Having brought my 1971 750SF from France to Colorado, I need to make a few changes to the jetting to compensate for the altitude, and the carbs are long overdue for cleaning and some parts replacement. These are VHB30AD/AS. One of the things I'm tempted to replace is the slides, which appear to be fairly worn. The slides are #50. I can't find a spec for the slide in the Green Book or on Jean-Louis's website, but searching the internet seems to show that the only slide available for VHB30 carbs now is a #60. The #50 slide is listed for smaller sizes of VHB. Is a 750SF supposed to run a #60 slide? I am running this with open bellmouths.
Dell'Orto VHB for 750SF
- Thread starter eabergman
- Start date
chrisk
Hero member
- Location
- Brisbane, Australia
There was a lot of talk about this issue here a month or two ago.
Use the seach function, I'd do it but am about to head out the door.
Use the seach function, I'd do it but am about to head out the door.
henrywillms
Hero member
- Location
- Canada
Check with Wolfgang, he lives in the mountains slightly north west of you, though I never saw any square slides on his twins, he would have some experience and may have the slides you need.
Gravelroad
Hero member
- Location
- Central Europe
The number on the slide is the height of coutout, given in 1/10 of a mm. I probably have a pair of 55 laying somewhere on the shelve, but no 50 slides. Looks like they're hard to source these days.
If all else fails, you might swap over to a pair of new PHBHs of the same size. They are rather cheap moneywise and can probably run on the same size of idle and main jets as the VHBs. Close look to the needle charts will be required to find the right atomizer/needle combination, though.
If all else fails, you might swap over to a pair of new PHBHs of the same size. They are rather cheap moneywise and can probably run on the same size of idle and main jets as the VHBs. Close look to the needle charts will be required to find the right atomizer/needle combination, though.
IIrc, the slides have a 45 cutaway. Not much goes wrong with them, wear is usually just superficial, rarely has great effect on engine performance. Haven't been available for ages. Needles and needle jets require replacement far more often. I can supply new V3 (also normally non-available) needles as a set together with needle jets. Most other bits and bobs are readily available from the usual sources, I have quite a few bits in stock.
piet
piet
Wolfgang recently acquired some V3 needles but I'm not sure if he can supply the 265N atomizers, so I may get in touch with you about that. Poking around the archives I saw several references to #50 slides in early SFs so I think that was probably the standard fitment. I discovered an air leak on one carb from the thermal isolation block behind the intake manifold. The entire inner ridge that is supposed to retain the o-ring was eroded away and a big loop of the o-ring was hanging into the intake port. I expect I'll be able to back down from the 150 main jet after I fix that. The other carb had nothing so dramatic but the o-rings on that isolation block were thoroughly flattened and it may have been leaking too. It had required a larger main jet also. The bike ran surprisingly well that way, and both plugs (B10ES) were looking rather good, with a nice tan color.
Laverda SF
Hero member
That is typical damage from using too thick of an O-Ring as it will damage the Spacer as you describe and can break the spacer when torquing it in place.
The original thickness of O-Ring are about impossible to find. I repair the spacers with Metal Epoxy, fill in the Ring Grooves and file them to shape.
I use Permatex Anaerobic Gasket Maker between the Spacer to Head and Manifold - Same stuff you use when joining a split case together. Works great on the Distributor Cover as well (Just let it dry on the cover and it forms a permanent reusable gasket and drill a small hole in the bottom of the cover to drain moisture - keeps the distributor cavity clean and dry - saves the point too).
Laverda SF
Hero member
Hate to say it Piet but them rubber O-Rings are subject to Gasoline Rot after a couple of years and my solution works best.
Been there - Plus you had better use a stiff Manifold Balance Hose or it will Collapse (Suggest a Hydraulic Hose).
Been there - Plus you had better use a stiff Manifold Balance Hose or it will Collapse (Suggest a Hydraulic Hose).
Laverda SF said:
NOTHING lasts forever Ron, not even us... Laverdas were not built for eternity, the factory did hope to sell a few more bikes.
Replacing consumables such as these o-rings should be part of regular maintenance. Of course they are often forgotten, so no use crying when they eventually crumble. Replacing is cheap and simple, a lot easier than re-inventing the wheel.
piet
Laverda SF
Hero member
Piet: Them Crumbling O-Rings could easily cavitate air, lean out the mixture and melt a piston.
"Re-inventing the wheel" is necessary sometimes.
"Re-inventing the wheel" is necessary sometimes.
P
Paddy
Guest
I had loads of needles for VHB, cant find them at the moment 
Found some other bits, emulsion tubes and jet holders etc.
Found some other bits, emulsion tubes and jet holders etc.
Gravelroad
Hero member
- Location
- Central Europe
Laverda SF said:
Ron, I would actually love to replace only a couple of O-Rings on the inlet stubs of my early triple for maintenance. But no, it's them f...ing rubber hoses, which now start to creep through the retainers after only 3 yrs of use. This means not only getting the carbies off and have them resynchronized when back on, but also spending a whopping 90 euros for replacement rubbers. This kind of shit is what I would call being overdue for a re-design.
