THE OFFICIAL QT50 THREAD!

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re: THE OFFICIAL QT50 THREAD!

Postby danabike » Fri Feb 18, 2011 1:09 pm

Hey! It's been some time since I posted on the QT and I've made some of the mods I outlined earlier. I've got a K&N filter on it, jetted the carb up, am in the process of mounting the IRC tires. Fenders will be another story. I put on a new seat cover and mirrors. I just picked up a PW50 differential online for cheap and I'm going to do a swap.

I need a little clarification on the gear swap. I don't plan on simply swapping out rear ends. I re-did the stock differential and it looks too nice. From what I understand the large gear with the axle shaft (driven gear) has a longer axle length on the PW. Do you re-use the QT driven gear and just replace the small drive gear and do they match up? I hate to have to grind the axle shaft down on the PW gear. To me, that's kinda hokey, but I'll do it if there's no other way. I already have the QT differential gars removed, so it would be no problemo throwing the other ones in or whatever combination works best.

Also, does anyone know offhand if the brake shoes are the same for the PW and the QT?
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re: THE OFFICIAL QT50 THREAD!

Postby danabike » Sun Mar 20, 2011 8:48 pm

Figured out the fender problem with mounting IRC NR77's. I ordered 2 of the NR 77 front tires, which were the same size as the stock rear, but larger than the stock front tire. I first made some extensions for the fender stays, but they were bulky and the hardware required put them too far away from the tire. It looked like crap and I was stuck. I ten considered making a fork bracket to mount at the base of the headtube under the fork, like a bicycle. Then I was looking in my shop loft and found some universal fender stays for 26" fat tire bicycle fenders. I believe the manufacturer is Wald. I used the old fender stays and a fender as a pattern to shape the top of the stays since they are not a straight arc. After a little bending by hand and with some pliers, the tops were shaped and fit nicely into the underside of the fender, without the little bend inward that the stock stays have. That little inward bend is what screws us on the use of the stock ones, so the bicycle stays provide an immediate 1/4" on each side simply by virtue of not having that second bend. I gave myself a little more extra clearance on the tire, and then lined up the stays to the same holes on the fork for the stock stays and cut the new ones to fit. I then took a hammer and and pounded the first inch of the cutoff end of the new stays flat on the anvil of my bench vise. Since the new stays are formed where they were cut off, there's a clear center line on the flattened blade end. Center punch the new hole location and drill it out. Voila! new stays that are almost indistinguishable from the stock ones! You can even use the mud flap! I attached everything with carefully measured stainless screws and nylon nuts. The rear tire I had no fit problems with and used all the stock stuff. Check it out!
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79 & 84 QT-50 Yamahoppers
87 Honda Helix
2006 Harley VRSCA V-Rod

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re: THE OFFICIAL QT50 THREAD!

Postby Ryan C » Mon Apr 11, 2011 1:30 pm

Image
Image
16" wheels front and rear. lengthened driv shaft and tube. chappy cylinder with second carbureator, intake and reed block. progressive throttle opener dealio. clip ons. self supporting fiberglass seat. Flipped frame. two speed engine. right side swing arm. pit bike forks. drilled drums on face and sides. lightened clutches. pw rear. adjustable cdi. minarelli vertical head. mild porting and head work. that's all i can remember, thought i'd share.
Built not bought
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Re: re: THE OFFICIAL QT50 THREAD!

Postby beanoil » Sun Jun 05, 2011 10:49 am

danabike wrote:Figured out the fender problem with mounting IRC NR77's. I ordered 2 of the NR 77 front tires, which were the same size as the stock rear, but larger than the stock front tire. I first made some extensions for the fender stays, but they were bulky and the hardware required put them too far away from the tire. It looked like crap and I was stuck. I ten considered making a fork bracket to mount at the base of the headtube under the fork, like a bicycle. Then I was looking in my shop loft and found some universal fender stays for 26" fat tire bicycle fenders. I believe the manufacturer is Wald. I used the old fender stays and a fender as a pattern to shape the top of the stays since they are not a straight arc. After a little bending by hand and with some pliers, the tops were shaped and fit nicely into the underside of the fender, without the little bend inward that the stock stays have. That little inward bend is what screws us on the use of the stock ones, so the bicycle stays provide an immediate 1/4" on each side simply by virtue of not having that second bend. I gave myself a little more extra clearance on the tire, and then lined up the stays to the same holes on the fork for the stock stays and cut the new ones to fit. I then took a hammer and and pounded the first inch of the cutoff end of the new stays flat on the anvil of my bench vise. Since the new stays are formed where they were cut off, there's a clear center line on the flattened blade end. Center punch the new hole location and drill it out. Voila! new stays that are almost indistinguishable from the stock ones! You can even use the mud flap! I attached everything with carefully measured stainless screws and nylon nuts. The rear tire I had no fit problems with and used all the stock stuff. Check it out!


Now that is just trick. Very sano, great job.
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re: THE OFFICIAL QT50 THREAD!

Postby pete in pa » Fri Feb 10, 2012 5:33 pm

Hello everyone! My first post here. I've got an 81 Yamaha QT50 since brand new. $300 back in 81 BTW.

It's never ran the greatest but has 2300 miles on it. With all the advice here I've drilled out the rear of the muffler, opened up the airbox, running #70 main,Cleaned out pilot jet, (don't know how long that's been plugged) milled down the head, altered the throttle cable junction box so it now gives full throttle to the carb, and various other mods.

It now runs at 31 mph vs the 27 it's ran at since new. These things are fun to work on! Don't think I"ll spend the $$$ on gears or bigger engine unless something breaks.

Hope I didn't miss the popular time which seems to have been around 2005 acording to posts here.
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re: THE OFFICIAL QT50 THREAD!

Postby Aceface » Fri Feb 24, 2012 9:11 pm

MLM qt50 pipe- sidebleed. enough said.
78 kromag
84 maxi sport
yamaha qt50
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re: THE OFFICIAL QT50 THREAD!

Postby pete in pa » Sun Feb 26, 2012 1:38 pm

How much and where is the pipe?
1981 Yamaha QT50: Yamaha 60cc hop up, PW gears, stock pilot, 75 main, red Uni filter, BP7HS plug.
2006 Honda ST1300
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re: THE OFFICIAL QT50 THREAD!

Postby Aceface » Mon Feb 27, 2012 8:01 pm

email or call Devin at Motion Left Mopeds ( http://www.mlmopeds.com/ )
dude bros are putting out the most quality parts and pipes, and
right now they are currently the largest manufacturer of moped parts in the US (I'm pretty sure of this fact), and made in Indiana, FTW
78 kromag
84 maxi sport
yamaha qt50
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re: THE OFFICIAL QT50 THREAD!

Postby pete in pa » Sun Mar 04, 2012 12:40 pm

Well I just removed the front slider tubes, cleaned, and regreased them. I now have a moving front suspension again! can't remember it ever moving.

Already did the bearings and gears in the drive shaft.

I'm slowly going through the whole bike and cleaning and regreasing.

I wish I hadn't already mounted new Kenda tires. I like those IRC NR77 tires! Could have gone with a 80/90 rear and that would have geared the bike up without having to change the shaft gears. Might have had to mod the rear fender though.

According to the table in the Dennis Kirk catalog a 70 tire is 2.75 a 80 tire is 3.00 a 90 is 3.50 etc.

A larger front tire probably makes the speedo read lower also. Have to check sometime.
1981 Yamaha QT50: Yamaha 60cc hop up, PW gears, stock pilot, 75 main, red Uni filter, BP7HS plug.
2006 Honda ST1300
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Re: re: THE OFFICIAL QT50 THREAD!

Postby Space Dynamics » Mon Mar 05, 2012 7:45 pm

danabike wrote:I need a little clarification on the gear swap.


Same here, I have read many posts on it but I am not %100 sure what I would need to get.

And from what I read, it's recommended to go from a 65 to a 70 jet after you put a good filter on, and no other modifications?
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re: THE OFFICIAL QT50 THREAD!

Postby pete in pa » Fri Mar 16, 2012 3:45 pm

The factory jet IS a 70 which is too rich unless you open up the air filter box. Then it's about right.

I'll be getting my "60" parts this monday, can't wait.
1981 Yamaha QT50: Yamaha 60cc hop up, PW gears, stock pilot, 75 main, red Uni filter, BP7HS plug.
2006 Honda ST1300
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re: THE OFFICIAL QT50 THREAD!

Postby sloped » Sat May 19, 2012 8:46 am

anyone mess around with rejetting the pilot jet after adding a k&n filter?

i'm finding a 47.5 is probably going to be best with a 67.5 main jet.

anyone have any experience with this?
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re: THE OFFICIAL QT50 THREAD!

Postby pete in pa » Thu May 31, 2012 8:50 am

Since I went to a 60cc and the factory pilot is still in there working fine I don't think you should mess with the pilot jet.

With a K@N the 70 main should be right at your location in Des Moines.
1981 Yamaha QT50: Yamaha 60cc hop up, PW gears, stock pilot, 75 main, red Uni filter, BP7HS plug.
2006 Honda ST1300
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re: THE OFFICIAL QT50 THREAD!

Postby CameronR » Wed Jun 20, 2012 8:18 pm

Hi everyone, I have just recently acquired a 1980 QT50 that starts only half the time. When I was buying it I started it up to test drive it and it started the first time. Drove it around and it seemed to run great. I shut it off and started it back up a few times just to make sure. The guy I bought it from said that every so often it doesn't like to start up but if you "mess with it a bit" then it will start just fine. So I loaded it into my trailer and drove about an hour and a half on a really bumpy road to get home. It was really getting shaken around. So I unload it from the trailer and go to start it up and it starts just fine. I went to give it some gas and nothing happened. So I took apart small case around the throttle handle and noticed the cable snapped. I replaced the cable and now I can't get it to start at all. I can get it to start but it will run for maybe 8 sec. before the engine cuts out. I'm mechanically smart but not as engine smart as I should be to figure out whats wrong with it. I'm not sure exactly I need to "mess with" to get it running or maybe it just needs a general tune-up. Any Ideas?
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Re: re: THE OFFICIAL QT50 THREAD!

Postby Gramuly » Fri Jun 29, 2012 5:21 am

CameronR wrote:Hi everyone, I have just recently acquired a 1980 QT50 that starts only half the time. When I was buying it I started it up to test drive it and it started the first time. Drove it around and it seemed to run great. I shut it off and started it back up a few times just to make sure. The guy I bought it from said that every so often it doesn't like to start up but if you "mess with it a bit" then it will start just fine. So I loaded it into my trailer and drove about an hour and a half on a really bumpy road to get home. It was really getting shaken around. So I unload it from the trailer and go to start it up and it starts just fine. I went to give it some gas and nothing happened. So I took apart small case around the throttle handle and noticed the cable snapped. I replaced the cable and now I can't get it to start at all. I can get it to start but it will run for maybe 8 sec. before the engine cuts out. I'm mechanically smart but not as engine smart as I should be to figure out whats wrong with it. I'm not sure exactly I need to "mess with" to get it running or maybe it just needs a general tune-up. Any Ideas?



I bought one just three days ago. I seem to have the same problem you do. The bike had only 887 miles on it. The seller also had warmed it up for me. So when I looked at the bike it ran fine but if you let the bike get cold it wont start as it should.

I asked him what oil he put and where he put it. He was putting 10w30 in the fuel mix compartment. There is two places for oil. One is for the 10w30 and the other is for two cycle oil.

I fixed it and now it runs like a new bike and is alott of fun.
It could be as simple as just let out all the oil in the (two cycle mix compartment) Its next to the gas.
Then refill it with two cycle mix-not 10w30(that goes below on the bike.)
Then start it with starter fluid in the carb and run it for as many miles as you can.

I went a step beond that. I did not know if the two cycle oil pump worked. I did not know how to bleed the air out of the pump so I just let out all the two cycle oil and put the mix into the gas itself. This way I was sure it was getting to the engine.

I found that I also wanted to disconnect the twocycle oil pump itself.

(To make a long story short.) Many people try and put the wrong oil in the gas mix oil compartment. This clogs the thing up. Clean it out and go for it.)

On a bike that has run alott you may need to take off the muffler and throw it in a fire. This can burn out any deposites that may clog the exaust.

Good luck. Its a fun toy and or tool. Quiet fast just fun. I have these speed bumps in my neighborhood. They are fun I get a few inches of air off them. The bike seems to be strong. Enjoy
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