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Well, now I'm vested in this one.
Rebuilt one end of last week doing the same.
450 with stock carb and exhaust. "Stock" .25 over piston.
Plug is grey/Brown at the top, New plug.
Revs normally, haven't put the plastic on and rode it yet.
Turning red after a minute same as yours.

Have you changed the timing chain?
I'm going to take it for a brief ride to see if it's a 1/4 throttle issue.
I may have a plugged exhaust... from your video you've eliminated that !
 

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Discussion Starter · #22 ·
i honestly i think its the high comp piston on mine. yes i did the cam chain and tensioner about 900 miles be for the top end. my exhaust seems fine blew air through it no restrictions im going to pull the front cover and verify time and check the oil pump. i think i might be going back to stock everything and getting rid of the lift only keeping the gr and tires.
 

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Alright, New question.
Have you tried fresh gas?
This tank has been sitting outside of my shop for two months.
Considering how much alcohol is in gasoline these days, the water would never be visible but would lean things out a bit.
 

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Discussion Starter · #24 ·
Yeah brand new gas been ridding it for a couple months then One day it started making a weird sound on the exhaust looked down and it was glowing


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that sounds to me like it might have jumped timing
going from good to bad like that
and for issue's like these, I tend to stick to stock set up's
got old and well, tired of building bigger motors out of things for the small gains, the headaches don't some times be worth it
My new rule of thumb is if I want more HP, I buy bigger from the start LOL
I want or rather a ATv or?? with a LONG warranty and don't do anything to void it LOL

Man I hope you figure this out soon,I feel for you !
 

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Discussion Starter · #26 ·
i dont think it jumped time because it starts fine no backfiring no hard starts no backfiring through carb runs fine through the whole rpm range and through all the gears no hesitation but im gonna check time to be 100% sure
 

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Sticking slide/scuffed slide/porous diaphragm?
Did raising the needle help?
 

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Discussion Starter · #28 ·
Jetting lean or rich made no difference carbs spotless nothing wrong with the slide


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Discussion Starter · #29 ·
well removed the front cover and time is good
 

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could there be a bad bearing in the motor some place that is binding and making a ton of friction??
 

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Discussion Starter · #31 ·
I hope not I don't think so I found nothing unusual in the oil


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Scott, are you sure that your intake is nice and tight? No leaks anywhere? Have you checked to make sure the boots on either side of the carb do not have any tears in them? And that you line them up with the marks when putting them back in? Just tossing out ideas here, didn't see them in this thread yet. If the intake checks out, I'd say try and find another complete carb from a buddy to swap onto your machine and test it out.
 

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Discussion Starter · #33 ·
intake good to go sprayed it down with either no leaks i have a spare carb made no difference. i thin the next step is to pull the head and cylinder and put it back to stock lol
 

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As riccnick suggested ......
It has the symptoms of a manifold/air leak somewhere ...
 

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U could leave it bored out but maybe not a hc piston this time. That's the only difference from what I can tell


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Discussion Starter · #36 ·
As riccnick suggested ......
It has the symptoms of a manifold/air leak somewhere ...
thanks checked a couple times sprayed everything no leaks intake or exhaust
 

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Discussion Starter · #37 ·
U could leave it bored out but maybe not a hc piston this time. That's the only difference from what I can tell


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that's what im thinking maybe going back to oem
 

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I'm not saying you shouldn't go back to an oem spec piston, but, if in fact the bike was running good before with the HC piston, then this will not solve your problem. It may cover up your problem and the bike may seem to run fine, but I don't think it will solve it.
 

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Discussion Starter · #39 ·
I'm not saying you shouldn't go back to an oem spec piston, but, if in fact the bike was running good before with the HC piston, then this will not solve your problem. It may cover up your problem and the bike may seem to run fine, but I don't think it will solve it.
well next steps going to be pulling the head after that im about out of things to check so far every things 100% so that would only leave me to believe it's something with the hc piston
 

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Scott ..... could you run a thicker head gasket to drop the compression a little bit?
 
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