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1971 Yamaha AT1C build thread

20 May 2020 15:21
JHof44
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1971 Yamaha AT1C build thread #1
I figured it's bet to just put all of this in one place, because I'm going to have a lot of questions. Anyway, my intro is here: www.yamaha-enduros.com/index.php/forums/...w-guy-from-san-diego

And some info on my engine is here: www.yamaha-enduros.com/index.php/forums/...s/12430-input-needed

I've owned the bike for 29 years but haven't ridden it since I was a kid. Luckily it's been stored inside during all of that time in sunny San Diego, so rust is minimal. I'm the 2nd owner, my uncle was the first. He paid me for a summer's worth of brick laying when I was 11 by giving me the bike.

Today I got the wiring harness removed. I'll want to replace it. Normally I would hire my brother for the job, but he's neck deep in building my '67 F100 so it's best not to bother him. I dug out the pressure washer and gave the frame what I'm sure was its first bath in 49 years.

From here I need to replace a crank seal and clean or replace the armature. I have the seals and gasket sets, so it's just a matter of finding the tools. I also plan to address the clutch while I'm in there and replace all the cables.

I'll likely go the same direction I'm going with my truck build, which is to retain the 50 years of character while making it a more capable vehicle. New suspension, 175 top end, new tires etc are all on the list...but paint is not.

Anyway, I appreciate any and all input anyone has to offer!

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20 May 2020 15:26
JHof44
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1971 Yamaha AT1C build thread #2
Oh, I probably should mention this did start as a complete, unmolested stock bike. And yes, the Yokohamas are beyond their best years. This was the bike 3 days ago:

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21 May 2020 10:17
mdscott
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1971 Yamaha AT1C build thread #3
cool story you have keeped the bike for 29yrs. Is that your son, I'm sure he is thinking, someday-it will be mine.



Thanks Mark
Roseville, Ca.

'76 Bultaco 143 Frontera
'06 GL1800
'01 KDX220
'68 YG5T 80 Trailmaster
74 DT360
75 Norton
73 CB500K
63 C200
87 PW50
64 McClane Edger

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21 May 2020 14:12
JHof44
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1971 Yamaha AT1C build thread #4
Yep that's my boy! He's 4.5 now and thinks he;ll be riding it to kindergarten in the fall. Little does he know that he's actually getting a 50 for his 5th birthday.

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21 May 2020 15:33
Mothersbaugh
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1971 Yamaha AT1C build thread #5

JHof44 wrote: Yep that's my boy! He's 4.5 now and thinks he;ll be riding it to kindergarten in the fall. Little does he know that he's actually getting a 50 for his 5th birthday.


My sons are 24 and 26, and even though I told myself at the time to enjoy every second of it, and I gave up a terrific high school orchestra job to spend more time with them when they turned 9 and 11, I still wish I could take them on one more baseball trip at that young age...
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21 May 2020 16:05
JHof44
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1971 Yamaha AT1C build thread #6
I'm not having much luck finding a rebuild kit for my Mikuni vm24sh. Can anyone point me in the right direction?

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21 May 2020 18:50 21 May 2020 18:59 by Mothersbaugh.
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1971 Yamaha AT1C build thread #7
Most o here would fault any kit you buy: the gaskets would be good, and usually the gas valve is good, but the quality and accuracy of the jet sizes and the needle will vary widely and are often just dead wrong. Go to partzilla.com and find your bike, and see what you can still get through Yamaha. If not there, then ebay for the individual parts.

www.partzilla.com/catalog/yamaha/motorcy...1971/at1c/carburetor

I'd start with the following parts:
2, 3, 6, 7, 37, 43, and
13:
Clean it and see how it runs after that, and then decide how you want to change it through re-jetting, if at all.
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21 May 2020 19:28
JHof44
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1971 Yamaha AT1C build thread #8
Thank you!

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22 May 2020 10:56
JHof44
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1971 Yamaha AT1C build thread #9
I'm slowly but surely confirming the direction I want this build to go. I plan to make it a street legal version of the AT1MX but with some modern suspension upgrades. Did a quick mock-up and got excited, might be time to start cutting and welding (only fenders!). Now, if only my wife would stop making me buy food for the family so I can buy a new top end I'll be styling!

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25 May 2020 16:16
JHof44
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1971 Yamaha AT1C build thread #10
While I’m waiting on parts I had time to go through the bottom end and get her all cleaned up. I’ll be replacing all of the seals this week and hopefully dropping the cylinder off at a machinist. When that’s done I’ll install the Wiseco the MX head. I still need to rebuild the carburetor but I’d like to find a largerCarb to use along with the MX head. Anyway once the engine assorted I will start tackling the suspension stuff.

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