Jetting for SSF25A carb-Moto Guzzi Airone

[Mark Skinner]

Good Evening, 

About 6 months ago I bought a 1951/2 Airone that needed some work. 

After a good clean, some fresh fuel and a new plug, the bike starts and runs, just goes to show how good these little engines are.

I have slowly been collecting the replacement bits over the last 6 months. 

I found a SSF25A carb for sale and purchased it, I have fitted it to the bike. 

I set the tick over screw to just lift the slide off its stop and the mix screw is turned out by 1.5 turns.

After setting that all up the bike will start occasionally (after tickling the carb), tick over for a bit and then die. (my suspicion is that it is fuel starvation, the plug is bone dry and when I open the throttle to rev it up it just coughs and dies)

I have opened by the carb to check the jetting, the needle is a M7, the main jet is a 115 and the pilot jet is a 50. 

From what I have read the needle and main jet are not correct, they should be M13 and 125/130/135.

Has anyone had a similar problem and how did you come right?

Regards

Mark

[Andrew Nahum]

Does the float chamber flood when you tickle it? If so, Are you sure that the passage from the float chamber into the main carburettor body isn’t blocked with old gasoline gum or white alloy corrosion?

On 29 Jun 2021, at 22:37, Mark Skinner <markski...@gmail.com> wrote:

Good Evening, 

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[Rick Yamane]

Sounds like the idle circuit is plugged. Did you clean the carb?

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Subject: Re: [guzzi-singles] Jetting for SSF25A carb-Moto Guzzi Airone

 

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[SED Sci]

The idle screw is probably an air screw.  Try turning it in to 3/4 turn out.

[Luc Racine]

Waisted 5 years trying to start my Airone, it went from first kick to push start for no rime nor reason.

Idling was erratic as best and high revs not always achievable.the bike ran and i used it quite a bit with the SSI .

Changing the slide did a bit of good but the block was worn and i could not undo the nut holding it without risking to brake the body.

As you will see in former posts a new 40 Euros Jikov carb from a JAWA solved all the problems straight out of the box with no rejetting and does not look out of place.

The SSI is now a very pricey ornament on my display shelf, for the Airone next owner to waste his time with.

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[phil.sk...@gmail.com]

Hi Mark,

 

I know the SSF25A carb is clean and that the bike ran OK on the smaller carb that was originally fitted.

 

There is no problem with the fuel supply as when tickled the carb “floods” as expected.

 

The SASF25A is the correct carb for your Airone Sport so it should work well.

 

The obvious starting point is the incorrect main jet and needle.

 

I would suggest starting with a 130 main jet, M13 jet with the circlip fitted to the middle slot.

 

The motor ticked over fine last night but would not pick up revs when the throttle was opened. To me, that suggests that there is not enough fuel coming through the main jet, the mixture goes weak and the engine dies. This view is supported by the dry plug (ie it is not dying due to over fueling).

 

Does this make sense? Does anyone have any other thoughts?

 

Cheers

 

Phil

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[Mark Skinner]

Hi Andrew,

Yes the float chamber does flood and I dont think there is a blockage because when I tickle the carb fuel runs out the air screw.

So I am assuming that there is no blockage.

Kind Regards

Mark Skinner 

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[Mark Skinner]

Hi Rick, yes the carb was cleaned before I installed it. 

I stripped it down again last night to check for any blockages but could not see anything.

Kind Regards

Mark Skinner 

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[Mark Skinner]

Hi Phil,

After our phone call last night I thought let me double check the needle, main  and idle jets, they are correct for that carb. 

I had misread the table (link: http://motoitalia.parts/ss-dellorto-carburetor-technical-manual/), so what I thought last night is not correct, but having looked through the information again, the main slide should be a 90, where as I have a 100 installed and the atomizer is a 265 and I should have a 260.

Kind Regards

Mark Skinner 

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[Rick Yamane]

It does sound like fuel starvation. I doubt you are close to getting it on the main circuit. I would adjust the mixture screw richer and raise the needle to its highest setting. 

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[Mark Skinner]

Hi Rick,

Thats what will be doing tonight.

Kind Regards

Mark Skinner 

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[Philip Packham]

Hi Lou

Well described, I feel your pain, having exactly the same bike. What model of Jikov carb did you order/use successfully? Who was the supplier please?

[jerry atric]

Mark, when you say the carb was cleaned, I assume you mean ultrasonically? When there's nothing to lose, a bit of wire poked through all the 'holes' can dislodge hard baked  muck that less invasive methods won't touch. 

[Don West]

I have a 1954 Airone Sport and had a nightmare of a time with the SS25 carb, it was constantly running very rich so replaced it with a Jikov carb, it now starts 2nd kick and runs perfectly.  This is the one I purchased.  

https://ebay.us/m/MSkmsZ 

Don  

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[packhams4]

Thanks Don, much appreciated. 

Today I processed various tips on the site and some others today, went to the bike and made a bit of sense of what does what. 

Id cleaned the carb and inadvertently had the adjuster on the carb cap holding the slide up more than was ideal. 

Adjusted that and got her running nicely with the mixture screw and the slide adjustment, rode it 800-1000m. Result! Thanks.