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1973 AT3 ATMX rides again

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1973 AT3 ATMX rides again was created by southernman_67

In my intro post I mentioned that I have an old bike that has not ran in several years. When I bought it, I was told it was a 1971 AT1 Enduro. After looking at the serial numbers on this site, I believe it is a 1973 AT3 ATMX. There is no evidence of it ever having been an Enduro. Here is our story so far. 

The bike ran when I bought it for my two youngest sons who were in their early teens at the time. They rode it for a couple of years, then we weren’t in a place they could ride it, then they grew up and moved out. It sat outside for a couple of years, then I moved it into the garage where it sat for several more. That’s the long story, short.

2 or 3 weeks ago my oldest son and I decided to see if we could bring it back to life. I found this site, and have done a ton of reading. I will pause right here and say THANK YOU to all of the members that contribute so much! I haven’t had to ask a bunch of questions, because the search function works really well.  Sometimes it doesn’t apply to this model, but it’s good knowledge that helps get my mind thinking right. 

I will post more on the progress tomorrow, but for now, I have to go find Mister Sandman. Thanks again, all of y’all!

 
25 Jun 2022 21:18 #1

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Replied by RT325 on topic 1973 AT3 ATMX rides again

Look forward to the updates & pics. Cheers.
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25 Jun 2022 22:17 #2

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

Here is an update on what I’ve done so far:
Pulled front wheel to patch a tube, and while it was off cleaned the brake drum and shoes, and got the front brakes in good working order. They had been dragging just pushing it around the shop.
Pulled the tank and let it soak in vinegar overnight. That cleaned it up pretty good. Pulled the carburetor and sprayed it with Berryman’s.
It wasn’t getting fire, so I bought a flywheel puller, cleaned the points, reset the timing, and still no spark.
I bought a new ignition coil, but the mounting holes were different. So, we fab’d a bracket to make it work, just so we can get it running. Had spark, couldn’t get it to start.
Fuel was just pouring out of the overflow, so I pulled the carb again and this time disassembled it completely and soaked it in a pail of Berryman’s overnight. The nearest place I could find a bowl gasket was about 30 miles away. My son had to go over that way for an appointment, so he picked it up while I reassembled everything. He got back with the gasket and guess what? It was wrong. Rather than drive 30 miles for a different gasket, I bought a sheet of gasket material and cut one out.
Got the carb reinstalled yesterday, and realized my mistake from the first time and why it was pouring out fuel. I had not gotten the needle perfectly centered before, so the throttle valve couldn’t close.
With the carb back on and assembled correctly, I opened the starting circuit and gave it a few kicks. It sputtered a few times, so I knew I was closer than before. I closed the starting circuit, opened the throttle wide open, gave her a kick and she roared to life for the first time in about 10 years.
I eased her out of the garage and made a couple of laps around the yard. Man I was grinning from ear to ear.
 

 
 
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26 Jun 2022 10:25 #3

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

Last night I couldn’t get the clutch to work properly. I was shifting with little or no clutch, and the rear drum brakes are not working. Today’s agenda is to pull the rear wheel and dig into the drum, and to try to adjust the clutch or go into it and clean the clutch plates.

I’ll post up results later.
26 Jun 2022 10:31 #4

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Replied by Ht1kid on topic 1973 AT3 ATMX rides again

Congratulations!!!
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26 Jun 2022 10:34 #5

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

So here I am again mixing misery and gin,
Sittin’ with all my friends and talkin’ to myself…

Latest update:

I pulled the left side crankcase cover off to adjust the clutch. Bumped it and the {inner cover} came loose. That didn’t happen when we had it apart to pull the flywheel to clean the points and set the timing. Must have been crud and the outside cover holding it in place. The inner part of the cover was missing the two pan head screws that hold it on. Thanks to Makotosun’s post in the tech library I was able to figure out the length of the 6mm screws needed to secure it. They’ll be here tomorrow.

The clutch return spring was missing. There was a rusted piece of it still wrapped around the pin. I made a new one out of a throttle return spring, so hopefully it will work.

The clutch cable was very sticky and hard to slide back and forth. It’s been hanging in the garage for a couple of days while I drop a little oil down it every now and then. It’s moving smoother now.

But, while she’s been setting, I have noticed an oil drip from the left side crankcase. I guess I will be trying to find an oil seal.

There was a good amount of oil leaking around the exhaust manifold. I pulled the exhaust off and it was full of oil. I think that came from me not assembling the throttle valve and needle right the first time.

I pulled the baffle out of the exhaust, and it is gone! There is nothing left except the tube, whatever fibers they used wrap around the internal tube were mostly 
disintegrated. I will power wash it and put it back together without whatever it is.

I am sure there is something I failed to mention, but I am going to bed.

 
Last edit: 02 Jul 2022 22:28 by Enduronut.
28 Jun 2022 20:45 #6

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

I am sorry the pics are doubled up, but the post was quadrupled up. I edited the best I could. After 173 tries, I really am going to bed.

.
FIXED . . .  Enduronut
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Last edit: 02 Jul 2022 22:31 by Enduronut.
28 Jun 2022 21:10 #7

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Replied by MarkT on topic 1973 AT3 ATMX rides again

To prevent the duplication issue do NOT use the "insert all" button.  Scroll down to each photo and insert them one at a time with their "insert" button. 

"insert all" just creates a mess. 

Great progress on the bike...  I have an AT3MX and it's just a blast to ride...  hard to keep the front wheel down when the rpm comes up. 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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28 Jun 2022 21:39 #8

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

Well y’all, here I am once again with another update. 

It turned out that there wasn’t a left side crank seal that was leaking. It was the carb leaking from the bowl seal. We had the left side cover off and it made me think it was coming from there, but it wasn’t. We got that rectified.

Received the screws we needed and got the left side reassembled. Clutch with the homemade spring seemed to be working fine. At least way better than it was.

We pressure washed the exhaust pipe, blew it dry, and painted it with high temp paint. I ain’t posting any pics because that was a disaster last night. MarkT gave good advice, but I’ll try it when it’s not so late.

Started her up, and she kicked off on the first try. What a joy to hear her run! So, easy on the clutch, let her breathe a little, and she blasted out of the garage.

My son did a couple of laps on her, then I rode her. I rode her a little harder than he did and that’s when I started having issues. She runs OK again now, but I’ll save my questions for tomorrow.

Good night, Y’all…
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29 Jun 2022 21:54 #9

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Replied by southernman_67 on topic 1973 AT3 ATMX rides again

Here is the painted exhaust:

 
 

I think it looks better.

Like I said, we rode her around last night. I took a jump and must have had 30 feet of air! OK I probably had a foot of air. But after landing, she sputtered and died. The only way I could get her started was WOT. Then I had to run between 3/4 and wide open to get back to the garage.

The throttle screw had vibrated nearly all the way out. I got it adjusted and fiddled with the air screw a little and had her purring in short order.

New kill switch came in today, so we got that installed and now don’t have to pull the plug wire to kill it.

I do have a few questions for you experts, though.

1) Would a stiffer spring under the throttle screw prevent it from vibratng out, or is there something else I should do?

2) The exhaust pipe was full of oil. Am I correct in assuming it’s from me not assembling the carburetor right the first time so the throttle valve was stuck wide open and we kicked it a lot trying to start it?

3) What was left of the fiber around the baffle came out when When I pulled it out of the exhaust pipe. I am going to assume  that it was asbestos as old as it is. I have access to ceramic fiber blanket. Would that be suitable to wrap the baffle, and is it even necessary?

4) Last question for now. Sometimes the kick starter returns, and others it won’t. Also, I’m hearing a whirring noise coming from the right side crank case. What should I be looking for when I open it up?
30 Jun 2022 14:13 #10

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