YamaSaki YFSex-250 build

ITS ALIVE!!!!

sorry for the long wait guys and gals. life's been getting in the way. Had a trip to north dakota to see my mother and another out to vegas to look for a new home.

But, the long weekend as finally given me some time to sit down and wrench a bit and I now have a running quad - sort of.

I got the radiator fully mounted and all plumbed up. Found some carbs and got those all cleaned up and installed. Modified my throttle cable so it works with those carbs. Cut out the nasty exhaust you see above and welded up some nice clean new stuff using mandrel bent pipe. re-did the entire wiring harness to eliminate eveything not needed and then fought with the ignition for 3 weeks.

Couldnt get any spark at all on the thing. I went through way too much money buying new Ignitors for the hting and anotheing seemed to work, then i by accident, stummbled across a site that someone was converting a ninja 250 into a track bike that was having the same problems. Turns out, Kawasaki had this bright idea to add an "anti-teft" device to the mix. There is a tiny 100 ohm resistor buried in the stock key ignition that go to an arming lead for the ignitor. This is apparently so that someone could not simply unplug the stock ignition and hot-wore the bike. Naturally this was not listed in ANY wiring diagrams or anywhere in the service manual.

Anyway, got that sorted out and finally got spark. Put everything together and she runs!

Had to do a little modification to the gas tank to clear the carbs so I filled it with water, broke out the torch and went to town softening and re-shaping the bottom of the tank. all worked great but i am going to smear some gas tank exopy over everything to make sure i wont have problems in the future.

Now I am waiting on proper air filters and a new rear fender set (anyone have one for sale cheap?). Other than that, it is just a matter of finishing up the charging system (went seperate from ignition circuit) and then comes the fun part of taking everything apart again and finishing up some of the welds, reinforcements of the fram, and getting everything painted and cleaned up.

Will post pics and video later today. I was so excited once i got spark. i had like 3 different people and myself working that damn thing for too long. i was about ready to throw in the towel on this.

More coming later today.

- Justin
 
Radiator:


Exhaust:


Carbs Mounted:


The mess that is my project and garage:


And just for fun, some of the other toys in the stable:


And this is another fun project of mine. 47cc pocketbike with a 70cc big bore kit, adjustable compression head, timing advance, performance exhaust, wave rotors and upgraded brakes, and the crown jewel of this one (that you cant see in the pic) is the 9oz nitrous bottle mounted on the other side and stainless braided lines for it. will do nearly 75mph luggin my 220lbs around:


video once i get it off my phone and onto youtube. Enjoy.

- Justin
 
I'm about 99% sure its due to it only running on one cylinder.

Ding ding ding ding ding! What do we have for him johnny?

At the time was running on one cyl... is on 2 now and runs good. A tad on the lean side but im fixing that tonight. No filters either so that will change things. It revs like crazy now. Ill try and get another vid.

- justin
 
damn dude you don't mess around. I just found this build and you are bangin this thing out. very entertaining. Keep em comin man.
 
Clearly, I am not married - fortunate that my fiance digs this sh*t too.

And the whole time I thought I was dragging this out. This is going really slow for my norm. I love fabricating things tho... especially when it involves shoe-horning some large motor into something that its not designed for.

This is all running in parallel with my YZ-250 suspension swap onto my 84 yamah IT490 - But that's for another forum.

Thanks for the comments guys. Hoping to be test riding in the next few days.

- justin
 
Excellent thread Justin.
Nice to see original ideas on how to do things.
You kept the center of gravity low with the engine and rad placement.
It helps to keep in mind and build toward a purpose, it looks like you are doing that?

Nice job, your ideas and pictures will help others.
 
and it drives....


This was the first chance i got to drive it. It has since been tuned, exhaust finished up, frame reinforced, cooling system plumbed and functioning, cooling fan hooked up, lighting hooked up.

I did run into some problems with the charging system as I discovered that the Reg/Reg was bad and pumping 19 volts into my battery. So i ripped that out, grabbed a single phase reg/rec I had laying around and wired that in leaving one of the 3 stator wires unhooked and Im getting a perfect 13.9v on the battery in the run condition.

Should have it all fully buttoned up this afternoon after some test riding.

just a few more little things after all of this and it should be complete.

The tuning is mostly done except that I have not synched the carbs (other than a bench synch) but that really only impacts idle and the first 1/4 of throttle but who uses that range anyway. They are pretty close so I may not actually do that prior to my dunes trip this coming weekend.

Just paint is really the only thing (and obviously anything that may fail or not work correctly during testing) and it is finished. Probably not going to get to paint before the trip this weekend though.

enjoy and feedback is welcome.

- Justin
 
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Excellent thread Justin.
Nice to see original ideas on how to do things.
You kept the center of gravity low with the engine and rad placement.
It helps to keep in mind and build toward a purpose, it looks like you are doing that?

Nice job, your ideas and pictures will help others.

Thanks a lot.... this is one of the few projects like this that I have embarked on with an actual plan. most of the time i just wing it. This one was built with a purpose. The biggest drive on the planning was primarily my finace as I am mostly doing this for her (she really wanted e-start). The added ponies are just a bonus.

The last thing I want is for this thing to be unsafe or unreliable. My past projects have all been "lets see if this works." and then lots of going out to risde and something breaks or discover that it didnt work like planned or that it was unstable, so on and so fourth.

This one I wanted to keep the geometry as much the same as I could so it had familiar handling charectoristics. I really want to gear the piss out of it but I fear that may make it too much for her though. it is alright as it is.

- Justin
 
sounds mean, hows it ride?

Seems to ride pretty good. I havent taken it anywhere other than down my street and back and pissing off all my neighbors (im out of there in 3 weeks anyway so im not concerned).

I plan to have it out this afternoon once it cools off a bit to see how it actually rides. It is noticeably heavier (mainly because of the added reinforcement and the heavier engine i assume) but seems to have ample enough power. It definately pulls WAY harder on the top end of the RPM band but thats typical of this little 250 engine at 14.5K RPM redline. The lowend from idle on up is about equivalent to the begining of the powerband on the stock motor so its a bit better.

Has a nice mean rumble. I LOVE the sound of the little 250s though with a good set of pipes on em. They have the low bass tone but still wind out real nice and that high pitch scream when the revs are up.

- Justin