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Makotosun

Re:Building the AT2 sleeper hot rod

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Building the AT2 sleeper hot rod was created by dose

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So to start this story off I live in the small town of mammoth lakes that is 4 miles long and 4 miles wide and wanted something to scoot around on in the summer. I came across this yamaha and picked it up for a good deal from a friend that could never get it running right. This is what it looked like when I got it.


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72 AT-2 with some mods
03 Jun 2015 12:03 #1

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Replied by dose on topic Building the AT2 sleeper hot rod

So I told myself I could be happy just getting it running so I could putt it around to the post office, work and to freinds houses. :haha

That didnt last long. As a kid in so cal I grew up riding and racing BMX, motocross, standup jet skis, off road trucks and buggies so I have been blessed (or cursed) with some mechanical knowledge and experience. I have never be satisfied with anything I have and can NEVER leave anything stock.

Its so bad that alot of times I have already bought aftermarket parts for toys I havent purchased yet. That should be enough background to see where this story is headed
72 AT-2 with some mods
03 Jun 2015 12:28 #2

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Replied by dose on topic Building the AT2 sleeper hot rod

Maybe I had the bike home for a hour before I bought a hooker pipe for it on ebay. The bike wasnt even running yet but how could I pass up a good deal on a period correct mod?

I figured the problem was with the carb so with some reserch on the computer I found out I could upgrade from a 24mm to a 28mm carb easily since a yz80 carb and boot would bolt right on.
Bigger carb is a better carb I told my self and it was only $30 with the throttle and cable. SWEET. Let the mods begin!
That was about the about the time I joined this forum and started learning more about these bikes
72 AT-2 with some mods
03 Jun 2015 12:48 #3

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Replied by dose on topic Building the AT2 sleeper hot rod



The hooker pipe had 2 heat sheilds on it with the hearts that were in pretty bad shape and was jerry rigged on by the previous owner. I decided to just remove them and grind off the tabs flush. I then wired wheeled the rust off the pipe and put a fresh coat of high heat black paint. It turned out pretty good.
72 AT-2 with some mods
Last edit: 03 Jun 2015 17:00 by dose.
03 Jun 2015 13:32 #4

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Replied by dose on topic Building the AT2 sleeper hot rod






I never liked the stock low fender and was able to find a preston petty with the bracket on ebay that bolted right up.
Also a period correct mod and I get alot of compliments

I got the yz80 28mm carb bolted up with a k&n style filter. It was nice to remove the stock airbox.
It seemed like the air had to do 3 90 degree turns before it got to the carb so that had to restrict the flow.

I also hated the big swept back Fonzie handlebars with horrible stock grips and put on a set of straighter pro tapers with half waffles like im used to on my other bikes. While I was at it I also took off the rear rack and turn signals. The rack seemed useless to me since it was so small and I kept catching my leg on the signals when getting on and off. Finally starting to look more like a dirt bike and less like a street bike
72 AT-2 with some mods
Last edit: 03 Jun 2015 17:01 by dose.
03 Jun 2015 16:48 #5

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Replied by dose on topic Building the AT2 sleeper hot rod

I was pumped when the bike started first or second kick with the new pipe and carb. It ran great with the yz80 jetting and screw settings. The pipe was pretty loud but sounded real good and there was no mistake there was a 2 stroke coming. It was awesome to start ripping the bike around town. The hooker pipe would hit HARD at 6K rpm and pull good up to 10k+.
2 things that werent that great
1. the pipe was a leg burner if you werent careful when you put your foot down
2. the pipe was VERY LOUD.
The loudness was fun at first but it starts getting old, but man the powerband was so fun when it came on.
72 AT-2 with some mods
03 Jun 2015 17:16 #6

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Replied by Makotosun on topic Building the AT2 sleeper hot rod

Your original bike was really very nice from an originality standpoint.

The mods you have done for power are quite interesting - as that is a lot of carburetion for the 125 motor. The chamber likely makes it all work, as well as the fact the carb was originally for an 80cc. You should do a plug reading (or a plug chop) to see how you are actually jetted to assure you don't burn a piston.

I was about to post that you may want to have some sort of heat guard on the pipe, but apparently you figured that out yourself :EEEK Chambers do get hot, and even denim is not enough to protect against some nasty scars.

The easy way to increase your performance - to really make a sleeper - is to bolt on a 175 top end (piston, cylinder, head, small rod bearing) which will give you about a 40% increase in displacement. It is a bolt on job once you source the parts. You can get some guidance from my thread HERE: yamaha-enduros.com/index.php/forums/rest...project?limitstart=0

I am in the process right now of doing some additional upgrades which will make the bike even better and more bullet proof!

Keep the build pictures and progress coming.
IF it isn't one thing, it's another.
03 Jun 2015 17:42 #7

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Replied by dose on topic Building the AT2 sleeper hot rod

Mako I forgot to say it has a 175 top end
Plug chop looks good, I am new to these enduros but not new to 2 strokes
Heat guard sticks out even further than the pipe, and not in the proper place to protect your leg anyways.
many racers have run up to a 32mm carbs on these 175s

Im only 25% in to my story so it will start to get good when I have more time to update the thread

Hint: I made a new freind named Dave :)
72 AT-2 with some mods
03 Jun 2015 18:00 #8

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Replied by Makotosun on topic Building the AT2 sleeper hot rod

Looking forward to it. I am in the process of some cool upgrades on mine which also include a "Dave" . . .
IF it isn't one thing, it's another.
03 Jun 2015 18:09 #9

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Replied by Bigdog302 on topic Building the AT2 sleeper hot rod

I have a friend named Dave that helped with some mods on a 175 for me too. :haha

the DT175 in question is a little more than it appears. Sleepers are fun! :woohoo:
2 1968 DT1s,1970 RT1M,1970 DT1C,1971 RT1B,1971 Honda Z50K2,1974 DT100A 1974DT250A,1974 Honda MT250,2 1975 DT400Bs,1975 Honda CR250M1,1978 DT175E,1979 Honda CR250R.
Dave
Jesus is Lord!
03 Jun 2015 21:20 #10

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