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

"Project Bantam" - Fan Shroud

The Briggs and Stratton 14-FB fan shroud was completely rotted through on the bottom.  Even back in the 1980's it had a patch pop-riveted to the bottom.  This repair stretched my bodywork skills (or lack thereof).

The electrolytic de-rusting process got the part down to what was left of the base metal.  It was pretty ugly.

The patch was made of comparable gauge material with the worse of the rusted sheet metal cut away.  The back plate was used to hold the correct diameter and curve of the fan shroud.  I kept it bolted in place while the patch was tacked into place using oxy-acetylene and a brazing rod.  The brazing rod wicked pleasantly into the new patch material and surprising well onto the original part.

Here's the finished part after all the brazing was completed.   Brazing was certainly a much easier option than straight welding, but still it resulted in some distortion of the sheet metal.  I ground off the excess material and hammered any distorted surfaces flat.  The Bondo stage and glazing putty is always the hardest for me.  The Bondo sets up too fast, so I have to work in small batches.  When it is sanded it always sticks to the sand paper.  The glazing putty is easier to work with since it dries harder, but only covers small areas at a time.  Altogether its not too bad considering what I had to start with.  Its by no means perfect, but I did it myself, which is what counts for me.  Its only the bottom, which is obscured when the engine is installed in the tractor anyway.  You can't see straight into the shroud for this reason as well, so imperfections will be difficult to see.

The current plan for the exhaust and muffler is to use the original.  It went through the de-rusting electrolyte tank and actually came out without any holes in it.  The EMT conduit fitting is still serviceable into the exhaust manifold elbow, so instead of risking cracking the block, I'll just keep it.  I can always make a new exhaust later if I want.  I have no idea what the stock Bantam exhaust was like.  My father fashioned the current muffler from a spent propane torch tank.  It slings neatly under the floor board and attaches to the bolt holding the transmission in place.  The nice thing about this exhaust arrangement is that it keeps the heat away from the driver.

Imp Electric Fan

The shaft driven fan on the Red Imp just wasn't moving as much air as I liked.  The advantage of the electric fan is that it moves just as much air at idle as it does when you are going down the road.  So if the car overheats, you can be assured that pulling over to cool down will actually cool adequately without MORE overheating.

Here's what I did.  I removed the stock fan and shroud along with the rubber.  I got an electric fan off an old Toyota in the junkyard.  I can't remember which model or year (sorry).  It was the same diameter as the Imp fan shroud.  I just created three clips to attach the two together.  It runs off the generator output.  This way the fan only comes on once the engine starts and doesn't steal any amps away from the starter.

Its not pretty but it works.  The air flow is from the engine compartment towards the front and under the car.