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Airbox Removal Options

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ratatooie
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Location : Isle of Man

Airbox Removal Options

Post by ratatooie on Mon 09 Nov 2015, 2:25 pm

Does anyone have any experience of successfully removing the airbox and either installing an after market/custom airbox or just pod filters? 

My issue is that in the current build, due to the previous owner embarking on a project, (which I am trying to salvage), the stock airbox will not fit without being completely butchered. 

Secondary question is what would the best jetting be for the pod style filters with straight through exhausts? A search of the forum gives the following jetting as a base, but this was with the stock airbox, K&N filter and baffleless aftermarket exhaust:



@alexibrow wrote:The standard fuelling set-up for the CB500 is as follows:

- Pilot screw set 2.5 turns out
- 38 pilot jet
- 122 main jet
- One needle shim.

My bike engine is standard, except for the following modifications:

- K&N panel filter
- Pipewerx Hawk SL silencer, with baffle removed.

the fuelling on my bike is set up as follows:

- Pilot screw set 3 turns out
- 38 pilot jet (standard)
- 125 main jet (one size up)
- Two needle shims (ie one additional shim).



I'm wondering where would be a good place to start tweaking if no one has "the answer"? 

I have the 6Sigma jet kit, which comes with a bunch of needle shims, 130 and 135 main jets, and 42 pilot jets (and some unneeded drill bits and pieces). 

It will be drawing more air than the K&N, which leads me to think I should whack in the 42 and 130 jets with one extra shim over stock as a base, but then I may also be well to just stay with alexibrow's tried and tested settings above even if they will probably be too lean.  scratch
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eternally_troubled
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Re: Airbox Removal Options

Post by eternally_troubled on Tue 10 Nov 2015, 1:56 pm

@ratatooie wrote:
It will be drawing more air than the K&N, which leads me to think I should whack in the 42 and 130 jets with one extra shim over stock as a base, but then I may also be well to just stay with alexibrow's tried and tested settings above even if they will probably be too lean.  :scratch:



Sounds like it might be worth a try.

The slight snag with removing the airbox on the CB500 is that (I think, based on the difficulty people have had getting the bike to run well without it) it has quite a complicated interaction with the jetting and the exhaust, which may make getting the right settings rather difficult.

Anyway, I suspect that you will be able to get it to run, which will be good for your project :)

Do you have access to a dyno/exhaust analyser?  I suspect that setting up the jetting will be a lot easier if you do...
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Beresford
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Re: Airbox Removal Options

Post by Beresford on Tue 10 Nov 2015, 3:30 pm

From stuff I have read elsewhere, the airbox issue seems to be that you can tune an engine to run at any specified RPMs without one but at the price of having to put up with other areas in the rev range where there will be massive flat spots.

Sods law is that that'll happen right in the middle of your favourite cruising speed zone.
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ratatooie
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Location : Isle of Man

Re: Airbox Removal Options

Post by ratatooie on Wed 11 Nov 2015, 5:49 pm

Great thank you guys. I think I will try the richer options first. The jets that came are actually 135 and 140, so the 135 will be going in to start off. 140 seems pretty huge!

I guess the nature of the build means that it is never going to be a commuter so spot on tuning isn't the biggest priority. That said, I don't want it running too lean or rich for any longer than I have to.

There are a few dyno places over here so they will be worth investigating when the build is nearing being finalised, but like everything in life, they cost!
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Basil Moss
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Re: Airbox Removal Options

Post by Basil Moss on Sun 15 Nov 2015, 9:56 am

I think the general findings from people who did stuff like this was that performance suffered badly. The airbox generates acoustic effects which basically supercharge the engine at certain parts of the rev range, and the stock carb setup takes advantage of this. That said, if the airbox isn't useable any more you'll have to see what you can do with pod filters, and fiddle about with the jetting to get it as good as it can. It'll look pretty cool.
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ANDYC
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Re: Airbox Removal Options

Post by ANDYC on Sun 15 Nov 2015, 12:27 pm

I'll be ditching my airbox on my track bike as the monoshock set up won't allow it, so I will have to run individual filters. Past experience taught me that individual filters can be fitted much easier to early slide type carbs than the CV type that are used on ours.
It can be done with CV carbs but there is as mentioned in earlier posts there is always a price to pay. This is normally in the midrange and throttle response area.
I will be testing my engine running such filters to see if I can get the gains that I'm after without having to go to FCR39's at great expense Shocked I'll post the dyno results in my trackbike thread.
As this is being built as a track bike I'm not too concerned about loosing bottom end drivability, above 5k is where I want to get the gains.
If you ride under 5k then keeping the airbox is the route to take. Otherwise it will feel like a 2 stroke. Those that remember the 250/350lc's (before the powervalve) will know what I mean Very Happy
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skyrider
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Re: Airbox Removal Options

Post by skyrider on Sun 15 Nov 2015, 6:26 pm

yea I used to have 2 lc's wicked machines Twisted Evil
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eternally_troubled
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Re: Airbox Removal Options

Post by eternally_troubled on Mon 16 Nov 2015, 2:30 pm

@ANDYC wrote:If you ride under 5k then keeping the airbox is the route to take. Otherwise it will feel like a 2 stroke. Those that remember the 250/350lc's (before the powervalve) will know what I mean :D

Maybe he wants it to be like a 2-stroke :)
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ratatooie
Running out of unique names
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Posts : 180
Location : Isle of Man

Re: Airbox Removal Options

Post by ratatooie on Mon 16 Nov 2015, 2:35 pm

@ANDYC wrote:I'll be ditching my airbox on my track bike as the monoshock set up won't allow it, so I will have to run individual filters. Past experience taught me that individual filters can be fitted much easier to early slide type carbs than the CV type that are used on ours.
It can be done with CV carbs but there is as mentioned in earlier posts there is always a price to pay. This is normally in the midrange and throttle response area.
I will be testing my engine running such filters to see if I can get the gains that I'm after without having to go to FCR39's at great expense Shocked I'll post the dyno results in my trackbike thread.
As this is being built as a track bike I'm not too concerned about loosing bottom end drivability, above 5k is where I want to get the gains.
If you ride under 5k then keeping the airbox is the route to take. Otherwise it will feel like a 2 stroke. Those that remember the 250/350lc's (before the powervalve) will know what I mean Very Happy

Great. In that case I will keep an eye on your track bike thread. 

I'm no stranger to 2t so that wouldn't be the worst thing in the world, but as you say is not ideal for puttering about town.

@Basil Moss wrote:The airbox generates acoustic effects which basically supercharge the engine at certain parts of the rev range, and the stock carb setup takes advantage of this. That said, if the airbox isn't useable any more you'll have to see what you can do with pod filters, and fiddle about with the jetting to get it as good as it can. It'll look pretty cool.

Huh. That is really interesting. I had no idea that a supercharging effect could be had in that way. The original airbox just is not an option any more I am afraid with the mods to the frame and new tank. It will have to be pod filters or nothing. It looks like a lot of testing is on the cards!

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