YZ250 Blaster Build Log

[79 bronco]

Is your right foot peg on the bike? There is a kicker stop that is part of the foot peg. You may be able to stop the kicker before it hits the swingarm web. What is the spline size and tooth count of the yz motor? What is the stud size where the lever slides on?

 

[Tbrock77]

The washer idea is what I'm gonna try, I measured it today. M20 washer will fit, with that it should be enough to clear it. Mocked it up yesterday, I have to make a small tube for the air filter to carburetor.

will the stock length (92 link) blaster chain be enough?

Just remembered, I did a compression test, went up to 190psi. Is it safe to run 91 octane in that?

 

[Tbrock77]

Is your right foot peg on the bike? There is a kicker stop that is part of the foot peg. You may be able to stop the kicker before it hits the swingarm web. What is the spline size and tooth count of the yz motor? What is the stud size where the lever slides on?

I'm not sure what size the spline is or what tooth count it is. I do know the blaster one does not fit, I have a blaster kicker but the screw is stripped so taking it apart isn't an option.

 

[armengcorp]

The washer idea is what I'm gonna try, I measured it today. M20 washer will fit, with that it should be enough to clear it. Mocked it up yesterday, I have to make a small tube for the air filter to carburetor.

will the stock length (92 link) blaster chain be enough?

Just remembered, I did a compression test, went up to 190psi. Is it safe to run 91 octane in that?

Good to hear spacing it out will get you the clearance you need. Were you planning on using just one washer between the boss and case? Might put the the kicker in a bind when you tighten down the cap and screw.

Yep, stock length chain will be plenty long even for 15/40 gearing.

As far as the gas is concerned, I can only give you a solid Maybe. Some run fine on pump premium, some don't. There are a ton of discussions in YZ forums on this. I mix 25/75 Sunoco purple (leaded 110)/ethonol free 91 and runs like a champ (but I'm one of thoes lucky ones to have race gas at the pump just a few miles away). Since detonation is so hard to detect in a 2 stroke, I figured its cheap insurance.

 

[Tbrock77]

I'm not so lucky, the closest 110 pump is 20-25 minutes away, but the closest 91 no ethanol pump is just down the road. Since I'm at such a low altitude (300-800ft) I can imagine I might have to run a mix, I'll look on their forum.

 

[Tbrock77]

got the carburetor and throttle cable today. The new TM carburetors are massive compared to the old ones, almost twice the size. The throttle cable is way to short, need about another 6" total length and more throw in the cable itself.

To the guys who have done this swap what cable did you use? I have a mikuni carburetor.

 

[armengcorp]

got the carburetor and throttle cable today. The new TM carburetors are massive compared to the old ones, almost twice the size. The throttle cable is way to short, need about another 6" total length and more throw in the cable itself.

To the guys who have done this swap what cable did you use? I have a mikuni carburetor.

'98 YZ has a Keihin PWM38. I used a motion pro Honda 250 R cable (so I could use a thumb throttle), but I know the Mikuni used on the 78 YZ works with the same cable. Hope that helps.

 

[Tbrock77]

How did you guys get around this?

 

[armengcorp]

Front couple of inches from YZ airbox, 2.5" O.D. aluminum tube, stock blaster airbox.

 

[best]

I went a very similar route with my KTM Blaster:

Make sure to level the carb. This above worked well, this below did not.

See! It broke the chain!

I had to flatten a frame tube to make room for my kicker:

 

[YZ Otis]

I just ground the kicker to clear .. still plenty strong (below)

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Extended shifter about an inch so it was easier with a boot. (below)
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If you don't have the YZ boot you can make one with some hardware store parts. (below)

~

 

[Tbrock77]

Third throttle cable "works" but the yfz450r thumb throttle doesn't have enough throw in it to open the carb all the way.

What's the exact set up you guys are running? Carburetor, cable and thumb throttle? I'm sick of wasting money

 

[YZ Otis]

I used a dremel to modify the stock Blaster thumb throttle for more travel .. used it on overbored 38's to a 41mm alky carb with no problems .. but I'm a low budget guy .. burp

 

[Tbrock77]

Might just switch to a full trx250r set up, PWK38, trx250r cable and thumb throttle.

 

[Tbrock77]

I used a dremel to modify the stock Blaster thumb throttle for more travel .. used it on overbored 38's to a 41mm alky carb with no problems .. but I'm a low budget guy .. burp

what throttle cable did you use?

 

[best]

Here is my carb, stock KTM 38/39mm:

My thumb throttle is stock Blaster with some work to open up the travel.
The cable is stock KTM with a 40mm spacer to take out any slack:

Had my 240 Blaster out tonight. It ain't a 250 for sure but it is still a sweet ride.
Gear ratios in the Blaster are much better (wider) than the MX gear boxes.

 

[Tbrock77]

fired it up today, I'll post a video when I get the chance. Took a bit of convincing to start, I had to crack the throttle open half way, once it started it idled perfectly. I'm thinking the pilot jet is too rich? I'm running a 45 pilot, 360 main, 2.5 turns out on the idle screw and air screw just as base settings.

Also, do I have to run a different plug using 50/50 91-110. I'm running a b8es now.

 

[Tbrock77]

 

[best]

...do I have to run a different plug using 50/50 91-110. I'm running a b8es now.

Why are you running 50/50 91-110? Just use pump premium and you are good.
My stock 2003 KTM250 makes more power than my Blaster can put to the ground.
Your YZ should be the same. Expect wheelies in every gear and lightswitch acceleration.
Keep it close to stock and you will have no problem with a BR8ES plug and stockish jetting.
Go strange on it and you'd better be prepared to be a research scientist.

 

[Tbrock77]

Why are you running 50/50 91-110? Just use pump premium and you are good.
My stock 2003 KTM250 makes more power than my Blaster can put to the ground.
Your YZ should be the same. Expect wheelies in every gear and lightswitch acceleration.
Keep it close to stock and you will have no problem with a BR8ES plug and stockish jetting.
Go strange on it and you'd better be prepared to be a research scientist.

I'm at 400ft above sea level with 190psi of compression, I've looked on other forums and a lot of people run a higher octane at the same compression to avoid pinging. Figured I'd start with a higher mix than needed and pull the head after a few hours to see if I can lower the octane some.