carb help please

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Steveshipley
Posts: 69
Joined: Mon Apr 01, 2013 9:07 pm
Main scooter: Sx150
Contact:

MBRT195 MB CLUBMAN 30mm delorto no filter.
timing 17 degrees.
40 slide
128 main
70 choke
55pilot
Av264
X13 2.5 clip
air screw 2.5 turns

runs great on half to full throttle, but really boggy low down. struggling a bit now. any suggestions gratefully rec'd

Cheers Steve
Daggs
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Posts: 776
Joined: Wed Jan 07, 2009 1:23 pm
Location: Addington Kent
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You need to look at your pilot jetting area.
Maybe a 50 pilot, which should allow you to reset the air mix screw to about 1.5 turns.
You don't mention what effect the choke has ................
You could fit a gauze filter which would help low speed running. But of course it may well affect mid and high.
Avantone
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Posts: 297
Joined: Wed Jan 07, 2009 7:41 am
Main scooter: Lambretta GP
Location: Bromley, Kent
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Check the float height if you haven’t already as quick and zero cost.

If it’s wrong, once corrected, check the needle height and main jet size as these might have been adjusted to compensate.
Tony

Download the (Original) Lambretta Gearbox Visualiser
www.lambrettagearbox.com
Daggs
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Joined: Wed Jan 07, 2009 1:23 pm
Location: Addington Kent
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The Main jet is irrelevant to low down running.
Avantone
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Posts: 297
Joined: Wed Jan 07, 2009 7:41 am
Main scooter: Lambretta GP
Location: Bromley, Kent
Contact:

Daggs wrote: Sun Jun 10, 2018 9:23 pm The Main jet is irrelevant to low down running.
They overlap.

Image
Tony

Download the (Original) Lambretta Gearbox Visualiser
www.lambrettagearbox.com
Daggs
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Posts: 776
Joined: Wed Jan 07, 2009 1:23 pm
Location: Addington Kent
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Hi Tony.

When someone is clearly having some difficulty in accurately jetting' the carb. on his scooter, as is 'Steveshipley' I feel it's best to advise treating the 'low' 'med' 'high' areas of the carb. separately.

As your chart shows, the main jet plays no role until quarter throttle and only a tiny role between quarter and three-quarter, effectively irrelevant.

I take this approach to try and avoid confusing anyone asking 'jetting' questions. So often on forums such as this, posters offer all sorts of advice, veering into 'is the exhaust the right one, perhaps the gearing is wrong, maybe you've bought dodgy fuel and so on.

When I first began to teach myself 'jetting' I stuck to the three areas method and have had plenty of success (often over a frustratingly long time, but I got there)

Sorry for the lecture and I'm really not having a dig at you. But simplicity is the key to helping someone in 'Steveshipley's' position.
Steveshipley
Posts: 69
Joined: Mon Apr 01, 2013 9:07 pm
Main scooter: Sx150
Contact:

thanks chaps, great help as ever. 52 pilot and air screw 1.5 turns made a difference. happy now.
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