73 Kawasaki G3ss 90cc

It seems like all the small (sub 200cc) 2 stroke machines end up here, so i figured i'd post mine here as well, even if i feel that it's a cafe. Not too much to say about it. Bought it for way too much money about a year ago without really researching it at all. At the time, small 2 strokes were hard to find in my area, so i snatched it up. I have very little money in this bike, and it shows. Compared to 99% of all other builds on this site that is. What can you do when you're broke though.

But onto the pics:

The first day


Wanted the seat to be as low as possible, so cut everything off the frame.


After making a foam mold and fiberglassing a seat pan, i decided i wanted something metal, so i came up with this.


Bent the actual seat pan.


All welded up


Didn't like how square the seat pan was, so rounded it off a bit.


I then powdercoated it (along with the tank, after doing some dent filling with jb weld).


Tank and seat powdercoated and back on bike.


Figured i might as well powdercoat some other stuff while i was at it anyway, so took off the side covers and prepped them for powder.


After they were done cooling off.


Decided to make a laser cut acrylic magneto cover as i have access to a laser cutter. I also polished the raised lettering.


Installed them back onto the bike. I had also powder coated the kick start and shift levers.


About a week ago i got a job at an indoor motorcycle junk yard. So i got my hands on a complete G4 with a recently honed top end and wiseco piston which i had read swaps right on. I took the top end off the G3 and was ready to do the swap. The G4 / kv100 cylinder is a 5 port aluminium cylinder at 100cc and 11.5hp where as the stock G3 cylinder is a cast iron 3 port at 90cc at 10hp stock. Needless to say, it's not a direct swap. While the cylinder studs line up just fine, the transfers are not the same size/shape. And also, the small end of the con rod is bigger on the G4. Now i MAYBE could have ported the bottom end to match the transfers (not sure there was enough material) and swapped the rod, but i figured i'd just wait to find a good 5 speed 100cc kawi donor engine. I think we might even have one laying around at work. I could have swapped the entire engine from the G4 onto the G3, but it's a 10 speed and i'm sure i can dig up a good condition 5 speed soon.

Needless to say, while i had the G3 top end off, i decided to blast and paint it.


The stock rear shocks were extremely rusty and very small. I'm not a big guy, i'm only about 140lbs, but the tire would sometimes hit the seat pan (now much lower than stock) so i dug up some shocks from work and threw them on. Much better.


My boss had me part out the G4, and keep whatever i wanted off it. So i took the forks and triple tree (the stock forks had a non adjustable triple tree, and i didn't really like their style.) They swapped on just fine. Only problem is they were a few inches longer than the stock forks. Not a big deal as i could just raise the tubes in the triple trees. But then they interfered with the handle bars. The plan is to find or make some 30mm clip ons so i can put the forks wherever i want them. So i ditched the stock fork ears and threw on some from a kx100 that are adjustable.


That's it for now. I just took that last pic today after my first WOT ride of the year. It's still pretty cold here. Future plans include possibly a different front wheel with a better brake. Clip ons, And at some point a 100cc motor swap with some porting. Maybe even a pipe if i can figure out mounting it around the kick start and center and side stands. I was also fortunate enough to be given a vintage quarter race fairing from work. It's slightly damaged, but i'll either try to repair it and use it, or try to vacuum form a new one using the vintage one as a mold.

Sweet bike! What have you done with the front forks?

It's in the description above the last picture. But to sum it up, the forks and triple tree are off a kv 100 / G4. I should add that i know you (walms) were looking for some parts on ebay. My place of employment sells strictly o ebay. Feel free to check us out! http://www.ebay.com/sch/mistermonkeyclaw/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686

Sorry, my iPhone clipped the last of the description.
I take it you could still use the crank with a 100 rod though right?

Any center stands?

I'm guessing you could swap the 100 connecting rod onto the 90 crank. You might even be able to swap the entire crank from a 100 to a 90. Problem at that point is the transfers of the 90 are too small for the 100 cylinder, and i doubt there is enough room to port the stock 90 cases to match the 100. I could swap over the the entire 100, but i don't like the fact it's a 10 speed. So i'm waiting for a complete 100 5 speed to swap. Something like a ke100. And here is a enter stand: http://www.ebay.com/itm/1973-Kawasaki-G3-G3SSL-GA-90-cc-k103-center-stand-/250702914231?pt=Motorcycles_Parts_Accessories&hash=item3a5f0ee2b7

http://www.ebay.it/itm/STEEL-CLIPONS-30MM-SES-MADE-PERFECT-FOR-CLASSICS-/280750272800?pt=UK_Motorcycle_Parts&hash=item415e053120

I bought a 100 TR 5 port cylinder and using KE100B cases. I also picked up a KE100B tranny to go with the 96 cases.
I really wanted a steel rotary valve and 5 port cylinder to start with as I'd imagine more potential. I'll port the assembly to G31M specs and hope for about 18-20 HP
The only thing G3SS will be the side covers and possibly the crank and clutch...

That's kind of what i'm going for as well. Just not as extreme on the porting. I heard the g31-m is extremely peaky and looses all of the bottom end. My machine is already pretty quick with a stock top end. I'd be happy with 15hp. Do you know what year they switched to the new gear change pattern? I'd like to stick with the old style. I have a few manuals if you need g31-m port specs...

I know they changed the shifter mechanism around 80-81 but I believe the gears are the same right through.
I don't have the name or link handy but there are websites that have the part number lookup's so you can see what is in common. I'm not familiar with the high/ low range tranny, is it external or are the cases unique?
As far as peaky goes, I think it can be tempered with less aggressive rotary valve timing. Another advantage of the steel valve is getting plenty laser cut .

Yes, the high low range engine has unique cases, sadly. It mounts to the frame the same way however. The high low range mechanism is located on the outside of the case. I think i'll be tearing that engine apart this week, so i'll try to get some more insight into its inner workings. And true about the rotary valve! It's too bad rotary valves aren't more common in 2 cycles. So much potential.

Agreed!
I'm looking forward to this one!

It's official, so long small port 90cc 3 port cast iron top end. Found a km100 that i'll be taking the complete bottom end from and throwing on a kv100 aluminium top end with some porting and wiseco piston.

Cool! What year of KV? I know in 74-75 is when they made the swap from 3 port to 5. The 3 port pistons are not compatible with the 5 port cylinder because of ring pin location. Plus the newer piston is 7mm taller above the pin. (The cylinders are as well)
In 81 they started to Nicasil the cylinders so I'm not 100% certain that the rings are compatible with a cast iron cylinder ( not sure if they are chromed or not)
As far as I know, Wiseco only makes pistons for the KE100 and they told me they are not compatible with the earlier cylinders although the guy couldn't tell me why???
Wiseco was considered seizeco back in the 70's so for that reason I'm staying away from NOS wiseco's...
At the moment, I'm thinking the path of least resistance is a NOS cast piston... I makes me shutter to say it but it "might" be the best alternative.

The top end i'll be using is off a 74 kv100. It had the wiseco piston already in it. Top end looks brand new inside. Piston # was 369m05000. Looking at the specs, it doesn't say it works in the kv100, but after turning the crack a few times with the head off, it seemed to do it's job just fine.....

Thanks for the part number, good to know that it's working well, I had my heart set on a forged piston.

threw that top end on a km100 5 speed bottom end. got it in the bike and fired it up. horrible knocking from the bottom end. only happens once every full rotation. doesn't seem to effect anything, so no idea what it is. 90cc engine is back on. just drew up a template to modify the stock rotary valve. taking 15 degrees off each side. should be cut and installed within the next few days.

Got it installed last night and took it for a spin today. BIG improvement even on a otherwise stock 3 port cast iron top end. I have the template i drew up in cad and can save it in any file format needed if anyone wants it. Works with laser and plasma cutters, or low tech with just printing it out and tracing it on your stock rotary valve and cutting it by hand.

Good to hear! This is something to consider as well if you ever go to a bigger carb...



I was playing around with the old fiber valve to see what I could do to improve the inlet cross section... I think I'll need to cut the port so it's lower as well meaning the base circle of the rotary valve would need to be smaller as well.

Stock vs ported ( JB weld would be required at the base of the spigot plus the end machined off and a piece of thin walled tubing pressed in...
The 19mm carb just has to go!

hmmm interesting work. And thanks for the scan about the port shape! Where is that from? Anything else interesting in that publication? I'm actually ok with the 19mm carb for now. I think that's part of the reason i didn't notice any bottom end loss. Intake velocity is still high from having a "small" carb. And it doesn't seem to hold back the top end yet. That might change with a 100cc cylinder with porting and an expansion chamber though. Guess i'll find out.