A new cause for high and erratic idle

I've been chasing an irritating high idle on my 961 SE since the first ride of this season. I've read through all the posts on the forum, and talked to Matt Capri at SBN, and all comments point to an air leak in the fuel injection system. I checked everything I could think of to check, and found nothing amiss. The other day I renewed my renewal registration and took off the seat to stow the documents in their assigned spot, and noticed something interesting: my air filter was dangling at an angle in the airbox, barely held in place by a torn rubber flange that is part of the filter! The bottom of the filter was being destroyed from banging on the bottom of the airbox.

Here is a pic:

Now this filter is the original factory unit, installed at the factory in March 2015. My bike has about 4K miles on it from one year of riding, and is ridden relatively moderately, considering that I'm a 72 year-old but reasonably aggressive rider. My opinion: this is a poorly designed air filter system! The plastic retaining ring puts downward pressure on the core of the filter, which is supported only by the rubber ring, not surprisingly resulting in the tear that you see. I ordered a new filter, but wanted to ride before it gets here, so I experimented and came up with a round foam Uni filter that I found at a local cycle store, supported by a homemade wire mesh, and held in place by the stock plastic piece that normally holds the filter. It ran great, and the bike now idles normally at 1100 rpm!

This might be something to put on a check list for routine maintenance, or a definite thing to check for a high idle situation. The jury is still out on my homemade filter, but I'm inclined to like it better at this point in time. The engine receives the amount of air that the plastic air filter holder allows through it, and the cleanable oil-saturated foam filter keeps the air clean. And I don't have to pay $50 every year for a new Norton filter. How can you beat that? Comments solicited!

Precisionbob
2015 USA 961SE

This is definitely not good. You’re on to something here.
An air leak like this certainly can’t be good for the EFI system.
I agree the filter is poorly designed given its mounting method within the airbox.
The airbox itself is a real design compromise. It’s beautifully shaped, but has too many issues.
Oil collection from the valve cover breather
Rather small volume plenum for a 900+ cc twin
Intake partially blocked by the seat.

Clearly some attention from the engineering dept is required here.

I discussed this with Precisionbob and told him that the plastic hold down piece on my bike, '15 Sport, didn't in fact make contact with the top of the filter thus not sealing it. I use a common adhesive to just "glue" it in place. Britjunkie.

I called K&N company and they are not interested in making an air filter that fit our 961's . I bought an extra air filter and was prepared to send it to them , but no go . A question for Bob , Is the foam cylinder sitting on the bottom of the air box then ? Could I just buy a large UNI and cut off the rubber flange ? Thanks , Tony

BritTwit said:

This is definitely not good. You’re on to something here.
An air leak like this certainly can’t be good for the EFI system.
I agree the filter is poorly designed given its mounting method within the airbox.
The airbox itself is a real design compromise. It’s beautifully shaped, but has too many issues.
Oil collection from the valve cover breather
Rather small volume plenum for a 900+ cc twin
Intake partially blocked by the seat.

Clearly some attention from the engineering dept is required here.

Click to expand...

I agree , It probably should be twice the volume . I suppose it could be fabricated , there is plenty of room to go wider and deeper with more entry area maybe even screened side scoops . If there was a factory 961 racing effort , the air box would be the first thing to be replaced .

As a side note, I rode my bike without a filter for 15 minutes to try it and it ran no different.

I believe it ! It may even run better without the filter. So essentially this may not be the reason for Bobs idle ?

I bet it indirectly is tho.. take apart your idle air motor and clean it. Maybe its sticking and that is the actual cause because of by pass.... I have a manual on it if you need...

Hello Richard-7 , Makes sense , Is it okay to squirt a little WD40 inside the idle motor ? Is there a better product ? Silicone spray maybe ?

Could any debris from the rubber get sucked down and clog an airway?

Britfan60 said:

Could any debris from the rubber get sucked down and clog an airway?

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I did think of that and found a few small pieces on the bottom of the airbox, but couldn't feel anything at the sucking end of the box, and when it ran so well with the homemade filter I decided all was ok with that concern.

TonyA said:

I called K&N company and they are not interested in making an air filter that fit our 961's . I bought an extra air filter and was prepared to send it to them , but no go . A question for Bob , Is the foam cylinder sitting on the bottom of the air box then ? Could I just buy a large UNI and cut off the rubber flange ? Thanks , Tony

Click to expand...

Tony, here is a quick sketch of the filter I made:



The Uni filter was a flat round filter slightly larger than the filter opening in the airbox, and I just cut it to size, as wall as making the wire mesh disk to put under it so it wouldn't get sucked into the box. Obviously it needs to be checked often for cleaning because the cross sectional area is small, but it allows plenty of air through.

Hello Bob ,Oh I see , It is a round disc shape covering the opening at the top. I was thinking it was cylinder shaped. Thanks again for the info .

TonyA said:

Hello Richard-7 , Makes sense , Is it okay to squirt a little WD40 inside the idle motor ? Is there a better product ? Silicone spray maybe ?

Click to expand...

I took it apart and wiped it clean with WD-40

richard-7 said:

I bet it indirectly is tho.. take apart your idle air motor and clean it. Maybe its sticking and that is the actual cause because of by pass.... I have a manual on it if you need...

Click to expand...

Richard, which of your manuals has this - I'm on your list and should have the email with the manual if you can give me the title. Thanks! Bob

TonyA said:

Hello Bob ,Oh I see , It is a round disc shape covering the opening at the top. I was thinking it was cylinder shaped. Thanks again for the info .

Click to expand...

Tony, here are a couple of pics of the homemade filter:

Very nice and tidy, Bob! I hope mine comes apart so I can make one like yours.