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Thermostat? YZ250....

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I've noticed after getting the head squish done ,my YZ250 runs much cooler.And the vent tube always has a few drops of clear condensation.I dont remember this happening before..

I went to a place to get my jetting right and was watching the coolant temp and even on long uphill pulls, on the pipe riding, coolant between head and radiator wouldnt go over 145* (3800'-60*F). most of the time the temp is lower.. So when I get into the woods where the pace is slower I wonder if people use a Thermostat to get a better burn?..  Squished head, About 200 PSI compression,Slide cut to #8, NECJ needle clip3 168m ,45P 100 octane Sunoco-amsiol interceptor @32-1> this jetting is where it runs the best so far.. I also run a Qstealth so I know they spooge more than other sparkys.

 

So anyone use a Thermostat? does it help? which one and where do you put it?

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Try running BP7 NGK, I run woods and often struggled with a motor that ran too cool. The BP7 drives the heat in deeper and works nice for me. I run interceptor at 50 to 1 and that seems to still get plenty of oil. Also make sure your jetting is not too rich.

Edited by Kinger317

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Try running BP7 NGK, I run woods and often struggled with a motor that ran too cool. The BP7 drives the heat in deeper and works nice for me. I run interceptor at 50 to 1 and that seems to still get plenty of oil. Also make sure your jetting is not too rich.

Thanks, I'll keep the hotter plug in mind.... I bought a in-line thermostat from a KTM two stroke on E bay, it opens at 150*F.I'm going to put it in the hose going from the head to the left radiator. Hope thats the right place to put it!!!.  I'll report the results....

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I had major issues until I fixed the squish. I could a foul plug every time I slowed down, even with lean settings.

I'm running a projected nose 5. Yes a 5. No knocking, pinging or any problems. My son rode off with the choke on last year. The bike stopped and wouldn't crank. The plug was fine. Turned the choke off and cranked right up.

I don't think the 5 is needed now but I'm using what I have.

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My yz250 had a 5 installed in it when I bought it, never had any troubles running it. Did surprise me when I pulled it for the first time!

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On 20/11/2015 at 9:12 AM, Snider said:

I bought a in-line thermostat from a KTM two stroke on E bay, it opens at 150*F. I'm going to put it in the hose going from the head to the left radiator. Hope thats the right place to put it!!!.  I'll report the results....

What happened when using the inline thermostat?

If it worked, then what's the part that I should get?

Now that winter is here, I'm having problems with cold seizing. The EG 295 kit is more susceptible to it with the thinner cylinder bore metal cooling too fast by the coolant if there is lots of airflow of the rads while the piston remains hot and fat from a power burst.  I've slightly enriched the jetted to cool the piston faster, but it's not the correct solution for maximum top end life.

I will experiment with blanking parts of the radiators from too much air flow, but this inline thermostat part sounds like the perfect mod, if it is small and works.  In summer I can ride in 40C (105F) and with a little air speed the motor never cooks. Running too cold is the issue.

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Remove the left radiator? I've seen that work in applications I won't get into here!

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Thanks for the thought Kinger.

But I want a solution that is quickly and easily tuneable for the conditions or riding speed.

So either a KTM inline thermostat (in the pipe exiting the head), or else I'll make a few sets/sizes of simple plastic air blocker "plates" to insert into front of the lower radiators. Zip-tie them in place for the day or something like that.

I suppose I could very easily completely bypass the right side radiator with pipe mods, and drop a little coolant weight as a bonus, but before doing that I'd probably try a basic rubber hose inserted into the head exit pipe to reduce the internal diameter. That's a modification I could probably add/remove in a few minutes before a ride. But a radiator front air blocker plate seems better to me, since at low speeds I would retain nearer to stock cooling with no extra pump pressure at high RPMs. I want to avoid that over cool rush when I shut the throttle at speed after a power burst.

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Although some KTM riders use aftermarket hose kits to remove the thermostat unit, they are incredibly reliable and a good idea if  you fast road sections where there is a lot of airflow but the motor is just cruising and not under load. Worth a try on the YZ, let us know how it works out.

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Sounds good.   Do all late model EXC 2-strokes have them?

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6 hours ago, kiwi_rider said:

Yes, from 08' onwards on the 2 strokes at least.

Thanks.  Unfortunately KTM in Aus want AUD204 for thermo+hose parts labeled as 25 in this diagram.  So I'll try some radiator partial blocker plates first. Made some today using ice-cream container lids and about 50c spend on 8 cable-ties.

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15 hours ago, numroe said:

Thanks.  Unfortunately KTM in Aus want AUD204 for thermo+hose parts labeled as 25 in this diagram.  So I'll try some radiator partial blocker plates first. Made some today using ice-cream container lids and about 50c spend on 8 cable-ties.

Good idea. Do you have a temp gauge of some sort to evaluate how that's working or if the motor is getting too hot etc?

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17 minutes ago, kiwi_rider said:

Good idea. Do you have a temp gauge of some sort to evaluate how that's working or if the motor is getting too hot etc?

No I don't have a temp gauge. I should.

Now that winter is finally here, I've had a couple of cold seizes when coasting at pace with throttle shut. After a WOT power blast then the rush of cold coolant.  While in the earlier summer severe heat the motor coped really well. Sometimes some overflow, but it was often around 40C air temps.

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