1981 KX 125 Dilema

Discussion for swapping a KDX motor in a MX frame...
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redlinegw
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1981 KX 125 Dilema

Post by redlinegw » 06:09 pm Mar 14 2021

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.

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rungrandpa
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Re: 1981 KX 125 Dilema

Post by rungrandpa » 09:56 pm Mar 14 2021

The KDX 200 has WAY more horsepower. Way more.

redlinegw
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Re: 1981 KX 125 Dilema

Post by redlinegw » 11:17 pm Mar 14 2021

Hmmm, now to see how hard it will be to fit it.

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bufftester
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Re: 1981 KX 125 Dilema

Post by bufftester » 10:38 pm Mar 16 2021

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

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