It is possible to drill a hole in the standard SI24 carb air filter. This allows the carb to suck air more freely and, combined with correct jetting (normally a slight increase in main jet size and check it is correct by reading the spark plug), gives a cheap and easy performance boost. It is also possible to buy a filter which does not require the drilling (see below).

The reason that the holes aren't there on our scooters in the first place seems to be that the US and Australian markets were provided with detuned carbs (someone from Europe please confirm). This is just a guess and the fact that old Pinasco installation instructions talk about drilling a hole, suggests that "holeless" carbs were also sold in Italy in the past. This could also be a Cosa airfilter.

./European air filter.jpg

Dyno results show that the having a this hole provides a pretty big increase in power and at the cost of a main jet, is probably the best value for money performance enhancement you can get. See Air Filter Hole and Sito Plus lab results for more detail.

Here are is a picture showing the difference in air filters and the approximate size of the holes.

Retrieved from "http://www.vespalabs.org/Vespa_Tuning/Air_Filter_Hole"

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File			Size	Date	Attached by
		European_air_filter.jpg No description	143.22 kB	08:46, 23 Aug 2007	internetscooter	Actions Attach new version Move/rename Delete
		original_vs_holes.jpg Airfilters side by side	136.26 kB	06:59, 26 May 2009	internetscooter	Actions Attach new version Move/rename Delete

Images 2
European_air_filter.jpg	Airfilters side by sideoriginal_vs_holes.jpg

Comments (8)

Viewing 8 of 8 comments: view all

vespavintage says:

I've done this to my PX with a 118 main jet and Sito Plus exhaust. Is there anything I can do with the other jets? Just seems to bog down a bit on take off.

Posted 02:31, 12 Oct 2008

internetscooter says:

I plan to do some testing with an oxygen sensor at some stage so I don't know for sure. Low down you should play with your mixture screw.

Hopefully with the oxygen sensor I'd be able to measure just how much each jet impacts over the whole range.

Posted 23:45, 20 Oct 2008

vespavintage says:

I suspect something is up with my carb. Twist throttle to take off, delayed engine revving. Or maybe I am after something a little more responsive/sensitive.

Posted 19:56, 11 Nov 2008

F64VAL says:

hello there. how much would it cost to do the hole and sito setup ? thanks

Posted 06:25, 19 May 2009

internetscooter says:

The hole is free (make sure you clean properly after drilling). Sito exhaust will cost differ depending on country. I think about $150-200 for Australia.

Posted 22:24, 19 May 2009

mini_me says:

Thank you very much for this information. ;-)

I tried this the other day by making a heart shaped hole (Would this thing have a negative effect?) instead. 118 is not readily available so I tried 120 and made some minor adjustment on the A/F mixture screw, so far the spark plug looks OK. edited 03:18, 26 May 2009

Posted 03:04, 26 May 2009

internetscooter says:

The indent is heart-shaped, the extra hole is in the top part of the heart. Drilling out the whole heart shouldn't have any negative effect (as long as the jetting is right). 120 should be nice and safe.

I'll add a close-up photo tonight.

Posted 05:38, 26 May 2009

vespavintage says:

And it sucks more fuel too. I find I run out a lot quicker but have a nicer mid range.

Posted 08:21, 26 May 2009

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Air Filter Hole

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