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Makotosun

JT1 shifting issues

  • Schu
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Replied by Schu on topic JT1 shifting issues

I will try those suggestions Mark. I also plan to dispose of the fuel in that tank since I have no idea how old it is. This bike had trans issues and was never ridden.

I’m going to head out there shortly and place my thumb over the tube that the carb mounts to. I assume that I should feel a pulsation effect when cranking it over. Not sure how much I can do out there today. I wrenched my back yesterday and can hardly get up out of a chair….
Schu

CT1B, CT1C, JT1, JT2, CT2, RT3, DT360A, GT80B, DT100B, DT125B, DT175B, DT175C, DT250B, DT400B, Z50

Someday, you'll own some Yamahas
19 Jan 2026 06:42 #21

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Replied by RT325 on topic JT1 shifting issues

Deleted my post as I'm wrong looking at parts pics. I thought the center & dis were one item disc bonded to the center but shows as two on parts list. As the piston goes down the dis. Should be covering the inlet pretty much. The splines are so coarse it'd either be cirrect orientation or very wrong I'd think. As piston rises from bdc the inlet should be open. Or am I thinking wrong. Just looked at yg1t lanscout & the center is part of the disc but all slides on a spacer with is pinned to the crank plus pin extends into the disc steel center. Learning as we go I am as have replaced a few of them on yg1 models that ripped the center out-- but that was in "63 haha.
Last edit: 19 Jan 2026 13:01 by RT325.
19 Jan 2026 12:41 #22

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Replied by RT325 on topic JT1 shifting issues

Your pic looks good on my computer compared to phone. There would have to be a timing mark on the disc like a dot or indent & on the center. Plus the steel center is pinned to the shaft, so can't go wrong "i'm thinking". If no mark visible on the center then is it upsidedown.
19 Jan 2026 14:57 #23

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Replied by Schu on topic JT1 shifting issues

The disc does have a double dot mark to ensure proper placement at TDC and yes the cutout starts closing off the inlet as soon as it rotates past TDC.

I didn’t mess with it much today but I did verify that the timing is good. I also verified that it is not puffing air out of the inlet when spinning it with the drill motor. I simply feel a slight pulsation as I expected.

Hope to get back at it tomorrow with fresh fuel, known good plug from my other JT. 
Schu

CT1B, CT1C, JT1, JT2, CT2, RT3, DT360A, GT80B, DT100B, DT125B, DT175B, DT175C, DT250B, DT400B, Z50

Someday, you'll own some Yamahas
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19 Jan 2026 15:55 #24

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