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Moped Riders Association • View topic - qt50 cylinder mod questions

qt50 cylinder mod questions

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qt50 cylinder mod questions

Postby matt76 » Sun Jul 12, 2009 7:13 pm

i talked to the guy that owns PAX racing. i told him i wanted to do everything i could to get better low end power. i'm not worried about my top speed, 35 is fine, but i want to get there quicker. this is what he told me.

shave the cylinder anywhere from 30 to 45 thousands, not the head.
jemco pipe
tighter clutch springs
keep the qt gears
k & n air filter
no boyseen power reeds, he said he didn't like these, he said he used to modify the reeds from a KX60 to fit the qt.


what does everyone think? she's only a 50, no 60 kit yet. i have done everything except shave the cylinder. he also said porting and matching would not help much with the low end, only if i wanted more top end would i port.
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re: qt50 cylinder mod questions

Postby champ50 » Mon Jul 13, 2009 10:51 am

which part of the cylinder where it mates to the engine or the head? also if ur gonna do that its gonna give it more compression, therefore needing more fuel to fire it and more vacuum to suck the fuel in and air so porting the intake and exhaust is gonna give it more power. Basically a smoother air and fuel flow through the motor and increasing its effientcy..
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re: qt50 cylinder mod questions

Postby supercub » Mon Jul 13, 2009 2:38 pm

To shave the cylinder you need machine shop grade tools to mill or grind the head. If you don't like the results the cylinder is trash. Shaving the head requires the same tools but if your'e not happy you can add gasket thickness to go back to where you were. You can start with a thinner gasket. A pipe with the expansion chamber close to the cylinder will give you more top end.
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re: qt50 cylinder mod questions

Postby champ50 » Mon Jul 13, 2009 4:50 pm

so what end do i shave?
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re: qt50 cylinder mod questions

Postby matt76 » Mon Jul 13, 2009 7:27 pm

pax told me they shave the face of the cylinder that mates with the head. they have a jig there they made to accomplish this. i was clear with him that i was looking for the most bottom end power. we talked about the head shaving only for top end.
anyone have any first hand experience with this?
PAX does all kinds of upgrades for the pw's and similar other bikes.
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re: qt50 cylinder mod questions

Postby xrongor » Wed Jul 22, 2009 8:45 pm

"In this world there's two kinds of people... Those with loaded guns, and those who dig." -- Blondie to Tuco
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re: qt50 cylinder mod questions

Postby maddog » Thu Jul 23, 2009 8:27 pm

Some people dream about speed! blink and im gone!
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re: qt50 cylinder mod questions

Postby xrongor » Sat Jul 25, 2009 9:31 pm

there is no front pulley. its a QT50 with a centrifugal clutch. spings might help a little, but not nearly as much as an extra 10 cc's with higher compression.

randy
"In this world there's two kinds of people... Those with loaded guns, and those who dig." -- Blondie to Tuco
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re: qt50 cylinder mod questions

Postby matt76 » Sat Jul 25, 2009 9:55 pm

i have the heavy springs on there, i also have a set of extra heavy that i haven't tried yet. the rpms run a lot longer before she really takes off. but its nice.

i'm just trying to figure out what shaving the cylinder and not the head does for you. it has to do something different.
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re: qt50 cylinder mod questions

Postby maddog » Thu Jul 30, 2009 6:38 pm

Some people dream about speed! blink and im gone!
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re: qt50 cylinder mod questions

Postby matt76 » Thu Jul 30, 2009 9:28 pm

is there any difference in milling one over the other? or is it just three ways do get the same result?
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re: qt50 cylinder mod questions

Postby xrongor » Mon Aug 03, 2009 2:09 am

if you just mill the top of the cylinder, its exactly the same as milling the head.

randy
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re: qt50 cylinder mod questions

Postby oilyhans » Mon Aug 03, 2009 12:57 pm

by milling both head & cylinder you increase
compression more than just shaving the head
you should also turn down the piston if you mill head & cylinder.

you can do the head real easy if you put some med/fine
wetordry paper on a piece of 1/4" thick glass plate
and rub the head on it.

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Re: qt50 cylinder mod questions

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