New Carbs??

Hi again,
having loads of carb problems, and wondering if they are creamcrackerd as i dont know history, :question: so now thinking about replacing existing phf 32’s with 36’s .I believe they should fit straight onto existing inlet stubs if i cut a little groove in.Since engine was rebuilt it has had bigger pistons fitted, so i believe the original 860cc is now closer to 890cc but not to sure of exact size.
My question is would phf36 carbs benefit the performance or should i go for phf 40’s ?

cheers phil :question:

I reckon the 36’s are the better bet. Most 900SS owners reckon it’s overcarbed on 40’s. Great for racing (when it was new the 900SS was a competitive proddy race bike) but are too much for the road.
The 36’s also have the benefit of proper chokes instead of those silly tickly things.
I’ve gone this route on my 900 Bitsa. Trouble is it’s still to turn a wheel yet so I can’t verify the theory! :unamused:

Like wot Spaggy says. To get the top end performance of the 40s you need to:

  1. Run a more open silencer system, traditionally designated by the name ‘Conti’ :wink:
  2. Get more oxygen into the engine, i.e. fit bell mouths.
    (3. Ideally go the whole hog, and fit the remainder of the factory racing kit, e.g. larger inlet valves …)

You will, however, lose bottom and mid-range tractability.

36 carbs are reckoned a good compromise. That said, my SSD still pulls an indicated 120 mph on 32s … but than again, that’s probably nearer 75, given that Veglia made the speedo drive :slight_smile:

(Note to self: stop using those bloody stupid Smilies - please!)



Hi …
The 36mm carbs will be better than the OEM 32’s, they will give a power gain (although less than the 40’s) and be more tractable than the 40’s.
Lets be honest/realalistic here how many bevel owners rake the tits out of their bikes theses days?
So a more torquey motor is probably what you want these days…
I differ here.
As for the need to cut a groove on the inlet stubs to fit them?
Are they rubber mounted Guzzi Mk1 Le Mans items? If so you will also need to shorten the stubs by an 1/8" of an inch or so.
Only this week I’ve bought a new pair of rubber mounted 40mm Mk5 Le Mans carbs (£345 the pair) from Eurocarbs to replace the 41mm rubber mounted race Dellortto’s on my 900SS which had gained a blockage in the idle circuit on one carb due to corrosion, everything I tried couldn’t shift it.
I’d have bought 41 or 42mm items but these are NLA…
Unlike Spaggy I don’t hold with cable operated chokes, thinking ticklers far superior!
They’re simple, they can’t go wrong, there’s no cables etc to break and when you press them down the carbs flood as intended…
Job done IMHO!
So today has been spent removing the choke systems drilling the carbs, filling the choke passages/drillings with ‘Devcon’ to accept Amal Mk1 extended ticklers which cost £13 the pair.
Also removing the accelerator pumps and carrying out the same blanking procedure as above.
To these modified bodies I then fit No6 chromed solid brass slides, huge springs that fill the bodies and different carb tops, all of which are available from Dellortto’s.
The result of all this work/fannying around is the lightest action smoothest set of period Dellortto’s you’ll ever use.
I also use a quick action Yamaha TZ350 throttle, which meens that full throttle is only just over a 1/4 turn away!
These slides never wear out and the carbs stay intune for a whole lot longer than the standard set up.
Later this yearI I’ll get them bored to 41 or 42.5mm after fitting the HUGE short bellmouths fom the original 41mm racing carbs, which involves machining off the threaded stub on the carbs that usually accepts the plastic standard items and machining a step to take the bellmouths.
This set will then be the same as the carbs fitted to the NCR Endurance Racers of the time, which’s as good as you’ll get short of fitting a pair of modern 41mm FCR’S.
These carbs are good enough to make over 100rwbhp in a highly tuned motor, although my ‘Mildly’ tuned motor made 87rwbhp which is/was a fair jump from the 65-67rwbhp that the standard 70’s 900SS made.
My bike went through the speed trap at Snetterton at just over 143 mph, I later tuned her futher but never put her on a dyno.

Steve R

thanks for all the comments and advice. I am still weighing up my best options and will probably cut my losses on money spent on the old 32mm and go for 36mm. I am not that bothered about top end performance and would much rather have a nice crisp response to throttle up to legal speeds for everyday riding, thats if I ever get to ride the thing?
Just on a final note re 32mm I met guy in I.O.M last week with an 860 sort of cafe racer thing and was asking him for advice as he was running the 32’s, he said change the pilot jets to 45 as the 60’s recommended in manuals in his opinion where too big and could contribute to difficult starting. Anyone any comments on that ??

Bye the way Craig re all your comments on engine smoking, I bought this engine last year as a fully refurbed unit by Witty Ducati so I am assuming that all is well inside the casings and once the carbs are sorted everything will be hunky dory? I have always been an optomist !!
Oh sorted out the speedo/rev counter got this great bit of kit with everthing on from

Hi Phil,

John Wittmann re-built my 450 engine and did a fine job. So you may be lucky!

P.s I thought he’d given up everything Ducati-wise since his move to Spain. Am I wrong? If so, do you have any contact details?



I bought it off a guy called Andy Williams who advertises in Classic bike, he led me to believe he could contact him in Spain? Can dig his number out if you want.
cheers phil

Hi Phil,

Yeh, I know of Andy Williams, if he’s the same guy who trades as Italian Motorcycle Engineering (or similar). Somewhere near Northampton, I believe?

Something I forget to mention is the valve guide oil seals. These harden with age - and can split anyway - and will cause you to smoke (well, not you personally, but you know what I mean). Easy and cheap to replace on the front pot. Do you know when the engine was overhauled?



Hi Craig, thanks for that info will bear in mind when get back to fettling the duc.Currently working on another project which is taking more time than expected trying to get a learner legal up and running for my son to practice on and get his license.
will get back to you all once ducati is on bench and have another go at carbs.
Cheers everyone Phil

Hi again, well its only 12 months but have got the cafe race project out again and need some advice.

I bought 2 new PHF 32 carbs, albeit rubber mounted and have got round to fitting them, low and behold after various problems with cables and throttle incompatability - now all sorted, I am having troublestarting the bike.
Before it would start but would not run .
I have noticed that on the rear carb when I twist throttle it sqirts a jet of petrol down the manifold but the front does not ! Advise please could this be my problem, or one of them?

Cheers Phil

Hi Phil,

No, most probably not (but see next paragraph). It just means that one of the accelerator pumps is working and the other isn’t. And the pumps are really only there to overcome a temporary lean condition inherent in this type of carb when the throttle is whacked open quickly. (Btw, the faulty pump may self-prime. If it doesn’t, there’s a way of doing it yourself. But, for now, let’s stick to the issue at hand …).

(Here comes the afore-mentioned ‘Next paragraph’ …)
That said, twisting the thottle when starting can cause the engine to flood so that it won’t start. So that could be at least part of your problem. Ideally, you should be starting the bike with full/partial choke and no/little throttle (ok, before everyone jumps down my throat: yes, particularly when starting from warm, you can use the pumps to prime the engine instead of using the choke. But let’s not confuse things :wink: ).

So, question time:

  1. Is either cylinder igniting at all, or are both dead?

  2. When you kick the engine over with the choke on, but without twisting the throttle first, are both plugs getting wet or at least smelly?

You say you bought new carbs. We need more info:
3. What internals have you got, especially what size idle jets? (Size 60 was specified for the AD/AS carbs, 55 for the later, emissions-compliant C range).

  1. Do you know the float heights are correctly set? (17.5 - 18.5mm set as per the instructions on page 10 of the manual here . There is another way too, if this doesn’t work for you).

  2. What settings have you got the idle and throttle stop screws set to? (Screw in gently and then back out 1½ turns for the idle, 2 turns for the throttle stop).

And can we assume you’ve got a decent spark on both cylinders?



Thanks for the info Craig,
I have now moved on from the carb problem, you where right the other pump is now working and had nothing to do with problem.
My new problem is no compression on front pot due to stripped plug thread! it looks like its been helicoiled before and its now nearly smooth .Have ordered a uni thread kit to see if I can repair. will keep you informed of progress.
When it did start it seemed ok but when I released choke on front it cut out, it was quite smokey also , would this be caused by lack of compression or am I in for another suprise once plug is sorted.
Oh the joy of owning old italian bike, although must say the guzzi never lets me down.
Cheers Phil
PS now added mhr 900 to stable its mint and looks the dogs!