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Help please - Best carbs for Lemans 2

M

Murraydali

Just got it firing!
Joined
Mar 30, 2012
Messages
9
Hi,
I'm a new member, but a long time avid reader. My first Guzzi was a Lemans 5 which I owned for about 8 years and sold in 2005. I loved that bike and poured money into it - used it for daily commutes and cross country jaunts. I sold it and got out of bikes for awhile.

My next bike was an old 850T I bought in 2010. I didn't ride it much, but spent time pulling it to bits. Was planning to cafe racer it, but once I stripped it down realised the cost would be way too much. Besides I always wanted a nice Lemans 2, so I sold the 850T and bought my dream bike a couple of months ago.

It is a 1981 Lemans 2. Appears to have had a heap spent on it rebuilding all of the engine and driveline, powdercoating the frame, etc. It has some nice kit on it and is mechanically in great, superclean shape. Cosmetically, needs a tidy up and new paint. Will then look awesome.

It currently has 88mm barrels (not Gillardoni, and probably not nikasil - I need to check if they are iron bores). It has alloy timing gears, P3 cam, new exhaust with Lafranconi competitzion mufflers, agostini rear sets and PHM40 carbs with unfiltered velocity stacks. The carbs look like the factory race kit ones - no pumpers or choke. It sounds superb. Just needs some fine tuning.

The carbs are just not practical for street use. I'm going to replace them, but am undecided whether to go with PHM40 or PHF36. I would really appreciate some knowledgable input from you folks. I won't be using it as a daily driver - rather weekend blasts in the local hills, but mainly sedate cruising. I'm getting too old to be too crazy...

And before you ask - yep, I'll take some photos and post them up as soon as I get it out of the shop.
Many thanks,
Paul
 
As for carb size, it depends where you want the optimum RPM. I'll attache a zip file for a spreadsheet that can help you select the carb size you want. Input bore, stroke, and carb size and it will give you the theoretical optimum RPM. I will be good (in theory) for running 1000 RPM below and above that number. I'd recommend checking the alloy gears for premature wear, if present, go back to a timing chain with a good aftermarket tensioner like this one http://www.mgcycle.com/product_info.php?products_id=347 Also be sure to fit air filters, it may not look as nice, but your engine will appreciate it.
 

Attachments

  • carbsize.zip
    1.1 KB · Views: 125
Thanks for the quick reply John.
I'm having trouble downloading the file - my mac won't recognise the file format. Can you steer me in the direction of a link please?

Thanks
Paul
 
Murraydali said:
Thanks for the quick reply John.
I'm having trouble downloading the file - my mac won't recognise the file format. Can you steer me in the direction of a link please?

Thanks
Paul
Click to expand...


Don't have a link. .zip is a standard format. I can't post an Excel spreadsheet to the forum. If you can emulate windows on your MAC, use IE, right click the link and save target. Once you have the file, extract it. Or, find a friend with a computer and download it there. BTW, for an 88mm bore, 78mm stroke, and 40mm carb, the calculated Sweet spot is 7266 RPM. If you have 36mm carb, that spot would be 5885 RPM.
 
Thanks John. I'll give that a try. Sounds like 36mm is going to be the ticket.

Paul
 
Paul,

The 40's should give you a bit more top end speed.

The 36's will be more responsive.

Both should cope but it is hard to tell without knowing valve sizes and how well the engine breaths.

All else being equal I'd go for the 36's. Came out originally on the LM II. My personal preference.

Rod
 
I have the 40s on a V7. They were part of a performance package. Once adjusted they run fine, very smooth throughout the rpm range. As an experiment I put back the 30s and the bike ran like crap. No power until after 4,000 – 5,000 rpm. So I quickly went back to the 40s, but the tickle is messy.

http://home.comcast.net/~gustofur/MG1.wmv
 
My SP 11 - V1000 goes like the proverbial haunted sh....house.Shes got a pair of Mikuni TM 38-85's.
She pulls seamlessly through to 6200 rpm , and then feels like she fades a bit , or just loses the edge , needing more fuel . Im busy checking for fuelling as I write this , 230 Main jets going in today .Report later .
Its an easy fix , Im confident of that .
Good luck .
Regards Supaflee
 
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