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Yeah, premix.  The exact premix I'm going to figure out literally last thing.  It's been about twelve years since I had an RD, and relearning all this is harder than I thought.

totally different.  I mean, I've done it but I had to change everything. as said, the needle and seat seat diameter might be too small. 28sarwnt hard to come by, where are the original carbs?

I'm putting together this bike from parts, because budget racer.
I got (foolishly) an RD motor sans carbs, which looked to have been stored underground somewhere and was only good for the six speed transmission and heads. An RD roller frame with decent wheels and forks, and a non running R5 that came with a pile of junk and a single VM28 and something like a 34 that wasn't worth anything because the slide was stuck. But the inside of the tank looks like new, so...
I'm giving myself six months to put this together, probably optimistic there, whether or not I make it doesn't matter. I have another bike I race but I was looking to get into a smaller displacement category next season.

Hm. I only ask because I found that VM28's seem to be hard to come by, and these are on an old '71 340cc snowmobile, a little googling shows one being started with a cord like an old lawnmower. A hundred bucks gets me the whole motor with the carbs and that's it, I don't know if this is more hassle than it's worth or not.
I figured, 2cyl 2T at 340 cc's, jetting must be close?
Or should I hold out for a set of 28's.

I came across a set of VM32's for pretty short money and was wondering if they'd be fine to run on an RD motor.
Right now they're on an old 2T snowmobile motor.
If they'll work, what do I do about the intake boot?

So the R5 crank I have checks out okay. The bike was on the original bores and when it came to me had no carbs on it but turned over easily, seemed like it would have good compression.  I'm curious what the labrynth seal does in relation to the pressure between cylinders. Obviously the shaft has to turn within it, and the timing of the strokes being 180 degrees out, theoretically anything bleeding through would be negated within the seal? 
Another thing, I was looking at the Vito's cranks and the lobes of the crank aren't like stock, it looks like they're cut away some to make them lighter.  How does this affect the internal volume and compression with respect to jetting?
Maybe I have too much time on my hands to dwell on the esoterics of 2 strokes, I don't know.

Yeah I'll just use the other one I have. 

nothing needs to be ground . it should just press apart

Yeah unfortunately for me the pins are welded in.  On both sides.  It also has aftermarket rods. Racebro thought he was dealing with a 100hp bike or something, IDK.

The R5 crank is dead nuts on, less than 1 thou, one big end bearing might have a little bit of end play but it's not terrible. The R5 motor was on the original bores, probably low hours.
I might take a shot at the RD crank; I have time and I can't make it worse. The crank pins need to be ground off to get it apart?  And is a 12 ton shop press enough to press it apart?

Post some pictures so we can commiserate.

It's probably not that bad. Unless the bearing surfaces are heavily rusted/pitted it can almost certainly be saved.

Yeah IDK where I'm going with this.  I have two motors.  An R5 with a good crank but questionable cases and an RD with a sh*t crank and good gearbox but a terrible crank gallery (though the bearing mating surfaces look okay). 

I'm tempted to throw the R5 crank into the RD cases, that saves me moving the transmission bits around.  But the crank gallery over there is atrocious.  The R5 cases, the cylinder hold-down bolts are severely perished and I'm afraid to take them out because they seriously look like they'll snap right off.

I'll try to post pics later, I have a laptop and all the pics on the phone.  Edited:  Pics from L to R, RD crank, R5 cases, RD cases w/ gearbox, R5 crank.

I guess I'm just looking to find out where to put the R5 crank because I need to get the right seal kit.

I have an R5 motor torn down and want to measure it to see if it's in spec before doing anything else.
I have v blocks, dial indicators, feeler gauges etc but idk what am I looking for?

Okay I see. I would just be embarrassed to send this out to anyone, it's in really rough shape.

What's required to disassemble an RD 350 crank?
I realize there are experts who provide this rebuilding service but I was curious if this was something I could do on my own.
Thanks

Thanks Mark, that's very encouraging. As an aside, do the R5 and RD share the same rake and trail numbers? This R5 I have seems to have a little more rake but it could be the Honda wheels someone put on it. They're aluminum, and if they weigh less than the spoked ones I might try to keep them.

Ah, great. I just took the heads off the R5 and they're stock bores. The RD motor is junk, I don't think the crank is much good and one of the cylinders had a cracked liner going from the intake port out to one of the transfer ports, probably why it was retired but who knows. It looked like it had been kept under a chicken coop.
So I'm going to get a set of the "new" cylinders. I remember using the banshee pistons in my old bike, I assume they should fit right in but I might send them out for a fit check at a local shop first.

So it's been awhile and I just picked up a project, I have a roller RD350 and then I picked up a motor that only has a good transmission. Then a buddy found an R5 that has good compression, but is missing the carbs. For $300 I couldn't say no.
Anyway my goal is to put this thing together and put it on the track so I can race lightweight, formula 4 or maybe it's 3. Anyway.
Someone check me here but I'm pretty sure I can direct swap the gears right into the R5 cases, along with the clutch and shifter. I can also directly bolt up a set of RD cylinders?
Are the cylinders available from that eBay seller any good? I understand I might as well buy three sets in hopes of getting a set with the same porting. On that note, do they come with the same porting that was on the original RD's?
Any advice is greatly appreciated. Thank you.