MX 400B advice

Hey guys, I just picked up a '75 Yamaha MX400 and before I start tearing into it, I'd like to get a shop manual like a Clymer or similar. But I'm having trouble finding one for this particular bike. I can find them for earlier MX models, for the DT's and for the later YZ's, but so far nothing for this exact bike. Does anybody know if I can use a manual for a different model Yamaha that is interchangeable with the 400 MX?

Also, any advice on a good supplier of vintage Yamaha parts, other than fleabay? And is it still possible to get the monoshock on this thing rebuilt? Thanks for any help!

The 76 YZ 400 is almost the same. Alot of the parts interchange.

That's what I needed to know. Thanks Chayzed, good info.

I just found one too. it's a pretty unmolested bike. Ugly paint incorrect fenders seat and number plates.


I'm in the top end right now and it doesn't even need a rebore, it mic's a perfect 85mm, so a deglaze, new piston, rings and wristpin will make it crisp again.


I also cleaned the reed block and just installed the Boyesen 606 dual stage reed valves.


I'll probably pull the motor and split the cases in the next week or so just to make sure everything is clean and tight.


Probably do new crank seals while it's open.


These are photos I shot when I went to buy it, I thought $350 was a pretty good deal considering the condition.



Edited by RustyBones

Could you guys tell me the numbers on the engine and frame, also fork tube dia?

I have what I was told was a MX, had the white tank at least, but with the round tubed swing arm.


If I recall, 510 should be the number for the 75mx400. Also 34 mm comes to mind on the fork tubes? But it's been a couple years since I sold my 75mx 250,,(same frame) the 76 have slightly larger forks with the same motor.

If you want to go all new white plastic.. I might sell you a "Euro white" restored tank to match(no bondo) for 400.00,,just sayn..

Edited by scalejockey

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