constricting airbox...individual air filters possible?

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frankinstyn
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Joined: Sun Sep 24, 2006 12:09 pm

constricting airbox...individual air filters possible?

Postby frankinstyn » Fri Oct 13, 2006 10:21 am

Hey all. So this bike runs great...besides the little bit of oil going past the valve stem seals and I was wondering if its possible to swap in individual air filters? I figured that it already has quad carbs right? So why did Honda then stick an airbox in there? Why not just stick with one carb if you're going to be restricting like that.


So are individual air filters a viable idea?

If so, will I need to retune the air-fuel ratio when I do this?

Will they even be able to suck in enough air with the air rushing past at such a speed? I mention this because when I removed that plastic cover for the single air filter on there now, it wouldn't suck in enough air to run well at speeds over 50mph.

Lastly, which air filters are the right ones to order if some of you have done this already?

If not then I can just measure the carb suction diameter and order individual k&n filters of that diameter right?

I'm thinking of something like this...

Image

or this...

Image
Is the above comment is complete idiotic or ignorant please attribute it to the alchohol.

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Chris
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Location: New York, USA

Postby Chris » Fri Oct 13, 2006 12:04 pm

I haven't done this modification, but if you're gonna uncork it, you'll have to uncork both ends and rejet the carbs. Most people refer to those filters as 'pod filters' and you can find threads on them. Also, I've heard mention that it'd be a good idea to fashion some sort of bracket to help support the carbs in the absence of the stock airbox. My guess(it's just a guess) is that you would gain a bit of top end power but sacrifice bottom end at the same time. Also, once you uncork both ends and rejet, you'll probably be looking at a cam modification next... one thing leads to another. If you're really looking for that much power from a SOHC4, why not go for the 650's big brother the 750 and keep that beautiful 650 stock?

Sounds like you went lean when you removed the plastic cover from the stock filter... too much air, not enough fuel... must rejet. Hence the 50mph limit. If I'm wrong, I know these guys will correct me.
1980 CB650c

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bandwidth69
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Postby bandwidth69 » Fri Oct 13, 2006 12:51 pm

oh boy! has this one been covered in detail here! mostly, in recent times because of me! I have fitted the filters you have the pictures of. Theyare great - BUT you need to do a lot of work. To reap the benefits you need to re-jet, balance and then adjust the mixture of the carbs correctly. This is critical. If you don't then the bike usually runs horribly. I'm addicted to the induction noise the bike makes when they are fitted. Its awesome! I'm not sure if its the same for your bike - but here in the UK when fitting these filters on you can leave most of the airbox on the bike. here we have a kidney shaped collector box directly attached to the carbs - this is then connected to the air filter housing under the seat. The small box can be removed - but you may have to adapt the connecting rubbers (trumpet shaped ones) for the two inside carbs. I have left these on the carbs and have slid the new pod filters over the top - sealing everything with duck tape. This is because even though I bough CB 650 pod filters - they fouled the choke mechanism when fitted, jamming the mechanism as soon as it was operated. Look out for this. Apart from the noise - my bike actually ran better with the stock air box. A simpler modification is to remove the cover plate from the standard airbox, replace the cartridge with a K&N one and keep it in place with some oversize washers. You get improved breathing and you can, say the experts on this forum fo which I am eternally grateful, continue to re-jet the bike as you wish as they were tuned a bit on the "safe" side at the factory shall we say?

Oh - you will have to sort out a suitable crankcase breather - im not sure if it upsets the emission tests for the MOT test? as the bike isnt drawing in the waste gases anymore - though I have sen some filters with this feature on them. :?:
i dont watch big brother

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Ibsen
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Postby Ibsen » Fri Oct 13, 2006 3:39 pm

Also beware that Emgo pods, and maybe others as well, might block off the air jet intakes on the airfilter side of the carbs. The rubber flange on the filters have got an edge that is very large making this happen. At least on Mikuni VM's for older Kawasakis this is a problem. K&N filters works fine though.
Some owners also fabricates a "shield" that is installed on the outher side of the filters on carb #1 and 4 to avoid running problems caused by turbulence from the riders legs, and sidewinds.

frankinstyn
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Postby frankinstyn » Fri Oct 13, 2006 5:43 pm

allrighty then. Sounds like its more work for almost no gain besides a much more appealing sound. Personally I prefer performance over sound so I'll just stick with stock airbox. Thanks to all though. I'm really glad I asked before I bought these. I would have been in a world of work.
Is the above comment is complete idiotic or ignorant please attribute it to the alchohol.

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Volker_P
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Re: constricting airbox...individual air filters possible?

Postby Volker_P » Mon Oct 16, 2006 12:27 am

Good decision. It's hard/expensive to really beat the stock setup for the CB650. Honda did a quite good job here and also achieved a quite reasonable fuel consumption. :)


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