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Makotosun

1974 dt250a back from the grave

  • Jewelkutter
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1974 dt250a back from the grave was created by Jewelkutter

After 2 years of off and on tinkering, it started 3rd kick and runs good . I tried to upload a video but it wouldn't  go . I have a few bugs to work out like the 2 wire kill switch doesn't work , not sure if thats because the headlight isnt hooked up yet , dont know. The gas tap may have an issue , I only put about a pint of premix in the tank in case it leaked , and it did, so I removed it and fit a new oring gasket in and tightend the snot out of the screws and the bowl ring on the bottom of the gas valve and a miniscule of rtv where it connects to the tank, leak stopped but flow was minimal when i turned it to reserve probably not enough gas in the tank?
next issue I noticed was 2 drips of oil at the new head gasket , I'll retorque it tomorrow.  Another issue is when i turn to the left the throttle increases on its own , i followed the cable layout from the shop manual , i have to check throttle cable routing .  
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31 May 2023 16:35 #1

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  • Jewelkutter
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Replied by Jewelkutter on topic 1974 dt250a back from the grave

The 1975 Foto1971 slightly different rotor fits the 1974 model
31 May 2023 16:56 #2

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Replied by SKYDANCER46 on topic 1974 dt250a back from the grave

Nice looking bike. When you check your throttle cable routing be sure you didn't tape it to the frame somewhere. It should be able to move freely under the gas tank where it runs.

1970 DT250C
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31 May 2023 17:16 #3

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Replied by Jewelkutter on topic 1974 dt250a back from the grave

The manual seems to show 3 cables crammed down thru between the key switch and handlebar tree area . one is the throttle cable , it travels down the frame neck thru a wire loop on the frame ,between the gas tank and frame, behind a spring clip that's supposed to hold the cable splitter and it splits into 2 cables throttle cable travels along the frame under the tank with a cable tie and then into carb. oil pump cable straight down , i put no tape.
31 May 2023 17:44 #4

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Replied by Jewelkutter on topic 1974 dt250a back from the grave

I think I forgot to put the cable tie under the frame
31 May 2023 17:46 #5

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Replied by Jewelkutter on topic 1974 dt250a back from the grave

Thank You SKYDANCER , i went thru it in my head and the cable routing diagram does show both wire harness and throttle cable being connected to the frame with a cable tie , i did put one there but forgot to grab the throttle cable only the wire harness,  i have to dial things in on it tomorrow. Hopefully the head leak won't be to much of a problem and just retorque will cure that, I did not coat the head gasket , probably should have. Looks like I'll have to undo the exhaust to torque the head, any thoughts on this leak greatly appreciated
thanks 
john
31 May 2023 18:03 #6

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Replied by SKYDANCER46 on topic 1974 dt250a back from the grave

jewelkutter,

Don't use cable ties either unless you leave them loose. Yamaha had black bands so the cables will slide in them. That's why i said don't use black tape. It keeps the cable from moving freely when turning the steering . Route it like Yamaha shows and as long as you have the cable clip holder then use 2 black bands or cable ties if thats all you have but leave them slightly loose so the cables can move freely.

As for the head gasket, as long as the surfaces were clean and flat you should be good to go with the proper torque specs with a cross pattern sequence. I myself have never used coating on a head gasket in 40 plus years working on these bikes. Did you use a genuine yamaha gasket?

1970 DT250C
31 May 2023 19:05 #7

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Replied by Jewelkutter on topic 1974 dt250a back from the grave

Thanks SKYDANCER, i have all the original coated aluminum ties i appreciate your advice to leave them a little loose so the cables can move freely . as far as the head gasket I used an IBCO vintage kit bought off eBay the copper gasket looked identical and I did cross pattern tightening . More than likely Will be getting a genuine Yamaha head gasket .
Thanks again
31 May 2023 19:50 #8

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Replied by Jewelkutter on topic 1974 dt250a back from the grave

I thought I checked the surfaces for flat with a steel straight edge when I had the top end apart. , it looks like I have to loosen up the exhaust pipe to check the torque on the head or maybe even removed it . I also noticed an exhaust leak where the tail pipe attaches to the front pipe . I reused the old asbestos gasket that was there and it was in rough shape , i have a hi temp silicone one i think i got from enduro doctor but couldnt get it to fit on , i probablly didnt try hard enuf.
31 May 2023 20:03 #9

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Replied by Ht1kid on topic 1974 dt250a back from the grave

I was taught when I worked at Butler’s Yamaha to retorque the head a couple of times heat and cool cycles retorque in the morning 
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31 May 2023 21:34 #10

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