A 3mm spacer should sort that.

They’re also drilled and lighter by design.

Time with a dial gauge at 2.3, carb resynched, new motor etc. Bog standard.

When I synched the carbs, it wouldn’t idle with the slides down, even with rubber bellow off, so I had to use the idle stops and screw them in quite a bit… the stumble comes back!

IS there a good way of making sure both carbs are synched and at same height AFTER setting the idle speed?

I used to set the slide height for idle with cable adjusters on top of carbs, but that means no free play… not too good.

Thanks for the input.

EDIT: ANSWERS:
Have you stripped those carbs and given them a good clean out. These carbs work well but every orifice must be clear.
Espescially the pilot jet with your problem.

RDLY:
I had a similar problem until recently and it was the carbs. One was lifting before the other and then falling before the other. It confused the hell outta me. 

The correct way to adjust them is: 
1. Back off or even remove the tickover screws. 
2. Remove the air-box tubes. 
3. Open throttle to lift the slides then close throttle and listen for 2 distinct taps. 
4. Adjust the carb cable adjuster on the side that taps last. Repeat until they are in time with eachother. 
5. Remove the inspection screws (10mm hex) on side of throttle slide bores. Wind the throttle until you see a small pimple appear on each slide through the inspection holes. They should be within a mm of eachother. If not recheck the above. 
6. Adjust top cable adjuster to get a few mm slack. 
7. Replace the tubes and screws and start the engine. Now adjust the throttle stop (tickover) screws for best idle (comparing the exhaust pressures is a good indicator) 
8. Thrash Bike !!! 
9. If it’s the same >>>> Thrash Something Else

Spike:
Thanks guys,

yes everything is clean and carbs synched… with the lolly stick/wd40 red nozzle/fingers in the carb trick. They hit the bottom of carbs together with a big CLUNK! 
After doing that the bike won’t idle (like slides too low??) and no messing about with the airscrew seems to help. Slides are the correct type (as per Haynes) so I have to use the stop screw to make ‘em higher , right? 
This is where it seems to lose synch… back comes the stumble… it’s a really low/almost no opening stumble… like when you shut the throttle coasting downhill. Stumble/bucking, etc .

Some people sugested upping the idle jet as it sounded too lean… but I’m not too sure about that. 
Adjusting the airscrews has almost no effect if static, when you drive the bike you feel it. Setting them to 2 turns makes the bike having a hard time returning to idle. and closing them a bit makes the stumble worse. 
So should I change my idle jets (27.5 mm were suggested) or should I get my timing (2.3 now) closer to 2.0 BTDC?

ANSWER: Seattle smitty.
Worn, loose-fitting slides can cause blubbering idle. Very common on older bikes with rigidly-mounted Amals and Bings, but could happen to rubber-mounted Mikunis if abrasive dust got past the filters. I have fixed these slides with a baked on moly coating. Order a small can of “Gear-Kote” from KG Industries (Google it). Works good on worn (or new) pistons, rotary valve housings, aluminum-on-aluminum stiction situations, and many other applications. Follow their instructions precisely.

Interesting I might try that.

1) the HVC/Motion pro dial gauge and adapter is too long…can’t use it on a 400… you can’t fit the gauge in the adapter in situ, hits the top frame tube… chop about 1cm off, drill tap new stop bolt hole… ready to roll. 
This kit would work perfect on a motor out of frame… just not plug and play on that (?) bike.

My question is: in Mark’s excellent guide (under my tools in pic ) it says turn motor in the direction of running, which is counter clockwise (CCW) untill you reach TDC… easy enough and then says to keep turning CCW untill you see the reading you’re looking for (2.3 for me). Seems to me that if you proceed like that you will end setting your timing to 2.3 AFTER TDC and not before? I set my TDC and then went backwards (CW) 2.3mm (or a bit more and then forward to it, to take up play) and set my timing there… 
Am I totally backwards thinking? or just not getting it? 
EDIT: No you aren’t… most people find TDC and then back quite a way and THEN come back to get proper reading.

Bike seems happier now (just did the LH Cyl which was defo not OK)

Again, advices and hints welcomed!

EDIT: Answer from Martin:
i think you need a larger pilot jet,struggling to return to idle is a symptom of lean jetting.

It’s been restored motorwise completely last winter.

It ran well for a couple weeks and then probs crept in. 
It seems to pot-pot-pot more on the LH side and the exhaust downpipe is also turning blue (there used to be small streak of sludge running down it too, that has stopped)… it also killed a plug one cold morning when i gave some strick from cold. The other pot runs quite happily and has a more metallic sound to it… more like a 2stroke pipe.

PROB N1 Both my plugs look like this: 

The external electrode is quite like in the pic, not white but lighter (very light choccy color) the inside electrode also has a ring on top of the same color. Rest of the plug looks rich (safely).

I reset the carbs, synched them (oilpump too, off by a mile) reset points and put fresh plugs later. The syncing didn’t seem to make a lot of difference, but the new plugs did. I’m running B9ES, but am doing a lot of town work and partial throttle.

Advice gents?

Should I change plugs (B8ES?) Retime the whole thing?

It is gearbox oil and seems to come from the top… It could also be the 2stroke oiltank overflow but my oil is red and this is clear. What strikes me is i have oil ON TOP of my crankcase…
Can it come out of the tacho cable fixation?? is this a “standard” problem on RD??

It is making a mess and I’m getting tired of cleaning. Suggestions?

EDIT: Turns out it was the oilseal on top of crankcase where the tach cable connects.
Thanks, I didn’t see it…
I take from that topic that having oil spewed from the the tach cable connection on the cases is fairly common? is that really so?
I hate oil (and gas leaks), I clean that motor so well it’s really pi$$ing me off to do it again…just to check if it’s leaking again.:chunks:
Try this thread from the ACRD forum

Gotta say: I REALLY like it! Probably one of the best vintage bike around. It is really up there with my T20, the Kawasaki A1 & the Rz500. Bikes that I will have a hard time to sell

I really like the torque down below and the screaming top end. I might still have some carb and iggy realted probs, but the infamous 3’500k flat spot is really gettin’ on my nerves.

Was it really a “feature” of the bike when new? If so, I am amazed yamaha managed to sell so many RDs. As i said, less-that perfect timing & carbs might make it worse, but everything is set std.

Is the RZ/RDLC rubbers block with cross-tubes the solution?, if yes what jetting do I need?

I can’t afford a speed fine in town, it’s lethal here!

EDIT Answer from johnB from the ACRD Forum:
Standard the mid range stutter /flat spot shouldnt be too bad if the timing & carbs are set up right.The E/LC or powervalve rubbers with the ears cut off & the crossover tube will make it better.No jetting changes needed.6mm reed block spacers also help beef up the mid range a bit.
ps. if you think the standard stutter is bad I don’t think you’d like a bike with expansion pipes/k&n’s!

Still when I give it a fistfull and change gears up, as soon as you pull the clutch in, it revs up. Clutch out revs go back to where they should be… it takes a good 500-800rpm up on clutching.
Also when you give it just a bit of throttle (say 3500 rpm) and you go back to idle, the revs stay at 2000 rpm before slowly going to 1200 rpm. I can’t find any air leaks.

Any hints & Clues as to what to check? My MOT is due on Monday, and I’d like the bike to be spot on.

What i really didn’t like too much is this:
If you open it up, like seriously 6’000 rpm and more up to a good 120kmh and then change gears, the revs don’t go down during the change… revs up when you clutch it.
Nothing dangerous but a bit uncanny.

Other thing is at same speed/revs, when you slow (you have to at some point!), without clutch, just letting oof the gas grip,
it displays the worst “ramheading” (direct from the french, sorry!) I’ve ever felft: ie revs decrease but not nicely, but you get the feeling of bom-bom-bom-bom and it’s hard enough that you get the impression the motor is moving in the frame … it isn’t, probably just the rubber bushes transmitting the motor’s behaviour.
I am not a newbie with old two stroke, and expected the motor to just rev down and not fight it. ” ramheading” feels a bit like when you close an old water tap and your hear that noise in the water pipes… know what I mean? Correct Engrish word anybody?

Both my mechanics mates told me this sounded like the bike was too rich, specially the surging at high speed when changing gears.

Apart from that, the bike is quite impeccable, but starts very often without choke… another hint of richness? Idles great, revs well,plugs OK, baffles too, new everything, etc…
Very flickable… I like it!

What do you guys think? What should I do next? Oh, and now I know what you were talking about the 3500 flat spot!