Sat Oct 10, 2020 2:51 pm

Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
 
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
Sat Oct 10, 2020 2:51 pm linkquote
Greetings:

Desperately seeking a size 36 N424-21 Pilot jet for ET4 ISO, I stumbled upon the answer to a mystery described Lo these many moons ago. What is the significance of the "S" behind the Size 35 Pilot Jet that came stock on the S50?

Power Barn in Wisconsin has a website that shows a side-by-side comparison of the Keihin jets. (For Honda XR650's "Secondary" carb, in this case... Yes the 600-650 singles had Two (2) carburetors. Not fun to tune.)

So the "S"-marked jets have much smaller emulsion holes in the stem of the nozzle. Evidently this was to improve fuel atomization when low-intensity of vacuum pulses were present. Mystery Solved! Not sure why Punkin's 4-valve engine had such low-intensity pulses, but that's the answer.
Wed Oct 14, 2020 8:33 am

Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
 
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
Wed Oct 14, 2020 8:33 am linkquote
S-Jet Mystery Solved
Greetings:

S50 came with this #35 pilot jet - I think there's a pic back a few months. Here's PowerBarn's comparison shot.


Emulsion holes in the stem are pretty different. Size of the Vertical/parallel hole defines the jet size.

⬆️    About 8 months elapsed between posts    ⬇️
Mon Jun 21, 2021 6:33 pm

Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
 
Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
Mon Jun 21, 2021 6:33 pm linkquote
Wheelman-111 wrote:
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?
⬆️    About 1 month elapsed between posts    ⬇️
Tue Jul 20, 2021 6:08 pm

Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
 
Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
Tue Jul 20, 2021 6:08 pm linkquote
Wheelman-111 wrote:
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*
hi! i know its a long time ago ,but would you happen to remember if you had any gain in performance by removing that db killer ,beside being more loud?

ive done it and might reinstall to eliminated back fire,hot gas will burn more slowly instead of back firing,i should have tried the pipe before removing it?
thanks for the answer!
Fri Jul 23, 2021 6:33 pm

Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
 
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
Fri Jul 23, 2021 6:33 pm linkquote
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.
Sat Jul 24, 2021 9:03 pm

Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
 
Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
Sat Jul 24, 2021 9:03 pm linkquote
Wheelman-111 wrote:
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.
Ok thanks! Was hoping you might remember if performance ( power) change after removing it
Thanks!
Sun Jul 25, 2021 5:45 am

Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
 
Addicted
2010 S50 Modified "Punkin"; 2003 ET4 Malossi 187 "ISO"
Joined: 18 Feb 2017
Posts: 732
Location: Deepinnaharta, Texas
Sun Jul 25, 2021 5:45 am linkquote
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.
Sun Jul 25, 2021 7:16 am

Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
 
Member
typhoon,pgo metro
Joined: 21 Sep 2020
Posts: 31
Location: montreal
Sun Jul 25, 2021 7:16 am linkquote
Wheelman-111 wrote:
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.
Thank you for your time!
Its my sons scooter,got the same upgrades you got except the polini high speed is replaced by a multivar,and no cdi (80 km is enough for his use).just install the gp4 exhaust,huge difference at the throttle response.
Controlling the back is my priority too,will put back the db killer,sincenthe install of the pipezrpm hangs up longer and come down slower wich is usually a case of lean mix ,ordered a new cop gasket and will check the pipe junction again.
Not easy installing this on a floored scooter,think i tighted it toobmuch last time,will redoo according to specs👍
Tx again
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