Forum -> General Discussion
Search Topic
Decel pop/backfire Advice needed.
OP
@driller avatar
Driller
UTC
Hooked
Scarabeo 150, SC 250, 2t Stella
Joined: UTC
Posts: 166
Location: Tryon NC
 
Driller
Hooked
@driller avatar
Scarabeo 150, SC 250, 2t Stella
Joined: UTC
Posts: 166
Location: Tryon NC
UTC quote
The "BlowFly" project is nearing completion. The Fly 150 has been converted to 200cc with a Piaggio jug and a PM Tuning Pipe installed.
No changes to jetting or intake.
On the initial 10 mile run to check that we had everything back in order a lot of popping/backfire occurred when rolling off the throttle from 20mph down.
Bike runs smoothly and accelerates well other than that.
What suggestions would those with experience installing BBKits on the Leader 150 engines make?
Main jet increase?
Idle jet mixture adjustment?
Idle jet increase?
Thanks!
flyangler
UTC
Molto Verboso
portofino green GTV 300
Joined: UTC
Posts: 1413
Location: w.ma. Northampton
 
flyangler
Molto Verboso
portofino green GTV 300
Joined: UTC
Posts: 1413
Location: w.ma. Northampton
UTC quote
It sounds like you have a lean backfire , you may want to reconsider that rejet.
@web-tech avatar
WEB-Tech
UTC
Veni, Vidi, Posti
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8954
Location: Ashburn, Va. Home to the Internet
 
WEB-Tech
Veni, Vidi, Posti
@web-tech avatar
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8954
Location: Ashburn, Va. Home to the Internet
UTC quote
Ride a little more then look at the plugs.
OP
@driller avatar
Driller
UTC
Hooked
Scarabeo 150, SC 250, 2t Stella
Joined: UTC
Posts: 166
Location: Tryon NC
 
Driller
Hooked
@driller avatar
Scarabeo 150, SC 250, 2t Stella
Joined: UTC
Posts: 166
Location: Tryon NC
UTC quote
Moving Forward
Thanks for the replies.

From what I could find, the Liberty 200 has a 27mm CVK Kehein carb.
Main is 80 and pilot is 35. Idle screw out 2 turns.
Thought it interesting that for the Liberty 125 the main is listed as 82 and pilot 42 with 2.5 turns on idle screw. Don't think I got the numbers reversed.

The Fly is listed as having a 26mm CVEK Kehein carb.
Main 82 and pilot 35 with 1.75 turns on idle screw.
Pretty sure the ports on the head and valve size are the same on both bikes.
Guess we will go up some on the main first after checking the plug (perfect on stock set up) and idle screw adjustment.
Post Reply
Forum -> General Discussion

Modern Vespa is the premier site for modern Vespa and Piaggio scooters. Vespa GTS300, GTS250, GTV, GT200, LX150, LXS, ET4, ET2, MP3, Fuoco, Elettrica and more.

Modern Vespa is made possible by our generous supporters.

Buy Me A Coffee
 
Shop on Amazon with Modern Vespa

Modern Vespa is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com

All Content Copyright 2005-2025 by Modern Vespa.
All Rights Reserved.

[ Time: 0.0100s ][ Queries: 3 (0.0036s) ][ live ][ 335 ][ ThingOne ]