1975 Yamaha MX 500 Prototype

1975 Yamaha MX500Do you know your Yamaha MX history? This week we received a bike submission from Mark in Numurkah VIC, Australia. Here is the description:

This bike is believed to be a prototype of the MX500 from Yamaha that didn’t go into production. 13 were built according to Yamaha in the USA and 3 were sent to Australia of which 2 are left. Anyone with more information could help please…


Do you have more information on this Yamaha? Leave your comments below!

1975 Yamaha MX500 Prototype Gallery

Published: November 25, 2011 7:06 pm Categorized in:

1975 Yamaha MX 500 Prototype & Parts

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8 Comments

  • robin deatherage says:

    I owned one of those MX 500 Yamaha P’s. But they made these from 1973 through 75 but were not manufactured. Mine I purchased second hand from a Police Auction in 1975 in Texas. Apparently a Yamaha Team Rider was pulling it on Interstate 40 near Amarillo Texas heading to Bakersfield California. As I was told the trailer with two factory bikes mine being one of them were stolen in 1973. Well the bikes were found in 1975 and the company or Yamaha Team that owned them had already declared them for Insurance. The Insurance company then forfeited this bike to be auctioned off. So I bid on it and bought it. I rode this monster from 1975 to about 1979 and had it parked in my dads Barn on the Farm. Sad story from there though–After sitting for many years my dad not knowing its worth had it cut up and hauled off for scrap metal. I know right ! I still hurt over that. I owned owned a 1973 MX “600”cc Yamaha also that is not suppose to exist. I sold it to a friend years ago to. Have not seen it sense.

  • James Hamilton says:

    I purchased a 1975 DT400 last week. While cleaning it today I found the “50000” or 500cc casting on the cylinder. The stamped code on the transmission matches the frame. It looks like some felt the DT needed 360 like hp. Very odd to me.

  • Jan says:

    Hi,
    I have a Yamaha 125cc from 1975 in my barn, does any one know where to buy parts for it?
    – Greetings Jan

  • Mark says:

    James Jacks more information please.. David thank you, but it does not say 5000 on the cylinder it says 50000, an extra 0 which would probably means 500cc. The frame number starts in 509- which is the mx250 engine serial # start.. The engine serial# start is 574- which is not shown in any list of Yamaha serial numbers.. So thank you for your help but still coming up short.
    Thanks

    • Ludo Vanwiddingen says:

      Hello, I am from Belgium and I started a new project. I have such a cylinder with 50000 on it. Is this a 500cc, because the boring is 86.00mm (so i think its a 400cc). Can anybody help me with this please?

      Greetings from Belgium

  • Dave Davidson says:

    The “5000” on the intake and cylinder is the prefix model number for the 75MX 400. You have a common MX400.

  • Faoro Giovanni says:

    Hello I have a Yamaha Mx 400 B 1975 or don’t know the real cc of the bike? Frame number 510 106, this number is pre-production number I have read in a vintage yamaha forum. What is the real cc of this Yamaha mx 500 proto 1975 and you know the frame number and motor number?

    Thanks
    Giovanni

  • james jacks says:

    Yamaha made mx 500 proto type in 1973.

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