500 Two-Stroke Tech

I'm going in on the "parked next to the Titanic" 1984 RZ/RD500 Canadian I have here in my garage.

As someone who is going to go "by the book" in this rebuild I wonder if anyone has ever noted ALL of the places the Yam service manual is WRONG. Any suggestions?

Crickets ...

There are a few mistakes, nothing major, Theres a thread on here somewhere with them listed,,,,,,

Good luck finding an old thread.

The only major thing I remember is different float heights that were corrected later.

Holy toledo are you serious? What is the correct float height? On a bike that is globally notorious as a model that pisses fuel constantly the correct float height should be a sticky in my opinion.

Correct height is 24mm.
The fact that a bike pisses fuel constantly is by no way related to the float height.
It is just a matter of float valve, and particularly the o-ring in it.

Sure.

You've been a member here for four years and haven't seen that mentioned numerous times on multiple threads?
As far as why the float height was changed, I expect it was due to leaking at the normal/standard/specified height with carbs side mounted. And that in turn necessitated the jetting changes.
Of course if you recall mikuni revising the height for all other bikes with this carb, then my guess/theory is wrong.

I don't know if you are from Europe or what but when someone here says "Holy toledo are you serious?" that means no, I did't see that anywhere previously.
Why did Mikuni revise the float height? the guy on top of you says the fuel piss has nothing to do with the float height.

Holy toledo. Are you serious?
Because you commented on my smartcarb thread, where I said one of the issues I had with stock was a specified float level that is too low.
And here I said "my guess/theory", so others may not share that opinion. Making the carb like new seems to help and solve the issue for many.
There are those with stock bikes who are able to get satisfactory results with the revised factory settings. Changing air cleaners /pipes and increasing rpm seems to make this task more difficult, and there are different theories on why these carbs show strange dyno results in non-stock situations. And other solutions, like Ivan's needles etc. Which some are happy with and some not as pleased.

The float height wasn't really "changed".
Yamaha stated it was an error in the first prints of the 1984 maintenance manual and corrected that in 1985.
So you can assume that stock bikes were delivered with the right height, but dealers had issues when "correcting" it to the wrong value of their manuals.

Jetting changes? Sure.
What was really changed was making the partial throttle mixture leaner by increasing the idle air jet from 1.1 to 1.4 mm.

The decrease in the main jet is no decrease due to my measurements as the later #165 flow quite the same as the previous #195.
Check here for the extended version : https://www.rd350lc.de/downloads/MK-Dok ... nglish.pdf

As I said, my theory.
It would seem to me that if one changes the float height by 4 mm, then the clear tube method, specified in the manual with engine running, cannot be correct.
It also seems to me that Google searching low float height symptoms correlates with some reported issues.
And dyno tests showing engines getting leaner at high rpm, regardless of main jetsize, looks to me like a fuel delivery issue, not an inability to flow sufficient air.
Of course I could be wrong, I never considered myself a tuner, even though I had to do "some" tuning to race.

You've got the point with the clear tube method.
I don't even bother what is the float height, the important is the real fuel level with the clear tube and adjusting float level accordingly.

Yes - but the clear tube method would have to be modified to match the 24 measurement. Or they didn't match in the original manual - but I expect that was mikuni spec for that carb (20) that yamaha subsequently had to modify for this application. And yes, I could be wrong.
Regardless of that, the float pivots on one side of the carb, so if the bike is leaned ( on the stand or while riding) the float height will be altered differently on each side.
Not an issue for conventional mounted carbs , but I think it compounds issues with this setup. Again, just my theories.
Later carb designs with the float locating pins straight in the center of the bowl (mikuni included) seem preferable to me in this application.