S3 1300 tune for trumpets

[Bainesy]

Hi all, I have read all the old posts and understand that the standard air filter box is better than gauze trumpets and foam filters, but for a couple of hillclimb events I wanted to enjoy and share that lovely sound. 

I've fitted the trumpets and of course there is a flat spot around 30mph and accelerating hard from 2500rpm.  Therefore, just for these two events Im willing to do what is necessary to 'lose' this flat spot.  Question then:  Is there a simple way (as I'm guessing its mixture) to tune/adjust the carbs for this (Fulvia Series 3, 1300 with Solex)?  any thoughts welcomed.  Thanks in anticipation.  Keven

[lancialulu]

The only thing I think you could do is try to up the size of the slow running jet. I run 60 (after trial and error) on my 1.3 HF in quite a high state of tune. I still have a flat spot....

The emulsion tube on the 35PHH Solex is already designed to richen the mix at low revs so not much you can do from transition to main jet running IMHO.

I guess you are suffering from bogging down on the take off because after that you should not see the flat spot in any gear.

Specifically the 1.3 benefits from the air box design, not so much the 1.6 which can run on trumpets.

[Neil]

The Solexes may require different air corrector jets if you are running open trumpets to cure the flat spot.

[lancialulu]

The Solexes may require different air corrector jets if you are running open trumpets to cure the flat spot.

up or down in size Neil?

Very difficult btw to separate the air corrector from the emulsion tube, if not impossible.... generally they are bought in Solex land as a complete assembly.

[Bainesy]

Thanks guys, think Ill save the trumpets for my HF resto?  Keven

[Neil]

I understand it is not a matter of changing one set of jets, making them smaller if they are available, then checking if that cures the flat spot, but may also further changes to the main jets by increasing, but a rolling road test might resolve the problem. I am not sure if alternate Solex jets are readily available, unless you solder them and drill the jets as required to new sizes.  Certainly an art of to knowing which to fit which would need a carb guru really to advise.

[lancialulu]

I understand it is not a matter of changing one set of jets, making them smaller if they are available, then checking if that cures the flat spot, but may also further changes to the main jets by increasing, but a rolling road test might resolve the problem. I am not sure if alternate Solex jets are readily available, unless you solder them and drill the jets as required to new sizes.  Certainly an art of to knowing which to fit which would need a carb guru really to advise.

Alfa1750 ebay site has a lot of Solex jets and can I tihnk supply anything you want, but it gets expensive as you have to 4 at a time....