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305cc CL77 or perhaps a rarer CL72 250.

Great motors but limited by stock 4 speed indirect trans.  I still have an NOS crank in its box for a CL77.

Mark pointed out that LA Sleeve recommends 2.5 thou or thereabouts for those pistons, so if the owner wants specific pistons and specific clearances it is his responsibility to clearly ask for that.  If not he gets what the professional (you) recommends.  That's why we use professionals.

If I want something machined a certain way it is my responsibility to communicate that clearly to the machinist and 100% my responsibility if they do what I ask them to do and it doesn't work. The OP doesn't actually know enough to know what he wants, but thinks he knows enough to be a critic.  Touch of the old Dunning-Kruger effect there methinks.

Just to throw a money wrench into the mix, that RD does sound loud to me with my acoustically perfect (cheap) computer speakers and calibrated (not) ears. Is it possible that his big ends are a touch loose? Or is that just the effect of a cheap phone microphone?  If he seized it when it ran out of oil, the big ends may be damaged. Just a thought. I expect to hear a higher pitched tapping/ringing sound with piston slap (clearance).  On my PC that sounds deeper than I expected.

Either way, the OP is acting like a dick.

Nice video.  Thanks for sharing.  Racing old cars and bikes  is a fun pastime and as they get faster and older, things start to break.  Make that part stronger and something else starts to give up under the strain. 

I like the fact that the car still looks like it did and hasn't morphed into a carbon fiber, modern interpretation.

Engine sounds good.  What's the chirping under brakes?  Is that brakes or tires or something else?

Any idea what the old/long pipes are?  I first thought they were DG and this evening I took a better look.  They look like Bassani pipes which were really good for the time.  Will be interesting to see how they compare with the new/replacement pipes.

Yes, aftermarket.  Racers are always looking for a weight advantage.  Mag wheels were supplied by Morris, Kimtab, Campagnolo and many others. They were fitted to Kawasaki triples and Suzuki TR750s and TZs and they are all decades old and way past their use by date.

I have a matching 3.00 x 18 rear wheel on a TZ special here and it will be fitted with the old hard as nails slick tire if I can get it back on the rim for static display. 

Interesting chart.
I suspect that PO = Pilot outlet ie the small drilling above the pilot jet. 
BP might be something to do with the pilot circuit so Bleed Pilot ie air jet size perhaps

The rest all translate OK

Mark: on the choke boss indicates the bike it was set up for
M.J: Main Jet
J.N.: Jet Needle
N.J.: Needle Jet size
C.A.: Slide cutaway
B.P:   
P.O: Pilot outlet
P.J.: Pilot Jet
A/S: Air screw turns from lightly seated.
V.S.: float Valve Seat diameter in mm
S.J.: Starter Jet, pressed into the float bowl

Look for a raised M, indicating that it's a Morris magnesium wheel which is perfect for a TZ museum restoration but really has no place on a bike that will be ridden.  Magnesium age hardens and cracks internally which will cause you to instantly empty your bowel just like taking too much magnesium in your diet will do, but more catastrophically.

It might be an aluminum copy but looks like a Morris.  I have one that looks very like that and after it gets blasted and powder coated it will be fitted to a museum/private collection TZ.

The answer is that the main air jet changes the mixture as revs rise, but with a Primary type needle jet, it doesn't have much, if any, effect because it just provides air to help break up the fuel into smaller droplets as it leaves the needle jet.  On a Bleed type, the air mixes in the needle jet, so a larger jet means a leaner mixture.

That's why they are typically a 2.0 or 2mm diameter to provide as much air as is needed, and in many carbs, the air jet is left out altogether.  On a Primary needle jet, the height of the spray bar or Primary choke as it's called plays the same role as an air jet in a bleed type.  Not so much because iof the air but because a tall choke sits closer to the center of the carb where air flow is faster so it has more effect.

Where are you seeing "BP" and "PO".  The needle jet is a 159 series I believe and it's size is P-0 which is 2.650mm diameter each letter increase equals 0.05mm and each number increase is 0.005mm so P-0 is 2.650, Q-0 is 2.700, Q-1 is 2.705, Q-2 is 2.710 and so on.  Could that "BP" actually be 159 by any chance, if you are looking at the needle jet?  That would be the "series" 159 is used in VM34 carbs and uses a large hex main jet. #188 is almost identical but is drilled and tapped to take Large Round main jets which flow differently so Mikuni gave them a different thread to stop us from mixing them up and using the wrong type of jets.

According to my notes and not to be taken as gospel, C&D models came with 115 main jets, but in Australia our 400F with carbs marked 2R9 came with 145 main jets in #284 series needle jets which are the ones with tall spray tubes and create a different fuel curve than earlier carbs.

LEDAR used to recommend 240 main jets which I think measured something like 1.4mm and that caused some confusion back in the day. We ran #40 pilot jets with lightly ported cylinders, foam filters and what I think were DG pipes but that's far from sure.  Might have been Aussie copies.

We ran fJ6 needles in 3rd slot and that's all my notes say.

Are you running oil tank(pump) as well s premix or just pre-mix?  That oil spray suggests an oil build up in the crankcases and pipes that needs a few hard miles to burn clean.

teazer,

actually, its the other way round, the aircooled runs hotter, so the clearance can be less, as the barrel and the piston are expanding at roughly similar rates so the clearance remains predictable.
watercooled barrels run cooler so the piston expands more in comparison and reduces the clearance more, i believe that to be the reason that recommended clearances for water cooled pistons become debatable when the piston is going in an aircooled barrel.

even the above quoted pro x paper states that the manufacturers recommendation supercedes all of that information.

just my 2 euros worth.

les.

Yes and no... Pistons and barrels expand at different rates and one reason is the ability to transfer heat from piston to barrel to cooling material (air/water) and more clearance usually means less heat transfer.  I wasn't really trying to calculate the actual expansion rates but rather just drawing attention to the many factors (variables) that we can't effectively measure outside of an engine lab.

My refernece to the UK wasn't to put anyone down.  It's just that thrashing a bike down a US freeway in summer is a very different thermal load that tooling around the average British road where temps tend to be lower and engines typically spend less time at high load. Lots of issues with those generalizations of course because that's the nature of anecdotes. 

But point taken and lots of other relevant input.     

Using pistons designed for a water cooled motor in an air cooled top end can be an interesting exercise.  Let's talk about some of the differences.  Air cooled top ends tend to run hotter so they need slightly more clearance than in a comparable water cooled top end.

On an RD that's ridden fairly hard without careful warm up, the chances of a 4 corners seizure rises significantly, so I tend to increase clearances a little on any ported motor.

The flip side of that is that when an AC motor is carefully warmed up it will tend to have a hotter barrel which in theory will run a little looser than a W/C.

So there are lots of variables.  My take is that Chuck Q and Scott C both say .002 is good, then .002" is good. They are experts and know what they are doing. I get what the OP is saying about the change in noise as clearance increases and it's interesting and until he can document that, it's just another internet story.  Stick to what the experts say and if they say 2 thou, then that's what I would use.

The internet unfortunately is a dangerous place where it's easy to harm someone's reputation.

Out of idle curiosity,  are those "experts" in the UK or the US where running conditions tend to be very different?

And you can take out the main jet and still get it to idle and up to about 1/4 throttle or more.  And many of us know that form finding main jets loose in the float bowl bottom.

In theory, there should be little to no flow through the needle jet at idle, but as soon as the throttle is even cracked open there's a depression across the needle jet and it will flow - even if it's not much.

I suspect that in this case, the slides may be high enough at idle to allow for some fuel flow from the needle jet and maybe enough to upset idle mixture enough to have an impact.

Cool project. 

FYI, on our RD350 drag bike, I had the OEM stem machined out and pressed in a slightly modified GSXR750 stem I had lying around. Weight may not be as critical on the salt as at the strip, so your priorities are probably different.

Can't wait to see how this project develops.  Thanks for sharing.

Mark is correct, that the needle and needle jet should not effect idle or just as you crack open the throttle, unless something is way off.

Is the problem just as you roll on the throttle? That could be the slide cutaway, but I'd want to get idle and mid range closer before buying slides.  I have taken a file to slides to correct that situation before but I had a pile of slides I could offer as sacrifice.

Try a smaller needle jet and see if that's enough to clean it up. Jet's aren't cheap but cheaper than slides.....
 
But the big issue is 1/2 or 3/4 throttle IIRC.  Did you check those needles I suggested earlier? I think I may have a pair here that I bought for some obscure reason and were never used - yet.  They're longer so I'm not sure if they will work, but worth a try.

At 1/2 throttle it's mainly about needle and jet, but by 3/4 the main jet is exerting more influence.