may be sucking air into the line. Also maybe strip and clean carburetor/s. I doubt whether the prop would have anything to do with it.
 
I think it is a fuel flow issue to the cylinders. Whatever you do, don't push it. STOP NOW! You'll fry cylinders at high RPM as I learned the hard way about partiallly clogged fuel jets. Pull those brass fuel jets from every carb and make sure they are perfectly clean and clear. Blow carb cleaner through them. If I were to guess, you have partially clogged fuel jets gummed up with this ethanol fuel we have been subjected to. The problem doesn't show up until you are trying to feed serious fuel at higher RPM's. Clean those jets and see if the problem goes away. Even if the problem goes away, pull all the carbs and clean them all thoroughly with carb cleaner. Restricted fuel to any cylinder in a 2-stroke is the kiss of death. Low fuel at high RPM = Low lubrication provided by the oil in the fuel to that cylinder.
 
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