So, which one?

[Bison]

I am confused slightly. I have VHBZ 25HS carbs on my Sport, I read the main jet should be 112, I have 115's .
Which should they be?.
I have BD atomisers. With 40 pilots, I still have a stumble from pickup, which is very annoying, especially when it stalls while pulling away,.
Alan.

[Bison]

I should say I realise these two observations are unlikely to be related.
Alan.

[Daddy Dom]

Hi Alan,
have you seen the chart at the bottom of this page? http://www.motomoriniclub.nl/buy.html
Dom

[hendre]

there is a even bigger table in http://www.motomoriniclub.nl/carb.html
I think somebody changed the Jetting to a Sport '74 while your Sport should have the '79 setup? (educated guess)
Comparison of the two:
carb body idle main atom. choke needle slide float
350 Sport - 1974 VHB 25BS 50 115 260BD 50 E17 2nd 50 2 x 14 gr
350 Sport - 1979 VHBZ 25HS 50 112 260D 50 E17 2nd 50 2 x 14 gr
I would try and lay my hands on a set of 50 idles, 112 mains and 260D (or 260CM from the K2) atomizers and see what happens

[Bison]

Hi Hendre, and DaddyDom.
Thanks for your reply.
It so happens I have 112 mains and 50 pilots, I'll fit them one set at a time and give it a try. The bike is running pretty well right now though, perhaps slightly rich.
Thanks,
Alan.

[EVguru]

What fuel do you use?

[Bison]

Hi Paul,
Shell super unleaded.
Alan.

[EVguru]

Every bike is a bit different, but in general modern fuel tends to make our machines run rich at idle. The idle jet works in conjunction with the mixture screws to set idle mixture, but as you come off idle, the progression mixture is controlled by the idle jet and the slide cutaway. The needle is parallel until about 1/8th throttle, so isn't involved.

I'm running 43 idle jets and have almost eliminated the stumble. The atomisers affect mid range and acceleration and the main jet is just that, so really you're looking at just idle jet and slide cutaway. They're quite sensitive to carb balance and I like to remove and blank off the balance pipe. Both the idle screws AND the cables need to be balanced. I often find it best to do the cables first, but the first action should be checking the valve clearances.

[Bison]

Thanks Paul,
I'm running my valve clearances at .006" rather than .004", I'm pretty sure I have a stock Sport cam. Wouldn't take long to set them to the correct size though. Carbs are balanced both at idle and on the throttle, but I'll check them again. Don't have a balance pipe.
Alan.

[EVguru]

The valve stem wears the rockers in the center of their pad, so a feeler gauge is measuring the distance between the valve stem tip and the UNWORN parts of the rocker leading to a larger than desired clearance. You either need a feeler gauge narrower than the valve stem (or a feeler wire), or reprofile the rocker tip. I do the latter with a diamond lap.

Why were you running overly large valve clearances in the first place?

[Bison]

There was some confusion as to whether the cam was standard sport or L5. The previous owner had the cam reprofiled by NLM to what he assumed was L5, I checked with a valve timing dial, the duration matched exactly to the Standard sport, so I assume that's the profile. I mistakenly set the clearances to L5 spec. But I'll go out tonight and set them to .004"
Alan.

[hendre]

Thanks Paul,
I'm running my valve clearances at .006" rather than .004", I'm pretty sure I have a stock Sport cam. Wouldn't take long to set them to the correct size though. Carbs are balanced both at idle and on the throttle, but I'll check them again. Don't have a balance pipe.
Alan.

do your carbs have the brass fittings? If so: these are the balancing connectors... to what are they connected? They should be connected to each other with a piece of tubing...
a Guzzi friend also had a Morini and had problems adjusting his carbs... after a while we figured out that the balancing connectors were not connected and had small pieces of tubing that led out into the open... drawing in false air running the engine lean

[Bison]

Hi Hendre,
No, brass connectors aren't there, it's just plain aluminium, no blanking plug or anything.
Alan.

[EVguru]

do your carbs have the brass fittings? If so: these are the balancing connectors... to what are they connected? They should be connected to each other with a piece of tubing...

The balance pipe was fitted to later models to make them less sensitive to carb balance.

You remove the balance pipe to connect the vacuum gauges, but when you're done and put the balance pipe back the idle speed goes up.

Now you have to adjust the idle speed screws, but with no gauges to show the balance!

I take the balance pipe off and cap the ports. I find the bikes tend to run better.

[Bison]

Paul,
My balance connections are in the rubber/plastic inlet manifolds.
Alan.