First off, the #1 resource on the net for Quadracers is
QuadracerHQ. That's where I would go for advice. But, having owned five Quadracers, I can give you some advice.
The 1985-86 engines have a hybrid reed valve/piston port intake setup. Make sure the bottom of the intake port has a serious chamfer on it, or the piston skirt catches the port and shatters the skirt. This can also happen with excessive piston to cylinder clearance. You'll know this has happened when your engine starts filling your airbox with pre-mix. This happens when cranking pressure from the engine flows backwards through your carb.
The little screws that retain the reed block and reed stops like to loosen up. If you're really unlucky you'll loose a screw into your lower-end. Best case scenario, you have a set of loose reeds that make starting your quad next thing to impossible. To get to the reeds and fix the problem with blue Loctite, you have to pull your cylinder off. Convenient, huh?
Make no mistake, all Quadracers have the thrust washers on each side of the wristpin, and they do have a habit of coming apart and destroying everything in their path. I've never experienced this, but I've heard too many horror stories for it not to be true. There are billet washers available from Doctor Q on quadracerhq.
The 1985-86 LT250R's were only a five-speed. The 1987-92 were six-speed with a power-valve. I don't think any of the LT250R's were slow, some are definitely out-of-tune though (nice way of saying trashed). The 1985-86 swingarms have an eccentric chain adjustment, like a Honda, which is a major plus compared to the four-bolt chain adjuster found on all the later year Quadracers, unfortunately they're weak and I personally have dealt with two broken swingers.
Any year plastic will fit and usually someone on quadracerhq is selling some. The stock carb is a Mikuni TM flatslide carb, 34mm I believe. However, a common upgrade is a 34mm Keihin PJ (stock Honda 250R carb), which are plentiful on eBay and usually sell for cheap, they fit the stock rubber carb boots, and are usually in the ballpark jetting-wise. The downside to the early Quadracers are the frames tend to crack, the swingarms tend to crack, and they seem to have always been owned by people who rigged them and ran them to death. I sold one to a friend of mine who had nothing but bad luck with the quad. I actually felt bad enough for him that I traded him a 1992 Honda TRX250X even up, just to bail him out of the Quadracer.
One of my Quadracers was an '85 LT250R that ran like a 250cc sewing machine. It started on the first kick, made good power, and held together well. To get it to that point, I rewired the whole quad and rebuilt the engine. As much satisfaction as I got out of finally having that machine all dialed-in, I sold it...quickly...before something went wrong. I just don't trust the old Quadracer's ability to stay together, but for $300 you might be alright.
