Weber Carbs

[Rodney]

does anyone know what your approx idle speed is on these carbs. Is there a setting for the main jet needles
can anyone help me with a reason why i get an occasionsal back fire in the carbs or is this a common occurance with these carbs

thanks
Rodney

[fasterdammit]

I seem to recall the proper idle speed for a warmed up pair of Weber 44 DCNFs is like 1500rpm.

If you do a search, you'll find a couple threads in here about the 44s ... myself, I'm looking for a pair of Mikunis to swap in which seems to be the prevailing 'best advice' for our bikes. I've heard similar noises from one of my local shop owners (also a one-time Paso owner).

I tried swapping in a reubilt 44 with a different jetting set up - it runs great when you're in the upper registers, but it's a pretty rich mix overall. I'm not thrilled with it; I may go back to the original jetting but it's 6 of one, half dozen of the other ... and they're all stale if you catch my drift. :thumbdown:

I haven't had any backfire issues with either carb though - maybe once, and that might've been due to bad gas & nearly flooding it (starting up after a winter's rest). Yank your plugs - what condition are they in?

[motiztab]

Funny thats just what happened to mine on Monday.
Engine cold and it gave one heck of a backfire then missed for a while.
When it wants to idle mine sits around 1200.
Still running a out of balance webber.
What gets me is why do these carbs go off tune?

[fasterdammit]

What gets me is why do these carbs go off tune?

They're actually an automotive carb, if that makes a slight difference? (Anyone?) IMO, I think they'd be better off on a farm tractor ... :neener:

[jfiore]

The "correct" idle speed for this carb is supposed to be 750 RPM. If your carb is set up right, it will idle at that speed, but it leaves a larger hole in the off/on throttle response. I have mine set at 1000 RPM.

I'm not sure what you mean by the main jet needle. If you are referring to the idle mixture adjusment, there are two screws with spring tensioners at about 45 degree angles at the back of the carb which are the idle mixture adjustments for the respective cylinders.

From my experience, the carb tends to backfire, as well as popping on deceleration, when the idle mixture is not set up correctly. Since re-jetting and adjusting the idle mixture, I have not had any more backfiring.

First, you need to change your idle jets to .060 size. Then you need to set your float height to 46 mm from the gasket surface of the carb cover. This will require removing the airbox, the air intakes, and the carb cover.

With the carb cover back on (don't worry about the air intakes or the airbox), close the two air bypass screws which are near the idle mixture screws. Then set the idle mixture screws to about 2 and 1/4 turns out from fully seated. That should be a good starting point. Start the bike and get it warm. If it won't idle at this point, then there may be an air leak in one of the intake manifold sleeves, the carb cover is not fastened down tightly, or the carb cover gasket may be leaking. If the bike will idle (you can adjust the idle speed so that it idles around 1000 rpm) then you just slowly turn one mixture screw out , listening for the engine to start running rough, or rpm dropping. Note that position on the screw, then slowly turn the screw in until the same thing happens. The best setting is about halfway between the two settings, where the engine should be running the smoothest. Do the same with the other mixture screw. You can repeat this a couple of times, to satisfy yourself that you have the best setting.

With .060 idle jets and a proper idle mixture, you should find that the bike has a much less abrupt throttle response when accelerating from idle.

[redpaso]

good info for those of us persisting with the Webbers, thanks

[Rodney]

thanks for all the suggestion will try them, at present mine is idling at 500 rpm so i will increase the rpm

thanks
Rodney

[Skins]

Just a few thoughts:

I've had no experience of the Weber, but I'm just wondering if all you guys have fitted the fuel pressure regulator apparently required to make the Weber work properly on the Paso, and also what the real benefit is of a low idle speed.

Even riding mostly in the city and suburbs as I do, the time my motor spends at idle is really not much, and the engine is under no load, so it doesn't overheat or use heaps of fuel at idle. I believe having my bike idle at 1100 to 1200 rpm keeps the plugs clean and the oil pressure good. Oil pressure is not so important in a low-load situation, but it can't hurt to keep it up. However, keeping the plugs clean keeps the bike smooth and fast. :lick: :lick:

With a good shift action and clutch I never have any trouble selecting first. Of course I never sit at idle in gear and holding the clutch in. :toofar:

[Sean]

If you are working on your Weber one thing you may want to look out for is the plastic "Y" connector that splits fuel flow from the pump to the carb and recirc line. When I was rebuilding my Weber, the "Y" literally fell apart in my hands, probably due to age, etc. I ended up replacing the "Y" as well as all the fuel lines.

I've got a fuel pressure regulator, however, I have yet to install it but I will shortly. I'll let you know if it makes an appreciable difference. Good luck.

[4away]

I have fitted a petrol king fuel regulator between the fuel filter and the carb and reduced the fuel flow by turning the aduster screw on the regulator anti clockwise. This has virtually eliminated "popping" at idle and low speed caused by flooding in the carb. The pressure from the standard fuel pump is too much for the 44 dcnf carbs and excess fuel is dumped into the front cylinder causing it to flood and mis-fire. Fuel consumption also improves after fitting a petrol king fuel saver. They cost between £25 and £33 new. I also cleaned and set up the carbs (including fitting a pair of 058 idle jets) and balanced them. I then fitted splitfire spark plugs (from mandp.com). The bike runs like a dream (not superdream). Tick-over is best between 1200-1500 rpm.

[Marinus]

First, you need to change your idle jets to .060 size. Then you need to set your float height to 46 mm from the gasket surface of the carb cover. This will require removing the airbox, the air intakes, and the carb cover.
.

How do you actually take this measurement? Do you gravity feed some fuel down the pipe with the carb intact and then remove the top of the carb with the float and make the measurement of the fuel left in the empty bowl.

What is the practical way to test the valve? I just put my thumb over the supply tube and blew down the return line.

[Marinus]

Where on the webber carb is the model number?

[Rodney]

the part number is on the fuel bowl side of the carb should read
44 DCNF-107 7D
hope this is of some help to you

Rodney

[ducapaso]

In my experience, there's no great difference in fuel pressure regulation or float height: the paso runs good with float at 44 or 48mm and the extra pressure will flow back to the fuel tank; best help from a pressure regulator in the bypass is to prevent vapour lock in the fuel pump.
In order to help you, here are my suggestion to fit a proper tuning to vacuum balancing:it's quite a work but it will make your paso run very fine!

First of all:
How to build Your own vacuum balancer
Components:
1) plastic trasparent (neutral color) pipe, diameter 8 mm (3/8 inch), about 2 meters (6 feet)
2) fuel pipe (or similar) about 4 meters (12 feet)
3) one 8 mm tap
4) two small tanks for fuel pipe (fuel filter #0370083350 original ducati or similar will do)
5) two holed nozzle screwed 5mm (these must fit on the fuel pipe too!)
6) one standing (about two meters,see picture)
7) blue water color
water , one glass

assembling:
Cut in two parts the trasparent pipe and put the tap between them
Put the tanks at the end of the two pipes
Cut about ½ meter of fuel pipe and save it
Cut in two parts the rest of the fuel pipe, and put them on the free ends of the fuel tanks
Fit it upon a standing, the tanks on the top and the tap about in the middle
Get the water color ready, just some drop of color in the water (you don’t need to paint anything)
Put the water inside the pipe, just to fill 50% of the pipe
Screw the nuts on the inlet mainfold duct, under the carburettor (you will find two standard screws in the place; you can see the workshop manual, adjustments chapter, idling adjustment, image 22.gif and 23.gif)

Put the rest of the fuel pipe between the two nuts on the engine

Using the vacuum balancer:
_First of all you’ll need to be able to reach easly the carb, so you’l have to put the fuel tank off and provide a different fuel inlet to the carb.
_ Insert the two ends of the pipe in the two nuts you have screwed
_close the tap of the balancer
_start the engine
_open the tap.
_Now you can see how the two cylinder inlets are balanced: the water level in the plastic pipe will be skipping colse to the average vacuum level. The difference between the two levels will show you how to work: 10 mm (5/16”) is quite good, more needs to be corrected.
_Fear not to see the water flow into the engine, as a very small quantity of this will not damage anything, moreover the small tanks at the end of the plastic pipes are fitted there in order to receive the water before it’s going inside the engine.

Tuning the vacuum balance
This is the absolutely hardest thing to do. If you aren’t skilled for this, STOP NOW!!!
Otherwise you can start working on the carb.
In the workshop manual you can find how to make an idling adjustment, see 22.gif and 23.gif
Anyway it’s not enough! YOU NEED TO FIT IT FOR BEST PERFORMANCE ON MIDDLE RANGE OF RPM!!! so:
Turn slowly the forward handle until ~2000 rpm
Watch the water levels: they often happen to be unbalanced, compared to the idling adjustement. It happens because of the lever and throttle shaft clearance!
This means that the throttle of the orizontal cylinder opens more than the other and this makes the forward irregular.
So, that’s what you have to do:
Stop the engine(of course!)
With your hands, turn the throttle shaft colckwise on the pump side, and with opposite spin on the lever.
Test the level again (close the tap before starting!)
If the handwork is not enough, try with some tool to lock the throttle shaft on the pump side and handle the lever side. YOUR MAIN PURPOSE IS TO SAVE THE SHAFT FROM ANY DAMAGE!!!
Repeat the test and the work until vacuum lever at 2000 rpm will be good
Repeat the test at idle. You’d better have a good balancing at middle rpm range than a good idle.

tuning the mixtire
you will need to install the airbox filter to tune it properly.
Spin one of the screws of mixture clockwise until the end; if the engine stops, unscrew for one turn and start the engine.
now spin it unclocwise for 1/2 turn each step... wait for a while and listern the engine running. When the idle speed begins to grow, you are near to the right tuning: the highest idle speed you can reach is almost a good tuning.
An additional spin of 1/2 turn unclockwise will get the mixture "rich"
If you can't see a great difference in regulating the screw, spin it again clockwise 'til the end and repeat.
Do the same thing to the other screw; maybe you'll need to do again the work on the first part, just for a bit of additional tuning
A rich mixture will help you in riding

You can see my carbureteur balancer here:
http://it.msnusers.com/pasochisti/shoebox.msnw
Have a nice work!
Nicola
dukess 751582