Thursday, September 3, 2020

Additional Cooling for the Vespa PX engine

 My friend Bill installed Stella Auto cowls on his 2 stroke Stella shifty.  These are vented cowls that maintain a tasteful original look.  The Auto version of the Stella was only imported in small numbers in the United States (300 I believe) and parts are not readily available.  The claim was that additional engine cooling helped pull fresh cool air into the engine compartment to be available for the fan.  The engine does run cooler with no cowl at all, so any advantage is a plus.  Bill was seeing 15 to 20 degrees cooler cylinder head temperature.  That is an advantage I could use!

 I don't have the means to cut louvers or vents into the original cowl and make them look have decent.  The original cowl on my bike was damaged in a crash before I bought it.  The body filler and stickers make it look presentable today.  I do have a square sheet metal punch that is slightly smaller dimension than the checker tape on the lower part of the cowl.  This gave me an idea that I thought was pretty brilliant.  If I cut square holes in the center of a few of the black squares of checker tape, the holes wouldn't really be noticeable.  The additional airflow should be exactly what is needed to give the additional cooling.


The final carburetor settings after all the modifications DR177 kit, SITO+ exhaust, UNI foam air filter come out to be:

Stock 20/20 carb
40/120 idle
160 air
BE3 atomizer
106 main jet

I take the same road over Reesers Summit every Wednesday to meet up with the Three Mile Island Scooter Club.  This road run is the temperature test bed to prove if I knocked holes in the cowls for any good reason.

CHT without holes = 315 °F

CHT with holes = 306 °F


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