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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    UPDATE 04/15/2024 Received the Jets from Sudco Kept. #190 mains Installed #40 pilots From 0 - 1/4 throttle there was still a slight flat spot and very slight hesitation, but when allowing engine braking the bike ran perfectly and did not buck or stutter at all. From 1/4 to full throttle...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    UPDATE 04/09/2024 Received the Jets from Sudco Installed #190 mains Installed #35 pilots From 0 - 1/4 throttle there was still a slight flat spot and when allowing engine braking a slight bucking very slight but still there. From 1/4 to full throttle bike ran beautifully. Yesterday I...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    I called up SUDCO this morning and ordered Mains #185 and #190 Pilots #30 #32.5 and #35 Should have them by end of week. I will put them in this weekend and make a few more test runs. I only bought the cheap amazon ones to kinda get a ballpark range before buying the Mikunis. Was like $10...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    UPDATE 03/30/2024 So I decided to put in #190 mains and the #30 pilots. Bike started great and ran smooth at idle. Took for test run and it still has some slight hesitation from 0 to .25 throttle and some very slight bucking when letting it engine brake with no throttle. Figured I’d go up to...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    What do you think would be the best size main?? #185, #190?? I want to get the engine running its best without overheating or over working it. I am at 2500 ft elevation in Tucson AZ
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    LATEST UPDATE: 03/25/24 Main Jet: #180 Pilot Jet: #27.5 Air Screw: .5 - .75 out from closed Needle Clip: #3 Needle: 6F09 Needle Jet: 159 P-6 Slide Size: 2.0 Air Jet: Removed Called SUDCO today who is the Mikuni Carb West Coast Distributor. They build and sell...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Am I good with those or do I need to adjust??
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Ok pulled 1 carb apart tonight and this is what I have Slide - 2.0 Screw Jet / Needle Jet - 159 P-6 Don’t know what it means 😂
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    I’ll get the info tomorrow and post.
  10. H

    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Yes have filters on it. They seem to be the K&N filters that come in a kit. They do not block the air passages on the filter side of carbs. Where is the needle jet? I only see the pilot and main inside the bowl section? Slide? As in throttle slide? I didn’t know there were options variants on...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Yes they appear to be the barrel K&N ones that come in the usual kit. They are clean and they do not have a lip on them blocking any ports.
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Are you referring to the round slide?? I don’t know. Is there a model number on it? I was assuming all VM-34s had the same slide in them. Have not checked needle jet. Don’t know answer to that question. Will look tomorrow.
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    UPDATE: Upped the main jet to 180 and upped the pilot jet to 27.5 today. Bike ran a bit smoother but back fired at times. Still has a dead spot between 1/4 & 1/2 throttle. Bucks a bit and then the power comes on 1/2 throttle and above. Stumbles when off throttle and letting engine brake bike...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    Sonic Cleaned the carbs. Put everything back together. Sync’d them, the left was taking off slightly before the right. 175 main 25 pilot Needle on 3rd position Air screw 1 turn Ran up and down the street to warm it up. I can’t post the Idle video I took. Don’t know how to post short videos...
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    I pulled the needles tonight. They are 6F09s so that’s a good start. They were clipped on #2 so I moved both to #3 slot. Will test ride tomorrow like this and with air screw @1 turn to 1.25. Let’s see how it goes 👍🏼 Picture 1 - How I found the needles Picture 2 - Adjusted clip
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    Let's See The XS's

    I’m still trying to figure that out. Just bought it off a guy 3 weeks ago. Runs like shit. Trying to tune the carbs. Learning curve involved 🫣🥴
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    Let's See The XS's

    Here’s mine 1972 XS2
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    Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)

    I think the needle clip was on the 1st or 2nd setting when I installed the new throttle cable. I’ll move it to the middle and start there. Haven’t had a chance to work on the carbs these past few days. Will go through it tomorrow. I bought the Sudco Mikuni carb manual but it seems 1/4 manual...
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