Weinert tribute retro graphics KX/KDX

Edit: Bigfoot, I was mostly wrong on the hybridization details, though in my defense it was two years ago that I heard about it. Whole new post coming below, but the process is relatively easy, especially given how good the resulting bike is--

Thanks, kiwi & Bultaco--it was cool to be able to do something like Bultaco's avatar and keep the original brand, should work a treat on an '81 KX. For the swap & rebuild thereof, my brother tells me:

It was built in late 1991, commissioned by an accomplished Texas hare scramble rider in the Dallas area with an 89 KDX E-series motor and 91 KX 125 frame. It was likely inspired by a Dirt Rider article shown down a ways in this forum thread, which tells all about the build details. KDX/KX hybrid thread at KDX rider forum

This copy is almost exactly like the article, though I wish it had the blue plastic. As I got it, it had a 38mm PWM carb (predecessor to the modern Air Stryker) similar to the stock carb on 98 YZ 250.

The engine was ported in a "hogged out" fashion, so it was intended to be run wide open. The stock exhaust, modified to fit the frame came on the bike with a stock KX silencer; I mistakenly passed on a beat-up aftermarket one already cut to fit. The suspension had been revalved by RaceTech, with new springs at each end.

For the rebuild here, the engine was sleeved to 236cc with an LA Sleeve kit. The crank was rebuilt and balanced for the heavier piston. New mains and seals throughout, plus lots of repair parts: both side KIPS valves and the governor drive gear were replaced. The ports were built up to match the ports in the sleeve. I cut and welded a late-model used FMF pipe with a rusty head pipe to fit. I read that port timing was the same between E and H series KDX200s, and because the H series frame is based on the older KX frame, there was minimal fitting. The whole idea was to increase the air/fuel velocity in both the 38mm carb (too big for 200cc) and to improve the transfer velocity for better refresh. The old piston only showed a small area without carbon buildup, which indicated poor breathing [broken powervalve or not].

A pipe guard is fitted to hide the ugly welding and flaking silver paint. Oversize radiators were added just in case, and the clutch was freshened with a EBC kit to handle the extra HP. A new rear spring was added (interestingly, a stock KDX value), and Race Tech Gold Valves added up front this time..

Cosmetically, the frame is painted silver because too much green gives me the shakes. The white front fender was added, and rear was painted white until I can try to fit a 92-94 white fender, which should be really close to matching the side panels. The graphics are just white auto vinyl with 1/4-in black pinstripe tape. The Kawi stickers are eBay items, and of course I bought spares. To ensure symmetry in the white part,, I first cut a long rectangle and then split it to make two peices that were identical, except at the ends. They were placed so the front edge is nearly parallel to the front edge of the shrouds, and then bisecting the lower mounting bolt. The only gotcha arose too late to correct for: the pipe-side shroud, where I measured from and used as the basis, is shorter than the other side by about an inch or so, so the left side has a tiny bit of green at the bottom of the white were it ran out. Just passing this along so someone doesn't make the same mistake: Measure twice. Both sides. Cut once.

I am looking into adapting a locking ring clutch as some have done on the later model KDX engine, but that's a down the rode (bad pun).

It runs like a 12-yr-old who thinks he's a teenager: it thinks it's a 250 MXer but it's not. While still in the final jetting stages, it revs out way more, and has way more throttle response and power everywhere. Some of it is from the freshening, but most is from the mods. And the crank balancing really is noticeable.