THE OFFICIAL QT50 THREAD!

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re: THE OFFICIAL QT50 THREAD!

Postby hypermiler » Mon Sep 08, 2008 1:01 pm

Seems like this should have been linked in this thread earlier. The site has both the owner and repair manuals perma-posted. You can download the pdf files for your own use.

Repair manuals: http://www.mopedriders.org/article_view ... fldAuto=45

Owner's manual: http://www.mopedriders.org/article_view ... fldAuto=41

You'll find the stator, and basically every other part of the bike described in these manuals. For the simplicity of the bike, the manual is quite comprehensive.

Parts can be had at several places online, as well as your local Yamaha dealer. Some prefer local (no shipping) some online. I use: http://www.bikebandit.com I really like this site, as it allows you to use the OEM drawings to identify parts, and their location. Prices seem reasonalbe to me, but you don't have to buy new. Parts are often available through the classifieds on this site (and others), and on ebay.

There are some items that are hard to find, but the stator should be available. If you do the work yourself, you'll need to look into a couple of specific tools. A flywheel lock, and an impact driver are pretty much mandatory.

Another side note here is that the Yamaha PW50 (often called the 'PeeWee') is fundamentally the same bike as far as the drivetrain is concerned.

I'm still new to this myself, please don't consider my input the be-all and end-all of tips for these bikes. ;)

Have fun and good luck...
1980 QT50 Yamahopper
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re: THE OFFICIAL QT50 THREAD!

Postby dcbarner » Mon Sep 08, 2008 2:40 pm

Would this part work?

http://www.partsforscooters.com/Stator_assy_50cc-2#

Thanks

Dane
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re: THE OFFICIAL QT50 THREAD!

Postby hypermiler » Tue Sep 09, 2008 4:39 pm

It might, but you'd need to decode the wiring and rewire the plugs to match the Yamaha setup.

http://www.bikebandit.com/houseofmotorc ... 4sch223162

http://www.bikebandit.com/houseofmotorc ... 79/o/m7454

What you've linked to is for a Chinese bike, not sure I'd recommend it. It is cheaper than the OEM parts, but if you look in the classifieds here or post a wanted ad, I'd bet you could find one that is correct for your bike.
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re: THE OFFICIAL QT50 THREAD!

Postby broped » Thu Jul 09, 2009 1:10 pm

Can anybody give me any info about changing the brakes? I may not need to but here is what is going on...

I have twisted the adjuster by the handlebars about as far as it can go, and also tried to play with the one down by the wheels, but it doesn't seem to work, so I thought I may need to do some brake work. Does anybody know what would need to be replaced/where to find it/some how to info? I would hate to buy more stuff than I really need for what could be a minor problem

Thanks
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re: THE OFFICIAL QT50 THREAD!

Postby Kewball » Sun Jul 26, 2009 2:11 am

On mine the brakes were fine, but the cables were stretched. There is a pointer on the brake lever. It needs to fall inside the box. If it does your brakes have some life left.
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re: THE OFFICIAL QT50 THREAD!

Postby Kewball » Sun Jul 26, 2009 2:17 am

My qt50 will not seem to go over 15 miles per hour. It takes forever to speed up. I think the clutch is slipping, cause it will rev high until it hits around 6 miles per hour, than you fell it engage until around 15. After that it starts poping and will not go any faster. It seems like it is hitting a rev limiter, cause it pops and bogs down for a second than starts accelerating for a second, then pops and bogs down, repeat. I don't understand. New air cleaner, perfectly clean carb, burned the exhaust, decarbonized the head, new plug. Cant get it to do anything. Any have a good clutch cheap or know where to get one cheap. Thanks a million
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re: THE OFFICIAL QT50 THREAD!

Postby xrongor » Sun Jul 26, 2009 5:11 pm

what you are describing is classic 4 stroking (fred's guide in moped repair explains this). the air/fuel mixture is too rich.

drilling some holes in the airbox (on the side that will still allow the air to be filtered by the element) will likely solve this. if you want to test it without drilling the airbox, just run it without an airbox for a mile or two in a non-dusty situation.

but you will still want to do some plug chops after drilling the airbox to make sure you are properly jetted.

randy
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re: THE OFFICIAL QT50 THREAD!

Postby Kewball » Mon Jul 27, 2009 7:07 pm

Thanks I was told by someone else that, that may be the problem, shortly after posting my thread. Do you know a good place to get the jets to do a plug chop, and can you please explain this plug chop alittle. Sorry I am new to this, and can use all the help you have to offer me. Also do you know anywhere to get a clutch, or do you think that this could be causing the clutch to not fully engage during launch. Thanks a million
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re: THE OFFICIAL QT50 THREAD!

Postby xrongor » Tue Jul 28, 2009 1:35 am

my gut feeling is that as soon as the engine experiences 'load' (i.e. the clutch starts to engage) it starts to run poorly because the air/fuel mix is off and your problem has nothing to do with the clutch itself.

plug chops are explained in fred's guide in the moped repair section of this site. as is 4 stroking and jetting.

you can get jets from any motorcycle dealer, but you likely won't need to change it after you drill the airbox.

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: THE OFFICIAL QT50 THREAD!

Postby Codis8 » Fri Dec 18, 2009 8:32 am

In need of some QT help here. I have an 80' QT that I'm trying to get going as a Christmas present but time is running out so some assistance would be appreciated. I do have a good running 83' to swap parts off of to narrow my problem. First I had no spark. Swapped the CDI box, now I have spark. Then I bought a magneto, flywheel and inner coils, whole assembly. Now it acts like it has a timing problem. I know it is not adjustable though. It starts and runs for about a second with choke on. Small puffs of White smoke come out the carb, not tailpipe. Removed pipe, not clogged. Put on carb from running bike, same problem It wont start. Gets good blue spark. Plug is wet. Any thoughts? Checked the oil pump, not stuck open.
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Re: re: THE OFFICIAL QT50 THREAD!

Postby RebelMob » Fri Dec 18, 2009 4:08 pm

Little smoke puff is reversion. Reversion out of the carb means the reeds are not sealing. Check the seals or perhaps there is dirt between the reeds and the block maybe a broken or bent reed. Swap the reed block off the donor bike.
Processed on shared equipment that may have come in contact with nuts.
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re: THE OFFICIAL QT50 THREAD!

Postby danabike » Mon Dec 21, 2009 1:48 am

I am so glad to see this thread. Last year I did a quick fix-up on a QT and rode it for like a month before selling it. I liked it so much better than the Honda Express models, that I picked a couple up for a decent price last month for a winter project, and to have one to bomb around on for keeps. I'm not new to bikes, and some of you may have seen my work on other boards, so I'll give up some ideas I have for these little peds.

I've already popped off the rear rack for restoration/cleanup, and I've pulled the carb for inspection. The tank shows some surface rust, and this was evidenced by the fine rust powder I found in the bowl. It's jetted with a 70. We'll see how well the carb cleans up. I'd like to replace the stock airbox with something a little K&N, since I never really liked the side covers. I definitely want to do the 60cc thing. BTW, what kind of compression am I looking for on these engines? Anyone? I'm reading 90 and wondering if that's high enough, but couldn't find it in the shop manual.

I'm also looking to do a lot of 6v LED replacement of lights, especially the turn signals, so I'll end up replacing the flasher relay with a low threshold job. I've also found some interesting tires that I'm wondering if anyone has fooled with. They are IRC NR-77's. The QT50 stock sizes are 2.00-14(F) & 2.25-14 (R). The IRC's come in 2.25-14, which is listed as a front tire, and 2.50-14, which is listed as a rear tire. I was thinkin' a pair of fronts would do the trick for both front and rear, and they have a much better rubber compound, as well as a more modern tread.

So, there you are. Any advice would always be helpful, and I'll keep you all posted on the progress. :)
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Re: re: THE OFFICIAL QT50 THREAD!

Postby RebelMob » Mon Dec 21, 2009 9:05 am

They certainly are fun bikes.
To calculate the approximate pressure on a compression test you need to take the true compression ratio (calculated after the exhause port closes) and multiply times 17. If you do not have the true compression ratio toy can go by the volumetric ratio (calculated on combustion chamber volume at bdc/combustion chamber volume at tdc) and multiply by 10.

For tire size playdoh is your best friend. Load up the bike with you and the stock tire fully loaded and look for where the clearance problems might be then whack on a slab of playdoh onto the tire. Remember that the larger tire will be larger in three dimentions so make your playdoh slab go from rim edge to rim edge. Look for tight spots with the suspension static and take note of what the tight spot is, some you can move or remove some you can not. THEN position the tire where the tight spot is and jump on the bike and bounce around and even get someone heavier to help by getting on and bouncing. Again the playdoh will show you if you ran out of room or not.
If it is only a tire strike when the suspension is under severe compression you can always limit the travel by adding a bump stop to the shock.
Processed on shared equipment that may have come in contact with nuts.
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re: THE OFFICIAL QT50 THREAD!

Postby barndoor » Fri Mar 19, 2010 4:46 pm

Hi,
I'm a new MRA member.I just picked up a 1979 Yamaha QT50 2 days ago.It had been sitting for years,I just got it running.I have a question:I have removed the oil pump gear to run pre-mix,and the extra cable(s).I need a longer Throttle Cable now.I need about 4".What bike would use the correct cable stock? I want to buy a cable downtown,but the guys needs a year model to look it up.
1979 Yamaha QT50
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re: THE OFFICIAL QT50 THREAD!

Postby xrongor » Sun Apr 04, 2010 3:39 am

personally i just left the junction box in place, removed the oil pump cable only, and put a plug in the box to keep krud out.

randy
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