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Old 04-24-2013, 05:27 PM
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Default Low compression on Kx250 after top end rebuild

Ok so I had a previous rebuild on my bike. It got a new crank, bearings, resleeved cylinder, piston and rings. The bike ran amazing after that, had a ton of compression would pop up a little in 5th with enough traction, started 1st or 2nd kick and wouldn't even have to touch the throttle to keep it going as soon as it started up. After about 30 hours it somehow developed an engine knock and the piston was scratched on the sides and the cylinder was a little as well but just surface scratches.

So I just did a simple top end. New piston and rings and the cylinder got honed out. Now after that the bike runs poorly. The kickstart feels a lot weaker which is why I'm thinking low compression and I either have to have the choke on or blip the throttle a lot to keep it going after 3-6 kicks to get it going. Once it's warm it will idle in neutral just fine but if i'm in gear just sitting and holding in the clutch it will die almost instantly.
I don't really feel like I've lost power just the easier kickstart and engine dieing concerns me. Also the piston it ran good on was a vertex piston and this time I got a Wiseco piston. Bike is also a 96 kx250.

Maybe I just need to tune the bike to the different piston? I haven't touched any of the settings on the carb yet.
Thanks for the help in advance!
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Old 04-24-2013, 05:30 PM
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Default ????

Did you check the ring end gap when installed?
What did the plug look like?

Paw Paw
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Old 04-24-2013, 05:33 PM
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Yeah I did before I installed and the manual said it was in spec. As for the plug I'm not sure I haven't looked at it since the rebuild. But I could easily go and check
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Old 04-24-2013, 05:38 PM
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Default OK

Did you check the ring gap in at least three places?
Ok, I want to know about the plug before the rebuild and the one after the rebuild.
The reason is the scratches that were on the piston and the plug can tell us a lot.
Also as I recall your engine 's cylinder has an exhaust bridge, so the question has to be asked if you put a piston in it with the holes for the exhaust bridge?

Paw Paw
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Old 04-24-2013, 05:39 PM
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Default

1 st try a compression check
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Old 04-24-2013, 05:45 PM
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Well actually my dad checked the rings because he is way better at that stuff so he may or may not have checked in 3 places. But I don't know a lot about plugs, I could just take a picture of what it looks like now. The other thing is i'm not too sure we even got a new plug when we rebuilt it last. I didn't see the plug before my dad put it in and I don't think I remember getting a new one.
Sorry for the lack of info but like I said I can always go look at the plug now or anything else
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Old 04-24-2013, 05:48 PM
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Default ????

Understand, but what about the piston?
A good photo of the plug would help.

Paw Paw
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Old 04-24-2013, 05:52 PM
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Just noticed what you said about the exhaust bridge
Well I hope so we said we needed a piston for a 96 kx250 and they gave us the Wiseco piston, it was identical to the vertex piston obviously different material though so it should have had the holes for the exhaust bridge.

---------- Post added at 06:52 PM ---------- Previous post was at 06:49 PM ----------

Yeah I will take a picture of the plug right now
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Old 04-24-2013, 05:53 PM
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Default Not really

Not really....Most pistons come without the bridge holes in them and instruction on how to put them in the piston by the rebuilder. If they are needed and are not put in then you will have a issue.

Paw Paw
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Old 04-24-2013, 06:14 PM
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Darnit, I really hope it did. Would I be able to see if it did i f I took off the pipe and looked through?
And working on uploading the picture now
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