Very boggy quarter throttle

[sydduckett]

Have RB20 which is really boggy at quarter throttle regardless of what gear your in. it will clear and goes really well when the revs pick up but low down it's really boggy. I recently had the Augusto re-installed with a new BGM stator as the original one started to break down on the way to the dyno causing it to misfire. anyways the dyno doesn't seem to have worked so I need a rethink. details below. also I'm currently on the top clip of my U16 with a reasonable brown plug but when I move the clip down it becomes greyer the further I go?

Franspeed Race pipe
5 speed box
Ron Moss Head
B8 plug
VHSH carb
40 slide
U16 needle top clip
145 main (have tried 143' leaned off to much and didn't fix issue)
B40 pilot
60 choke
60 starter
DP 266 (have tried DQ266' to lean and didn't fix issue)
air screw half out but doesn't fix issue when adjusted)

scooter also ticks over to fast. don't think I have an air leak but plan to test this weekend

Ta
Sef

[Lambretta Sash]

Id look at carb set up if rest of engine is ok, I've used vhsh for a few years on high hp motors and never go over 130 on main jet, where did it get dyno'd ?

[dansacred]

you should be getting richer dropping the clip/raising the needle, not leaner??!

[sydduckett]

you should be getting richer dropping the clip/raising the needle, not leaner??!

Yes I know hence the question. does seem strange though. I think it may be an issue with the pilot as opposed to the main at it seems to happen at low revs but when the main comes in it clears. I did wonder if the cooler head may be an issue?

[Markpm]

Any luck with this
I have a very similar setup with similar issues
Would be interested to here if you sorted it??
I fear though this is the nature of the RB motor

[Chris in Margate]

Try setting it up with NO main jet to start with and tune in the lower throttle openings. Trust me it will run and you can then get correct pilot size and airscrew sorted first. Finish up with the main jet.
I still wonder why needle clip position has the opposite effect though.

[mick1]

I'm wondering if the RM head is working too effectively and you're running "cold". Might be worth dropping the plug to a 7 and seeing what happens.

[Muppet]

U16 why?

[sydduckett]

In the end I looked at the slide which was a 40' didn't have any 50's so got the Dremel out and it's now it's a 50. This appears to have sorted the issues out, running a lot sweeter now.

Ta Sef

[Markpm]

What did you do to the slide
I have a 40 in mine and it's really rich 1/4?throttle
50 pilot helped but I got paranoid as it seemed too sweet to be right