Hi again fellows. CT1C project going well with new clutch, and top end.
But we noticed that engine is really hot. This is concerning.
Airscrew is only 1/4 turn out
IdleScrew is almost all the way in.
50:1 gas oil
Not a lot of smoke

Any ideas?

I have a CT1C running with the oil pump. I believe the autolube varies from about 40:1 at slow speed to 16:1 at high speed. Plus I like mine with a slightly higher fuel to air ratio. Mine smokes some. I don't think 50:1 premix is enough oil.

I agree 50:1 is too light on oil.
Look at it this way, too much oil and at worse you'll foul a plug, too little and you could seize the engine.

Ok Pete and 1971DT250. Much appreciate your input. I’ll increase the oil ratio. I pulled the plug and it looked super dry and smelled “burned”. I don’t believe it’s an air leak as the crank seals are new. Perhaps an air leak vicinity of cylinder. I’ll investigate.
But I think you two are correct.

Try 32/1 and 1 1/4 turns out and see if the bike runs cooler, - better or worse. You could run it the other way ( perhaps not on the break-in of the fresh top end later ---- if you so desire to )....

Just curious on how you are determining it's running hot and under what conditions it's happening?

I run a Trailtech TTO temp gauge on all my bikes for piece of mind. Get the 14mm version that mounts under the spark plug to read head temp. I watch the temp as I ride and give it a rest if it gets up much over 325 to 335. A long pull at highway speed might see 350.
A little slow riding and idle time and they get back under 300. These are Dt400 and Rt360 bikes. I assume the smaller bikes are similar. The temp gauge costs about $50 but nice piece of mind.

The ratio of mix depends on what oil you are using. If you're using a full synthetic you'll want to get into the 40-50:1 range, especially if you're not riding WOT everywhere. If you're running a petroleum, or castor, or some other base premix then you may need to be at lower number than 40:1. If I premix Redline 2Stroke Racing, a full synthetic, I go between 45-50:1. Never had a problem in 20 years at this ratio but I'm also not a pro roadracer/MX'er.

Also...more oil in the mix = less fuel and leans out the mixture. Have to keep that in mind. That's why oil pumps are awesome.

Running hot...have you had a 2 stroke air cooled street bike before? What exactly is hot? I don't mean to be flip but everyone has an opinion of what hot is. My buddy who has a '72 360 has complained for 3 years that his pipe is too hot and has to wear jeans, and I just laugh...his bike is tuned perfect, it is what it is.

Usually...a legitimate "running hot" issue is retarded timing, lean condition, or air leak, or a combination of any of these three.

Amen to what Pedalcrazy said about the Trailtech, though I push mine to 390 with no issues. At that temp I pull over and cut the engine off. It's amazing how fast these two strokes go up and down in temp compared to even an air cooled 4 stroke like the XT225.

Always remember that the CHT will build slowly... so on an unknown set up you can blow up before the temp gauge reacts.

I don't recommend the following

On a well-tuned 175, not uncommon for me to see 400 F. 450 F I'm getting a little careful depending on throttle/load/speed... I have seen over 500 F on a well-tuned engine under full throttle, heavy load, and high speed (80+ mph in deep sand) No ill effects at all.

I have also seized engines at under 400 F. Last one happened at just over 300 F. Full throttle uphill run and suddenly went lean. I heard it before the temp gauge registered. Backed off and pulled the clutch... Trail Tech temp gauge kept climbing with bike parked. Luckily it was a soft seize and was able to ride a few miles home after letting it cool. Did need to replace the piston on that one though.