Falcone Sport SS29 needle

[Derek Wardell]

I have a 1955 Falcone sport with an SS29 carb.  It runs pretty well except for a hesitation on the first 1/4 of the throttle.  Spec is

Idle jet   50

Needle   M13

Atomiser  270

Main    130

Surprisingly it ticks over well and runs well enough except for hesitation and the occasional spit back on small throttle openings.  I only run it on Esso Supreme fuel (which is Ethanol free in UK).

On my Parilla 175 (UB22 carb) I had a similar issue and was advised to change the needle as these are aluminium and wear quickly.  A new needle here dramatically improved the carburation, I was quite surprised.  I thought I'd try the same on the Falcone.

Is the spec above correct?  Needle should be M13?

Thanks for any advice,

Derek

[Alan Comfort]

Spitting back at partial throttle opening indicates that the cutaway in the slide may be too large. It may be a challenge (and expensive) to find a slide with a smaller cutaway for an SS29 carb. I would try experimenting with the needle position first. It is easy to do and does not cost anything. While the needle is in your hand, examine it carefully for wear with a magnifying glass.  A small amount of wear on the needle can have a big effect on the fuel/air mixture at partial throttle openings. A little wear on the needle can often be compensated by adjusting the position. I usually start with the needle in the middle position and go up or down from there.

Carb tuning is a bit of a black art and can take a lot of time and effort to get perfect. It may be impossible to get it perfect with a sixty year old carb, and you may have to live with some compromises unless you go to a conversion to a modern carb. Even then, you are faced with experimenting with jetting, needle position and all of the other variables.

Alan in Roberts Creek

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[pouma1954]

Check for slide and/or carb body wear as well Derek.

Paul

Envoyé depuis mon appareil Galaxy

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De : Alan Comfort <alan.c...@gmail.com>

Date : 04/08/2021 17:18 (GMT+01:00)

À : guzzi-...@googlegroups.com

Objet : Re: [guzzi-singles] Falcone Sport SS29 needle

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[Rick Yamane]

Check your valve adjustment too.

 

Rick

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[jerry atric]

Shawn Sci on here, glued a little bit of brass on his slide to reduce the cutaway with good results. That must have been a year ago and I haven't seen him report it falling off.

[Rick Yamane]

That reminds me,

When we were racing a Fiat X1/9 I had to profile the edges of the foam float to combat the centrifugal force pushing fuel up the sides of the float bowl shutting off the flow through the needle. I would use epoxy to seal the cut areas. Never had an issue with leaking or the epoxy coming off. You could probably use JB Weld to build up the slide and reshape it. I’ve heard of guys using JB Weld inside of ports to improve flow too.

 

Rick

 

From: guzzi-...@googlegroups.com [mailto:guzzi-...@googlegroups.com] On Behalf Of jerry atric
Sent: Wednesday, August 04, 2021 12:15 PM
To: Guzzi Singles
Subject: Re: [guzzi-singles] Falcone Sport SS29 needle

 

Shawn Sci on here, glued a little bit of brass on his slide to reduce the cutaway with good results. That must have been a year ago and I haven't seen him report it falling off.

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[Derek Wardell]

Thanks for your replies.  I'll start by evaluating changes in the needle slot.  Doesn't look like new M13 needles are available in UK.

Cheers,

Derek

[SED Sci]

Don't know if it helps but the 1954 Falcone manual shows needle (spillo) N.13.  Not M.  Pretty sure the needle is "Number" 13. Page 68 here: https://www.rpw.it/Files/GUZZI_Falcone-MO.pdf

As needles and needle jets wear they admit more fuel, not less, but the needle doesn't really contribute much fuel until about 1/4 throttle.  It seems reasonable that if you have a 13 needle, it is not the problem, even if it is worn.  The manual shows needle clip in 2nd notch from top in summer and 3rd in winter.

The '54 manual shows that the idle jet should be 55, not 50.  (for Dellorto 55 means the jet diameter is 0.55mm) Spitting back in the carb is usually a sign of lean mix so installing a 55 idle jet is the first thing to do.  The larger idle jet will increase the fuel in the transition between idle and needle jet which is probably where it is spitting and hesitating.  Adjust the idle mixture just after the engine has warmed enough to run, but not hot.

While you are replacing the idle jet, check that the float level is not low.  I'd raise the float level to the upper end of the spec - i.e., higher fuel level.

 

I've been fighting popping through the carb (and also banging in the exhaust) on the GTV and I've tried all kinds of things including gluing the bit of brass to the inside of the slide like Baconsli mentioned.  Isocyanate super glue is gas resistant, but JBWeld softens and swells in gas.

Let us know what works!

 

[Gordon de la Mare]

Interesting comment regarding adjusting float level.

Most of my float chamber needles have just a single groove but a couple from my race/competition bikes have multiple grooves.

The 1939 Dellorto manual says for SS and SSF carbs the slot should be 22mm from the top of the needle but other carbs should be19mm for smaller engines and 23mm for 600-600cc motors (regardless of brand).

Has anyone actually played with these settings?

I ask because I am have some difficulty getting a a good mixture on my 1938 GTC/L which is consistently running very rich.

As it is a race carb there is no air mixture adjusting screw only a fuel feed screw for "idle" or very slow speed running. .. it isn't exactly an idling engine.

Cheers

Gordon

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[SED Sci]

Regarding float level, I raised it to cure a lean transition. Float level seems to have a big effect on the transition from idle to needle/needle jet, ie., from just off idle to 1/4 throttle. The MD26 carb that came with my GTV is worn out so I decided to install a PHBH28 from my Monza and adjust the settings and the transition has been a real headache with popping through the carb and banging in the exhaust. ( This was also a problem with the MD26.)  The most effective solution, other than running incredibly rich idle jet, slide or raising the needle too far has been to raise the float level about 2mm.   Raising the fuel level richened the transition, but there is little change above 1/4 throttle and the bike is running much better.  Perhaps that velocity through the throat is so low that it will not entrain enough fuel with the fuel level lower.  

Page 4 of this Dellorto guide shows multiple needles and 2 different positions for the notch for SS carbs.   https://www.rpw.it/Files/Tabelle_Dell_Orto_fino1939.pdf

I seem to remember seeing another Dellorto table that had different length needles given letters A, B, C, and D, but can't find it now.

It may also be possible to adjust fuel level by changing the thickness of the gasket under the needle seat in the float chamber.

Hope this helps,

Shawn

[Gordon de la Mare]

The needle types are here:

https://www.dellorto.co.uk/shop/dellorto-motorcycle-carburettors-parts/dellorto-vintage-carburettors-and-parts/ss1-ss2-parts/float-needle-pull-up-type/

In my case I may need to lower the float. 

The nearest engine to mine is the Condor but that, like the Dondolino, is a bit scarce on documentation with just 69 of the former and 57 of the latter built there isn't a lot around.

The factory notes that I have seen from the 1990s indicates the Condor has a SS1/32 carb but they actually have SS1/30 as per the fino1939 Files you indicated. 

 Not even the factory always gets historic data right.

Gordon

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