1971 750SF carb specifications

O

OTR002

Junior member
Location
Brisbane, Australia
I'm at that point of rebuilding/correcting the carbs fitted to my bike, they are 36PHF (round slides).

What are the specification from new?

Currently I have,
The older style slides, 50/1
Main needle is K2
Main jet 155
pilot jet 60
Emission tube is AB265
The springs are the lightest as 1.10mm wire

And the cables, splitter and throttle were all packet with grease!!
Cheers
Rod
 
OTR002 said:
I'm at that point of rebuilding/correcting the carbs fitted to my bike, they are 36PHF (round slides).

What are the specification from new?

Currently I have,
The older style slides, 50/1
Main needle is K2
Main jet 155
pilot jet 60
Emission tube is AB265
The springs are the lightest as 1.10mm wire

And the cables, splitter and throttle were all packet with grease!!
Cheers
Rod
Click to expand...
155 is way too big, 140 is standard.
55 is standard for the pilot jet. I've gone down to 50 on mine, it was too rich on low to medium throttle. I've gone down on the pilots on all my Laverda. The S is running 45s.
Paul
 
Last edited:
OTR002 said:
I'm at that point of rebuilding/correcting the carbs fitted to my bike, they are 36PHF (round slides).

What are the specification from new?

Currently I have,
The older style slides, 50/1
Main needle is K2
Main jet 155
pilot jet 60
Emission tube is AB265
The springs are the lightest as 1.10mm wire

And the cables, splitter and throttle were all packet with grease!!
Cheers
Rod
Click to expand...
https://uk.laverdamania.net/OLD/carbgb.htm any good to you?
 
If you are using the fuel squirter pumps, the spec ramp was /3. Many people have removed the pump levers to no detriment, in which case it wouldn't matter which pump ramp was there.
As Paul says, the main jets are way big, I run 145, it came with 140 but holed a piston after extended running at full throttle, too lean. Based in Darwin with no speed limit, 145 was spot on.
And if you replace the slides due to the scoring as shown in your other post, it would pay to fit filters instead of the insect screens.
 
Have you determined what head your bike has on it yet? If it's got the original small valve head and small inlet ports I doubt it will want the same setup in the 36mm carbs as a later SF1/2/3 they will have come off. Maybe someone has fitted a later model head to it?
 
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Tippie said:
If you are using the fuel squirter pumps, the spec ramp was /3. Many people have removed the pump levers to no detriment, in which case it wouldn't matter which pump ramp was there.
As Paul says, the main jets are way big, I run 145, it came with 140 but holed a piston after extended running at full throttle, too lean. Based in Darwin with no speed limit, 145 was spot on.
And if you replace the slides due to the scoring as shown in your other post, it would pay to fit filters instead of the insect screens.
Click to expand...
And make sure that your carb bodies aren't worn. They wear as much as the slides do and are good for the bin after a while.
Paul
 
rez said:
Are your SF with Airfilter ( standard) or open?
What kind of Exhaust is mounted.
Why the Mainjet is 155???
Click to expand...
Good question - because 1971 SFs came with open stacks I think, whereas SF1/2/3s that used the 36mm carbs had airfilters. Why I asked about the head.
Why the main jet 155? Simple answer: DPO (same reason for a K1 needle in one side and a K2 in the other!!). Wonders NEVER cease when you buy a used Laverda.
 
Schurminater said:
https://uk.laverdamania.net/OLD/carbgb.htm any good to you?
Click to expand...
Thank! that's exactly what i was chasing. It's always good to start with what the factory set up and then go from there.
piranha-bro2 said:
Have you determined what head your bike has on it yet? If it's got the original small valve head and small inlet ports I doubt it will want the same setup in the 36mm carbs as a later SF1/2/3 they will have come off. Maybe someone has fitted a later model head to it?
Click to expand...
No!! so what head do I have? Ignore the cracked Tach drive housing, just another thing to fix.

IMG_2711.jpeg
 
piranha-bro2 said:
Good question - because 1971 SFs came with open stacks I think, whereas SF1/2/3s that used the 36mm carbs had airfilters. Why I asked about the head.
Why the main jet 155? Simple answer: DPO (same reason for a K1 needle in one side and a K2 in the other!!). Wonders NEVER cease when you buy a used Laverda.
Click to expand...
It has open velocity stacks. I'll be addressing this issue as i get to it, are there clip on filters available? I could just us a filter sock..
 
Tippie said:
If you are using the fuel squirter pumps, the spec ramp was /3. Many people have removed the pump levers to no detriment, in which case it wouldn't matter which pump ramp was there.
As Paul says, the main jets are way big, I run 145, it came with 140 but holed a piston after extended running at full throttle, too lean. Based in Darwin with no speed limit, 145 was spot on.
And if you replace the slides due to the scoring as shown in your other post, it would pay to fit filters instead of the insect screens.
Click to expand...
Thanks Trippie, I do tend to ride my bikes to enjoy their performance and have been know to pay for a few tickets to the PoPo's ball. I have several sets of jets for these PHF's as they are fitted to my Guzzi so I'll go with your recommendation and see what the plugs tell me.

As for the open bellmouths, they do sound and look sweet, but as you'd know we do live in a dusty country so I'll have a look at what I can do. I take it original air boxes are non-existent!
 
That is a "big-valve" head, as fitted to SF1/2/3. Easily identifiable by the straight inlet stubs. They are not interchangable with the angled stubs of the GT/S/SF/GTL. Well, not without some serious surgery.

All VHB-equipped bikes came with open trumpets, except the GT and GTL, these used a half-decent filter system. Perhaps there were some exceptions for certain markets, but these don't show on the factory homologation sheets. All PHB-equipped bikes came with a filter ex-factory. Pretty simple...

There should be hundreds of original airboxes kicking around in messy sheds and garages, they just need to be un-earthed. ;) The connector tubes to the airbox are horribly expensive and original filters are obsolete, but there are alternatives for those.

piet
 
sfcpiet said:
That is a "big-valve" head, as fitted to SF1/2/3. Easily identifiable by the straight inlet stubs. They are not interchangable with the angled stubs of the GT/S/SF/GTL. Well, not without some serious surgery.

All VHB-equipped bikes came with open trumpets, except the GT and GTL, these used a half-decent filter system. Perhaps there were some exceptions for certain markets, but these don't show on the factory homologation sheets. All PHB-equipped bikes came with a filter ex-factory. Pretty simple...

There should be hundreds of original airboxes kicking around in messy sheds and garages, they just need to be un-earthed. ;) The connector tubes to the airbox are horribly expensive and original filters are obsolete, but there are alternatives for those.

piet
Click to expand...
Air filters or trumpets depends on markets. As did a lot of other things in those early days, including "official" factory photos. Not useful for writing books.
Factory homologation sheets have very little to do with the motorcycles.
Paul
 
Definitely a big valve head, as Piet says. So assuming later model cams (no stamp or 5/1 = SF1 or 7/1 = SF2/3) and pistons, jetting as recommended previously will be a good start.

Is it possible the entire engine is from a later SF? What's the engine number? And if you look at the left side rear crankcase low under the brake pedal (and rearward of the primary cover) there should be a stamp. Not sure about earlier models but a big valve post-1973 motor will have the stamping SF1, SF2, SF3 or (if you're REALLY lucky!) SFC.
 
Get a copy of the Green Book manual for lots of specs and contact DAM Classic Racing for parts. Use some sort of filter to prevent the carb slides from getting scored. DNA air pods will work w/ the air box snorkels attached to angle down and DAM has angled Malossi filters and OEM filters. They make a nice billet sump pump cover w/ magnetic drain bolt worth the $$. Bevel Heaven in CA sells online Dell Orto tuning info and
Venhill makes custom made cables any size. Consider dual throttle cables w/ angled ends to ditch the splitters.
 
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