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Lemans 5 aftermarket carbs

groundhog105

groundhog105

Cruisin' Guzzisti
GT Contributor
Joined
Dec 29, 2008
Messages
292
im looking for advise on using aftermarket carbs on my Lemans. What has been tried and what works. I currently went to the expense of putting on a set of mikuni flat slides that we sold to me as 40mm but it turned out that they ar 38s that have been bored out to 41.5mm. Now these carbs work great except the fuel mileage on the street is about 30 mpg. I thought they could be rejeted but when I took the bike in to a shop I use that has a air fuel analyzer the bike is very rich on small throttle openings but cannot be rejetted because when the carbs were bored they were bored out too much and cut into the slow speed orifices causing the carbs to pull too much fuel. On a race track this is not a problem but not good for the street. I can get replacement TM38mm pretty cheap but throttle pull is quite heavy. I’m looking for suggestions

Thanks
 
Back in the day, I acquired a set of Keihin 40mm smoothbore flat slides for my LMV that came with the recommended jetting starting point. They were beautiful pieces, but sadly I never did have time to fit them and tailor the jetting properly ... both because I'd put so much effort into making the original Dell'Ortos work perfectly that I was loathe to have to reinvest all the time, and also because that was right around the time that my hip was disintegrating so quickly that I had to stop riding from the pain.

I sold the LMV in a fit of despair that I'd ever be able to ride again, and the Keihins to a friend some years later. I don't know if he's ever fitted them to his LeMans 1000...
 
Godfrey said:
Back in the day, I acquired a set of Keihin 40mm smoothbore flat slides for my LMV that came with the recommended jetting starting point. They were beautiful pieces, but sadly I never did have time to fit them and tailor the jetting properly ... both because I'd put so much effort into making the original Dell'Ortos work perfectly that I was loathe to have to reinvest all the time, and also because that was right around the time that my hip was disintegrating so quickly that I had to stop riding from the pain.

I sold the LMV in a fit of despair that I'd ever be able to ride again, and the Keihins to a friend some years later. I don't know if he's ever fitted them to his LeMans 1000...
Click to expand...

If he still has them I’d be interested in purchasing.
 
What is wrong with the stock carbs? Are you still using the external springs? If you are, they can be removed and internal springs can be used like on other Del O'rto carbs. That is what I did with my MkV.
 
john zibell said:
What is wrong with the stock carbs? Are you still using the external springs? If you are, they can be removed and internal springs can be used like on other Del O'rto carbs. That is what I did with my MkV.
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JR1967. Those look very interesting. I’m checking them out
John. The stock delortos with the external spring are impossible to keep in synch. I will look at following your suggestion. How did that work out on your Lemans
 
groundhog105 said:
JR1967. Those look very interesting. I’m checking them out
John. The stock delortos with the external spring are impossible to keep in synch. I will look at following your suggestion. How did that work out on your Lemans
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Worked great. Stays in sync. Howerver if you chop the throttle, be aware that you can't open up again until revs drop or you squeeze in the clutch. The vacuum just sucks the slide to the side and you can't open it again until vacuum drops. Maybe the same with the externals, but I didn't have them on for very long.
 
Yea with the external spring the slide returns right away. I’m not sure I want to put up with that issue. I’m going to leave it as is for now until I decide what to do. It runs quite well it’s just rich off the bottom.
 
groundhog105 said:
Yea with the external spring the slide returns right away. I’m not sure I want to put up with that issue. I’m going to leave it as is for now until I decide what to do. It runs quite well it’s just rich off the bottom.
Click to expand...

I've learned to gradually reduce throttle. The slide sticking on opening doesn't occur if you don't let vacuum spike. I would think that would be an issue with the external spring as well.
 
I had my LMV set up with spring in slide return springs, and ditched the stock throttle for a Tomaselli dual cable throttle. I had the Dell'Orto bores and slides treated with a micro polishing finish too. No vacuum sticking and a much more manageable weight to the throttle action, if a somewhat long twist. The Tomaselli throttle's friction adjustment made it a pleasure on long touring rides, as did the (no longer available) OEM BMW K1 grip rubbers I used.
 
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Godfrey said:
I had my LMV set up with spring in slide return springs, and ditched the stock throttle for a Tomaselli dual cable throttle. I had the Dell'Orto bores and slides treated with a micro polishing finish too. No vacuum sticking and a much more manageable weight to the throttle action, if a somewhat long twist. The Tomaselli throttle's friction adjustment made it a pleasure on long touring rides, as did the (no longer available) OEM BMW K1 grip rubbers I used.
Click to expand...

I have thought about using that throttle but didn’t know if it would work. Thanks for the reply
 
groundhog105 said:
I have thought about using that throttle but didn’t know if it would work. Thanks for the reply
Click to expand...

Works well, but again it's a slow throttle twist. I believe I used throttle cables from a 1976 850 LeMans race kit (same carbs as my '89 LMV), but I'm sure it will be easy to source cables anyway. They're not hard to have made up to whatever spec you want.
 
Godfrey said:
Works well, but again it's a slow throttle twist. I believe I used throttle cables from a 1976 850 LeMans race kit (same carbs as my '89 LMV), but I'm sure it will be easy to source cables anyway. They're not hard to have made up to whatever spec you want.
Click to expand...

Thank you for the tip.
 
I not only ditched the external springs on my LM2 36mm Dell Ortos but I replaced the stock internal springs with light weight ones too. I've never had one problem with the throttles sticking and the carbs stay in sync. I replaced the original throttle cables with Venhill low friction items. The throttle is now about as light as it'll go.
 
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