Apologies for my first newby post but I'm struggling to find out exactly which model I have, Its a 400cc monoshock and according to the v5/log book its a 1977, frame and engine numbers match which start with 1R6. I have checked the tech library but cannot find it on there. Really need to be sure as I need a gasket kit because the base gasket is blowing.
Thanks in advance. 

Model code list in Tech Library shows 1R6 as a 1977 or 1978 DT400MX. 

If someone has a Haynes Manual from Europe/UK it might have more specifics...  or Yamaha generally followed a "pattern" of starting the next model year with a jump in the suffix portion of the VIN.  Comparing your full number to other models that used a common prefix over multiple year models might help guess if it's a 77 or 78.  In terms of gaskets, it likely doesn't matter.

One thing to keep in mind is that 99% of the information available online is specific to US models.  European models had different lighting and switches for some years so finding a 1R6 parts manual or consulting a local Yamaha dealer for some parts may be necessary.  It's unlikely the engine parts like gaskets are different than US spec.  Carburetor parts may be.

The VIN tables here are predominantly for the US bikes and yours is UK/European one. 

If you haven't done so already, I would get hold of UK/Euro parts and service manuals and work from those. These are on fleabay at the moment, although there might be others - pump a part number into CMSNL or Partzilla and you'll get a list of which US models also used that part.

YAMAHA DT400 MX 1R7 1R6 PARTS LIST MANUAL CATALOGUE 1977 nos | eBay

Yamaha DT250 1R7 DT400 1R6 (D) Supplement Manual Review Tecnical Workshop | eBay





 

Thank you Mark, I did look but couldnt find 1R6, need better glasses I guess ha ha. I think it is a USA import as the exhuast muffler has US patten stamped on it. 

Thank you, I do think mine is a US import because of the US patent stamp on the muffler, would it help if I put the full frame number on here?

1R6 was not a US model.  Someone probably bought a muffler from the US at one point? 

 

Agreed.

Alternatively, Yamaha might just have used the same outer body for the exhaust, but without the spark arrestor fitted - a comparison with another UK/Euro model would be required in order to confirm this.

The "patent stamp" is likely the USFS approval for the Yamaha-Krizman spark arrestor?

It seems very unlikely that Yamaha would include that approval on a part that did not contain a spark arrestor. If they did and in some alternate universe a spark from the exhaust caused a fire, can you imagine the liability lawsuit?

Someone once posted pictures of the difference between US and non-US mufflers on the later models. If I remember correctly they looked similar with the US version having a removable insert and of course the approval stamp... the "other countries" version was welded solid with no insert.

(A means to clean out loose accumulated carbon is required in the USFS standard. Yamaha usually met this requirement with a removable insert... some USFS designs had a removable plate covering a "clean out" access port .... Honda and Suzuki used a plate sometimes.)

Yes, fair point Mark, so US exhaust fitted at a later date it is! 

I can confirm that the 1977 UK/Euro spec DT400 came fitted with the US style " lollypop" krizman spark arrestor rear box with removeable baffle.


Credit for pics.  Daves Bike Brochures.  A remarkable resource for old paperwork.  I even got my UK market DT175 parts book from him.