Author Topic: air filters & jets  (Read 1469 times)

andy b

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air filters & jets
« on: September 24, 2006, 07:34:35 PM »
Hi, looking for a bit of advice, i own a honda fx 650, i have cut open the exhausts removed a baffle plate, in an attempt to let the gases flow a little freer and sound a bit more like a big single, next is to tackle the air box.Is anyone aware if k&n do a filter? or could i cut holes in the air box, then screen it with fine mesh?The thing is i guess the carburation will need fettling if i go this far.At the moment with just the exhaust its standard and running fine.

GB500nz

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Re: air filters & jets
« Reply #1 on: September 25, 2006, 09:50:09 AM »
If it's running fine, why stuff it up? The airbox does an important job, and you'd have a fair engineering job ahead if you wanted to improve it. You might be surprised if you look at comparative tests of filters: K&N might be famous, but in some tests they come out way worse than the stock item.

guest27

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Re: air filters & jets
« Reply #2 on: September 25, 2006, 07:31:49 PM »
Hi there
Often the air box is restricted on the inlet trumpets - it is from here that the roar will come.  If you look (and I do not know the fx) it may well be that the inlet trumpets are heavily baffled (like me) and have a number of direction changes etc.  The filter will lie next and then the actual inlet trumpet - which may well be lovely and rounded and smooth etc.  If this is so and the inlet trumpets can be modded without ddamaging the box (you may want to replace them) or removed in some way this may let you know what is happening.  ON strokers of the 70s to 90s often all that was needed was for the air box lid to be removed and the filter foam wired inplace - the pelumn chamber - if there is any will only be after the filter.  On more modern bikes with a (tuned) pelumn chamber it can be that replacing the filter with a foam one - like a ramair - will allow the chamber to work.  Not many bike made in the last 10 to 15 years will work better without an airbox than with - because often the airbox is big enough to not restrict the breathing and supply still air, and act as a tuned, or a completly untuned (dont want a partially tuned anything really - (works wonderfully at 6500 rpm but mucks everything up below 6250 and above 6750 for example) - air chamber.  However this may all be bo11ox in relation to the fx as I have not ever pulled one apart (note pulled apart - I have boxes of bikes that I have pulled apart and not alot I have put together again!)

Only real way to find out is on a dyno, but playing can be fun, and does it matter if you end up with a bike that does not run quite as well as it did if you are happier with it - happiness covers a multitude of sins and explains why people get passionate about old Brit bikes and Landrovers but not about Honda commuters and Toyota Corrolas)

R

Steve H

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Re: air filters & jets
« Reply #3 on: September 25, 2006, 08:36:15 PM »
From memory one of the features of a good air box is that it should have sufficient volume, that on the induction stroke, the pressure in the air box should not significantly reduce. Any drop in pressure would result in a reduction in the volume of air entering the engine and hence effect volumetric efficiency. On a four cylinder bike were there are many small induction strokes, this is possible. However with a single it takes its air in one big gulp. So to acheive the above you need a huge air box on a single cyclinder bike. I beleive this is also why its difficult to turbo/supercharge singles as you need a huge plenum chamber to store the charge between intake cycles.
So I'd argue that the airbox is less critical on a single. That said I decided to refit my airbox to reduce the intake noise.
Ive wandered off topic now, but I also remember seeing a supercharged JAP single sprinter which went very well and nearly blew my eardrums out once, so it must be possible. 
« Last Edit: September 25, 2006, 08:47:14 PM by Steve H »

002

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Re: air filters & jets
« Reply #4 on: September 25, 2006, 09:32:29 PM »
Was that "Sledgehammer" by chance.
Supercharged Jawa Speedway engine running on Nitro......
 Absolutely amazing sound.....when we were racing I stood several feet behind it at Santa Pod.
Bad mistake !  Not only deafened but it must be the only bike that you can feel in the pit of your stomach until he shut off..quater of a mile away !

Mind seen blown Vincent single and twins Mini Mouse and Mighty Mouse,also spectacular.

Jethro
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Steve H

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Re: air filters & jets
« Reply #5 on: September 25, 2006, 09:40:44 PM »
Could have been a Jawa, I saw it at Pembrey a long time ago. I was standing at the start line camera in hand waiting to take a picture, it was so loud I just dropped the camera so I could cover my ears.

andy230

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Re: air filters & jets
« Reply #6 on: September 26, 2006, 09:20:53 AM »
My 2 pence worth:

None of the Supermono racers use an airbox.  So its probably better to ditch it for maximum breathing capability.  However, this does not necessarily make for a very good road bike!!

a

Dave #22

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Re: air filters & jets
« Reply #7 on: September 28, 2006, 01:25:36 PM »
Hi, on my recently completed DR not so Big I had no room for the std airbox (due to shortening the subframe) so I obtained ( Ebay) a pair of 65mm bore K&N cone filters and mounted them on the battery carrier (as far from the carbs as possible) and connected them with the same bore alloy tube, with rubber sleeves. I was expecting set up problems, but I ended up raising both needles one notch, and going up in main jets from 120 in increments to 140 until it pulls cleanly on full throttle, and from tickover up. The only downside is the induction noise on hard acceleration. I also used a road legal Laser silencer, but the pepper pot in the outlet pipe was causing a restriction, so that went, making a noticable improvement in acceleration.
    Dave

guest7

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Re: air filters & jets
« Reply #8 on: October 01, 2006, 03:26:35 PM »
Hi, looking for a bit of advice, i own a honda fx 650,

Am i being a bit thick - what's an FX650?

GC

J Hop

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Re: air filters & jets
« Reply #9 on: October 01, 2006, 06:04:39 PM »

002

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Re: air filters & jets
« Reply #10 on: October 02, 2006, 09:43:11 PM »
FX650 VIGOR.

An SLR with slightly different clothes on....!

Jethro
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andy b

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Re: air filters & jets
« Reply #11 on: October 15, 2006, 10:07:01 AM »
  many thanks for all your replies, still a bit undecided wot to do, just brought myself and XBR to tinker with aswell; so i my leave the fx alone for a while carb wise,
             thanks again
                        andy