Jog "John Deere" 49cc Project (port question)

[jellety]

Hello all,

My Name is Jelle and live in Queenstown, New Zealand. I Run a workshop here where i mostly fix diesels and farm equipment for farmers around the area, Plus I mess around with my own vehicles where i like to turbocharge and tune older cars.

A client came in with a MG Metro, and wanted a carb clean and tuneup, and some suspension work done. But didn't have to much money at the time, so he offered me his scooter. I've never owned a scooter, but it could come in quite handy to nip to town and back, so i happily took it. Its a 2 stroke Yamaha Jog from 2007, and i loved it straight away.

What it looked like:

My mate (that apparently never driven a scooter before) took it for a test drive, and it ended up like this:

He slid out, and hit a pole, and folded the scooter in half, he was wearing an helmet and miraculously got away with only bruises and scratches. But there is no doubt the helmet saved his head, as the helmet was pretty much done for.

I found a donor bike for 600 NZD (363 UDS) that still runs but has double the kilometers:

The scooter is pretty rough, seized front shocks, all plastics cracked and broken, engine goes, but not even close to how my old one goes. But that, doesn't matter as I've got a donor anyway.

[jellety]

So I started the swap, and in the meantime I ordered some parts from all over the internet to unlock a bit more potential from the bike. I've rebuild countless 4 stroke car engines, diesel and petrol and can fix almost anything, but know nothing about 2 strokes as I've never involved myself with them. I started reading up about the basics and am surprised by how interesting it is, especially as its still in its infancy, as it seems no one can tell anyone for sure what the best portjob or setup is. I like the term "black magic" when it comes to tuning 2 stroke's, as I've seen that come by plenty of times.

Started the swap from donor to the other bike:




Give everything a steamclean while I'm at it:


Plastics come out nice and black again after a bit of steam cleaning:


Difference in parts, the donor was quite rusted out as it came from Bluff (fishers village on the sea);


Light wire-wheel and a load of rust-convertor on the frame, and like new again:


Front fairing was clacked all over the place:


Found out they're ABS, and happen to have ABS glue laying around from a previous job:


Added some more abs glue to fill in some gaps, gave it a sand and cleaned up the front edge with a grinder and flappy disc




I still had some paint left over from a John Deere job I've done, so just went for it:


Started putting it back together, and wondering what these things are, I assume its some emission control, but I cant find any information:

(in the airbox, connected to a port on the carb)

There's a 1 year difference between the bike and the wiring loom already has multiple changes, including the charging system, trigger pickup coil and oil pump. Not the end of the world, but always wonder why:

(removed pins from old plug and pushed them in new plug, 1 on 1 fit)

Bike back together:




Its nice to be able to ride it again.

[jellety]

Slowly i had some stuff coming in (The package and post services are incredibly slow in NZ) First tihing was V-force reeds.

Unfortunately it is the wrong type:






After a bit of research i figured out why, this is a 5bm engine. I'm quite happy with this as i found out that the flow on these engines are way better, with the reedblock not blocking flow to transfers and having more open surface area. No need for reed spacer, and ordered a sheet of mallosi 0.35 "carbonit", so i can cut my own reed petals.

Ordered a 60 dollar expansion exhaust for fun, and didn't expect to much. Its a chinese made yasuni clone according to some dodgy info on the internet:




As expected the quality is extremely low and had to cut the mounting bracket off, just to fit the exhaust. Positioned the pipe where I want it and reweld the bracket. While I'm at it I figured i check the "flow" of the exhaust. As its Chinese made i kinda expected the exhaust to be protruding inside where the expansion chamber meets header, and I was right:


Trimmed the pipe, cleaned up the header, and welded it back together:


Bit of clearcoat against the rust (will burn off but looks "good" for now"


installed it and upped the main jet from 70 to 75:


Ordered another cylinder head, as I would try to reshape the squish area, but its "pear" shaped?:


Cylinder head that's on the bike:


With the expansion pipe and some lighter rollers i noticed that the scooter was limited to 60 km/h. I tried to find a cheap cdi without rev-limiter. But unfortunately its a 8 pin CDI (and different again from the other scooter, even though there's only 1 year difference) So had to order a genuine Progress R cdi from japan, specifically for this years scooter:

[jellety]

Ordered a cheap cylinder head temp gauge, only goes up to 120C (248F) so pretty useless but looks really bling:








Proper "bush mechanic" style hookup to the ignition barrel wires:


It's got a 2 puck clutch 105mm, I'm 115 KG (253lbs) So i figured it could use a 3 puck Hebo Style, they are adjustable from the front, so i don't have to remove the clutch, only the bellhousing, to get it to engage on the right rpm range.




weight difference between clutches:



Whoops, got to exited and forgot to throw the bellhousing on, and gave it a start. At least i know the clutch works...




Bend up the clutchplate unfortunately, but straightening was quite easy;

measuring and bending it back, finished off with a dial gauge:

After that I threw the flywheel in the lathe and forgot to weigh it after the first run in the lathe.

I recon it would have been about 10 to 20 grams, and manage to drop about 100 grams after that, bringing it to 534 grams:

[jellety]

I haven't assembled it yet as I will put a new piston and rings in, and give the cylinder a bit of porting to wake it up. I've read that the original minarelli's can hold up to 10.000 rpm, correct me if i'm wrong... I've seen a post of 90GTVert where he ported his 49cc to 190 degree opening, and made some adjustments to the piston for the transfers timing, as they are easy to mess up. On this website martysgarage.info/reference/two-stroke-port-duration/ it tells the same story, about 190 degrees open. I'm aware that not all cylinders are the same, but it seemed multiple people porting minarelli's only had to remove about 2 mm of the roof of the exhaust port to get to that duration. But when I measure it out it shows I have to remove 10mm of the exhaust roof (after matching up port heights with piston with base gaskets), and that seems like an awful lot, there's barely any cylinder liner left for the compression part. I must be doing something really wrong with the degree wheel, who knows? I use the light method, so when the port opens and there's the slightest bit of light I zero the wheel and go over the whole port till it closes, and record that degree.

Degrees original, without base gasket adjustment
Exhaust port duration: 163°, opens at 99° ATDC
Transfer port duration: 111°, opens at 129° ATDC

Degrees with 3 additional base gaskets to match ports with piston BDC
Exhaust port duration: 171°, opens at 95° ATDC
transfer port duration: 124°, open at 119° ATDC





Inside the cylinder:



I don't really understand what the boostport does, as it just seems like another transfer port to me. But when i dropped the piston in, the windows match the port, so is that for the 2 stroke oil to cool the bottom of the cylinder and oil the small end bearing?


Portmap of this cylinder, Writing on the barrel says, Y-2 Yamaha, 4WX00...


degree wheel:


Dial gauge to find TDC:


4 base gaskets to raise the barrel, for the piston at BDC to clear the complete ports:

Can anyone point me in the right direction? Or see any mistakes i made?

If this all seems correct, any advise about the right port timing?

After the right port map, I will put the information in 2Stroke wizard, and design and build the right pipe for the setup

[broyager]

Great work! and documentation.

What type of spring, or where did you get your yellow torque spring for the clutch?

Also... I'm looking for a gear set for a Jog, are you interested in selling the set from the wrecked or donor machine?

I pretty much need the whole lot.

Also did your forks get damaged in the prang? Looking to convert a 2001 Jog with only drums to the disc from the later model.

I'm in Wellington

[broyager]

Also emission system can just be removed afaik, the closer to the exhaust the better. I don't have access or skills to weld so on my build / refurbish, I'll block it where it turns into rubber further up.

I piggy backed my temp gauge to the horn circuit before the horn switch (12v DC), which is only on when the ignition is.

I'm also after a kickstart assembly, largely. I might pm you.

[jackrides]

Are all New Zealanders geniuses or just the ones who like 2 wheels and/or sailing? Fantastic writeup! Back at you after slowly rereading.