Any tips on the forks? It looks like they might have the Webco fork kit installed (more travel and rubber gators that match a 1971 ad).
The Yamaha forks are pretty ordinary and I'd replace 'em with 35mm Betors but if your rules prevent that fit a set of YSS PD valves or Race Tech Gold Valve cartridge emulators. I've got a set of MX250 forks (
almost the same as DT1B alloy leg items)with Gold Valves and they work a treat. The Webco fork improver kits don't do much. I've been there with that stuff.
The class I plan to race it in has "Stock" in the name, so the Webco frame kit is out. (would have been nice to make a Webco bike out of it) Sad
Sad indeed :'(. Lowering the engine cradle 2" and lengthening the swingarm 1.5"-2" makes a shitload of difference. Seeing that you can't cut the frame you'll have to compensate by making sure you have the best forks and shocks your rules allow.
What non-reed upgrade were there for the intake system?
If you're restricted to a flange mount carb, use a 32mm from an RT1 but if you're allowed to use a VM style Mikuni go for a 34mm mounted on a rubber spigot. The Yamaha is a great, solid engine but they need some serious port work to be
really competitive with the Euros. Ditto the head, the GYT centre plug head is pretty good but a Webco or a Jones head (
unobtainium!) work much better. The Jones head looks identical to the stock GYT so that will get you around any rules preventing aftermarket heads. The stock GYT pipe is basically shit...go for a Bassani, Torque Industries or Hooker period pipe for noticably improved performance. Throw the points ignition in the shit can and find a 1975 and on DT400 CDI ignition, the external flywheel is reasonably close to the stocker in weight.
What lightweight items were available back in the day?
There's a guy on Marks Swapmeet selling original shape Preston Petty front fenders right now. Try and get one as they were available in the day and
almost every race DT1 used 'em. There are a bunch of plastic tanks available, most guys used a BSA B50 style on their DT1s. Remove the oil tank, find a fibreglass DT2MX airbox, slip in a DT2MX/MX250 rear wheel without the cush drive (a bit lighter+alloy rim), use an alloy rim on front with the stock hub if the rules say you have to but if you can use a period Rickman or REH hub as they were the lightest and best stoppers of the era.
I saw an ad for a plastic air-box that mounted in place of the oil tank. Anyone ever see or use one of these?
See DT2MX quote in previous paragraph. I know the plastic airboxes you speak of....unobtainium again.
Can it compete with square-barrel Maicos and side-pipe CZ's?
This is a tough one...how good a rider are you? Engine wise the Yamaha is
potentially as good as the Maico, CZ, Bultaco or anything else you can throw at it. It's just that these bikes were built for "dual sport" action and were waaay under developed. When you consider that the YZ250A is based on the very same engine will give you a hint of the engine's potential. My DT1 from Hell is ported, has a 34mm Amal MK2 Concentric carb and DT400 CDI ignition and a close ratio DT2MX trans and during its brief period of notoriety was easily as competitive as the rival side pipe CZ and Maico squaries.
What lets the DT1 down is the weight and poor chassis dynamics. In a word it's a pig to ride in stock trim.
'tis a pity you can't do the frame mods that are allowed by our rules. They really do transform the bike. The follow up DT2MX had the same geometry as the modified (or Webco) frame mods. It was still a pig but it was a
tamer pig
.
Our rules appear to be more lenient..allowing for period modifications such as the frame/swingarm mods and many other pre 1970 mods. Being stuck with the stock frame and forks is the big set back but I reckon the challenge in getting the bike to perform competitively is the beauty of the project. That's the reason I built my DT1 back in the early 90's. I had two class legal square barrel Maicos that were far more user friendly but I loved the challenge of turning a frog into a princess. I hope you do too.
