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 1978 GS80 125 any good?
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Brentb
Junior Member

USA
16 Posts

Posted - 03/14/2021 :  12:00:00 PM  Show Profile  Reply with Quote
I have enough parts to put together a either 1973 JP or 1972 6D Six Days both in 125cc.I have a frame and engine for each but only I set of everything else.
I like the idea of the newer KTM transmission but was wondering if later KTMs has similar problems to the 1976 125cc models?

Anyone that could weight in on the 1978 125cc would be much appreciated. Thx bb

Brent Banning

Mike Lenz
Advanced Member

1086 Posts

Posted - 03/14/2021 :  6:05:57 PM  Show Profile  Reply with Quote
Problem is same tranny as 250 and 400. Pretty wide spacing. Ktm never got serious about their 125's until 1980, in my opinion.
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Brentb
Junior Member

USA
16 Posts

Posted - 03/18/2021 :  11:26:47 PM  Show Profile  Reply with Quote
Thanks for the input. Im going to mic both barrels and see which motor has the most life left in it.

Brent Banning
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Mike Lenz
Advanced Member

1086 Posts

Posted - 04/13/2021 :  10:20:14 AM  Show Profile  Reply with Quote
Brent, just saw this again and realized I was a bit in haste. For woods riding that engine would be fine. For MX the gearing is a bit wide for a 125. That being said I am building a 125 for sportsman class MX anyway using a 73 175 (with the 125 clutch/primary drive, etc))and a 75/6 125 top end. It goes right on. Its a bit of a push on the rule book, but I think it will fly.
Many an AHRMA racer is using later year jugs on their Elsinores! I think that engine/tranny combo would be competitive in sportsman class. Where it would run into trouble is in post vintage mx where it would often be in the same class as bikes thru 80/81.

Since a 125 top end will bolt right on a 175 lower end, why did it take John Penton until late 1975 to get KTM to build one? Thats a question I have always wondered! Especially since when they did finally make one it was just that. Just a smaller jug on the same engine! IF they would have hit the market with that motor in 73 and then added a closer ratio tranny in 76, they would have kept ALOT of mx riders who switched to jap bikes. And probably kept them all along with the introduction of the 250 and 400 following. Huge marketing blunder by KTM...or maybe they knew it but just couldnt do it. Too bad!!
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Brentb
Junior Member

USA
16 Posts

Posted - 04/27/2021 :  7:08:11 PM  Show Profile  Reply with Quote
Mike thank you for the information. Since I wrote the original post I picked up a 1976 175 engine too, I was hoping the parts were compatible between the 1978 125 and the 1976 175. Glad to know parts can be swapped around.

Very helpful. Thank you



Brent Banning
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slvrbrdfxr
Advanced Member

USA
718 Posts

Posted - 05/04/2021 :  2:53:54 PM  Show Profile  Reply with Quote
Hi all,
I have a nice set of 78 125 cases that Id sell if someone out there is in need of them. Id be glad to send you some pictures if interested. You can contact me via email by using my screen name here on the site and adding @cox.net or text me at 918 - six four zero- two seven eight four.
Dave McCullough
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