Which carbs?

C

CDHE

Full member
Location
Boulder, Co
Hello All, Hoping to solicit on carburators for my SF2 build. It has a fresh engine with Engine Dynamics flowed heads, Megacycle 5C camshafts and 10:1 pistons. Save for some suspension upgrades and a likely Witt ignition, the rest of the bike is pretty much stock. I live at about 6,500ft above sea level. My rides will vary from 5-9,000ft. I was headed in the Mikuni RS36 direction, and was advised that the twin's vibration wears out RS slides prematurely and that stock Dell'Ortos do not suffer this problem. I'm open to really any possibility....FCR's, or maybe Mikuni BST's -I have them on my Elefant, and they sure cope will with the altitude changes that most all of my rides will encounter. Thanks in advance for your feedback.
 
SUDCO offers the Mikuni VM (round slide) carb in kit form for many bikes, Norton twins, Yamaha XS twins, Triumph twins, CB twins, Kawasaki H2 triples, and many others maybe you can find something suitable from them.
Were you running the Dels before your rebuild? I am interested to know what size main jets / idle jets you would use up there in the Rockies.
Cheers
 
78jotadave said:
SUDCO offers the Mikuni VM (round slide) carb in kit form for many bikes, Norton twins, Yamaha XS twins, Triumph twins, CB twins, Kawasaki H2 triples, and many others maybe you can find something suitable from them.
Were you running the Dels before your rebuild? I am interested to know what size main jets / idle jets you would use up there in the Rockies.
Cheers
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I bought the bike in pieces without carbs, so no jetting info. Have to buy something in any case and figured that all options might as well be considered.
 
Unless you are planning on doing huge miles it would be simplest to just score some new Dells, all known quantity with them. Available in UK at least. Use filters to keep them good. If you are keen and clever go for something more advanced.
 
have fitted Mikuni RS 36 Flatslides to a few 750 twins and a couple of 880cc Twisted Twins, never had an issue with slide wear
have a few sets nearly ready to send out, just waiting on manifolds to be machined
 
redax5 said:
have fitted Mikuni RS 36 Flatslides to a few 750 twins and a couple of 880cc Twisted Twins, never had an issue with slide wear
have a few sets nearly ready to send out, just waiting on manifolds to be machined
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what advantages do the Mics have over the Dell'Ortos?
 
Far more precise fuelling. And a smooth bore at full throttle. Ask triple owners on here who have them - chalk and cheese i'd say. I have 39mm FCRs but was happy enough with Dells for decades.

Your engine mods won't really offer much upper rev range performance advantage unless you fit some sort of tuned exhaust system. Standard Conti type mufflers will kill the advantages of a 5/C cam. With similar mods to yours I ran a factory 2/1 with a straight through tapered perforated baffle with a reverse cone at the exit - packed externally to quieten it down for street use. Didn't lose much from the open (extremely loud!!!) 2/1.
 
CDHE said:
the twin's vibration wears out RS slides prematurely and that stock Dell'Ortos do not suffer this problem.
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Someone is having a lend of you. Dells are only beaten by Amals in the slide wear championships and it is one of their main disadvantages. Keihin FCR (which I have on my SF) have the flat slides running on rollers, not sure about the Mikunis, but as Red says, they by no means eat slides. Seeing that Red has them in kit, they would be top of the list. And as Quentin says, don't fit a 5C cam without a tuned exhaust, and both Q and I have our 5C advanced a few degrees for stronger midrange.
 
Tippie said:
Someone is having a lend of you. Dells are only beaten by Amals in the slide wear championships and it is one of their main disadvantages. Keihin FCR (which I have on my SF) have the flat slides running on rollers, not sure about the Mikunis, but as Red says, they by no means eat slides. Seeing that Red has them in kit, they would be top of the list. And as Quentin says, don't fit a 5C cam without a tuned exhaust, and both Q and I have our 5C advanced a few degrees for stronger midrange.
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I would add, don't use a 5C for normal road work.
Paul
 
I have Mics fitted by Keith to my Jota...quite a remarkable difference though these things dont come cheap, plus mods needed, airbox gone, side panels now screw on etc
 
piranha-bro2 said:
Far more precise fuelling. And a smooth bore at full throttle. Ask triple owners on here who have them - chalk and cheese i'd say. I have 39mm FCRs but was happy enough with Dells for decades.

Your engine mods won't really offer much upper rev range performance advantage unless you fit some sort of tuned exhaust system. Standard Conti type mufflers will kill the advantages of a 5/C cam. With similar mods to yours I ran a factory 2/1 with a straight through tapered perforated baffle with a reverse cone at the exit - packed externally to quieten it down for street use. Didn't lose much from the open (extremely loud!!!) 2/1.
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Great advice all around, and a new idiom to boot. Suppose some was indeed having a lend with me about the Dell's. The 5c's came with the project. Here's an image of my actual commute. Really no use for them except on the occasional outing. Smooth, torquey response from idle would seem to be the ticket if I wish to remain a good neighbor.
 

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If Red has a pair of Mikunis ready, get those by all means. I've never come across even a whisper about RS's wearing prematurely on shakers. A better carburetor overall than Dells - better fueling, response, torque, and build quality.
 
CDHE said:
Great advice all around, and a new idiom to boot. Suppose some was indeed having a lend with me about the Dell's. The 5c's came with the project. Here's an image of my actual commute. Really no use for them except on the occasional outing. Smooth, torquey response from idle would seem to be the ticket if I wish to remain a good neighbor.
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I'd be seriously looking at the std SF2 7/1 cams. I reckon Wolfgang in Canada would have them no doubt. That way you get a great spread of power and can run a great sounding pair of Conti-style mufflers. By all means go the 5/C but don't expect much unless you can find a good exhaust system to go with them. As for rideability, my SF1 with an SFC crank, 5/C cams, 10:1 comp ration and the exhaust system I mentioned above, was very docile and well-behaved commuting and touring, and in any riding situation really - then had some extra mumbo for track days. And it's a myth that a bike with a 6/C cam won't idle or is rough as guts trying to do so - so the 5/C is not a prob in that regard. In fact a 5/1 from an SF1 or a 4/S from a 750S have profiles and lift not too dissimilar from a 5/C.
 
piranha-bro2 said:
I'd be seriously looking at the std SF2 7/1 cams. I reckon Wolfgang in Canada would have them no doubt. That way you get a great spread of power and can run a great sounding pair of Conti-style mufflers. By all means go the 5/C but don't expect much unless you can find a good exhaust system to go with them. As for rideability, my SF1 with an SFC crank, 5/C cams, 10:1 comp ration and the exhaust system I mentioned above, was very docile and well-behaved commuting and touring, and in any riding situation really - then had some extra mumbo for track days. And it's a myth that a bike with a 6/C cam won't idle or is rough as guts trying to do so - so the 5/C is not a prob in that regard. In fact a 5/1 from an SF1 or a 4/S from a 750S have profiles and lift not too dissimilar from a 5/C.
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Don't leave it idling anyway or the question will be : which replacement cam?
Paul
 
As has been mentioned , probably more important than which make of carb is which one takes the best filters. Carb wear is nearly all down to the filters if thats your worry. If you want new, bear in mind you will not get PHF in a std clamp fit new anymore.
 
Laverdas twins don't oil well at idle? My understanding is that foam (like Unifilter) doesn't flow as much air, but is quite a bit better at filtering dirt than paper (like K&N).
 
Most classic racers here, including me, if using filters use foam. Don't use those ones with chrome plates attached as they can suck themselves closed. With mesh K&N on my SF when it had Dellortos the slides would stick when riding in rain, great fun coming down mountain passes. Forget the idle oil bizzo unless you intend sitting idling in traffic jams in midsummer with shit oil. There are other things that can cause cam wear.
 
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