You can on the earlier CT1. I've done it in a pinch. Just make sure to use the washer under the main jet so the needle jet can't slide up.

A few years ago, someone... (maybe Apex?) recommended these common plumbing o-rings and said they work great... I have not tried them myself... though I do look for them at Home Depot occasionally... they always seem to be out of stock!

Edit: See post from Apex below... #61 is the part number... I'm not sure the Amazon link was the correct part.

I had the same issue on a '72 CT2 and '72 LT2, I ran by autozone or one of those chains and picked up a viton o-ring pack of assorted sizes for ~$9 and it had one for that part on each carb for both bikes, it was a good enough fit to substantially improve performance. I just brought in the needle assembly to make sure I was in the right size range. Congratulations on the new bike, I'm new to this world too and enjoy the perfect size of the 175

Yep, I use them. They work just fine, just make sure to use something to lube the o ring before installing the bowl. I use white lithium grease, just a little little bit to allow the roughness of the bowl cavity to slide over & compress the o ring. Labeled #61 on the package from my local hardware store.

Sorry, I am a little bit at a loss for what you are saying. The washer under the main jet so the needle jet can't slide up? Is that washer preventing the whole assembly from sliding up into the actual slide area? so basically just take that connecting piece with the o-ring out and put in the main right? Leave the washer in place?

Why would it work in a pinch, will the bike run poorly with that setup?

Yes, under the adapter with the o-ring is a washer... you need to leave the washer in place.

Biggest reason is that it's a real pain to change the main jet as you need to unbolt the whole carb.

Secondary reason is the Mikuni main jet style used is actually a copy of the old Amal design and the jet actually flows differently depending on which way the fuel flows through it... when you remove the main jet from the jet holder and install it right into the needle jet, you are reversing the flow direction through the jet. So it will change the jetting of the main circuit slightly.

I've done it when I tore an o-ring out on the trail and didn't have a replacement... (some debris plugged the pilot jet). It runs a whole lot better than it does with a bad o-ring! That said, I replaced the o-ring as soon as possible.



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Awesome. Thanks for the information. I thought it might have been along those lines, but wanted to be sure before I got too ahead of myself!

I look forward to getting the old bike up and running right so I can show it off in action sometime!

Cheers and Happy 2018 from Bend Oregon USA. Look forward to learning all I can about my new bike, a 1969 Yamaha AT1.
Lots of great info here for a newbie like me, to be honest I am scared to death I'll put a scratch on this thing!
First post here, hope I am in the right spot!

Babz

Babz.

Check out the Tech Library link at the top of most pages... there are links to service and owner's manuals and other resources... Also the search here works pretty darn good... and if you have a question, just ask!

Pictures are easy to post here using the "Attachments" button at the bottom of the posting window... look for the "insert" buttons after you attach to insert the photos into your post which makes the post a lot easier to read.

Here are a few direct links to some info in the Tech Library:

yamaha-enduros.com/index.php/workshop/20...on-sense-riding-book

yamaha-enduros.com/index.php/workshop/20...t-bike-owner-s-guide

yamaha-enduros.com/index.php/workshop/20...0-at1b-owners-manual

(Last one is not the exact owner's manual for your bike, but the 1969-71 AT1's are virtually identical except for color and even the1972-73 models are extremely similar.)

I am Carter Hutchinson a retired USAF F-15 Crew Chief. I have been employed by Midwest Motor Sports in Hartford, Il for 16 years now. I am a certified bike nut. I received this affliction at the age of 5 when my neighbor offered me a ride on the back of his brothers' new 69 z-50 mini-trail. I have been especially drawn to the Yamaha Enduros since . I currently own quite an array of these fine machines. I really need to do an inventory to get an accurate list but will shoot from the hip here. Starting from the oldest: 1968 Suzuki S-32, 1969 Honda z50, 2 1970 Honda SL 175's, 2 1970 Honda Ct70's, ( 1 is an H), 1971 Yamaha JT-1 mini enduro, 2 1971 Honda z-50 mini-trails, 1972 Honda SL 350, 1972 Honda CB175, 1972 Honda SL 175 , 1972 Honda SL70, 1973 Honda XL350, 1973 Yamaha RD350, 1974 Kawasaki G5 (100cc predecessor to the KE) , 1975 Honda z-50, 1975 Yamaha DT100, 1975 Yamaha DT125, 1975 Yamaha DT175, 1977 Yamaha LB80 Chappy, 1977 Honda XR75, 1978 Honda ATC 70, 1978 Honda XL80, 1981 Honda C70 Passport, 1982 Yamaha IT175, 1985 Kawasaki ZX900A Ninija, 1986 Suzuki RM80, 1987 Yamaha YZ125, 2001 Yamaha TT-R90, 2008 Yamaha YZ85, 2008 Kawasaki Concours14, 2012 Suzuki C50T

Carter67350!

Quite a collection you have there! Would love to see some pictures when you get a chance.