1990 kdx200 engine in 1991 kx125 frame

Discussion for swapping a KDX motor in a MX frame...
Post Reply
Railinandnailin
Member
Posts: 39
Joined: 11:32 am Aug 14 2014
Country: United States
Location: Central PA

1990 kdx200 engine in 1991 kx125 frame

Post by Railinandnailin »

Hey guys, i just picked up a kdx hybrid for a really good deal from a guy in my area. Its a 1990 kdx200 engine in a 1991 kx125 frame. Its in decent shape, the conversion was done pretty well. Supposedly he didnt have to drill out the swingarm hole in the motor for this chassis. The only thing i have to do is get a pipe for it. I picked up a 1992 kx250 the other week and was wondering if i could try that header on the kdx 200 motor. Would that do any harm? I know that it might be a weird powerband but for the sake of testing the motor out i would like to see that it runs good. I have already contacted Dyno Port to see if he could make me a custom pipe for it. He made a pipe for my dads 220 and its amazing. I'd like to get this sorted out because i just ordered a 1998 kdx200 engine off ebay for my 1992 kx250 and would probably have to test the same thing for that in a few weeks.
User avatar
KDXGarage
KDXRider.net
KDXRider.net
Posts: 14047
Joined: 06:45 am Nov 01 2004
Country: United States of America
Location: AL, USA
Contact:

Re: 1990 kdx200 engine in 1991 kx125 frame

Post by KDXGarage »

KX / KDX 250 pipe is 50 mm. KDX is around 39 mm.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
Railinandnailin
Member
Posts: 39
Joined: 11:32 am Aug 14 2014
Country: United States
Location: Central PA

Re: 1990 kdx200 engine in 1991 kx125 frame

Post by Railinandnailin »

Jason wrote:KX / KDX 250 pipe is 50 mm. KDX is around 39 mm.
Any idea if the 125 has a smaller diameter than the 250? Supposedly the guy had the kx125 pipe and it fit the kdx200 engine but he didnt want to run it because he worried that it would damage the engine.
User avatar
KDXGarage
KDXRider.net
KDXRider.net
Posts: 14047
Joined: 06:45 am Nov 01 2004
Country: United States of America
Location: AL, USA
Contact:

Re: 1990 kdx200 engine in 1991 kx125 frame

Post by KDXGarage »

I think that KX125 of some years is 39 mm also.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
Railinandnailin
Member
Posts: 39
Joined: 11:32 am Aug 14 2014
Country: United States
Location: Central PA

Re: 1990 kdx200 engine in 1991 kx125 frame

Post by Railinandnailin »

Jason wrote:I think that KX125 of some years is 39 mm also.
Okay thank you. Thats probably how he said the stock 125 pipe fit the kdx engine. Would it be harmful to run a kx125 pipe on the kdx200 engine?
User avatar
KDXGarage
KDXRider.net
KDXRider.net
Posts: 14047
Joined: 06:45 am Nov 01 2004
Country: United States of America
Location: AL, USA
Contact:

Re: 1990 kdx200 engine in 1991 kx125 frame

Post by KDXGarage »

If it was used, the pipe design would kill performance and especially low end.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128
BLosHybrid
Member
Posts: 5
Joined: 06:08 am Nov 24 2017
Country: USA

1990 kdx200 engine in 1991 kx125 frame

Post by BLosHybrid »

I have the same 1990 KDX200 motor in a 1991 KX125 Chassis. I was told to NOT use a 125 pipe, not enough flow. I have a Dynaport Pipe on my 220, love it so much, threw away the FMF's!

He has the pattern to make the hybrid pipe, that's what I now have on my Hybrid. It bolts right up, has power through entire rev range and looks factory!
Post Reply