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Another excellent article by Kevin Cameron.  He's right.  They were all golden ages.  I was in H/S in the sixties and used to wait for the two UK weekly magazines to read about Hailwood and Reed and Ago and so on.  It was a shame when that era came to an end.  After that it was all about smelly 2 strokes until I watched the Laverton GP with Ago getting beaten by  more or less stock RG500.  More special days.
The Sheene and Roberts et al days were amazing and so were the Freddie and Eddie and Wayne an Mick 80s and 90s and what a shame when they were replaced by MotoGP monsters and yet I watch every Superbike and MotoGP or moto 2/3 race I can see because the technology is interesting, but it's always more than that. It's about brave young men and entertaining older ones and fragile egos and amazing skill and people pushing themselves and the equipment. Some can only ride at their peak if everything is just so, and others are more like don't mess with the settings, let me just ride the damn thing.

Whichever era we prefer, it has been great to experience them all.

So here is my solution..
I won't be using the butchered frame for street use.. so I made sure that the number on the headstock matches the title.
...................

Fixed it for you, but smooth down the grinding marks from where you were "cleaning up, the OEM welds"....

I can confirm that I used to buy pre-mix at the petrol station from the pump.  That was when two strokes were cheap transportation in the UK and Europe with little or no sporting aspirations.  Cheap and cheerful ( but smelly) get a two stroke and if you could afford luxury or performance, you bought a shiny 4 stroke.

They disappeared as the economy improved and less and less people used bikes for basic transportation and no one wanted to smell of two stroke smoke, so the market disappeared along with Francis Barnett, James Arial Arrow/leader, and so on.

Bikes like the early YDS Yamahas and later the Super Six Suzuki (x6 or hustler) were a whole different market  and came at a time when the Japanese companies were pouring a lot of money into GP racing with 50,125, 250, 350 and hugely powerful 50-60hp 500cc bikes. Things definitely changed since then. 

....Pool cleaner isn't all that concentrated but using strong HCL will rust every steel part nearby....


IR8D8R

That is so true.  I had a partly used container of Muriatic Acid (pool cleaner) in a cabinet and the hinges are so rusty they had to be replaced.  That was from a "closed" container breathing a little.  Store it somewhere safe.

Or strip both motors and rebuild the original with the best parts from both plus new pistons and crank......

It all comes down to your level of comfort.  swapping a motor and riding that bike without telling the authorities would be a no brainer for most of us and in the extremely unlikely event that someone ever checked the numbers, you still have the original to swap back in. Checking frame and engine numbers against the record is something that would only happen around here if the LEO had a strong reason to believe the bike was stolen.  Otherwise they just write the ticket based on the plate number.

Some of us swap motors, or crankcases without a second thought.  It's still the same bike and all the parts were purchased legally, so not an issue.  But if you fear it could be an issue, use the stock cases.

Gloves on
Safety glasses on
small amount of muriatic acid on a Q tip to wipe away the mess. It will fizz, so make sure you have good ventilation. Take your time - it takes a while. That will remove all the aluminum, then wash it thoroughly and do a clean up hone - light pass and check the bores.

Regular Dyna or similar designs will run backwards.  I know my GT750 version did.

VS system uses dyna or similar pickups but I believe that he has extra magnets in the rotor so that if the thing kicked back, the timing would be so far off, that it cannot run.

Just kick it harder. The GT only did that once but it sure surprised me and took a moment or two for the brain to work out what was going on.

Those ports are beautiful.  It is seriously hard to get the rear transfers right.  Looks like JR did a really nice job.

That is an interesting solution for sure.  A butterfly choke will reduce airflow by 5-20%, so I hope they are larger than the carb bore.

But the fact that they work and regular enrichment circuits don't is more interesting.  It suggests that the enriching circuits are not doing what they are supposed to do and that suggests a lack of air velocity through the carb.  With that sort of choke, the pressure differential between the intake side of the carb and atmospheric will be substantial and consequently fuel will be dragged through every jet.

Makes me wonder if it needs softer reed petals that open further at very low engine speed.  In theory, two stage reeds would be perfect as long as the small reeds petals are thinner or are "softer" ie they bend with much less force.  I wonder what they came from and if there are more suitable reeds available.

Big advantage of reeds is the added transfer port area which that motor needs. 

Disadvantage is the studs tend to get in the way and they are challenging to fit.  Check out the barrels that Brett DeStoop cast for a 1000cc motor or his 750 reed motor that made something like 176HP IIRC.

I wanted to graft a set of snowmobile top ends onto a GT750 set of cases but that requires moving the left cylinder out a bit and changing the crank and at that stage, might as well saw the transmission off and weld on a GSXR trans with stepped gears for a shorter motor....

A Zeeltronic or ignitech programmable ignition would probably help to spread the powerband too.

There was a guy in Germany that built a 1000cc motor and added powervalves to the exhaust as well as reeds.  That was a huge amount of welding and machining.  You could probably machine a cylinder from billet with modern machine tools and an unlimited budget.

....
p.s. teazer I owe you a water pump gear, I haven't forgotten, I am assembling 8 more gears next week and one has your name on it.

No worries Chris.  I know where you live....

Back to the "double" thing.  As someone mentioned, it's not like that.  at roughly #100, both types flow the same.  at #200, the Mikuni will flow twice as much as the #100, but the Keihin will flow closer to 4 times as much.  The difference in flow increase as numbers (sizes) increase.

Here's the old Round Jet to Hex jet Mikuni chart to illustrate how it works.  But those are not keihn jets, just similar characteristics.

On CB750 carbs we ran #120 with race gas and #195 with Methanol which was equivalent to roughly #400 or more in Amal main jets. Numbers are just a place to get roughly into the ballpark as you just posted.

Basically, Mikuni HEX jets are rated in flow, where Keihin are the diameter.  At least that's true on older carbs.

Mikuni Round jets are close to diameters as keihin jets, so if you increase a Hex jet from say 100 to 200 that doubles flow but with round mikuni or keihin it basically quadruples flow.  a #200 Keihin is 2.0mm and roughly the same flow as as a #400 Hex jet.

I have no idea what size system OKO used.  I thought that they were a Mikuni carb body copy but used Keihin type and sized jets, but that's what I think I remember I read somewhere, so you need to ask what jets are in OKO carbs.

I don't have an industrial sized shop, just a regular 2 car garage and all I did was to slip a window mount home A/C in and it makes all the difference. Doesn't drop temps below about 72, but that's OK for me.

Things that made a difference:
Decent insulated garage door
Decent rear door
Insulated and drywalled all the walls
Threw some insulation sheets on top of the rafters. 

It all adds up

I ran Denso U grooves for a while in a classic (vintage) Honda CB77 350 on methanol and never had any issues with them.

More interesting is their range of Iridium plugs for different purposes.  Obviously they think it's necessary to have different designs and perhaps for road race on long tracks or land speed the difference might be between surviving and not, but I suspect that for normal riding the difference may be undetectable.