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Makotosun

1969 Yamaha AT1 starting issues

  • whs386
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1969 Yamaha AT1 starting issues was created by whs386

Hello everyone, I've been lurking for a few months on the forum and am gracious for the information here, been very helpful. I'm very much a beginner at this, but have fallen in love with the hobby. That said, I'm running out of ideas to get my AT1 running.  It was a total wreck and non runner without spark when I picked it up, incomplete. Right now, I have spark (points were seized) and can't get it to run more than 30sec-1 minute at a time, typically accompanied by some backfires/misfires between kicks. For some reason, it actually likes starting with the choke off (Can't get it to even gurgle with the choke on). There isn't much throttle response either to keep it idling. I'll break down what I've done so far:

1.  Replaced points and set the gap to 16 thou and set the timing with dial gauge to 1.8 BTDC with the mechanical advance arms open per the manual. Had issues with the timing and had to pull stator/armature and replace partially sheared woodruff key. 

2.  Battery is fully charged sealed MotoBatt

3. Pulled original carb and cleaned it 3 times total, third time rebuilt with a keyster kit. Just didn't rebuild the choke. Air mixture screw is 1.5 turns out. 

4. Fresh fuel and 2 stroke oil. Tank is clean and rust free. 

5. New air filter and rubber boot securely fitted. 

Thoughts:
1.  I'm thinking the carb is the issue.  Fuel mixture. 
2.  Maybe an air or vacuum leak? Not sure the best approach to check. 
3.  Maybe re-installing original carb parts back in tomorrow. 
4. The backfires make me think ignition timing but I feel it is set correctly. 
5. A new spark plug (even though the spark I have from the two in the bike is strong). 
6. Obtaining an original exhaust (see the strange exhaust in the photo that this came with!)

Photos attached - don't be distracted by the blue tank. The VIN (if I've looked it up correctly) is a 69 AT1 and not an AT3
Last edit: 06 Mar 2021 18:14 by whs386. Reason: Additional info
06 Mar 2021 17:54 #1

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Replied by whs386 on topic 1969 Yamaha AT1 starting issues

Also, what are some resources for engine rebuild components(bearings, oil seals, gaskets, etc)?  I've been using EBay and Partzilla for parts so far, I'm sure I'm missing some good places though. I may end up rebuilding (glutton for punishment). 
06 Mar 2021 18:08 #2

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Replied by Mothersbaugh on topic 1969 Yamaha AT1 starting issues

Welcome. Quite a job you've undertaken!
When you cleaned the carb 3 times, did you clean out and blow out with compressed air every passageway?
Slide is in the carb correctly, with the cutaway to the rear? What notch is the needle jet on?
The Keyster kits are OK for gaskets and maybe the fuel inlet, but they are notorious for having incorrectly drilled/sized jets. If you can clean your original jets, I'd place them into the carb again. And check the manual to see that they are the correct sizes. PO's are notorious for fooling around with jets like they knew what they were doing when they had no idea.
Does the pipe flow freely? Might try burning it out over a grill or a campfire. Seriously. They get a lot of oily deposits and build up and must be free flowing.
How are the armature brushes?
06 Mar 2021 21:48 #3

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Replied by MarkT on topic 1969 Yamaha AT1 starting issues

Check the jet in the well in the bottom of the float bowl...  it feeds the starter circuit (choke).

 


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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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06 Mar 2021 22:04 #4

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Replied by RT325 on topic 1969 Yamaha AT1 starting issues

Not easy to take a guess yet, but hows the fit of the small Oring that seals the bowl onto the base of the needle jet. If no tension or missing totally it drowns the motor like a 400 main jet, which is about what it becomes where that Oring fits & bypasses the side mounted main jet. I see choke jet has been pointed out in the bowl cavity so that's good. Other guess is are the points 'nice & free'--i see you unseized them--but could be condenser & a good way to check, i think, with your 12 volt system is to run it in the dark or low light & watch the points & if suddenly spark like a welder as it stops then possibly 'that' condenser Unlikely though as rarely play up. Everything tight in 'that' area, points wire, condenser wire etc. Is it a piston port motor as is a bit hard to see on my laptop but think it 'is' but tank & seat are later, not that it matters. Pipe is interesting too. You're in for a bit of fun but sounds like you have the ability to go looking & sort it. Good luck from NZ. ps i guess the exhaust pipe is clear.
06 Mar 2021 23:44 #5

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Replied by LETSJET on topic 1969 Yamaha AT1 starting issues

Buy a cheapo carb off ebay for about $30 or so, brand new and see if it runs with that knock off chinese carb.
07 Mar 2021 16:11 #6

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Replied by whs386 on topic 1969 Yamaha AT1 starting issues

Thank you all for the suggestions. So long story short I got her to run! I did a combination of a few things:

- cleaned the pilot hole in the carburetor bowl as noted above (pretty sure that was the issue)
- replaced the jet came with the carburetor (160, Which is a little bit over the 150 stock). The jet that came with the car rebuild kit was a 150.
- I kept the pilot jet from the rebuild kit (30)
- I moved the throttle needle position from the middle which was position three up one to position two. I'm not sure if I needed to do this or if this would cause any issues with leanness but the bike is working.
- I have attached a picture of the jet set O-ring, I'm pretty sure it's original with the bike and would need replacement. Would love to hear your feedback, and if you could provide a link for replacement.

Now I tried to put it in gear, pulling the clutch and going from neutral to first, and bike immediately stalled while the clutch was pulled in. So I'm guessing there's some thing going on in the clutch basket, with the old friction plates, or a loose clutch cable. Any suggestions? I haven't delved into a clutch before, but I'm thinking I need to clean up the steel plates, and buy new friction plates.
21 Mar 2021 06:18 #7

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Replied by Gr8uncleal on topic 1969 Yamaha AT1 starting issues

Good news, well done.

Hopefully the clutch is just sticky plates and easily solved. Some folks pull the clutch lever in, tie it to the bars and leave overnight. Others bump it downhill and go for a ride.

It's usually recommended to replace that O ring - it is still available from Yamaha.
Last edit: 21 Mar 2021 09:12 by Gr8uncleal.
21 Mar 2021 09:10 #8

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Replied by whs386 on topic 1969 Yamaha AT1 starting issues

Replaced the O-ring and it is able to rev higher now without a bog.

Pulled the clutch and tied it overnight, no improvement.  Ordered new clutch fibers, the others were very sticky.

On a slightly different note:  I purchased a new exhaust for the AT1 (an original), and it has the baffle.  I want to remove it to clean out the carbon (burning it with torch I guess).  It is STUCK.  I've heard of using a bent coat hanger and trying to hook it through the holes down the pipe, but it's hard to see.  Any suggestions?
09 Apr 2021 06:16 #9

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Replied by Ivas2311 on topic 1969 Yamaha AT1 starting issues

Howdy, currently experiencing issues similar to yours. Way too rich. Do you happen to have a part number or source for that starter circuit o ring? When you bought new jets, were they 6mm all around or did they have the groove for the o ring? All the replacement jets I see for these AT1s don't seem to accommodate the o ring. I have been looking around to see if I need to use the OEM o ring for this bike to run.

Thanks, 
Isaac 
Last edit: 05 Sep 2023 17:20 by Ivas2311.
05 Sep 2023 17:20 #10

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