New to me RD350

[2TFool]

A new member here, thanks for having me. I've owned a few bikes over the years, including a BSA Bantam, a couple of MZ 250 supa5's, a Benelli 250 twin and a RD400
I've just acquired this RD 350 which was built as a race bike and used as such, but the original builder was getting it ready for the road. I intend to clean it up and finish off It's return to the road.
It's been sitting for about nine years and has a little surface corrosion and dust, the tires are shot.
The guy who built it it's not very well and so information from him is not available, but a friend of his has filled me in a little.
What I know, it has a welded crank, no alternator(runs on a small lithium battery) larger carburetors, needs 110 octane fuel, barnett clutch springs. I don't know about porting or what the actual compression ratio is.
It has an aluminum swinging arm, Works shock absorbers, some kind of valving in the forks. I think the seat, swinging arm, expansion chambers and resets are Moto Carrera?
I would certainly appreciate some help on certain aspects and so if I may ask, here's my first question.
It has Buchanan sun rims front and rear, they are both 2.15×18. The tires are Avon AM23 130/65 (just clears the chain) and AM22 110/80, plenty of tread left, but the side walls are cracked and ruined from sitting.
Expensive tires if you can find them.
What am I going to replace them with? I've searched the Internet for size suggestions and what is actually available and it's not entirely clear to me. The Bridgestone BT 46 seems available here in the US in almost the right sizes, but it appears to be a radial tire. Should this bike have a bias ply tire? Back in the day I was able to change bias ply tires on smaller bikes with tire irons, would love to be able to do that again.
Thoughts or experience?

[1976RD400C]

Wow, whoever built that meant business. That's a nice race bike. Take the cover off and check what ignition it has. You may need to change that if it has no charging system for the lights. Do a compression test to get an idea if it needs real high octane fuel. Most of the 2 stroke race bikes long time ago used that 110, even though they probably didn't need it. You can use any tires and they can be mounted with tire irons. BT46 is a very popular one for RDs. 110 rear and 90 on the front for those size rims. You may want to tear the motor down and check things out if it's been sitting that long a time. Again, that thing looks like it could take the checkered flag. 

[m in sc]

sort of depends what the budget is  . I would be concerned with a few things before going too deep into the plans. such as: charging and ignition.  2: does it have to run on 110 or can it be tuned to run on punp 93 . 3: probably very important are crank seals. sitting fir almost a decade plus however long before that they are probably shot.

I would measure compression 1st. see where it is. anything over 140 psi will need race gas. below that can prob back the timing up and be ok.

as far as ignition/charging a vape or hpi cdi is my go to when I can. but pricey. but def consider a case split and crank seal change

[85RZwade]

You have some nice parts on that bike! 2nd the advice re: tires, charging system and compression ratio. Crank seals as a matter of course. If you ever decide to sell that seat and/or the shocks , remember who complimented your scoot!

[2TFool]

Thanks for the replies. I'll look for a set of Bridgestone tires.
To answer some of the points you raised, it has a PVL ignition system and a small lithium battery to run the lighting. I need to find out the capacity of the battery and measure the draw the whole system places on it. I should change all the bulbs to LED to reduce demand.
 I scrounged up a pint of 116 octane and mixed it up a little oily. The bike started third kick, I switched the chokes off, and it idled immediately, perhaps a little fast(no tachometer) Responded well to blips of the throttle. Ran it for only a few seconds. A little later, I couldn't resist restarting it, one kick. I think from that I can assume the seals are working at present.
I want to talk about compression and octane but I think I'll start another thread just to keep it tidy.

[automan]

Teflon tipped seals!
Plastic main cages!

That's what I wanna see.

[m in sc]

seals may be working but are assuredly hard as a rock. ive pulled crank seals oqut of super low mileage motes that ran perfect that were cracked and non flexible. but it ran great.  Also, total loss lighting is dangerous on a street bike, ive done it. you don't want to be out and the brake light run out of juice. 

[2TFool]

Point taken about the total loss lighting.
The crankshaft seals, I imagine if the left-hand one goes, you're gonna experience loss of crank case compression, what about the right hand seal? pressurization of the transmission, transmission oil in the crank case? How catastrophic is any of this?
I see there's an oil seal in the middle of the crank. I understand that my crank shaft has been welded though I haven't verified that. If so, I imagine changing that seal might require sending the crank to a shop that does such things?
Thoughts?

[m in sc]

middle seal is a labyrinth seal. not rubber. doesnt need changing. however if the bearings need to be done its tricky. but hopefully thats a long way off.

RH seal will suck trans fluid in. lh seai will suck air in. when it goes, it goes. a leak down test is ok, but like said, age kills them more than anything.

[85RZwade]

The seal in the middle is the labyrinth seal; it's there more to discourage fuel charge from moving between cylinders than to stop it and is rarely changed. A failed right crank seal will typically allow gear oil into the right cylinder, and a failed left side seal starts as a high idle from the lean condition it creates, can eventually lead to seizure. New seals are cheap insurance!
As Mark said while I was hunting and pecking.

[2TFool]

That sounds good regarding the middle seal. Can the two outer seals be replaced without splitting the casings? Automan wants to see Teflon tipped seals, what is it of which he speaks?

[m in sc]

technically no. but it can be done, i would not recommend it. with an ex race bike, its worth splitting the cases and doing a full inspection.

trust me, i've had bikes that 'ran'. one had a blown crank seal, the other was missing half a piston.  thersa slew of horror stories i can rehash.

always worth spending an afternoon to go thru the bottom end, re-gasket it, and replace anything suspect due to wear and know exactly where you stand. a gasket set is cheap. crank seals are cheap. good insurance.     

[2TFool]

OK, I appreciate that. I would like to take the engine to pieces and give it a thorough examination and I will. The clutch is not releasing, and I could measure the height and width of the ports and get some idea of the tune. It's just the monkey on my back whispering, you have enough to do already, mow the lawn, paint the trim.
Any particular brand of seals, genuine Yamaha, something off Amazon?

[1976RD400C]

The Yamaha service manual goes into great detail on how to disassemble, inspect, and reassemble. It's kind of a must have for people working on their own bikes. I have my ex-race bike on the road and what a hoot it is to ride. I love heading out on the back roads.

[m in sc]

amazon isnt a parts supplier. go thru a known vendor. economy cycle, yambits, partzilla, or hvc is my suggestion.

partzilla has online parts diagrams, and the tech library on here has manuals.