89 framed Hybrid, air cooled motor

Discussion for swapping a KDX motor in a MX frame...
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arjay200
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89 framed Hybrid, air cooled motor

Post by arjay200 » 04:24 am Jun 13 2020

Almost period correct, give or take a year. C2 motor in a 1989 G1 KX125 chassis. The frame was modded to single down tube by using the down tube and lower cradle of an 86 KX125. It all lines up nicely.

Ti shock spring and pegs from a YZ
RMX 45mm Showas
Hand made ally tank

Now I'm fettling and trying to get it ready for it's first sandblasting on the trails :grin:
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Re: 89 framed Hybrid, air cooled motor

Post by KDXGarage » 10:58 am Jun 13 2020

MAN! GREAT JOB! That really looks nice.
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Re: 89 framed Hybrid, air cooled motor

Post by rungrandpa » 03:02 pm Jun 13 2020

Lot's of hard work in that bike. Looks great.

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Re: 89 framed Hybrid, air cooled motor

Post by SS109 » 03:38 pm Jun 13 2020

Now that's a really cool hybrid!
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Re: 89 framed Hybrid, air cooled motor

Post by kdxsully » 05:52 pm Jun 13 2020

Super nice. I see you went with silver on the motor instead of the original black.
I like turtles

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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 07:55 pm Jun 13 2020

Thanks for the feedback guys. I'll post some pics of the engine soon when it's fully assembled. I've converted it to KDX H series flywheel, ignition and CDI - so I'll let you know how that goes.

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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 02:02 am Jun 14 2020

kdxsully wrote:
05:52 pm Jun 13 2020
Super nice. I see you went with silver on the motor instead of the original black.
Yep took it back to bare metal. I'm going to get plenty of riding time on it, mainly sand, so I went for the hardest wearing/easiest to maintain finish. More the C3 look, with the seat and graphics. Also the generator cover is off an E series because of the extra flywheel depth, so silver was the only option on that part.

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Re: 89 framed Hybrid, air cooled motor

Post by Pressingonward » 10:03 am Jun 22 2020

That's pretty cool. Let us know how it rides :)

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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 02:24 am Jun 26 2020

Here's some more pics. First ride was interesting. The timing was out - far too retarded, so the motor ran weakly. Weak bottom and mid, no top end. The carb was not too far off, but it was hard to tell. I've talked to a 2 stroke tuner and have got the timing in the ballpark now. I'm getting it dyno tuned next week so hopefully will get it running sweet. The suspension was great, firm but plush enough when needed. The handling was a bit funky. Stable and turned well, but too high at the back. riding downhill over drop offs (under the roots) was trying to throw me off the front :) I couldn't get myself fsar enough back not to worry. So I'll increase the sag (from 98mm to 110mm). I think the problem is that the forks are 5mm shorter from the top to the axle than the originals. Hopefully the sag will level things out.
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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 02:27 am Jun 26 2020

The other side.
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Re: 89 framed Hybrid, air cooled motor

Post by Pressingonward » 08:32 am Jun 26 2020

Cool, let us know how the dyno tuning goes - very curious to see how the power output looks with a Lectron. There's a sales brochure on Ebay that shows the stock power graph - a bit too expensive for me to buy it, but I saved a screenshot somewhere for reference.

How do you like the Yamaha pegs? Do you know if they'll fit the 88 KDX frame too? If so, what year are they from?

Very nice looking bike. I like that your custom tank blends in and matches the rest of the bike - they often look clunky and out of place, but you nailed it! What led to you building the tank instead of using a stock one? Fitment issues?

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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 07:29 pm Jun 26 2020

Pressingonward wrote:
08:32 am Jun 26 2020
Cool, let us know how the dyno tuning goes - very curious to see how the power output looks with a Lectron. There's a sales brochure on Ebay that shows the stock power graph - a bit too expensive for me to buy it, but I saved a screenshot somewhere for reference.

How do you like the Yamaha pegs? Do you know if they'll fit the 88 KDX frame too? If so, what year are they from?

Very nice looking bike. I like that your custom tank blends in and matches the rest of the bike - they often look clunky and out of place, but you nailed it! What led to you building the tank instead of using a stock one? Fitment issues?
The Lectron was one I had left from another bike (Husky 144). It's a 36mm. Lectron build a carb for the KDX which uses the 34mm body. I'm sure the 36 will make a good carb for the bike too.

The pegs seem fine. I had them ground flat and drilled to take the left over inserts I had for some Fastway pegs. This gave an offset and I run them in the lower position. I'm sure you could get them to fit a C frame (but it's years since I've had one of those for reference). The pegs were from an 04 YZ450F I think. I also found a cheap titanium shock spring (04 YZ125) that fits straight onto the KX/KDX shock body.

The ally tank was because nothing else would fit. I didn't want to have a rad cowl on one side like the '89 KX, and the air cooled KDX tank wouldn't fit at the back. Also it had to specifically work with the seat and side panels. If I keep this bike long term I might look into designing something a bit less like a box :shock:

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Re: 89 framed Hybrid, air cooled motor

Post by Pressingonward » 08:14 pm Jun 26 2020

Great info, thanks!

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Re: 89 framed Hybrid, air cooled motor

Post by KDXGarage » 10:51 pm Jun 26 2020

Throw a chain / case saver on the front. :-) Please don't hurt this KDX. :-)
Thank you for participating on kdxrider.net. :bravo:
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Re: 89 framed Hybrid, air cooled motor

Post by kdxsully » 01:12 pm Jun 27 2020

KDXGarage wrote:
10:51 pm Jun 26 2020
Throw a chain / case saver on the front. :-) Please don't hurt this KDX. :-)
Yes.
And where the heck did you get a fatty for that??
I like turtles

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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 06:51 pm Jun 27 2020

kdxsully wrote:
01:12 pm Jun 27 2020
KDXGarage wrote:
10:51 pm Jun 26 2020
Throw a chain / case saver on the front. :-) Please don't hurt this KDX. :-)
Yes.
And where the heck did you get a fatty for that??
New on Ebay 10 years ago, when they were still around.

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Re: 89 framed Hybrid, air cooled motor

Post by KDXGarage » 06:55 pm Jun 27 2020

Heck yeah! Back when people had not really started charging an arm and a leg for things!

I got mine when I bought a blown up bike from NY, and the guy mailed the whole thing in four boxes and the frame by itself. :boogie: :please:
Thank you for participating on kdxrider.net. :bravo:
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Re: 89 framed Hybrid, air cooled motor

Post by arjay200 » 08:23 pm Jun 27 2020

KDXGarage wrote:
06:55 pm Jun 27 2020
Heck yeah! Back when people had not really started charging an arm and a leg for things!

I got mine when I bought a blown up bike from NY, and the guy mailed the whole thing in four boxes and the frame by itself. :boogie: :please:
Good find! I'm going to start stockpiling a bunch of air cooled engine parts from now on.

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Re: 89 framed Hybrid, air cooled motor

Post by KDXGarage » 08:42 pm Jun 27 2020

Be careful. It can get out of hand, as I have found out. :rolleyes: :shock: :doh:
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