Airbox to Carb restriction

Mohawk · March 19th, 2016, 02:44 PM

I just cleaned & adjusted the carbs on my ZZR250, with the carbs out I noticed that the airbox to carb rubbers, have a strange internal shape that is designed to fill the sides of thew carb inlet whilst keeping the air jets free at top & bottom. What I noticed was that these appear to have contracted inwards & thus reduced the full throttle area significantly.

The carbs are 30mm outlet, with a 28mm venturi area, but the inlets were bent in to 24mm. So i trimmed the affected areas on either side back out to 30mm, this makes the central intake area match the carbs intake cross sectional area. Bike runs fine, will get a test run to see if it works better on full throttle soon.

ducatiman · March 20th, 2016, 04:58 PM

A neighbor lady owns a 250...during a long ago carb clean...I recall seeing the same and wondering why it was designed in that way.

I can only surmise its there to set up a directional velocity in order to control slide lift.

As her bike is completely stock, I opted to leave it be.

Sadly, the bike sits, unused, still there to the best of my knowledge.

Ghostt · March 22nd, 2016, 01:10 PM

I noticed those on my PreGen last year, I trimmed the internal rubber down quite a bit. The only difference I noticed was a decrease in mpg, now I get about mid 40's nothing higher than 47 now.

I made no changes to the bike, so I can only assume it was the modified boots to the airbox. I'll be looking for another set to put it back to specs.

Mohawk · March 22nd, 2016, 01:31 PM

Ghost did you just trim it or cut a big chunk out ? Mine looked like the inner pieces had folded in over time. I'd like to see what a new set look & fit like.

Ghostt · March 22nd, 2016, 02:37 PM

I trimmed out most of the rubber on the inside, leaving it at an angle.

Unfortunately I didn't take any pictures, when I finally change them, I will take one then.

March 19th, 2016, 02:44 PM	#1
Mohawk ninjette.org guru Name: Chris Location: Bristol, UK Join Date: Feb 2016 Motorcycle(s): ZZR250, VFR800 Posts: 479	Airbox to Carb restriction I just cleaned & adjusted the carbs on my ZZR250, with the carbs out I noticed that the airbox to carb rubbers, have a strange internal shape that is designed to fill the sides of thew carb inlet whilst keeping the air jets free at top & bottom. What I noticed was that these appear to have contracted inwards & thus reduced the full throttle area significantly. The carbs are 30mm outlet, with a 28mm venturi area, but the inlets were bent in to 24mm. So i trimmed the affected areas on either side back out to 30mm, this makes the central intake area match the carbs intake cross sectional area. Bike runs fine, will get a test run to see if it works better on full throttle soon.
	2 out of 2 members found this post helpful.

March 22nd, 2016, 01:10 PM	#3
Ghostt in your machine Name: Scott Location: Summer Shade, Ky. Join Date: Oct 2014 Motorcycle(s): 98 Ninja 250/F12 aka ZX-2R "SERENITY", 91 Ninja 500/A5 aka ZX-5R "Phoenix", 84 Honda GL1200A "SIREN" Posts: A lot. Blog Entries: 25 MOTM - Jun '17, May '16, Mar '15	I noticed those on my PreGen last year, I trimmed the internal rubber down quite a bit. The only difference I noticed was a decrease in mpg, now I get about mid 40's nothing higher than 47 now. I made no changes to the bike, so I can only assume it was the modified boots to the airbox. I'll be looking for another set to put it back to specs. __________________________________________________ *violente et ignorantia* ZX-2R BLOG *Twitter and Instagram = Ghostt_Scott* *I'm not here to change your mind, just to inform.*

March 22nd, 2016, 02:37 PM	#5
Ghostt in your machine Name: Scott Location: Summer Shade, Ky. Join Date: Oct 2014 Motorcycle(s): 98 Ninja 250/F12 aka ZX-2R "SERENITY", 91 Ninja 500/A5 aka ZX-5R "Phoenix", 84 Honda GL1200A "SIREN" Posts: A lot. Blog Entries: 25 MOTM - Jun '17, May '16, Mar '15	I trimmed out most of the rubber on the inside, leaving it at an angle. Unfortunately I didn't take any pictures, when I finally change them, I will take one then. __________________________________________________ *violente et ignorantia* ZX-2R BLOG *Twitter and Instagram = Ghostt_Scott* *I'm not here to change your mind, just to inform.*

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March 20th, 2016, 04:58 PM	#2
ducatiman ninjette.org certified postwhore Name: Gordon Location: new york Join Date: Sep 2009 Motorcycle(s): '95 DUCATI 900SS/SP '07 DUCATI SS800 '19 HONDA CBR650R Posts: A lot. MOTM - Nov '18, Mar '17	A neighbor lady owns a 250...during a long ago carb clean...I recall seeing the same and wondering why it was designed in that way. I can only surmise its there to set up a directional velocity in order to control slide lift. As her bike is completely stock, I opted to leave it be. Sadly, the bike sits, unused, still there to the best of my knowledge.

March 22nd, 2016, 01:31 PM	#4
Mohawk ninjette.org guru Name: Chris Location: Bristol, UK Join Date: Feb 2016 Motorcycle(s): ZZR250, VFR800 Posts: 479	Ghost did you just trim it or cut a big chunk out ? Mine looked like the inner pieces had folded in over time. I'd like to see what a new set look & fit like.