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Cycle Chaos > Cyclechaos Forums > Types of Bikes > Vintage > 1971 Yamaha JT1 Mini Enduro

1971 Yamaha JT1 Mini Enduro

This is a discussion on 1971 Yamaha JT1 Mini Enduro within the Vintage forums, part of the Types of Bikes category; Hello, I have a 71 Yamaha JT1 Mini enduro 60cc and have had problems finding documentation to help with getting ...


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Old 03-09-2006   #1
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Default 1971 Yamaha JT1 Mini Enduro

Hello, I have a 71 Yamaha JT1 Mini enduro 60cc and have had problems finding documentation to help with getting it running again. I had to split the case to replace the crank bearings and like an idiot I did not mark the rotary valve to replace it in the exact place I removed it from and now it will not even try to start. Does anyone have any info on this proceedure. I do have to manuals for this bike and both do not tell me what I need to know as the valve goes over a splined collar with 6 splines all of with are the same size. So it can go on in six different positions. Neither of the books tell how to aling the thing and the dealers have been no help at all as of yet. Thanks in advance. Gforce598
You can see it under epic bikes on the yamaha site but as I have not made 15 posts yet I can not post a link to it :(
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Old 04-07-2009   #2
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Default Rotary Valve...

I just saw your post and signed on to this Forum to help you... so I dont think I can post a picture of the directions for you yet... If you want me to fax or E-mail it to you I can...

I have 16 of the Mini enduros and have rebuilt many more!!

To install the rotary valve..
1. make sure the Metal Rotary valve cover is good and not rusted inside.
If it is bad replace it!
2. Always replace the rubber seal on the rotary valve cover! and the seals that go on the cover that protect the back of the carb and the oil injector too.
3. I assume you are using a new rotary valve? Place some Yama lube on both sides of the rotary valve and cover to pre lubricate the system.
4. Bring the piston to Top Dead Center.
5. Hold the New rotary valve so you can see the (2) dimples on the
rotary valve so they are out (away from Engine)
6. Install the rotary valve on the splines so that the rotary valve allows the hole on the carburator to be open/ visible .... you should be able to stick your finger into the fully exposed hole ..

There is a L shape in the rotary valve and solid part of the rotary valve shoud allign with the top (left) of the hole and the open part should be on the bottom. (right)

I hope this helps.. I do have a good graphic picture showing the install if you want me to fax to you!!
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Old 08-08-2009   #3
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Default

Wow! that is good advise. I have a similar problem.
My dad replaced the piston in his a while back and it has never run right again. I suspect it is too long or short. Now that it is mine I am trying to fix it. It runs very weakly and takes a while to rev up even in neutral. My rotary valve has a pin notch in it so there are only 2 ways to install it. It is pretty scratched up now because it was put on backwards first.

Can anyone tell me what the correct dimensions of the piston are? And would they be affected by having an after market performance pipe and air filter and who knows what else. And is a good seal really important for the rotary valve? (by seal I mean are my scratches and groves killing my power?)

BTW it ran great before taking it apart, just had no stop in the shifting. It would shift all the way up then back to 1st again. The piston broke due to poor handling.
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Old 08-08-2009   #4
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UM...
That was for a 1971 JT1 or JT1L
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Old 09-02-2009   #5
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Default Lose of power...with the rotary valve

You will definiately see a lower power feel if the ritary valve in scratched or damaged! as for the piston there are at least 4 sizes you can put in the JT1 , but all must have the right bore and clearances to ron properly.

you might check the seal that is on the magneto side, if it is loose or is letting air blow by, it will make the bike run boggy too. All the seals are very important and must be in good shape.

there is even a seal inside the engine case that the oil injector valve has that can cause problems from time to time!!

I would pull the cylinder and verify the piston and rings are correct first.
and remember the piston has to be installed correct!! not upside down, for the bike to run right!


Quote:
Originally Posted by jbrown View Post
Wow! that is good advise. I have a similar problem.
My dad replaced the piston in his a while back and it has never run right again. I suspect it is too long or short. Now that it is mine I am trying to fix it. It runs very weakly and takes a while to rev up even in neutral. My rotary valve has a pin notch in it so there are only 2 ways to install it. It is pretty scratched up now because it was put on backwards first.

Can anyone tell me what the correct dimensions of the piston are? And would they be affected by having an after market performance pipe and air filter and who knows what else. And is a good seal really important for the rotary valve? (by seal I mean are my scratches and groves killing my power?)

BTW it ran great before taking it apart, just had no stop in the shifting. It would shift all the way up then back to 1st again. The piston broke due to poor handling.
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Old 04-26-2010   #6
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Default 1971 mini enduro help?

i have a 1971 yamaha mini enduro and we need to find a new carburetor for it.. does anyone know any sites or anything where i can find parts?
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Old 05-03-2010   #7
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Default Carbs for JT1- JT2

There are no aftermarket Carburetors available for the Yamaha Mini Enduros You will have to find one through Ebay or from someone who will part with one....

Once you get one you will have to rebuild it with a carb kit.

THe Keyster Carb kit is the best!!! make sure you get one with all the parts and not just one with the needle seat and the float bowl gasket..

Mini Enduro Man
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Old 05-17-2010   #8
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I have parts for these, and sevaral bikes in different stages of need. Former Yamaha shop owner with barn full of leftover stuff. be specific and let me know what you are looking for. vintageracingmotorcycles@yahoo.com
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Old 06-11-2010   #9
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i need a float bowl for a jt1
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Old 07-02-2010   #10
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Wow I didnt realize there were such an interest for these bikes - takes me back 39 years -

Yea I thought I was hot chit back then - just like Steve McQueen






Last edited by EnduroRdr; 07-02-2010 at 10:54 PM.
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