Hello All,

I'm wondering what the operating temperature range should be and what I shouldn't exceed for my 1972 DT2 250?
I drove through the streets on two separate trips for about a 10-12 mile ride and had the bike die while idling at a traffic light around mile 9/10 on both occasions. Luckily I was able to start the bike up again after several kicks.
I suspect it may be the temperature running high causing the bike to die, as I had recently cleaned the carburetor before the trips. During these trips, I found when the cylinder gets hot the idling RPM begins to fall to around 1000 and I have to tighten the idle adjustment screw to keep the idle RPM between 1300 - 1400 range, as recommended by the manual.

I just installed this temperature gauge and will be keeping an eye on the temp on my next ride.

Thanks for your help in advance!

Bit difficult to guess at that one
First thought is--does compression still feel normal on the kickstart.
Secondly is it going lean for some unknown reason & just fading away.
Thirdly is it going rich & drowning it so won't idle.
Does fuel still flow freely to the carb.
I doubt temperature has anything to do with it but i've never measured 'that' so about time i got educated i think.
I know a video isn't easy to do on the run but sure does help diagnosing things.
Others will be along soon with good ideas.

Short answer is 350-390 degrees range. If it heads for 400 stop bike NOW !  Based on your post, I would remove the cylinder head to check if you have already done any damage to the top of the piston. With your new gauge, you will see the temp will go up and down constantly, as you ride, as throttle application changes. I recently went thru this only first I burnt a hole in my DT 400 piston. After repairs a Trail Tech gauge was installed. #1 cause of excessive heat is an air leak. #2 is incorrect carb jetting. And it could be both at the same time. Most problems are caused by more than one thing. There are no hard rules to the diagnosis or the repair .It will be trail and error until you narrow down in what RPM range the problem happens , not in what gear. Start with no holes in the connectors between the carb and the cylinder and between the carb and air box. Next, a new/good air filter, properly installed. Now a few short rides. At what RPM does the temp begin to rise quickly ? Low , middle , high ? Get some info, then ask again.  I'll be looking for your next post.

I installed a Runleader temp-only gauge on my '71 CT-1, and with air temps in the mid 70's it runs around 285 F to 325 F at 50-60 MPH. A few days ago, with air temps in the low 60s, it ran about 20 degrees cooler, topping out just over 300 F. It seems to be pretty accurate, comparing it to a good IR gun. I set it to blink at 325 F, so if it spikes I'll notice quicker. I'd imagine your 250 runs a bit hotter.

CHT is a good tool...  with limitations.  Biggest one is it reacts slowly.  If you go lean or into preignition and keep on the throttle, there is a time delay for the head to heat up and show a dangerous temp. So use common sense and your other senses if you are pushing the bike hard. 

For normal riding the temps stated are a good guideline...  again with a caveat...  I have a modified 175 engine that will creep up to 450F under heavier loads (full throttle) and hot days.  It's just fine.  At El Mirage a few years ago I ran it continuous WOT for well over a mile on the dry lake keeping up with (and even passing) guys on 360's and 400's.  My GPS recorded 89 MPH... speedo was at 95.  Temp creeped up to just over 500F.  It survived just fine.  I need to say that I have a lot of experience with running air cooled two strokes in desert races with long periods of full throttle running.  Before that run I had jetted the main up to where it was too rich at full throttle and then went back down leaner until it just cleaned up... basically one size below "too rich".   

If I was cruising around town without heavy load (hill, hard acceleration, high speed) and temp was running over 400F?  I might be concerned.  Temp does depend on conditions.  I agree that between 300 and 400F CHT is a good range to stay within for normal riding. 

As said, CHT is slow.
IR gun only measures IR reflectance on the surface and is prone to angle and color.

EGT's are best. K-type 1/8".
1300°F near max. but if it is that high and drops fast.....Means detonation/pre-ign.

cliff

My IR gun, aimed at the base of the spark plug the sensor is on, reads virtually the same as the meter. The meter shows increases fairly fast when cruising at higher speeds, then begins falling at stop lights. When I start the engine, it begins climbing fairly fast, reaching 120 F or so within a minute or two. So I think it does provides a pretty good indication of what's going on.

Agreed, your 2 choices are #1 cylinder head temperature, with sensor under the spark plug ( most of these are internally powered) or #2 exhaust gas temperature with sensor probe in the exhaust pipe, at the port outlet ( most but not all of these require a12 volt source and drilling or welding) . Each with their distinct advantages. Your wallet and skill level will help you decide. Both are good choices. Double checking both with an IR "gun" is an excellent idea as most are hand held, portable, and battery powered. Both give results that will get you to the problem and the repair if you pay attetion to them.

Interesting how tech might has changed....  The (analog) EGT's I used to use way back when were powered 100% by the thermocouple.  No power source needed at all except to light it at night.  Really hard to read the small dial while racing so I used tape on the glass to easily see at a glance when the needle was approaching or had gone past max temp.

When I got into racing mini-cup cars (1/2 scale NASCAR replicas) I believe I used a digital EGT gauge that was powered by AA batteries...  I think it was something from the racing go karts?

I never really looked for an EGT recently but there's no reason I can think of that they can't make them like the small Trail Tech or Runleader CHT...  same basic device with different range thermocouple.