Won`t start with air filter fitted??

[#1GP200]

Evening All
Helping a friend to get scooter back on road.
Standard GP/SX 200 engine
Old style performance pipe (origin unknown)
20mm SH carb
Problems are, with no air filter fitted it runs fine until you get to 50mph when it will cut out unless you
quickly turn the choke on.
When you `blip` the throttle with the filter removed there`s a cloud of petrol coming out of the carb
Tried fitting standard air filter and scoot doesn`t want to start.
Stripped carb, found small blockage in atomiser. re-fitted carb and same symptoms.
From memory i think all the jets are the correct size but can`t remember what size the main jet is.
Could it be too small a main jet? Any other ideas?

[#1GP200]

Anyone have any ideas??
Thinking too small a main jet (fuel starvation?) may be the cause of scoot
cutting out at 50mph???

[lifes a drag]

i think a bit more info is needed,
1, has the scooter been re built
2, if not did it run ok before you are trying now / how long ago did it run ok
3, dont worry about the cloud of fuel , lots do it
if it ran ok with filter before make sure the air intake under seat is not blocked ,,, seen that with cloth to clean scooter sucked in,,
The main jet starts to work at 3/4 to full throttle so does it cut out in all the gears or just in top at 50 mph ,
Try a new or bigger jet as even jets that look clean can be at fault,, try new fuel and clean the filter in tank,
Hope someone gives you more help than i can but its hard to diagnose something without seeing it ,,,,



Good luck

[WINTERMODEL150]

Hi,the jets in the 20mm sh1 carb you're using should be as follows,

slide..5914
atomizer..5899/2
main jet 103-110 according to exhaust
pilot..48
starter jet 50
float 5 grams
idle screw should be fully screwed in clockwise then turned out half a turn

Always put the biggest main jet in first then come down 1 size at a time untill the bike runs clean on full throttle.

Hope this helps.

Dean

[#1GP200]

Cheers for replies,
Scoot only cuts out at 50mph so am suspecting a too small main jet.
Cheers wintermodel, will re-check rest of jets etc.
Still puzzled why it wont run or even start with the air filter fitted.
Still, it wouldn`t be a lambretta if you weren`t looking at it scratching your head from time to time

[WINTERMODEL150]

Hi,it sounds too rich if it wont run with the air filter connected,(check the choke operation)if it was weak then it would heat seize at 50 mph.
keep us all updated with the progress.

Dean