Yamaha QT50 Performance Tuning

Got performance questions or a success story? Let the world know, and push the limits of your scoot!

Moderators: SLOWRIDER, Areomyst, scootertrog

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Areomyst
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Yamaha QT50 Performance Tuning

Postby Areomyst » Fri Sep 04, 2009 4:57 pm

This is a work in progress. I'm going to post up the photos now, and I'll post some details later on when I get the chance.

Stock Durations:
Ex: 150 degrees.
Tx: 100 degrees.
Bx: 98 degrees.

Deck height is .83mm.
Bore is 39.98mm
Stroke is 39.84mm
Not sure about conrod...

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How about that beautiful triangle exhaust port huh? Geeze, there's so much room for improvement there it's not even funny.

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Exhaust, two transfers, and a boost.

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Looking into the cylinder from the exhaust port. Lots of improvement room here also by simply matching the port to the pipe.

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The transfer port tunnel.

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Sorry for the blurry pic.

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My ghetto piston stop. Don't laugh, it works!

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I love my clear degree wheel. :)

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Ready to do the port map.

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After doing the initial pencil rubbing, I like to trace out the map in ink to get a cleaner map. This is also useful when using you scan the map and plug it into the software (http://www.porting-programs.com).

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Getting an approximate port width.

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See why it's important to roll your port map before measuring? The actual port width is less than the width shown on paper.

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I'm really trying to achieve better port symmetry. I'm getting there slowly but surely.

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before

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After. At BDC the hole in the piston lines up with the trench. I'm sure this could have been pushed much further, but I was comfortable with this. The bike won't have an expansion chamber for a while anyway, so there's only so much benefit that can be had from porting.

180 exhaust.
120-122 transfers (the roof is angled higher)
122 boost. I meant to have the boost lower but over cut.
I'm a little concerned that the transfers are a bit high in general, but I'm sure that it'll run a whole bunch better than it did before.

I wish I had gotten more photos. It seems like there's some missing or something because I swear I took more of the exhaust port and pictures during the porting also.

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Cheap and dirty exhaust block off plate.

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Leak # 1, which was an easy fix. Duh Josh...

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Leak # 2.

Sorry for the unorganized format of the post.

~Josh

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StepVino
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Postby StepVino » Fri Sep 04, 2009 5:12 pm

Neat little scooter, glad to see you having some
time to do engine mods. I'm wondering though,
does it have any gears, and if it will be able to rev
up under load. Look forward to the results!

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Areomyst
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Postby Areomyst » Fri Sep 04, 2009 5:14 pm

StepVino wrote:Neat little scooter, glad to see you having some
time to do engine mods. I'm wondering though,
does it have any gears, and if it will be able to rev
up under load. Look forward to the results!


It's got a 2 stage clutch basically. Before the porting the off the line performance was pretty weak. I'm sure it'll be better now, but I fear that the transfers are a bit high for low-end performance. I'm thinking it'll do pretty well overall though.

~Josh

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Areomyst
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Postby Areomyst » Fri Sep 04, 2009 5:15 pm

Forgot to mention that I can change to clutch springs to have it engage at a higher RPM. :)

~Josh

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StepVino
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Postby StepVino » Fri Sep 04, 2009 6:24 pm

Aha! That sounds great.

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Mexicano
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Postby Mexicano » Fri Sep 04, 2009 8:20 pm

Nice hop-up to that little engine, Josh!....Glad to see you keep busy.

Keep us posted on this...

Regards,
‘There is only one secret in scooter tuning – to know what you are doing and do it thoroughly’

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OveRReV
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Postby OveRReV » Fri Sep 04, 2009 11:01 pm

nice porting, just a little bit more practice so you can steady your hands when you cut the ports to shape.

i'll bet that scooter will be a screamer now. :lol:
Overrev Tuning

Timmy
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Postby Timmy » Sat Sep 05, 2009 1:44 pm

What year is the yamaha qt 50? But nice job on it so far.
2003 Aprilia sr 50 ditech Autism edition
1999 Derbi Mathattan Hunter

Sold
2001 Honda Elite Sa
2004 Yamaha Zuma
1979 Honda pa 50 1

manny
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Postby manny » Mon Sep 14, 2009 6:33 pm

ahhh brings back memories It was my first bike when I was 13 (1983)I loved that thing one time the exhaust fell off it and the speedometer almost made it bake to 0 down a slight hill
03 zuma polini evolution pipe crank and cylinder (70cc air cooled) mallosi reed block , mallosi red spring,malossi 13/44 gears, fly clutch, polini 9 weight variator 21gr speed drive 128mm, 21mm dellorto carb, polini inner rotor ignition

waxhead
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Postby waxhead » Mon Sep 14, 2009 8:03 pm

Great stuff
I wouldnt worry about the transfers 122 is not to high

Looks awesome to buy the way
I suggest getting a pocket bike exhaust of ebay and then chop the bends to suit

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Areomyst
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Postby Areomyst » Mon Sep 14, 2009 9:41 pm

Thanks waxhead. :)

I fixed up the crankcase leak too, but I need to get the pictures uploaded. That's the first time I've had that style engine split all the way down to the crank shaft.

I swear by the pressure test anymore.

I'll pass the note to the owner of the bike about the pocketbike pipe! Good idea too, since they're so cheap to come by.

Cheers!

~Josh

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StepVino
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Postby StepVino » Mon Sep 14, 2009 11:46 pm

I'm still concerned for you Josh, hoping it can
pick up speed. But holy..geez, if it works out,
especially with the pipe, are we going to see about
50mph out of it??

Nice smooth work on the boost port skirt btw.

Not sure if this would be worth while, but it looks
like the head is partially blocking the cylinder
fins. Maybe extending the head cooling cutouts
towards the center might be good?
Image

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Areomyst
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Postby Areomyst » Tue Sep 15, 2009 8:22 am

Yes, you could cut the head to make more usable area for the fins.

The bike is already back to the owner. Stock they'll do a tad over 30 downhill. After porting it was doing 30 easy on a flat and I'm sure it'll peg the speedo (only goes up to 30). It really needs the pipe and clutch upgrades. That'll really wake it up I'm sure, especially with the porting.

Next time the owner comes up from Charlotte we might play with it a bit more.

~Josh

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scootertrog
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Postby scootertrog » Tue Sep 15, 2009 7:34 pm

Cool project! I was wondering how long it would take for someone here to do one of these. Makes for a nice "sleeper" that will not draw any attention.

scootertrog

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StepVino
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Postby StepVino » Thu Sep 17, 2009 8:17 am

It would be interesting to hear how fast it goes down
hill now.


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