First post and carb jetting question LM2

[Dukedesmo]

My first post here. Quick story; always wanted a Le Mans since I first started riding in the late '70s, somehow never had a Guzzi and currently have 2 Ducatis.

Anyway I live in England but have family in Italy, a friend of the family has a collection of Italian bikes (Guzzi, Ducati & Aermacchi) and he's decided that he's getting too old to ride the bigger bikes and so is (reluctantly) selling some to fund his retirement. Knowing this and that he had a Le Mans, I went over and bought it.

Bike is a 1980 Le Mans II; under 12k miles and had little use over the last 20 odd years, was standing for the last 2 or 3 but we got a new battery, put some fuel in it and fired right up, settling to a steady idle. It ran OK but really needed some TLC before making the 1,000 mile journey home so I got it shipped.

As it's imported I need to get it registered here and I'm currently in the process of waiting for the authorities to sort out the paperwork so I'm going through the basics and making a few upgrades whilst I'm at it.

Rear brake was non-functioning but new fluid sorted that and the brakes are actually very good for a 35 year old bike - not sure about the linked setup though but I suppose I need to get accustomed to it before I do anything radical?

Along with the basic servicing, I have a deep sump, windage plate, Lafranconi 'Competizione' exhausts with 40mm downpipes to fit. Today I have been stripping the carbs which need new 'O' rings, gaskets etc. and I was thinking about the jetting - presumably with a straight through, larger bore exhaust I should up the main jets?

Currently it has 148 main jets, workshop manual states should be 140, so I don't know if it was like that from new or if they've been changed? anyone got any advice re. jet sizes and/or needles?

I'm sure there will be other questions as I'm a Guzzi newb but as I'm getting new carb parts for the overhaul it would be easy to get any jets etc. at the same time.

Any advice welcome, and here's a pic of the bike before I started stripping it down;



 ;-T

[Vasco DG]

148 mains are way to big. I'd go back to stock settings and then move from there. Needle and atomiser are far more relevant than main for everyday riding.

First thing on my list would be rebuild brake calipers and replace brake lines.

Pete

[Dukedesmo]

Interesting, needle and atomiser are as per the manual (K5, 265AB). Do you think 148 are too big for the Lafranconis or just the stock setup?

I do need to look at the brakes more closely, they work fine but one of the bleed nipples on the rear caliper is seized.  ;-T

[Vasco DG]

Much too big for either. I'd think a 135 or at most a 138. Do some full throttle chops when the brakes are fixed and see what the plugs say. Main is only really relevant at wide open throttle anyway unless it's grossly small. Most of your riding will be done on the needle and atomiser.

Pete

[dan_s]

It could very well be that 140 for a main jet is also too rich. Mk1's came with a 135 jet, Mk3 with a 115 (and a totally different air filter and exhaust).
Some more on carb jetting:
http://archive.guzzitech.com/Dyno-dockray.html
http://www.richcutler.co.uk/guzzi/guzzi/guzzi_06.htm
https://www.youtube.com/watch?v=gjMIV4CN7Ck
the first two writers had 950 cc engines.
On mine (lm2, phf 36, 844cc, stock pipes, k&n filters) I now use 130 mains. It runs well, not detonations, plugs look fine.
Congrats for your new bike.

[Vasco DG]

MKIII uses complete different carbs so the jetting isn't relevant for the Mk II

[Dukedesmo]

Thanks, not sure what to do with the jetting now?  ???

I think I'll replace the gasket parts, clean everything up and try it as it is for now, at least it shouldn't be running too lean. I've got a CO meter so will check it with that.

[dan_s]

Do some full throttle chops when the brakes are fixed and see what the plugs say.
Pete

^

[Chuck in Indiana]

Much too big for either. I'd think a 135 or at most a 138. Do some full throttle chops when the brakes are fixed and see what the plugs say. Main is only really relevant at wide open throttle anyway unless it's grossly small. Most of your riding will be done on the needle and atomiser.

Pete

What Pete says, although he's one of those weird fuel injection guys..  ~;  ;D Full throttle chops will get the main jet in the ball park and should be done, but the slide cutaway, needle, needle position, and needle jet is where drive-ability lies.