Well, I’ve got me a single carb manifold, the one that was on Ebay awhile back and a beautiful piece of kit it is too. Whether it works or not is a different matter! First step is to see if it fits. Then I need a carb. The general opinion has been that a Harley carb is probably best, so I’m now on the look out for a Sporty carb, should anyone have one.What I was wondering though and bare in mind these are the wonderings of someone who doesn’t know the ins and outs of all this Guzzi related technical stuff, is, could a Dellorto off anything, be jetted to work to save fannying around with cables and throttles and the like? And, on the subject of cabling and throttles, if I were to use a Harley carb what would be the ramifications visa vis its operation?
Mini Car SU carb easily available and you can alter the jets easy
Harley owners favourite conversion
Right, the manifold fits but only by removing this breather do dah.Question 1. What is the alternative to using it? Can I route the breathers elsewhere?I fitted an SU to my evo chop Tone, but I need a carb that mounts on rubber with jubilee clips and I fear an SU is just too big too.
Fell over this straight after reading your thread - might help[
Thanks Tris, I have searched the net from top to bottom and read everything I can find.There are a lot of people that say it won’t work - the inlets are too long, etc etc. And then there are the folk who have actually done it and are exceptionally pleased with their results, whichever way they have tackled it. This was one solution.And this is what I’ve got. Lovely stainless steel.Ive had to remove this to fit it.What can I do with the breathers now?
I thought most Harley owners junked the standard carb and fitted a Mikuni? Just a thought.
su’s with external float chambers dont like leaning over
later HIFxx series are much better at anglessingle carb is on my winter list as my wrist wont take the twin carbs even with new cables and springsguzzi-t52013-05-16 07:52:47
Hi John,
I’d be inclined to fabricate and weld on a flange to suit whatever carb you choose. I would use a Mikuni VM34 and scour the net for jetting information. It’s a popular conversion for 850 Commandos and such, and with your extra capacity you may need to jet-up very slightly.
Don’t go too large on choke sizes- 34mm is all you’d ever need.
Just looked at that same This Old tractor page that first manifold pic comes from, other pix on that page show Le Mans type breather box being used. It also says as far as carb sizing goes, get one having the same cross section in cm squared as is that of the 2 original carbs added together. E.g. diameter 44mm = 2 x 32mm, so I would have thought a PHF40 would do for 2 x 30mm (?)
Sorry that doesn’t make sense. Force is always acting ‘downwards’ relative to the bike, so when cornering it’s gravity plus inertia to keep going in a straight line, you balance them by leaning over, then the product acts exactly perpendicular to bike. (If it doesn’t then you go off the road!) Also what about sideways force on the float chamber when the car is cornering? Cars don’t lean over, so it should be better on a bike!
im sure if you tape a jam jar of water to your tank the water surface will stay horisontal as you lean, older su with the float chamber on the left dont like leaning eps to the left. I can vouch for this as my landrove sII would cut out on left hand slopes with an hs6 su fitted… an internal float chamber hif 44 solved the problemguzzi-t52013-05-16 11:52:36
Its shiny therefore it must be good
Try tying some string round the top of a jam jar to make a handle. Then fill the jar with water and twirl it round your head. Look at what the water does.
Mike H is right about the SU, but wrong about the carb. size. It doesn’t work like that. Only one cylinder is sucking in air at any one time. You need to go slightly bigger than one of the original (dual) carbs, but certainly not twice the size. A single 34mm carb would be optimum.
That was my experience too, but just retaining one of the original carbs will work almost the same.
If you go much bigger with a single carb it will not be pleasant to drive at low throttle openings.Brian UK2013-05-16 15:43:21
Has anyone got a Dellorto they want to sell that would do?
jmee542013-05-16 16:04:15
http://www.nortonownersclub.org/support/technical-support-commando/carburettors-other
Interesting reading. OK - so it’s for a Norton, but Physics are Physics.
yes centrifugal force will push the water to the base of the jam jar and keep it there.but a static float chamber on a bike it will push back wards or sideways, same as then fitted to a car in normal use. The links with sucessfull use of SU carbs all use the later HIF carb with the integrated float chamber
A static float chamber on a bike, when cornering, is just like the jam jar being twirled around your head.
Many years ago (think late sixties) I designed a single carb manifold for the Commando, and with a couple of mates, went into production.We had as a result, quite a bit of experience in single carb conversions. The standard twin setup was 32mm, one of which worked quite well with the single manifold. But a 34mm did give a bit more. Anything larger was counter productive, unless the ports in the head were opened up too.By the way, in terms of design, we were toldby many who had more experience in manufold design, that we should have a flat face opposite the intake part, and not attempt to put in a Vee, as that will always cause a bias to one side or another. With a flat face, the mixture sorts itself out.But we were using Amals of course. With Dellortos, the idle jet orifice is to one side, and invariably gives a strong bias to one side around tickover and just above. I also made a single manifold for the V50, using the original dellorto. Absolutely impossible to get an even tickover. Look for a carb with central orifices.
Brian UK2013-05-17 08:45:56