DRM 400

[Davey Crocket]

I've got Wilbers p/n (PD-03) Honda XL600 83-84 model springs in my RM250T 38mm forks, works out at .43 spring ratio which is about the heavy'st you can go.There quite a long spring so you may have to shorten them. I have PD valves as well. We worked out the std spring rate was .33 and thats why there too soft, and of course we all weigh 25 kg's more now as well !!!. Wilbers are over your way, they have a web site. Cheers John.

[cloggy]

 I think my springs were marked 49, which comes out to just over 27lbs per inch, assuming the spring rate is accurate. They needed a two ish inch spacer to take up the slack on a 10 inch travel fork
I weigh the same as I did in my 20s  about 12and a half stone with riding gear and tool bag
 I think the DR may run the engine closer to the front wheel than the XT, certainly there's not much room to steepen the head angle: so maybe that's why it needs a heavier spring

[SON]

Such a good thread I thought it should be bumped to current
Thank you to the major contributors for their hours of R&D

[David Lahey]

I just reread the postings about carbies and thought I'd put in my 2 cents worth. Mine has a 400cc SP370 motor with a free flowing exhaust and have swapped between the standard narrow oblong bore carby and a 36mm Dell Orto pumper carby for comparison purposes. The carby is obviously made by Dell Orto for large cylinder capacity 4 stroke road bikes, and I bought it from Geoff Udy in 1979 as a kit for the SP370 and it came with an adaptor to fit it to the head.
The reason I got the carby kit was not for more power, but to fix the stalling tendency when riding over big logs (sudden throttle opening at low revs). It is magic for this and the motor is highly responsive to sudden throttle opening at all RPM. I never tried the Dell Orto with the standard SP370 exhaust, but with the free flowing exhaust on the RM hybrid bike, it is vastly superior to the standard carby at all RPMs.
The only downside of the Dell Orto is the fuel economy. This hybrid bike was my enduro and trail riding bike at the time, and I found the dirt road fuel economy went from 100 MPG with the standard carby, to 60 MPG with the Dell Orto. I had a PE250B (alloy) tank that I used for longer rides, but it is easier to ride with the RM250C tank, because the seat is closer to the front of the bike with the RM tank fitted.
I read a few people have lightened their flywheel for better response. I find that with the way mine is set up, I would actually prefer a heavier flywheel to make it nicer to ride in loose/tight/steep terrain. However on an MX track where riding precision is not as critical, the motor is fine with the standard flywheel weight.