1986 kx125 project, won't rev out

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2/7/2018 5:42 AM

Hey Guys im Sham from Ireland, bought this kx125 e1 from a friend last week as an old school project for handy money, but cannot get her to rev out fully, thought it was carb needing tuning but there's no airscrew on the mikuni vm35ss, any ideas why it won't rev out? Cleaned carb and jets, too btw. Photo

Photo

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2/7/2018 5:53 AM

Very nice!

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2/7/2018 10:55 AM

check the following:
Is the Power valve opening fully?
Silencer plugged up?
Too big of a main jet?
Carb needle clip set too rich?
fresh fuel?
correct spark plug / gap?
reeds in good condition?
air filter clean?
ignition timing correct?

Check all those things and get back to us.
If everything above is good, you may have a faulty ignition component.

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2/7/2018 11:53 AM

Try pulling the choke open while reving it up and see if it gets worse (overly rich) or helps (lean)

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2/7/2018 4:46 PM

Fuel line missing in the photo.....Wet carb.....Water in carb?????

Paw Paw

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2/8/2018 10:22 AM

How is the compression? 125's need a good top end to run correctly.

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2/9/2018 2:24 AM

Okay I've gotten to do some bits during the week, checked main jet in carb and it's a 330.., I think it should have a 340, would this cause such a problem, needle clip position was okay, plugs and fuel are new, along with air filter, getting a really oily residue out of the exhaust and cylinder head, would this be an indication of to rich or lean? Compression seems okay but never tested it. Pulling choke when it's running stalls it right away, silencer is fine and clear .I'll try remove power valve assembly over weekend, have a clymer manual ordered as info is hard to come by online, thanks for the help lads ,

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2/9/2018 6:39 AM

Seamus_Kinane wrote:

Okay I've gotten to do some bits during the week, checked main jet in carb and it's a 330.., I think it should have a 340, would this cause such a problem, needle clip position was okay, plugs and fuel are new, along with air filter, getting a really oily residue out of the exhaust and cylinder head, would this be an indication of to rich or lean? Compression seems okay but never tested it. Pulling choke when it's running stalls it right away, silencer is fine and clear .I'll try remove power valve assembly over weekend, have a clymer manual ordered as info is hard to come by online, thanks for the help lads ,

oily residue out of the exhaust, and on the plug indicates a rich condition or a crank seal leak. Does it smoke a lot when its running?

I would check the powervalve next. The parts inside the cylinder were made of aluminum and were known to wear/break over time.

Crank seals also probably need replaced anyway.

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2/11/2018 11:31 AM

Okay took off the cylinder and power valve assy this evening, cylinder looks fine but piston has some damage below the ring gap, power valve assy wasn't to dirty. Still don't know why shes bogging down on me.. still convinced it's a carb issue but can't see anything wrong with it.Photo

Photo

Photo

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2/11/2018 1:21 PM

That is a lot of damage on the piston.

Paw Paw

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2/11/2018 1:33 PM

Think you found the problem...

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2/11/2018 2:37 PM

Pretty bad alright, but would it still have such an effect on performance because it's all below the ring?

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2/11/2018 4:35 PM

Looking at that piston, cranking pressure is probably pretty low. Is it hard to start ?

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2/12/2018 8:10 AM

Does it look and sound like this? I think this is the extreme- but I found it was a right side main seal issue.

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2/12/2018 2:04 PM

Ya man pretty familiar to that, gonna change seals and piston and see what happens?

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2/12/2018 2:44 PM

Seamus_Kinane wrote:

Ya man pretty familiar to that, gonna change seals and piston and see what happens?

Sounds like a plan. Keep up posted.

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