no top end power

[KX 500 fever]

i need some help i have looked in the search for the anwser but i'm not able to pin it down so here i go i have a 1987 kx500 i had the bottom and top end rebuilt by a dealer ship to the tune of $1200.00 after riding it for a while it started to leak coolent in to the gear box and  it started to sputter from midrange trough top end just as it hits the power band it falls on it's face it feels like it wants to make power but cant at frist i tough it might be the carb so i took it back to the shop to have the water pump seal fixed and the carb  look at they kept it a week and relived me of another $500.00 after they did some shock work and worked on the carb they said it was fixed but they were wrong it's not so now  i'am going to fix it after looking in the search guide i'm thinking it could be the power valve if it is how do i take it apart to look at it ?do i have to take off the top end or can i do it with it on or maybe i'm looking in the wrong place can any one help me Thx 

[hughes]

Did you get a change to ride the bike before the engine rebuild? If so how did it perform? Looks like you have 1,700 in repairs and still can't ride. Wonder if the dealer pressure tested the crank case / cylinder after rebuild!! Give details about the rebuild, did they rebuild bottom end with new crank seals/bearings, rod kit etc.??

[KX 500 fever]

i road the bike 5 or 6 times before the rebuild it ran ok it was hard to start so i ran a compression test and it came out to 85 to 90 psi so i pulled off the top end and the it was hosed it had deep grooves in the walls and when i drained the oil it was silver at frist then it cleared up a little this turned out to be what was left of the clutch at this piont i would rather be safe then sorry so i took the motor in to get rebuilt they put in a new crank kept the rod all new seals and lower main bearings new clutch new pistion & rings they sent the cylinder off to get replated all new gaskets when i got the motor back we installed it and at the time we pinched the vent tube closed we road it for a 1/2 hour or so then the bottom gasket on the top end started to leak we shut off the bike and found the vent hose and fixed it then we replaced the gaskets on the top end after that i took it for a ride and it ran like it should i almost dumped it in the street when i nailed the go fast grip bad idea nothing but sky. i road it two more times after that the last time i road it i was smoking across the desert at about 3/4 throttle and it started to sputter so i limped it home and the water pump seal went out and filled the trans full of coolant i call the shop and asked them if they had replaced the seal and they didn't so i took it back to the shop the whole bike this time i told them the ploblems and they replaced the water pump shaft and seal but it still has no power in the mid or top end   

[hughes]

O.K getting water in the trans would not limit power, so maybe you have another water leak into the engine crank/case area or top end. In your post you said you had to remove the top end due to cylinder leak, at this point maybe there's an issue with another gasket. When you removed the top end did you leave the head on the cylinder or removed it? What vent tube did you pinch? The one for the radiator over flow?

[KX 500 fever]

it was the crank case vent that was pinched there was even a little oil leaking from the gasket where the two half of the case meet .if there is a air leak in the case would this cause my power lose? and can a shop check this.Thx 

[KX 500 fever]

i did replace the head gasket .when i took it back to the shop they replaced the topend gaskets again Thx

[hughes]

it was the crank case vent that was pinched there was even a little oil leaking from the gasket where the two half of the case meet .if there is a air leak in the case would this cause my power lose? and can a shop check this.Thx 

No gasket between the two cases just sealer. Yes if there's an air leak in the cases you could have this issue. If you had the cases opened up you'll see that and how the crank case is sealed off from the gear box/clutch. The shop could pressure test the cylinder/crank case area with a pressure tester. Motion Pro sells a very nice 2-stroke pressure tester. What this will do is ensure that the crank case area, cylinder/head gaskets, reed/carb boot gaskets are holding pressure. The tester has a pressure gauge on it so you  can see if pressure holds or bleeds off, then use soapy water to spray around gasket area's to see if you get any bubbles.

[KX 500 fever]

i will get a leak down tester a check it .when the crank case vent tube was pinched it must of made enough pressure to push the sealant out of case halfs. it was sealant and not oil that was coming from the case halfs this is the only thing that makes any sence to me .why else would it be running great and then it start runing like crap

[Hillclimb#42]

Makes sense. When the cases are leaking, they can suck air or oil from the crankcase side. When they pull oil, they smoke and are real rich on the jetting no matter what you do and then would run like crap on top end.