Disappointing RB20.

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
dave wheeler
registered user
Posts: 260
Joined: Fri Feb 19, 2010 5:33 pm
Contact:

Sun Jul 17, 2016 2:33 pm

it does look rather rich but also sounds rather overgeared, rb`s are rev monsters arent they?

User avatar
Donnie
registered user
Posts: 1518
Joined: Mon Jun 15, 2009 6:56 pm
Main scooter: Lambretta Eibar Series 2
Location: Bedford, UK
Contact:

Sun Jul 17, 2016 2:41 pm

Does look a bit rich but was this you just running it then checking the plug or did you do an actual plug chop and what setting was this actually at throttle wise?
Donnie.

Jonn
registered user
Posts: 57
Joined: Sun Jan 04, 2015 5:31 pm
Contact:

Sun Jul 17, 2016 5:09 pm

From Rayspeed site instructions for RB20 fitting settings.
30mm delly
slide 35
x7 needle 2nd clip from top
AV266 needle jet
main jet 140
pilot 55 to 60
float 300
choke 80
mis 2.5 to 3.5 turns out.
your plug is very rich.These settings would be on the safe side,a starting point.

10 inch Terror
registered user
Posts: 1493
Joined: Tue Jun 29, 2010 9:17 pm
Xbox live gamer tag: I'm 46 not 6!
Playstation gamer tag: PLEASE!
ebay user ID: peter-fred-welch
Main scooter: Lambretta LI Imola 185
Location: Farnborough Hampshire
Contact:

Fri Jul 22, 2016 7:30 pm

Ok, I've stripped the carb to see what's in it and found it nowhere near jetted for the RB20. It was fitted with a K21 needle rather than a U16. The main jet a 130 rather than a 170. The Pilot was a 30 rather than 55 and the choke jet a 60 not 50. The atomiser and slide were the only things that were ok. Now here comes the silly question. Would all these incorrect parts cause the symptoms I discribed in my original post? I've managed to find a website that has all the correct bits I need. I supposed the obvious answer is buy them and see? Any comments very welcome as I really want this to work. I keep hearing how good the RB20 is and I'm missing out on it. Thanks in advance Pete.

sydduckett
registered user
Posts: 2166
Joined: Wed Jan 14, 2009 12:21 am
Contact:

Fri Jul 22, 2016 8:20 pm

Ifound the best set up was 18 47 on an indian gp200 box. Re the rally pipethat may be oneof the reasons you down on power. I found that the only nk pipes that produced a power band were the mid and the race. The rally didnt, so i flogged it.

Good luck

User avatar
wack 63
registered user
Posts: 1527
Joined: Fri Nov 27, 2009 9:33 pm
Main scooter: '71 GP TS1
Location: Lincs
Contact:

Fri Jul 22, 2016 9:39 pm

...
Last edited by wack 63 on Mon Sep 05, 2016 3:43 pm, edited 1 time in total.

Adam_Winstone
registered user
Posts: 1755
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP
Contact:

Fri Jul 22, 2016 11:12 pm

Short gearing and a pipe that likes to rev, so suiting the porting of the RB kits. If you strangle the revs (cut short because the pipe becomes a rev limiter) or don't reach the revs because the gearing is too long you will stop the kit from working as intended.

Re: U16 vs K21 - Unless the K needle has been cut short, which some some dealers have done over the years, the U needle range is shorter than the K range, meaning that you cannot consider them as like for like with regard to taper length and tip diameter. The longer K needles will be far lower into the atomiser than the U needle with the same profile.

Norrie Bodge
registered user
Posts: 449
Joined: Thu Oct 25, 2012 2:49 am
Main scooter: 80-P220e/71-GP230/60-S2-Ts-230
Contact:

Sat Jul 23, 2016 12:32 am

A mate of mine had the same issue on his RB20 with 34mm flatslide & using midrange NK

He had LI-150 box wi 16x46
Changed it to 15x46 & loads better

10 inch Terror
registered user
Posts: 1493
Joined: Tue Jun 29, 2010 9:17 pm
Xbox live gamer tag: I'm 46 not 6!
Playstation gamer tag: PLEASE!
ebay user ID: peter-fred-welch
Main scooter: Lambretta LI Imola 185
Location: Farnborough Hampshire
Contact:

Sat Jul 23, 2016 7:55 am

I built the motor 2 years ago and I'm pretty sure I used a 17/47 sprocket combo. I know I was aiming for AF's recommended final drive of 4.8. To be totally honest I'm doubting myself now. I think I'll whip the side casing off today and check exactly what's in there. If I jet the carb exactly to AF's recommendation and ensure the gearing is correct and useable the only thing left will be the pipe. Cheers guys I'll report back later.

Chris in Margate
registered user
Posts: 402
Joined: Thu Sep 03, 2009 7:53 pm
Main scooter: Lambretta 1964 225 Special
Contact:

Sat Jul 23, 2016 8:59 am

Too rich.
At what point did you remove the plug; after idle; after sustained high revving; or after parking up ?
The colour isn't truly telling you the mixture at different openings of the carb.


Sorry missed all the other posts.
Last edited by Chris in Margate on Sat Jul 23, 2016 9:25 am, edited 1 time in total.

Post Reply Previous topicNext topic
  • Information
  • Who is online

    Users browsing this forum: No registered users and 7 guests