Cylinder head temps

[Duke]

So I have about 130 miles on my Malossi cast/ Aero 50. It is running pretty good, not fouling plugs at the moment. I took a long ride on it the other day and was really pushing it, passing cars with ease The highest temp I saw was around 370f and I backed right off when I saw that. So what is a general guide to safe operating temps with a BBK? (19mm arreche and LVsp3)

[Wheelman-111]

Greetings:

All my Italian bores have tolerated temps approaching 400, but definitely borrowed time above that.

[maddog]

you want the malossi 8 to1 gear ratio, a high speed cooling fan and a #9ngk plug.

[Duke]

What is a 'high speed cooling fan' and where can I get one? And what about the temps? We are approaching summer here in central TX and the ambient temps will soon be 100's... I really want to keep this bore in its 'happy' range!

[Wheelman-111]

Greetings:

It goes against every shred of intuition I have, but the hot ambient temperatures are not an issue. What you want to watch out for is the sudden COLD snaps. Let me explain:

Air-cooled engines operate at a temperature so much higher than ambient air temperature that there is almost no difference between 75 degrees and 105 degrees ambient when that air blows over a 300+ Degree engine. However there IS a difference in the O2 density of that air being sucked into the carb. Colder air makes the engine run much LEANER, and results in significantly higher operating temperatures in the combustion chamber. Consequently, hot ambient air is actually going to make your engine run cooler - at least a little bit - than riding on colder days. If you're jetted for "summer" and the weather suddenly gets colder, you may find your temps go UP, not down. Weird huh?

[Duke]

That makes sense, Wheelman. So if I think I am still running a bit rich , that condition might improve... I have a range of jets on order as well as a leaner needle for my Arreche , hopefully I can get this thing running perfect. Yesterday it started giving me trouble again, misfiring and even a farty backfire at 30 something mph (part throttle) It seemed to clear its throat pretty quick, I keep thinking its getting some buildup on the plug then burning it back off.

[Wheelman-111]

Greetings:

What does the spark plug color tell us?
Do you have a CHT Gauge? Keep it above 300 or the plug about "cardboard" and it should be fine.

If it's really too rich now, it'll be worse in hot weather. Remember warmer air is thinner and contains less O2. Less O2 to burn about the same amount of fuel makes it richer still. Temperature, humidity, and altitude all have some effect on the mixture. Not a big deal for stock-ish output engines, but it gets to be an issue with modified mills. The tighter an engine is wound, the more critical the jetting becomes.

Last year found I needed to jet down that Flash 3.26 Corsa that ran fine all winter when summer came to Deepinnaharta. You can even tell the difference in engine performance between the cool (low 60s) morning commute and the warm (high 80s) evening one.

Wish these things had a screw-adjustable main like the old Tillotsons on snowmobiles. Less hassle than dropping a bowl and cleaning up my dress shoes...

[maddog]

cold fuel + cold air intake, thats what made the musclecars of 70's, rig up a cool can-fill it with ice and see fast you can go