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TOPIC: AT1 Carb Jetting

AT1 Carb Jetting 13 Apr 2019 10:15 #1

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Hello to all,
Scratching my head about what the stock configuration the Mikuni should be set up with for the AT1. I received two different bodies, a VM24 and a VM26 with my bike, and a whole mess of slides, needles, airjets, etc.. The manual I have only references the body size, jet needle, and main jet. I've also looked through the technical references here with no luck.. (please correct me if i've missed something?) Any help figuring out the following would be very appreciated.
Bike: AT1 (not export, if that matters. Bike was bought in Korea.)
1. Airjet
2. Pilot Jet
3. Main Jet
4. Needle Jet
5. Jet Needle
6. Slide Cut-out
7. Needle valve

Again, any help figuring out stock specs would be hugely appreciated. Thanks in advance!
Chris

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AT1 Carb Jetting 13 Apr 2019 11:26 #2

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I'd recommend you check the full serial number to see if you have a 69-71 AT1 or a 72 AT2 or 73 AT3. All had the AT1 prefix stamped in the frame and engine.

Assuming you have a 69-71 AT1 the stock jetting for both the 24 (enduro) and 26 (MX) carbs is in the parts list in the Tech Library. The only problem is that the original carbs did not have a removable "air jet". So if your carbs do, they might not be original, they have been modified, you don't have a 69-71 AT1, or ???

(I think I'm going to stop responding to questions like this that don't include detailed pictures and full information like serial numbers as it's often a waste of my time.)

From the Tech Library:
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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

AT1 Carb Jetting 13 Apr 2019 12:01 #3

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MarkT,
Thank you for your help, and making the vintage world so welcoming. Sorry to waste your time.

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AT1 Carb Jetting 13 Apr 2019 12:31 #4

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If your carb is an AT1 carb it will be marked 248 A2 on the flange. 150 main jet, 30 pilot jet, 2.0 slide, 4D3 needle N8 needle jet..
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AT1 Carb Jetting 13 Apr 2019 12:43 #5

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the2012 wrote: MarkT,
Thank you for your help, and making the vintage world so welcoming. Sorry to waste your time.


The comment wasn't directed specifically at you... and I didn't say you wasted my time.

The thing with this your question is none of the AT1 carbs had replaceable air jets... I don't think even the AT2 or 3 did... and there's just been so many questions with things like this that it wouldn't surprise me if you have a later reed valve bike or if the "box of carbs" turns out out to be Suzuki carbs or something. :)

And then what I posted would be a waste of time.

And you're welcome. I hope you figure it out.

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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

AT1 Carb Jetting 13 Apr 2019 14:31 #6

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MarkT wrote: I'd recommend you check the full serial number to see if you have a 69-71 AT1 or a 72 AT2 or 73 AT3. All had the AT1 prefix stamped in the frame and engine.

Assuming you have a 69-71 AT1 the stock jetting for both the 24 (enduro) and 26 (MX) carbs is in the parts list in the Tech Library. The only problem is that the original carbs did not have a removable "air jet". So if your carbs do, they might not be original, they have been modified, you don't have a 69-71 AT1, or ???

(I think I'm going to stop responding to questions like this that don't include detailed pictures and full information like serial numbers as it's often a waste of my time.)

From the Tech Library:


MarkT,

Spends an incredible amount of time here answering questions. Personally, I couldn’t do what he does for two or perhaps more reasons. He has notes and files from thousands of posts, and he is more knowledgeable than me!

But if MARK spent that time on his own projects, he would be able to travel the world, working on bikes that actually paid real hard cash.

I applaud Mark’s efforts, he has to manage his time his way.

Hey Captain, it’s time to plan a fishing trip up north, at least one time on the same boat.

a
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YAMA-LAND
818-521-2109
MINIBIKESERVICE@AOL.COM 1971 125cc AT1-C (DOROTHEA) 1971 175cc CT1-C (BRANDY) 1970 250cc DT1-C (MONICA) 1973 100cc Hodaka Combat Rat (ABBY NORMAL) 1975 DT400 (BONNIE BELL)
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AT1 Carb Jetting 14 Apr 2019 08:50 #7

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The non-replaceable air jet definitely had me scratching my head. I've only worked with one other set of Mikuni's on my Honda and I'll be honest, I thought I had stripped it trying to remove... so a weight off my shoulder there. What is *interesting* is that the two carb bodies I have are marked
-248A2
-248M2

Now, according to Capt. Dave, the A2 is the one that should be native to the AT1. However the A2 has a removed air-screw.. The M2 definitely has a pressed in air screw, so that's the one I will be putting back together with the specs provided.

Sincerely, thanks again for the help. Will post pics of the carbs and bits here shortly for those interested.

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AT1 Carb Jetting 14 Apr 2019 08:55 #8

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M2 is the ATMX carb code... should be 26mm.

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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

AT1 Carb Jetting 14 Apr 2019 09:00 #9

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Here are some of the guts that came in the box with the carbs.
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AT1 Carb Jetting 14 Apr 2019 09:01 #10

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and the bodies themselves
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