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I'm experiencing a weird problem with my RD400.  Basically, it goes like this: Let's say it's been parked on the sidestand with the petcock off for 24 hours. When I go to start it, I can kick and kick and kick until I'm out of breath unless I do the following: with the petcock ON, barely pull the right side fuel line off the nipple until it just barely dribbles fuel. Then hold the throttle wide open for like 3 or 4 kicks until it fires up as in a flooded condition.  Basically, what I have surmised is that the left carb is flooding and the right is getting an air bubble in the fuel line. And yes, it does leave a spot of fuel on the ground when parked for more than like an hour.  After start and warm up, it runs excellent. No complaints at all.

I've adjusted float height several times, changed needle/seat assemblies... I guess all that is left is to look at the petcock 'packing' itself and/or maybe the left float is sinking? Still, that wouldn't explain why the right carb is getting the air bubble, would it?

You might be thinking, "are you sure the right carb is getting an air bubble?" and my answer is, yes, because it will not start unless i burp that right fuel line.

I dunno, any ideas?

Okay I finally figured it out.  The speedo drive washer inside the wheel had been squeezed into a somewhat concave shape causing the tangs to not properly interface with the speedo drive.

So if you're reading this in 2048 and you have this problem, pull your speedo drive washer out and inspect it thoroughly even if it seems fine from the outside.  (Also, are motorcycles still legal in the future?)

77 RD400.  Speedo needle suddenly started bouncing, then reading slow, then stopped working altogether and never came back.
 
-Cable seems fine.
-I can make the needle move with a drill attached to the cable.
-I have thoroughly inspected the drive, as well as the tangs on the wheel and I am very confident that it is all good. 
-Visually confirmed that the wheel turns the cable
-I even went so far as to take the speedo completely apart and lube everything and I never saw anything out of place. 
-Finally, at a loss, I went ahead and replaced the cable anyway and still nothing.

I'm out of ideas... What in the living f*** is going on with this thing?! It's beautiful outside, I wanna go ride!

Edit: Just pulled the speedo end of the cable off again to re-verify.  This time it moved a bit as I pushed the bike and then stopped.  Is there some kind of clutch or something in the drive assembly that could have failed?

Update: I wish I had read Teazer's comment before I finished everything but I stumbled through the preload and valve setup and here's how it happened.

I had no idea what kind of preload to go with for my new springs so I decided to match what it had with the stock setup and go from there.  As for the valve: I understand that it is designed for a heavier bike but as someone who generally prefers a slightly stiffer ride, I figured I'd go with the suggested 2 turns. I also used 10wt oil set to the Race-Tech suggestion of 140mm.

As you might have guessed, that amount of preload was WAAAY too much but I still didn't have any idea what amount to put in.  At this point I guessed that the logical first step would be to start at zero preload and go from there.

So I did that and to be honest, I still think it's a bit stiffer than I'd prefer but it's rideable for now.  Do you think I should set the valves to one turn?

So I've got the front end apart and decided to clean up the speedo drive. I washed it all out with solvent and then noticed that it is very very stiff to turn by hand. As in, I have to put it in a vise and turn it with pliers to get it to move.  This is especially weird because it seemed to be operating normally on the bike.  Is it just supposed to be that stiff?  I took it all apart as far as I could but I can't get the worm gear out because it seems to be held in with a roll pin installed in a blind hole.  I even tried to drill out the roll pin but it must be made of something very hard because my bits don't seem to be biting into it very well. Anyone encounter this before?

hes right adjustable caps are def the way to go. on mine w valves:

It looks like the Economy Cycle caps are out of stock and, frankly, the price is a little higher than their value to me.

Use 10 wt fork oil. Anything thicker is too stiff.

Thanks for emphasizing that.  I was planning on using 10wt but in my travels I have seen a few people mention 15wt and wonder if that would be better... especially because I am generally one who prefers a stiffer ride. But yeah, I think I'll stick with the 10wt.

Hey everyone!

New to the forum.  I'm working on a new-to-me 77 RD400D.  I decided to do the Mike's XS Emulators and a set of Race Tech fork springs and I've been all up and down this forum, the Mike's XS instructions, and all the Race Tech literature and I've learned a ton but I'm still looking for one piece of information that doesn't seem to be clear:

The Race Tech emulators apparently come with "adapters" that go between the damping rod and the emulator.  It isn't clear to me what these adapters are accomplishing.  My best guess is that they are used simply to give clearance between the nut on the back side of the valve and the roll pin that runs through the center of the damping rod.  Is that correct?

I have already machined my damping rods to just below the upper holes and also machined a step into the top of the rod so that the emulator fits snugly.  I also cut out the center of the roll pin so there are no clearance issues with the nut.

As far as I can tell, I should just have to add the additional holes to the lower end of the rods and use the PVC tubing to add in the appropriate amount of preload and everything should work fine, correct?

Anything else I missed?

Thanks!