1981 KX 125 Dilema

Discussion for swapping a KDX motor in a MX frame...
Post Reply
redlinegw
Member
Posts: 4
Joined: 02:59 pm Nov 13 2017
Country: USA

1981 KX 125 Dilema

Post by redlinegw »

I have a very clean 1981 KX 125 I bought sight unseen from a guy in AZ and had it brought down to me in SoCal, it was supposed to have a completely rebuilt engine with a KDX 175 top end. When I got the bike it started easily and sounded very crisp but when the bike was under a load it would miss (not jetting) and it has pretty bad vibration. I came across a 1980 KDX 175 that was pretty rough but was supposed to run good so I swapped that complete motor into the KX. It runs good but is very slow so my guess is it needs to be rebuilt. I also have an 86 KDX 200 motor sitting in my garage that also needs to be gone thru. My goal is to have the ultimate vet race bike, I race 50+ intermediate and I am 165lbs so I love the 125 platform and the bike handles great. I guess my question is should I build one of the 175 engines which is a bolt in or go for the 200 engine and do the necessary fab to fit it? Can the 175 engine be ported and tricked out to make more power? Help 😃
Last edited by redlinegw on 12:22 pm Mar 15 2021, edited 1 time in total.
User avatar
rungrandpa
Supporting Member I
Supporting Member I
Posts: 230
Joined: 11:35 pm May 26 2018
Country: U.S.A.

Re: 1981 KX 125 Dilema

Post by rungrandpa »

The KDX 200 has WAY more horsepower. Way more.
redlinegw
Member
Posts: 4
Joined: 02:59 pm Nov 13 2017
Country: USA

Re: 1981 KX 125 Dilema

Post by redlinegw »

Hmmm, now to see how hard it will be to fit it.
User avatar
bufftester
Platinum Member
Platinum Member
Posts: 3455
Joined: 06:03 pm Oct 31 2012
Country: USA
Location: University Place, WA

Re: 1981 KX 125 Dilema

Post by bufftester »

Are you trying to race sanctioned vintage? Most don't allow hybrids. Or power valves like the 86 motor has.
Post Reply