New owner with a 1971 750..

OTR002 said:
Paul, it an SF with PHF's. It looks like I'll need to strip the whole assembly, throttle, cable and carbs and give them a good clean.

This is my first Laverda and I'm just learning it's quirks! But it did pull hard to 90mph until...
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In which case, there are 3 grades of spring, heavy, medium and light obtainable for the PHFs from Dell'Orto parts suppliers.
There is no sure way of knowing in which guise your 750 left the factory. All the parts are interchangeable.
A 71 SF should have a small valve head and 30mm square slide VHB carbs. The heads are interchangeable, the inlets tracts and stubs differ however.
If the numbers are matching, it's likely that the engine has its original cases. Get down on your knees left hand side of the bike and look at the lower case above the lower rear engine mount. It should be stamped SF or GT for a 71 bike, unless it's stamped C or SFC, it which case, I'll swap you for a basket case GT I have.

Send us a photo of your bike.

Paul
 
There's only one as far as I know. I bought mine from vintage Vee dub in Sydney. The wiring connections are the same. The old Bosch one is adjustable but I couldn't get it to come down from 17 volts Soundslike you have the opposite problem.

Vintage Vee-Dub Supplies
(02) 9789 1777

https://g.co/kgs/6jiFpTt
 
How is the regulator mounted? Is it free to swing around? Or does the engine breather hose squash itself past it?

When vibes hit a solidly-mounted regulator, the internal contacts can vibrate and charging will be compromised. In stock form, the regulator was mounted on a rubber strap spanning the frame tubes. It was free to move around, excellent vibration isolation.

Solid-state regulators are often the better option, the old contraptions have seen better days. Bosch makes an excellent replica in solid-state. Quite expensive, but just the ticket to keep rivet counters happy.

Properly-routed new throttle cables and some lube can work wonders. The splitter will also be pleased to recieve a blob of light grease. The single-pull throttle with splitter on the GTL is nice 'n smooth, no heavier than comparable bikes of the time.

A budget mod for the PHF would be to snip off about 1/4-1/3 of the throttle spring. Pre-load is greatly reduced with no danger of the slides not returning. Been using shortened springs in my triples for over 30 years without issues. Throttle cables do have to be in top condition though, kinks and rust may inhibit positive slide return somewhat.

piet
 
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From my experience with two 69 750's, you should clean all the connectors, including the connections on the Bosch switch in the headlight.
This switch uses sliding contacts, and they too will need cleaning. A can of electrical contact cleaner with a gentle puff of compressed air as it dries will help, but mechanical abrasion is required on the spade terminals. 00 or 000 steel wool works well, but battery totally disconnected first.

The positive supply wanders around the bike somewhat, as do the switched supplies, anything which improves contact surfaces/joints will be a help.

Not to be forgotten is the common or earth points. They need cleaning back to bright metal and when tightened up, a dab of vaseline or dielectric grease will keep them smick.

I wouldn't be riding the bike with the cables connected to the fuse block as per your photo. Shit happens - Murphy's 3rd and 12th Law of Relativity.
Expensive and damaging shit.

good luck
 
Thank you for everyone's replies. I've installed a new Bosch replacement regulator, as the old one may have functioned temporarily after cleaning and adjustment, but its long-term reliability was uncertain. Additionally, I replaced all the power cables and cleaned all the contacts. Now, everything is soldered, and the resistance has decreased to 0.01-2 ohms from the previous worst of 1.3 ohms. There is a growing list of parts and components that need to be purchased, especially rubber parts.

There is still much work to be done to bring this bike up to a reliable standard. However, it currently runs well and looks decent.

IMG_2670.jpeg
 
I have a complete wiring harness from a mid-1990s bike that I'm going to strip down and use to rewire the SF. It will provide me with everything I need: color-coded wires, a fuse box, indicator harness, starter relay, and instrument lights, among other components. This approach is much easier than creating my own wiring harness and color codes from scratch. Additionally, I plan to swap all the plugs for Deutsch Connectors to make the setup look more organized and aesthetically pleasing.

IMG_2651.jpeg
 
Next up is the carburetors! It's quite a mess, as I have both early and late series slides fitted, although thankfully they are both 50/1 so they somewhat functioned. However, the main needles are different—one is a K1 and the other a K2—so it seems like I'll need to strip these down for a thorough clean and refurbishment. Both slides were heavily soiled, scratched, worn and corroded inside, showing significant wear. I haven't yet disassembled the carbs to assess their condition and specifications, but at this point, I'm not optimistic about them being identical or in good shape.73372237632__09E13347-874D-47B5-8B70-D62DFC30E5FB.jpegIMG_2663.jpeg
 
Make sure your starter relay is rated high enough to cope with the amps drawn by a .95hp Nippon Denso starter motor! I found trying to get everything linked and still use multi pin connectors was too difficult. My new custom harness is a combo of old Sf blade blocks and multi-pin connectors. I want to be able to remove components easily. Sounds like you have a good plan - be interested to see the final product.
 
K2s only - no idea why anyone would put a K1 in with a std needle! Slides look serviceable from your photo - but hard to tell. You'd be surprised how forgiving they are, but if visibly missing metal, they will wear the carb bodies (= bad). Full ultrasound and replace anything that can wear or is important for sealing (fuel and air).
 
piranha-bro2 said:
Make sure your starter relay is rated high enough to cope with the amps drawn by a .95hp Nippon Denso starter motor! I found trying to get everything linked and still use multi pin connectors was too difficult. My new custom harness is a combo of old Sf blade blocks and multi-pin connectors. I want to be able to remove components easily. Sounds like you have a good plan - be interested to see the final product.
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Sweet, I was going to check the draw from the starter before committing to a modern relay. My harness is so hacked about it's simpler to tear it all out an start again, although it all currently works....until it fails!
 
piranha-bro2 said:
K2s only - no idea why anyone would put a K1 in with a std needle! Slides look serviceable from your photo - but hard to tell. You'd be surprised how forgiving they are, but if visibly missing metal, they will wear the carb bodies (= bad). Full ultrasound and replace anything that can wear or is important for sealing (fuel and air).
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The slides have grooves in them and well worn. The needles have a corrosion ring around their shaft! So it's a full strip and rebuild. Thank god I'm familiar with these PHF's and have some spares from my Moto Guzzi rebuilds.IMG_2659.jpeg
 
OTR002 said:
The main jets are very faded, may be 55 or 65? The secondaries are 60's. Is this correct?
Cheers
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Pilot jets would be 55 standard.
Main jets 140.

As for the battery, you don't need those huge batteries. Laverda specified them at the time because no doubt they didn't want to be a laughing stock because they hadn't fitted a kickstart, and probably battery technology has moved on.
An 18 or 20AH sealed battery is fine and leaves plenty of room for the sandwiches.
Paul
 
I have a 74 750 and after replacing all the cables, I think dual throttle cables w/ o the cable splitter is a better design- and angled connectors to the carb tops will prevent the cables from jumping out of the carb top holders. Venhill can make any cable configuration and DAM Classic in Aus has parts. your slides look shot- especially if you can feel noticeable slop within the carb body. Mine were scored and new slides was an improvement, along w new needles and atomizers, all new gaskets. Check for correct float height and check gas amount coming from the pumps is equal. Buy a complete Dell Orto gasket rebuild kit. And make sure all passage ways are clear/ consider ultrasonic cleaning if really dirty internals.
 
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TeddyG said:
I have a 74 750 and after replacing all the cables, I think dual throttle cables w/ o the cable splitter is a better design- and angled connectors to the carb tops will prevent the cables from jumping out of the carb top holders. Venhill can make any cable configuration and DAM Classic in Aus has parts. your slides look shot- especially if you can feel noticeable slop within the carb body. Mine were scored and new slides was an improvement, along w new needles and atomizers, all new gaskets. Check for correct float height and check gas amount coming from the pumps is equal. Buy a complete Dell Orto gasket rebuild kit. And make sure all passage ways are clear/ consider ultrasonic cleaning if really dirty internals.
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I think you're onto something! My MotoGuzzi has the same PHF36 carbs and twin-pull Tomaselli throttle, and it is noticeably smoother and lighter!

I've checked the springs in the carbs, and they are both the lightest springs available, although one is 3mm shorter than the other. They both have the same wire diameter, number of turns, and it's only the free length that is different. So, they will be replaced with new springs.

I've looked at a set of 70-degree angled cable tops for the carbs and suspect that they will ensure a smoother transmission from the carb tops.
 
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