SF1 carb conversions

[tyelav13]

I will be interested to see which way Mark goes.

 

[Canuck750]

I fought with the original Dellorto's on my 73 SF1 for a season and finally bought a new pair from Wolfgang.
The new Dellorto carbs do require a special rubber intake manifold adapter that Wolfgang supplied and I used the original manifolds as spacers along with the plastic heat isolator so the carbs sat in the relative same position to the air box boots. The idle and air screws are not the same as the originals.





This is a picture of a Guzzl Le Mans MKI carb boot to cast aluminum intake manifold, the rubber carb boot may fit right over the Laverda manifold, HMB sells the rubber boots

 

[redax5]

photo shows a set of Mikuni 38mm RS Flatslides fitted to a worked SF engine, Twisted and bored
have a stack of 36mm carbs in stock to do same conversion to

750 Mikuni conversion

21st July JF Mikuni carbs

 

[LJ-2]

Not things of beauty are they !

 

[Grant]

I like the way they look.
Form follows function.

 

[LJ-2]

Creep  Look far too out of scale,

 

[Tippie]

"The idle and air screws are not the same as the originals."
Unless they are just undrilled and unthreaded it looks like a RH carb on the LH side. Designation on them is D (destro-right) and S (sinistro-left). Are the adjusters on the other side of the carb in pic?

 

[Dellortoman]

This is a picture of a Guzzl Le Mans MKI carb boot to cast aluminum intake manifold, the rubber carb boot may fit right over the Laverda manifold, HMB sells the rubber boots

The annoying thing about the carbs on the Guzzi is the angle of the throttle cables. That little ferrule on the end of the cable sheath never sits straight in the cable holder that's bolted to the top of the carb. So the cable inner has to drag across a kink at that position. All it needs is a is a bit of curved tube at the end of the cable.

You can actually get a shaft conversion for those Dellortos on the early LeMans Guzzis. I've seen the kit (in a box - not fitted to a bike).  It looks like a bit of a fiddle to fit because the carbs aren't parallel, and the cross-shaft is actually mounted to bearings on the frame above the carbs. I dunno how well it works.

 

[Laverda SF]

That looks like a SF Piston Burner to me.

 

[markQLD]

I will be interested to see which way Mark goes.

& I suggest Mark doesn't even know the way he's heading?  :-\

Mark's thoughts? For what it's worth, I am still pondering which way to go.
i.e. kicking around any cost-effective' options that may be better than sinking good cash into an old worn out set of Dellorto's.

In the short-term, I suggest we ask Mike 'mik667' for some photos/details of fitting the Mikuni VM carbs?

i replaced my worn Dell's with mikuni VM's on my SF2 - simple task that involved .... If intersted i can supply pics etc - but having said that there was no magic involved

As this was one of the more appealing options for me, as that's what I fitted to my '77 T140V Bonnie, back in the day. The VM's worked a treat and as Mike suggests should be a simple enough process. The VM's also retain the cable activated slides so is less cost and dicking about with a completely different setup. Also probably a lower cost option compared to a new set of Dellorto PHF 36 carbs? Dunno?
Was nought wrong with the performance of the Bonnie's original Amal carbs except they also eventually wear out. And my old Amals had a bad habit of jamming at wide-open-throttle, which caused plenty of anxiety to say the least! And how I miss the need to tickle those Amal carbs before a start up, not!

For the long-term, I'll talk to the boss and probably fit-up a set of his surplus 36mm RS flat-slides that are sitting on the shelf. Maybe a good cost-effective option for some due to the local supply availability? But those RS carbs don't have pumpers, however I disconnected the pumpers on my SF2 Dellorto's years ago, as these days I tend to refrain from overtaking any modern sports bikes. Yes, tragic, I admit 
In my limited experience, the round-slide carbs seem to perform ok without pumpers (i.e. it suits my current riding style) but I'm unsure just how the Mikuni RS carbs will perform without. One can only try. And Dellortoman Cam has retro-fitted pumpers to these surplus carbs and kindly forwarded on the details but I'm also not looking for things to do at the mo, eh.

Although, to be honest, fitting flat-slides to a classic old SF twin still looks so wrong to me. Maybe ok for a hotrod twin but a classic old twin? Just saying...
I've also considered dropping down to a 34mm or 32mm carb instead of the 36mm?  WTF, lose power!! ?? Please spare me. 
cheers, Mark

 

[hooksey]

Those rnd slide vm Micky Roonies are bloody cheap to buy new (a c Hatrick) up nth .
Plenty of tuning ability with jets and slides availability.  8) Will obviously need inlet flange adaptors...

Run them (38mm) on my jappa flattrackers..... tt500 and xl 350 and they run sweet and rev out well.
Cant see why they wouldn.t be an economical option that would look and go good  8)

 

[Tippie]

There isn?t really much carb showing on an SF, few people even noticed my FCRs, so that isn?t much of an issue. 
My FCRs heve never had the pumps connected for riding, however I have to squirt in a pump or two to start it cold (I have a plunger on RH carb and a tube across to the LH one), without that it won?t start. That is almost guarranteed the reason I got the bike back after it was stolen, the start clutch had given up the ghost, for sure as the bastard just wouldn?t start!!
VM Mikunis do work great, but neither do they look like Dellortos. The SF I have seen them on had them with two individual choke levers, the RH one in to the centre between the carbs, it also did require choke to start, and needed a triple jointed elbow and wrist to get to. They didn?t need pumps either. The whole pump issue is moot to me, I have never missed them on my SFs, and have ridden plenty of triples without them that felt "normal", however they do have their supporters and good for them and I don?t criticize them.
The operation of the FCRs, and I gather the RS miks, is really very good, I haven?t seen anyone criticize them so far. They were the last gasp of carb technology for motorbikes and as good as you are going to get.
It is great that so many viable options are open to us.

 

[tyelav13]

Will catch up reading all this when back home from Turkey. Wifi very hit and miss .

 

[Dellortoman]

SF I have seen them on had them with two individual choke levers, the RH one in to the centre between the carbs, it also did require choke to start, and needed a triple jointed elbow and wrist to get to.

That would annoy the hell out of me. It's just lazy installation. It wouldn't be difficult to cobble together a linkage or cable so both chokes operate from one lever.

 

[markQLD]

..  It wouldn't be difficult to cobble together a linkage or cable ?

Well, that may depend on what one has available for work space, tools and skills? no?

Back in the day, it was simple enough for me to saw off the choke lever tag and weld it back on the right-side (#14)
And the VM carb has an 'air' screw (#29) on the right-side for idle mixture adjustment as opposed to the Dellorto 'mixture' screw.

Hatrick's Mikuni site lists a right-side version of the 34 mm VM for idle speed adjustment (#32) that would be handy to have. However, the choke and air screw remain fixed (left & right). The adjustment of the air screw for low speed mixture is not used often enough to bother me. The 36 mm VM's don't list a right-side version?
https://www.mikunioz.com/product-category/vm-carburetors/vm34-carb/

'tis a pity Mikuni don't supply a matched set of VM carbs for twin cylinder bikes. Maybe a single VM carb with a custom matching inlet manifold is not such a bad idea? no?
Yes, I can see the rivet-counters already starting to cringe! So, maybe not a large market out there for that  :-\

Note: The simplest 'plug & play' option for the SF1-3 twins is to replace same with same. i.e. a new set of 36 mm PHF Dellorto?
'tis nought wrong with the Dellorto's and they're staying on my SF2 and Jota for now as they're still performing well  8)
cheers

 

[markQLD]

The operation of the FCRs, and I gather the RS miks, is really very good, I haven?t seen anyone criticize them so far. They were the last gasp of carb technology for motorbikes and as good as you are going to get. ..

and that's a good valid point Lee. I agree that they were 'the last hurrah' for bike carbs before fuel injection was developed as a better alternative.
Thanks for your comments on the acceleration pumpers as I tend to concur, but was not aware they're not connected on your FCR's. I just assumed they would be beneficial for racing, but no not essential eh?

The Mikuni RS flat-slide carbs that Redax fitted to my '78 1200 were impressive for performance, starting, idle, economy, etc, etc.
Hence the interest I had in utilising the surplus #4 carb left out from the x4 bank that Red sources. But for me, it's not such a 'plug & play' option due to the need to source and fit all the missing throttle spindle, cam, springs, etc, etc. As all those items are still required for the x3 bank.

So, I'll just keep kicking the idea around for a bit longer eh  ???

 

[wavey_davey]

Just to wade in on a theme from an earlier posting in this thread, i.e single carb conversions.

I've just acquired a single carbed 850 Commando (VM34 Mikuni) and yes, it sips the juice, but it's performance above 4000rpm is pretty insipid. Yes this could be due to other reasons I guess, but there's plenty of informed opinion over on Access Norton (by far the best Norton forum) with dyno charts showing about 39 peak bhp compared to around 44 for a standard commando, v little difference up to around 400rpm which is a perfectly respectable way to ride a commando, hence why it's popular.
An SF is pretty much the same power give or take, with a fair bit more weight, not sure I'd want to lose 4-5bhp on a 500lb twin?

Personally, unless I had the dosh for something more exotic, I'd go with dells, nothing against VMs as I have a pair on my T140 Bonnie, but can't see them offering any significant advantage over a pair of PHFs, other than possibly cost, and that would soon be eroded by the need to faff with jetting?

I'd love to put a pair of PHFs on the commando (width is an issue apart from anything else) but will go with Amals now hard anodised slides pretty much cure most of the Amal ills. The BMW airhead fraternity still look at dellortos as a performance option for reasonable money compared to the relatively tame Bings.

 

[sfcpiet]

'tis a pity Mikuni don't supply a matched set of VM carbs for twin cylinder bikes. Maybe a single VM carb with a custom matching inlet manifold is not such a bad idea? no?

Looks much like the Mikuni VM range is being phased out, quite a few variants are no longer available.  VM34 are available with LH or RH idle screw, air screw is always RH... maybe they can be bored to 36mm.

piet