What's your cylinder head temperature?

If its below 300, you are ok. While 275 is higher than what I run mine, if you use a touch of castor (20% castor oil in your mix), you will never have to worry about temperature related engine failure.

I been googling to see the relation of altitude to engine temp differentials. Keep finding other subjects. I would be interesting to know how altitude effects temps.

Note I not talking about jetting. Re-jetting a motor for altitude is a given. It would be nice to see a generic chart of a given properly tuned motor at different altitudes.

Re: What's you cylinder head temperature?

biknut said:

My guess is high altitude would result is slightly lower temperature, mainly because of less hp. It might be kind of hard to tell how much though, because the ambient temperature would need to be the same too.

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I am thinking less dense air might have much less cooling properties. Water boils sooner food cooks different. Thing is while I never measured my china temp officially. I am getting higher head temps on my Morini.

That of course is a given its not the same motor but I have heard reports that they might be running cooler in So Cal at sea level dunno? I got one report of 260? I keep juggling this figure of 30% percent into my thinking.

I just put a 21mm carb on my 9.4 and a good hard run might go any where from 290 to 350 at night here ambient temp about 89. These are constant real time readings from my The temp fluctuates a lot at different speeds gas on gas off. I have never experienced any drivabiltity issues always ran great! I watch the temp a lot and have a LED alarm set.

Today at high noon I looked down and saw my blue smoke coming out of my exhaust so I mean I know I am not lean because full throttle will 4 stroke and my idle is rich red line is 3/4 throttle. When it idles and I rev it blue smoke.

390 is kinda the cut off point to me me thinks. 390 has pretty much been the hottest I ever saw it . When my jetting was wrong once when I first got it I saw it jumped just past 400 I just shut it down for a few.

June heat wave was ruff I ran the carby fairly rich but faired off nicely engine seams to have more power now than ever. I did some really longs runs temp was pretty stable and I never gave the motor a break. I can slow down by 10 miles an hour and see the temp drop right away. I have been clean across town in the heat wave at red line. To be fair about my report I am a big ogre sized 6' lumber jack guy. Motor had no easy task even with all manner of my cargo but did not ever complain.

This being my second Morini my old one still doing great. They have exceeded anything I have yet to see from previous china 2 smokes I have encountered. I have yet to wear one out. One motor with over 2000 miles miles the old M has 3500 miles . Still stronger and faster than previous Chinas were new to me.

thatsdax said:

Hi.. Ideal Running Temp measured at cylinder head is 375-385 degrees F. 410F is too high and will burn the motor up. Exhaust temp 1175 to 1185 is ideal. Measure 3.5 inches from Ring of exhaust port. Measure Exhaust Temp first, follow up by Cylinder head measurement. These are optimum parameters taken from Rotax 2 stroke motors using synthetic 2 stroke oil. Since our 2 stroke Bicycle Assist motors have such low compression, my Guess is that they run with less heat than the ideals I have posted. Enjoy the ride...

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I can make mine run cooler but I hotrod it constantly/relentlessly with no remorse have not broke it yet or the last M

Just measured the other day after a 5 mile ride using a Traxxas nitro rc gauge. It's got a thermal sensitive diode on a wire that you wrap around the head. Seems pretty accurate because I measured my body temp at 98.6 .


Temp was 260 degrees when I stopped to check it. Ambient temp was about 68.

Well I played for ever with my 21mm del carb . Got some gains in power here at 6000 foot. Took just one .005 shim out of my Centrifugal clutch from the stock configuration droping stall about 800 rpm's . Runs flawless late at night around about mebbe 2 seconds slower for a start to finish to full speed on a straight away. Night temp about 70 F. its a champ.

Here in the day today read at 101 F. outside ambient temp from my on board temp gauge and red lined clear across town got 316 F max motor temp but power is diminished on the big carb with changes in air density.

I fine tuned for fall season weather. July tuning would be a tad different but not by much with my currant configuration.. That would adversely effect temp too tho.

Id like to say in short all this tuning I have been doing is for absolute power. Moderation changes everything. I even have a barometric weather/temp gauge on my back porch. Just need The Barometric gauge on the bike too. lol

I ran a 19mm Dellorto phbg all summer. on the S6S air cooled I am referring to.

biknut said:

I found out some of my temp reading weren't as accurate as it could have been. I was pulling up to the garage and parking, and then getting the thermometer. I never saw over 275 degrees that way, but the other night I took the thermometer with me on a ride. While riding down the street at a little less than wfo I was seeing about 315-320 degrees near the plug. The OA was about 96 degrees. Later the same night, at cruising speed I was seeing about 275 degrees.

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Getting a constant read out from my computer unit I see it fluctuate quite a lot it has been very interesting to watch things like driving speed on the cooling etc. That tool has been the most fun interesting tool for checking my tuning I ever played with.

This is a fairly old thread but I was wondering if I can get any more input on cylinder head temps. I have the "trail tech vapor" combo that has spark plug temp sensor ring. At about 76 degrees ambient, I am running between 275 and 350 degrees(depending on how hard I am running it). On a long pull up a hill with a 40 tooth gear, it maxed out at 434 degrees. I guess my question or would like to have input on is...is anybody else seeing those kinds of temps. The engine runs fine at those temps, the plug reading is good, and oh by the way I am running the SHA 16.16 Dellorto carb. The temps I am stating here assumes the Vapor reading is fairly accurate. Any input would be appreciated but not sure what else I would do to get the temps down other than go rich on the carb and have it four stroking any running crappy.

I think these engines just like to run hot. I've never had a problem with it running at those types of temperatures. Just make sure you have good two-stroke oil made for high-temperature applications, none of that outboard stuff. Also, if you use Amsoil do not use HP Injector. It's made for outboards and liquid cooled snowmobiles. I recently read on Amsoil's website that they do not recommend it for air-cooled small engines for that reason, as the oil breaks down or becomes too thin at those temperatures. The best is Saber or Dominator (my dad carries Amsoil at his snowmobile garage so I have to know these things).

Thanks for the replies. Its about 88-90 degrees ambient around here now(Pennsylvainia) and the temps are holding pretty steady at the same range so its not like they are going up when the ambient goes up. Thanks again!

You can alter your head (and engine) temp significantly by changing to a hotter or colder plug, too.

When I ran HTs, I'd run a "5" or "6" in the winter and a "7" in the summer. I found running a "5" or "6" in a typically humid North Dakota summer (800ft elevation) would lead to a really hot engine after a half hour. A "7" worked out much better.

I saw the same thing with my Huasheng. The stock plug is a "5" and my engine ran pretty dang warm here in Cali with it. With a "7", it's about perfect.

Ya know, I was thinking the same thing but on another subject area I asked whether a colder plug would help the engines run cooler and the response I got from one of the senior members was that it would not make any difference. I am running the expensive "irridium" bpr6hix plug. I'm thinking I am going to get a 7 and try it...why not. Thanks for the reply!