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Discussion Starter · #1 ·
So, I finally got my 1975 Yamaha DT250B put back together after it failing on me many times in the past.. added some go-fast parts to it..

Rebuilt the top end with Webco head, wiseco piston, boyesen reeds. - Mikuni Flat slide carb conversion (VM28 -> TM28) and an open Uni 2-stage filter. Ran 93 oct. (always sunoco just for the fact different brand gas may run different..)

I ran out of gas at the trail, used regular 87, seemed to run fine, but I had 2 very noticeable problems which f'd the rest of my day up..

First the plug shit out.. I pulled it, black and oily. But- not to the point where it would foul. It had ran fine with that plug for two weekends on "moderate driving".

If I kicked it, it made a sound like when your lawn mower goes over a tree branch..

Right now I think its the woodruff key that split- which has happened a couple times in the past (often) - I think its because I used cheap gas. Need some advice! I just put it together!

Should I retard the timing or do you guys think it was a timing issue with the cheap gas?

BTW, since the top end swap and new carb, I'm running a B6ES (B8 is stock) and the plug is a dry charcoal color if I pull it after running. (on 93 oct.)

So heres what it could be from my perception:

Oil Metering pump too rich?
Carb too rich?
Cheap last resort gas?

The fuel line is also running dry if I WOT for too long and I have no top end power. (Shits out around 6-6.5k when it should be around 7.5k running strong) It's a 1/4in line and it runs dry quick.
 

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Discussion Starter · #2 ·
Also,

from what I remember hearing in some vague comment in the past.. I can use a blaster or banshee cdi unit & flywheel on my DT? Anyone know if this is true or can measure the flywheel-mag size with a caliper? I'd be all set with a 12 volt light setup.
 

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KamakazieX said:
Also,

from what I remember hearing in some vague comment in the past.. I can use a blaster or banshee cdi unit & flywheel on my DT? Anyone know if this is true or can measure the flywheel-mag size with a caliper? I'd be all set with a 12 volt light setup.
it would probably take a little machinework, but I don't see why its not possible. I would think blaster would be a better candidate cause of the similar engine designs (more similarities than a shee at least) I think you should work on that, and then let me know what works, I'd love to ditch the points and condenser setup on my 74 DT250 =)
 

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i do know that a blaster stator plate and the stator plate for my 74 are very similar....you'd probably have to re-wire the whole bike, but it might be worth it...I don't know if the small lighting coil on a blaster could make enough power to run the turn signals and everything....you might play hell getting the pick-up coil timed right.....it would depend on a lot of things.
 

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Discussion Starter · #8 · (Edited)
Maybe the magnets in the flywheel are shot? Would that explain why a b6 is running rich on a raised comp. motor?


This is it:



It's decent enough.. - when it runs. -- If it's free, it ain't broke.

Well- I bought 4 woodruff keys so if I get stuck next time I got backups.
 

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Discussion Starter · #11 ·
As I suspected the woodruff key was sheared clean in half..

Anyone know how to prevent the key from breaking all the time? Is there any fix?

Eg, Lock-tite (on the woodruff key?), Over tourqing?
 

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the flywheel key shouldn't break. Sounds to me like the timing is off, or your running too low octane fuel.

my DT looks like that too, but its a brownish-coppery color.
 

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Discussion Starter · #13 · (Edited)
Also-- I was using a std. key from the hardware store and the flywheel was NOT tourqed on, more or less hand tight /w a wrench. I did run 87 oct that day as a last resort. I just hope I didn't fuck my reeds up.

I'm running 2 steps hotter on the plug on 93 oct. and its runnign a little rich, charcoal color. The top end has little power- so I'm going to play with the needle clip and see if my top end opens up. This time I'm waiting for a real OEM yamaha shaft key before I shear the flywheel.

Also Bike Bandit has some good stuff on their site to shorten the gearing, Moose front and rear sprockets (for the 75/MX250). I'm probably going to invest in those as well.
 

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bwahaha you probably have this thing running by now .
the blaster is too smal on the flywheel if i can remember its the size of the dt 125 dt 175 if that helps
if you want to swap in a cdi unit the 77 78 dt 250 will work as well as the it 250's . you can also run the mx's and the dt 360 a and dt 400 will also bolt on but i think the flywheel will be out of balance
the yz is the same but vintage yz stuff gets expensive, and hard to take the inner type flywheel of the vertex mag off the crank
i like the it's because of the headlight option , hanging out till after dark then finding the way home with moonlight aint fun
swapping in the cdi is real e=z .
grab ahold of the compete wire from cdi box down to stator . then the only 2 wires in the cdi to whole harness needed is the orange coil wire and the black white stripe wich is the kill to ground .
getting my dt3 ratbike timed was a pain . and my 71 .. but usually they were pretty dam relaible except for getting em wet. points dt's dont run in the rain .
tip seal the heck out of everything and keep the coil dry.
look on ebay sometimes this time of the year you can get a bottom end with electrics .
if you get the important stator flywheel a blaster cdi should work
also if using cdi swapp in a yamaha coil for cdi . a banshee is supposed to work on dual spoarkplug heads . i have 2 from yamaha snow mobiles 1 wire 2 coil outs will try this myself
hope it helps
 

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i gave up on my 74 ts250 for like 100$ profit . i have a 78 185 ts and foor a profit i will give that up too.
now about my yamaha's , better fill out the mortgage papers!
 

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Discussion Starter · #18 ·
nuff said - i did figure it out, used oem yama mama key, bout 5, used 93, dropped 10 on the main, plug looks cleaner than my cars!!! cant ride it as of now, winter...

sooooo sexy now... ooooohhhhh.. :-D hahaha..
 

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i do know that a blaster stator plate and the stator plate for my 74 are very similar....you'd probably have to re-wire the whole bike, but it might be worth it...I don't know if the small lighting coil on a blaster could make enough power to run the turn signals and everything....you might play hell getting the pick-up coil timed right.....it would depend on a lot of things.
I'm new on hear 100% fact a banshee clutch arm oil seal for clutch push arm fits 75 dt250 so banshee parts are very close to these machines I believe I would love to know about stator my self if it fits the dt and banshee that should save some $$$ cause the dt250 parts are crazy expensive for stator banshee parts are cheap and lot more aftermarket options out there.
 
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