Air-filter carb question

[St George]

I have a new 22 Jetex 122 main 45 pilot on a Stage 4 SIL, AF Clubman. Question. why does it run better without the air filter ? Does the jetting sound right. It is running quite nicely apart from that. Thanks.

[scootersi]

I have a very similar set-up to yours and my Jetex is much happier without a filter particularly on start-up which is practically impossible with the filter on. I have tried remote filters as i would prefer to run with a filter but have pretty much given up trying.

Regards,
Simon.

[Storkfoot]

It is a sign that your engine wants more oxygen and less petrol. Consider whether you are jetted correctly. BUT don't just run without the filter and assume all will be good. Many an engine feels great running lean just before it seizes

[Knowledge]

If your carb wants more air (and I agree with Stookfoot about this), then perhaps you need to find a way to get more air through your airbox. A common problem is with the restrictive web in the mouth of the air scoop. This was eliminated on the GP200 to get more air into the box, and the diameter of the neck of the 'box was increased on later models for the same reason. Many people remove the swan-neck in the top of the air box to increase air-flow, and some drill big holes in the back of the box too.

Whatever method you use to get more air into the engine, keep an eye on the plug in case it is starting to run weak.

[St George]

Thanks so far.
I have a complete GP 200 Air box which I cannot fit as I am on a 1988 SX200 Servetta ( different frame ). These have a Kidney air box ( earlier ones had tool box filters ), I managed to get one from a 1982 model which has only done 500 miles from new. These were fitted with a smaller air tube to suit the 20 mm carb, so I have not fitted this yet ! I have tried a new Ramair, looks nice but slows the bikes performance.