Modern Vespa

Greetings:

I've had a few rides since the deletion of the intake Snake pipe. Turns out this item was much more restrictive than it appeared. Furthermore, evidently Punkin was running rather rich, as I suspected. because opening up the air intake by that few square centimeters, plus losing the double-curve in the pipe increased performance tangibly.

Quick throttle increases WITH the pipe were met with one or two "stutters" where engine RPM increased but stumbled disturbingly - especially when a quick pick-up was needed to dash across or merge into traffic. Harley riders talked about "carb farts" with too LEAN of a pilot, but apparently non-combustible mixture causes the same symptom when the mix is too RICH as well. Anyway that symptom is totally GONE now!


were you running with the db killer off and is there a perf. difference ? thanks

There's still an occasional chuff - sometimes 2 - when the throttle is cut rapidly, but not the loud semi-backfires I was getting with the intake pipe installed. At least for this hot Texas summer, the 80 main seems to be OK. When it gets cooler - C'mon, Cold Front! - I may check the spark plug and consider that 82 again.

It would appear that this deletion is the remedy for the non-linear carburetion I and others have reported with the 78cc/Malossi cam upgrades. One issue; it's considerably louder on the intake side. Small price to pay or Big Bonus?

Greetings:

Since uncorking the Technigas exhaust - removing the aluminum end-cap restrictor - my little Vespa had acquired a case of the BackFires - one or two sharp "POPs" whenever the throttle was cut suddenly. I have posted that a larger Pilot cured Harley-Davidsons of similar off-throttle backfires, and hoped that the Vespa 4-valve 50/78 would respond similarly.

I was mistaken. I had a collection of Pilots from a Polini carb that was once fitted to my Honda Elite 50/72, but my smallest was a 39. Meh, why not try it?

Well, it sucked, to make a long story shorter. Not only did the backfires WORSEN, but starting, idle stability, and throttle response all suffered. Back to the drawing board...

I reinstalled the stock "35S" pilot, and increased the Main from 78 to 82. Whoa! No more flatulence, and SoPD* said top end improved considerably. I plan a top speed run tomorrow and will post results.

*Seat of the Pantaloons Dynamometer*

Greetings:

Didn't change the noise all that much as I recall. I ended up drilling it out a little bigger, perhaps to 1/2". Improved but didn't eliminate the backfires altogether. I never did figure out what the problem was and eventually changed the pipe to a TecNo.

Greetings:

Gauging "performance" on a 50 or 78cc scooter is challenging! SoPD (Seat o' the Pants Dynamometer) isn't all that sensitive when the Thrill of Lightspeed Acceleration changes only by a few nanoseconds to 30, 40 or 50 MPH. Without instrumented testing or measured time-to-distance trials, determining the performance gains of uncorking the Technigas pipe cannot be ascertained. More practical issues, like controlling Backfires was my focus. I will admit that the installation of the 78cc cylinder and cam absolutely TRANSFORMED Punkin from a 39MPH roadblock to a scooter I can actually ride safely around town. SoPD is PLENTY sensitive enough to feel that difference. Same goes for the 187cc kit on ISO.