YZ250 Blaster Build Log

best · Jun 29, 2015

Tbrock77 said:
I'm looking into my options right now, the YZ is going to take a lot to rebuild. I do have a LT250R motor that's ready to go, I was trying to keep it in the yamaha family and I'm not sure how easily the lt motor would fit in the quad.

as for the radiator, I would like to mount it up front for simplicity reasons and the added airflow never hurt anyone.

Unfortunately the low front position is prone to sticks and rocks, as well as affecting the "nimbleness" of the Blaster by increasing the polar moment of inertia. I did find this high position on mine quite easy to mount (thanks to YZ Otis brain work) and the air flow is excellent. No overheating problems.

Asleep at the seat, or "The Old Man and the Quad":

Almost 50hp and only 300 lbs, I won't be at the back of this pack for long.
This quad is a real "Sit down, shut up and hang on!"
My only wish is for more gear ratio. More gears, wider ratios.

Steve

best · Jun 29, 2015

Tbrock77 said:
I'm looking into my options right now, the YZ is going to take a lot to rebuild. I do have a LT250R motor that's ready to go, I was trying to keep it in the yamaha family and I'm not sure how easily the lt motor would fit in the quad.

as for the radiator, I would like to mount it up front for simplicity reasons and the added airflow never hurt anyone.

Unfortunately the low front position is prone to sticks and rocks, as well as affecting the "nimbleness" of the Blaster by increasing the polar moment of inertia. I did find this high position on mine quite easy to mount (thanks to YZ Otis brain work) and the air flow is excellent. No overheating problems.

Asleep at the seat, or "The Old Man and the Quad":

Almost 50hp and only 300 lbs, I won't be at the back of this pack for long.
This quad is a real "Sit down, shut up and hang on!"
My only wish is for more gear ratio. More gears, wider ratios.

Steve

harley1-5 · Jun 29, 2015

what year lt250r engine?

Tbrock77 · Jun 29, 2015

harley1-5 said:
what year lt250r engine?

90 I do believe.

As for the radiator being prone to sticks and such, I think the bumper will block almost all of it, and it's simple to avoid slamming my front end through a bunch of sticks haha. As for the interia, yes it will change the center of gravity, but with as much power the motor will make, I want some forward weight so it isn't trying to pick itself up all the time. I do plan on putting some extended a arms and an extended swing arm to balance the power with handling performance.

Larry's Shee · Jun 29, 2015

Ya, that 87 might not be worth using. Keep an eye out for a WR250 or WR500

(WR = wide ratio)

YZ Otis · Jun 29, 2015

I understand you're set on the bumper radiator but I'll make a few comments anyway

I ride trails through woods & brush .. we're always pullin sticks out of the front suspension .. sounds like that won't be an issue for you.
Whatever water cooled engine you choose, as "Larry's Shee" has pointed out, the low radiator is a factor .. years ago I ran these old YZ's in Outlaw Karts with the radiator lower than the cylinder to maintain the lowest possible CG .. I melted a few top ends in the process .. I could tip the kart up on end so the radiator cap was the highest point in the system to "burp" it .. this usually worked but I only found out when it didn't in the early laps of the main .. on your 87 coolant enters & exits through the head, 88 & up the coolant enters at the water pump, travels through the case, up around the cylinder and exits out the head .. the 87 may be a little safer .. I don't know .. I do know the bubbles will hide in the head and a vapor lock there will disappoint you .. I tried to improve my odds with a short clear tube from the head to an elbow containing my temp sending unit (picture) .. figured if I could see the green coolant I was good to go .. unfortunately if trapped bubbles are knocked free from around the system while your attention is focused on driving they will likely gather un-noticed in the head ;(
That's just my experience .. I believe just about everything can be overcome with a bit of creativity with the possible exception of the gearing.
Regardless of the little problems these things are intense when they run and I don't regret my build which continues to this day

BTW .. I own a Predator and that's the radiator I would use if I did it again

~
red arrow = view tube
green arrow = diy temp sensor/elbow

Tbrock77 · Jun 29, 2015

I plan on running the motor for a few minutes with the radiator raised above the engine, shaking the engine to make sure I get the air bubbles out, and I will run an overflow bottle. As long as the system is completely sealed no air should be able to make it's way into the loop after that but you may have a point... The unlimited all stars karts are starting to run these 250 motors and most have their radiators a little below their motors and I haven't heard anyone complain of frying a motor yet... if air was too get caught it would either be in the head or the hose running from the head to the radiator, I'll have to look at the head and see if there's any stops it could get stuck, once it made it to the hose it would most likely be forced through.

this project is gonna get put on the back burner until I can figure out what I want to do motor wise, the lt250r motor makes 10 less horsepower than the yz does but probably has better gear ratios, I'd prefer not to run that though, I have 2 yz motors, both need a rebuild, the 87 and a 93. The 93 needs a new cylinder too. I'm not really sure what I'm going to do yet. any suggestions?

Tbrock77 · Jun 30, 2015

Had a set of raptor 250, maybe 350 plastics laying around and had to get them out of the way, not bad huh?

harley1-5 · Jun 30, 2015

not bad at all

Tbrock77 · Jun 30, 2015

harley1-5 said:
not bad at all

Not gonna actually use that though. Might be an idea for someone else?

harley1-5 · Jul 1, 2015

if you use that plastic might be able to tuck a rad in there

Tbrock77 · Jul 1, 2015

harley1-5 said:
if you use that plastic might be able to tuck a rad in there

It doesn't fit too well on there.

reckless · Jul 2, 2015

I used yzf450 panels to hide rads and because the look better than a blaster panel.

Mine are mounted under front archs no a single issue with any kind

Tbrock77 · Jul 2, 2015

Made a decision... Currently waiting for a 1990 yz250 motor to make its way here.

As for the radiator mounting, I'm not set in stone on the front mount, I would like to do it, but if it's going to cause air bubble issues then I will relocated it to behind the steering stem. I'm going to mount the engine and craft the pipe before I decide where I'll mount it and I'll do some research on radiators mounted below the engine in the meantime.

best · Jul 2, 2015

Hard to get a one piece pipe in and out of the frame. I slide a couple header couplers up the pipe for size, then cut the pipe and welded them on:

This made it easy to rotate the pipe for better fit and to split it for easy installation and removal.

Lengths are important. Small alterations in length will alter the performance of the pipe.

Steve

Tbrock77 · Jul 3, 2015

I'm going to try to mimic the blaster pipe with a 250 pipe I have. I have already looked it over and it looks like I should just have to make a few rotations at the weld seems to get it to work. I will have to make up one section of the pipe but I have already done he math to insure that I do not effect the volume (within reason) I want the pipe to come in and out with no issue and to mate with a stock style blaster silencer.

YZ Otis · Jul 3, 2015

might want to start looking for something like this
http://www.ebay.com/itm/1990-Yamaha...423-/301604897531?hash=item46390d82fb&vxp=mtr

Tbrock77 · Jul 3, 2015

Otis I could kiss you!

I had almost forgotten that I can run a lighting coil with this newer motor. With my light set up I'm pretty sure I would still have to use a battery but if anyone knows roughly how many watts one of those stators makes I'd really like to know.

Herpderplol · Jul 3, 2015

http://www.regulatorrectifier.com/catalog/19891996-Yamaha-WR250-WR-250-Lighting-Stator-Coil

doesnt say output amount but it says higher output

with LED lights it would be best to have a rectifier and a battery to run the lights smoothly.

Tbrock77 · Jul 3, 2015

Herpderplol said:
http://www.regulatorrectifier.com/catalog/19891996-Yamaha-WR250-WR-250-Lighting-Stator-Coil

doesnt say output amount but it says higher output

with LED lights it would be best to have a rectifier and a battery to run the lights smoothly.

I was figuring on running a battery anyway so if I could set it up to charge the battery while running that would be a big bonus, I'll work on a wiring diagram tonight and post it for critiquing.

YZ250 Blaster Build Log

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