Yamaha QT 50 "Noped" project

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yoothgeye

yoothgeye

I build stuff.
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So, last Summer I got my motorized bike together and running and rode it around town a lot, and though it was fun and got attention, it scared me. That little Chinese 68cc engine vibrating like crazy, having only a coaster brake (yeah, that was my choice) the thought that at any time the chain could jerk the tensioner into the spokes and try to kill me at 35mph, I just don't want the stress, especially since having shoulder surgery in the Fall from a mess up on a much smaller motor bike. So, I will do away with the motorized bike and do something else.

A couple years ago my dad bought an early 80s Yamaha QT50 (Cutie50) from a guy at my church, I had the option to buy it for $30, but didn't have money/time for it, so dad gave the guy $50 for it (to help him out). I picked it up for him and took it to VA to mom and dad's house. The wheels were locked, but in minutes dad had adjusted the drum brakes and had it rolling. It is missing the magneto engine side cover and has rust in it. It will need work, but I talked to dad and he said he's not going to do anything with it and I could have it.

So, I plan to have it running for the Summer and beyond. Lots of parts on eBay and a local Yamaha shop where I can get parts at or near cost (friend works there). The thing is, I don't want this to be stock, I just can't leave well enough alone. I'm not talking about the engine, I'm sure I'll hop it up along the way, but I want it to look different. So I grabbed a photo that Outskirtscustoms posted a while back, my QT is identical to this one, and I just did a quick mock up before/after.

I "lowered" the seat (less cushion), removed fenders, moved tail light, removed racks, added a top bar, and put on a lower bicycle stem with BMX bars. What does everyone think? Any more ideas? I don't need a rack, I have cars if I need to carry more than I can put in my backpack.

qtmock_zps18a808dc.jpg


I'm hoping this will eventually turn into a build thread.
 
Re: More reliable "motorbike" for this Summer.

Looks cool, I'll do a quick mock up to give you more ideas.
 
Re: More reliable "motorbike" for this Summer.

I might lower it a little too. The top bar would allow me to mount a motorcycle tank and eliminate the under seat tank which would better balance the weight. This would also eliminate the oil injector which might not be working now anyway so therefore I could run a more lean mixture of full synthetic.
 
Re: More reliable "motorbike" for this Summer.

yoothgeye said:
I might lower it a little too. The top bar would allow me to mount a motorcycle tank and eliminate the under seat tank which would better balance the weight. This would also eliminate the oil injector which might not be working now anyway so therefore I could run a more lean mixture of full synthetic.
Click to expand...

I would NOT lower the back as the carb sits right there in a really bad spot and if lowered you'd probably crush the air box and or carb at the first bump. If you can figure out how to lower the front that's cool. Here's a few ideas from my friends at Moped Army.
 
Re: More reliable "motorbike" for this Summer.

WOW! Some are really cool, the "TURD," looks frightening!
 
Re: More reliable "motorbike" for this Summer.

bmxerpete said:
Why does the QT50 remind me of Number 5, the robot from Short Circuit? :mrgreen:
A steampunked out QT would be cool...just sayin'.
Click to expand...

Johnny 5 is ALIVE!
 
Re: More reliable "motorbike" for this Summer.

To revive this thread a little, I have started work on the Yamaha.

Engine is seized, so I hoisted the bike up with a come-along and have Marvel's Mystery Oil soaking in the spark plug hole and crank case... wait, you can tell me I'm stupid, but why is there an oil plug on the motor of a 2-cycle... I've got some research to do.

Anyway, while it's hanging there I have removed the fenders, the gas/oil tank, the seat, the rear rack, the muffler heat shield, and have the carburetor off and soaking the bowl clean.

I have also started to remove the forward controls. All the QT50/Yamahoppers you showed above all use the stock handlebars and I HATE them. I will be using a bicycle stem and some low flat bars, maybe mountain bike bars. I have decided to make it a cafe racer style.

When I pulled the tank, obviously there was no gasoline, but I was happy to see that the oil injection tank was full of 2-cycle oil and it was clean, I think that's a good sign.

Why is the engine seized? When I got it, it had been outside for an unknown amount of time with the spark plug out and the magneto/stator side engine cover removed. There is some rust in the magneto, but a motorcycle mechanic friend of mine says it can be cleaned up.

I have done lots of work with combustion engines in cars, removed rings, cranks, replaced bearings, head gaskets, timing chains, pulled whole engines, swapped transmissions, but the tough stuff (crank bearings, valves, rings, etc...) was all done under the skillset of someone else, like my father or brother-in-law (not the same person :lol: ). So I am going into this a little blind, will seek help when I need it, but plan to come out knowing a lot more.
 
Re: More reliable "motorbike" for this Summer.

yoothgeye said:
Engine is seized, so I hoisted the bike up with a come-along and have Marvel's Mystery Oil soaking in the spark plug hole and crank case... wait, you can tell me I'm stupid, but why is there an oil plug on the motor of a 2-cycle... I've got some research to do.
Click to expand...

Hey stupid, it's not the crank case, it's the transmission oil fill hole!
 
Re: More reliable "motorbike" for this Summer.

The first cut is the deepest...

cutbars.jpg


I am going to have to make my own stem since the quill is smaller than a 21.8mm and the steel is much thicker, so I will feel better using the stock quill, plus, it has a key to keep it straight in the fork, so no slipping.

You can see here, I've been stripping it down, it should be pretty low profile without the stock bars and with a lower saddle since I won't have to have the saddle on top of the tank.

stance.jpg


By making the profile lower I won't mess with the suspension to keep the ride nice and reliable.
 
This thing is tiny, I took a photo for scale with a 20" Haro Zippo BMX bike. I weighed it tonight stripped down as seen and it's 68.5 pounds.

yamascale.jpg
 
A friend dropped off an old moped tank today, I have to clean the rust out of it, but it's absolutely PERFECT!!!

Here's the way I suspect it was supposed to be mounted to the original moped:
tank1.jpg


Here's how I plan to mount it:
tank2.jpg


I love it! I will be welding in a top tube to better secure the tank, but the nose of the tank fits the head tube perfectly at either angle.
 
Looks awesome! I think I have an extra carb off of a Yamaha Razz somewhere if you could use it. I have seen many people use a Razz carb on these because it has a manual choke and has an oil injection port so you don't have to mix gas.
 
outskirtscustoms said:
Looks awesome! I think I have an extra carb off of a Yamaha Razz somewhere if you could use it. I have seen many people use a Razz carb on these because it has a manual choke and has an oil injection port so you don't have to mix gas.
Click to expand...

That would be great as I am soaking my carb now but the choke is still attached because I don't know how to remove, though I have found the factory service manual online, so I will be looking into it.

The QT (cutie) is oil injection, but since I'm eliminating the tank, I am also eliminating the oil injection. I will have to mix fuel, but I can mix it leaner than the injection would allow for better performance and eliminate some cable redundancy and complexity.
 
Nice!!!! You should braze in a surgically removed down tube for the top tube ~ thin & light.

I like the style ~ oil injection usually mixes it thinner. I guess you can refer to the forums but most dirt bikes were 32:1 ratio. Outboards were 50:1 and Amsoil says you can mix their oil 100:1.

As for the tank ~ acid should eat the rust. Vinegar may take a while. I have the PRO stuff to do it sitting on the deck. I did (4) tanks last month. I'm out of the POR-15 fuel tank coating, but still have the cleaner / rust remover. I also have a late 60's Honda 50 tank that is just rough enough to mod with out hurting anyone's feelings.



GOt to play with the project you turned me onto today ~ BTW that si 50:1 boat premix + factory oil injection. COugh Cough!!!

 
I bought some synthetic oil (that smells like strawberries) so I want to handle the mixing, not a questionable pump, especially once I start actually modding it over stock.

Anyone got a smallish straightish expansion chamber exhaust I could have to chop and rebuilt for this thing?
 

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