K&N air filter

Post by **yellowpinky** » Sat Aug 22, 2009 9:04 am

I recently bought a K&N air filter for my 1 1/2" HS4 carb. When I fitted it I found that the bolt that secures the central spindle inside the air filter bumps into the side of the carb. It does this both ways up and leaves a small gap (please see picture). The question is what's the best solution for this? I have heard of using a stub stack, but am not sure what it's for or how it's fitted. Alternatively I thought of making a chunky gasket out of some thick rubber. Apart from the gap it fits really well. I hope I have bought the right part..<br>

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Post by **Kevin** » Sat Aug 22, 2009 10:15 am

Hi a stub stack is for improving the airflow into the mouth of the carb and won't help your problem.
I hope that the filter is for an 1 1/2" carb and not one for an 1 1/4", also is the hole in the backplate central because if its offset its for a mini.
I use a pancake style one rather than the cone type so I can't do a direct comparsion that would be of use, however I am sure it should have a rubber gasket to fit in that location as the pancake ones do if I get a chance I will try a take a photo as I thing I have a spare.

Post by **PSL184** » Sat Aug 22, 2009 5:06 pm

Yes, should have the thick rubber gasket / heat shield thingy in there...

Post by **paulk** » Sat Aug 22, 2009 5:52 pm

Can also use a spacer piece to give the space needed

Sat Aug 22, 2009 6:04 pm

to add to what kevin said.. the stub stack will not help as it sits inside the K&N filter and improves the flow into the throat of your carb by removing the right angle between the inside of the K&N and the throat of the carb.

the only reason the inlet is offset on the mini is because of lack of space between the carb and car body work there is no problem using one on a moggy.

the trouble with a thick rubber gasket will be cutting it perfectly circular or you will be introducing even more turbulance into the air flow into the carb ( if that makes sense )

what exactly is the screw for can it be removed? i would be tempted to take it back to the people that sold it to you and get your money back.

Post by **bmcecosse** » Sat Aug 22, 2009 6:43 pm

Maybe fit a countersunk screw ? ' Stub stack' - supposedly eliminates the vena contracta at the mouth of the carb - if it has a flange it will sort your problem - I suppose! Otherwise - amka simple gasket. The vena contracta can be sorted by simply filing a nice even radius around the mouth of the carb, and open up the hole in the filter to suit - no need to spend money! Is it a genuine K&N - or a copy ? Mine is a 'copy' and fits perefectly and works very well - i'm delighted with it.