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New member, new bike, please help

06 Nov 2019 16:40
Jim in SCal
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New member, new bike, please help #1
I am new to this forum, not sure if I am posting in the right place. Please let me know if I am not. Anyway, I just bought a restored 1972 Yamaha DT2 250 Enduro. It's similar to several bikes I owned 40 years ago, which is why I bought it. This bike ran well, except for one issue: In fifth gear, when under load, like going up a hill, the engine would speed up for a second or so with a jerk, then return to normal. This happened again and again when I first road the bike after buying it, but only in fifth gear. I assumed it was slipping into fourth gear, and then back to fifth. But the guy who sold me the bike said it was likely a slipping clutch because the one in the bike was fairly worn.

Today, he put in a new clutch and clutch springs, which I provided. For the first four or five miles on my ride home, the problem seemed to be fixed. Fifth gear was solid, no jerking or revving, even under load up a hill.

But on the last mile before I got to my house, the same problem came back. In fifth gear, under power going up a hill, the engine would rev up with a jolt, then return to normal. This happened four of five times. It seemed, however, that the amount of time the engine revved up was shorter than before the new clutch. But I am not certain.

Can anyone suggest what might be the problem? Could the clutch need adjustment? Could the oil in the gear box (10-40w Yamalube) be too slippery for a vintage bike? Any suggestions or ideas would be much appreciated!

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06 Nov 2019 16:43
darinm
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New member, new bike, please help #2
As it's wet clutch rated oil it should be fine, that's about the extent of my knowledge. One of the more experienced members will have some great suggestions though.

1972 Yamaha CT2 175
1972 Yamaha RT2 360
1972 Suzuki TS 185 Sierra
1995 Suzuki DR 350

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07 Nov 2019 13:26
Bwestern
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New member, new bike, please help #3
Hi Jim,
Try adjusting the clutch. There should be a set screw and nut to adjust the clutch. I have a 78 dt250 and mine is on the pressure plate (right side of the bike) but looks like yours will be on the left side of the bike. From the parts diagram on parts fish its number 27 and 28.

www.partsfish.com/oemparts/a/yam/5004169...00209bc784844/clutch

That's the first thing I would check- best of luck

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07 Nov 2019 15:29
Jim in SCal
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New member, new bike, please help #4
Would you mind taking a look at this video (linked below) and telling me if you think the clutch is the problem? Others are suggesting the worn dogs/slots on the 3rd gear in the transmission, which mates with another gear to create fifth. So far, the skipping occurs only in fifth gear, which is why I think they have come to that conclusion. The first skip on the video is more typical of what happens, especially when I am going faster at higher revs. (I have not tried yet to adjust the clutch from the plate on the engine case.)

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07 Nov 2019 16:59
MarkT
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New member, new bike, please help #5
Multiple threads with same question get confusing...

Again, the parts naming Yamaha used is confusing. First thing to know is every gear is a pair of gears, one on each shaft... one of the pair is splined to one of the shafts and the other of that pair freewheels. When all the gears that can freewheel are freewheeling, the trans is in neutral. To select a gear, the shift drum moves a fork that slides a part... that part can also be a gear... over so that a dog and slot arrangement locks one freewheeling gear to the shaft. Now you have both gears of a pair locked to the shafts and you are in that gear.

Third gear has dogs and is splined to the shaft. It can slide side to side moved by the shift fork. When it slides over and the dogs engage the slots in the freewheeling gear next to it, the 3rd gear teeth are not being used to make the bike move. Only the dogs on the side of third gear are being used to lock the freewheeling gear next to it to the shaft.

The part #7 gear with the slots that freewheels on the shaft? ...that's actually 5th gear (no matter what Yamaha named it). When the dogs and splines on 3rd are used to lock the freewheeling 5th gear to the shaft, you are in 5th gear. If those dogs jump out of the slots, the 5th gear freewheels until the dogs engage again.

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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08 Nov 2019 00:41
RT325
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New member, new bike, please help #6
As Mark said, & very well put too.
Here's another random thought. Take it for a ride & when in top gear hold the lever hard up with your foot & see if you can feel it kick as it forces itself out & back in gear. Drum may not be forced back against the cam plate plunger far enough to feel it but likely is, so just 'might' feel it come in contact with the lever. Lever only takes it about 9/10 all the way into the gear but still might feel the drum roll back 'that far' then go back into place. Won't be easy to do holding the lever hard up with your foot. One more thing i hadn't thought of [& unlikely but] if the clutch center nut was 'very loose' then the mainshaft could move sideways enough to make 5th gear less deep in mesh. with same end result.
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08 Nov 2019 13:14
Jim in SCal
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New member, new bike, please help #7
Thank you all for your help!
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08 Nov 2019 17:43
MarkT
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New member, new bike, please help #8
If you want to reach out to Meis his email is This email address is being protected from spambots. You need JavaScript enabled to view it.

He's in the Orange County area of So Cal

(Don't forget to inquire about the sleeper pipe mod) :Throttle

:Buds

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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