Airone Sport with SS25 carb

[Don-Spada]

Hi  

I have a 1953 Airone sport with the original SS25 carb fitted.  It has always run very rich.  It will start easily without any need to tickle the carb, if I do it fouls the plug.   The carb is generally in good condition, my friend made a new slide that fits well in the body as the old one was very worn. 

I was reading an old thread in the group recently talking about the idle mixture screw.  The owners bike had similar problems to mine, running rich.  His had a rubber bung over the hole on the left side of the carb which seemed to be the cause of his problems.   

 

Backfire on Kick start   

Looking at my carb, that hole has a brass plug screwed into the hole opposite the idle screw.  It looks authentic, it fits nicely, but the past conversation I was reading suggested that this should actually be an open hole to provide the air for the idle circuit.  See photos attached with the screw fitted and with it removed.  The air screw on the right side does seem to have a slight effect, the engine dies if I screw it right in or well out.  

My question is should this be an open hole or should it be capped off?  Can someone share a similar photo of the carb on a well running Airone sport     

Many thanks 

Don West  in the UK.  

[jef walker]

Hi Don,

This is a picture of my Airone sport 1953, it's blanked off on mine and runs very well.

Hope this helps.

Regards 

Jef Walker 

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From: 'Don-Spada' via Guzzi Singles <guzzi-...@googlegroups.com>
Sent: Monday, April 13, 2026 5:15:08 PM
To: Guzzi Singles <guzzi-...@googlegroups.com>
Subject: [guzzi-singles] Airone Sport with SS25 carb

 

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[Don West]

Thanks Jeff.  It's strange why the previous conversation suggested that this should be an open air hole?  

Don  

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[RICHARD YAMANE]

I have a similar port on my GTV carb. I thought it should have been plugged but was told that it is supposed to be open. My carb will drip a bit of fuel from the port which is why I thought it should be plugged. 

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[John O Regan]

HI All,

The hole opposite the pilot mixture is the pilot air inlet, 

Over time the incoming air  gathers road dirt which will affect the slow speed running 

It should be occasionally be cleaned, make a note of the number of turns from fully closed the pilot screw is

then remove it and flush through with carb cleaner, replace the pilot screw to the same position before any adjustments

John

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[John O Regan]

Hi,

Is there a hole  in the little boss just to the left  and in a little of the brass plug?

If so then that is the air inlet and the plug should be put back  in place 

John

[Don West]

Sorry for the delay in replying John.  I've only just had chance to take a look.  I can't see any air hole in the boss or the brass plug, see the photo below in my original post.  

All the drawings of the Dellorto carb I have seen are very poor quality and it's not possible to determine how the pilot circuit is supposed to work?  I assume it is allowing air in rather than fuel.  Some people say it should be blocked off, others say it should have an air hole.    

Does anyone have any other thoughts on why it is running so rich?  There is little option to alter the float height as the pull up float pin has no adjustment.  

Don  

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[John O Regan]

HI Don,

If I get a chance and remember I will try and get a decent look at the Dellorto on mine

To lower the float vs the float needle a couple of methods are possible depending on the style of clip used

Before doing anything remove the float chamber lid and measure down from the top to where the fuel level is (tap on)

then mark the outside of the chamber so as you can run a horizontal line around the carb body

On Amals, the level should be inline with the bottom of the pilot mixture screw, I cannot see why the Dellorto should be different???

If there's an "E" clip or similar on the float needle, plastic washers can be used to move the float downwards, Amals "Jewsharp" clip can be reshaped carefully to adjust the level.

I do not like the idea of cutting other grooves in the float needle🤬

John 

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