engine exploding?



You've never seen a piston with a hole melted through it? It only takes a short run with a mixture that is too lean to melt a piston dome.

No matter how much oil you use in the mixture.

Ultralight aircraft have an EGT (exhaust gas temp.) gauge to monitor the internal temps. When running WOT at take off, they run somewhere around 950-1000 degree F. At cruise, they run around 1000 1050 degrees. A very short run at 1300 (due to a lean mixture) will result in a holed piston, or at least melted ring lands, which in turn causes high heart rate, loud explatives from the pilot, and most times, other damage to the aircraft.

What I'm trying to say in laymans terms is-
"If you run downhill, wide open, engine screaming, long enough, expect the worst."

ie "asking for a meltdown".


Active Member
Nov 4, 2006
also...on kinda an opposite thought. you probably shouldn't get off the throttle completely on a long downhill with the clutch engaged. your engine will still be spinning fast with very little fuel/lube running thru it.
anybody have any thoughts about this?


You are coorect sir!

With any two stroke running pre-mix, one should always open the throttle slightly every couple of seconds while on a long downhill run.


Thanks for the info regarding the term meltdown. I agree that running lean or low on oil can cause this problem. I'm not sure if meltdown will occur at full throttle on a downhill assuming mixture was correctly set in the first place.

The type about blipping the throttle on a long downhill is pretty good to ensure that the internals are getting enough fuel mixture (which contains the precious lifeblood called 2 stroke oil mixed in with it).

I run EGT gauges on both of my turbocharged vehicles. My EGT is higher at lower rpms when load is very high and engine is straining to maintain speed or to accelerate. It is a little lower when acclerating hard at high rpms at full throttle and full boost.

If someone has an infrared temp guage, they should check their cylinder head temp(right next to spark plug). You should strive for a max temp range between 250-275 deg F. Any higher would shortern engine life and lower is usually better.
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