What happens when all those pipes and the airbox have gone?

martynmoore · L Plate Warrior Joined: 29 May 2017 Karma :

I'M building a custom bike out of a rotten old Kawasaki ER-5 and started pulling it apart yesterday. I will junk the airbox for separate conical airfilters and the silencer will be replaced by a short reverse cone megaphone.

There are breather pipes coming off the cam covers and one at the back of the crankcase. Last time I built a bike, 35 years ago, there was just one crankcase breather and it was perfectly acceptable to poke it into an empty Newcastle Brown can strapped to the frame (beer cans used to be made of sterner stuff back then).

What's the current wisdom on this sort of butchery and what will I need to do to the carbs to compensate?

Wafer_Thin_Ham · Super Spammer Joined: 18 Nov 2005 Karma :

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

No filters at all would work better than fitting a set of wanky cones.
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Nemo · Could Be A Chat Bot Joined: 30 Apr 2010 Karma :

The pipes coming out of the head will be coolant pipes, the other is a crankcase breather, so put a filter on that too
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Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

The reverse cone mega-phone was sort of an expansion chamber for a four stroke. In the 1960's, on a relatively modest reving single with a lot of exhaust timing overlap, thy cold 'sort' of work not too bad, and actually work.. at least well enough, on an all or nothing race-engine...

On something that has a rev-range twice as wide, that is expected to carburate cleanly at part throttle as well as full or idle, they are just a pain in the arse! Actually, they are a pain in the proverbial on a motor that only has to run well wide open, and even idle isn't important as long as it don't stall!

Most reverse or inverse cone mega's, or certainly the ones likely to work half well, actually aren't; they are a tapered muffler with reverse or inverse end cap, blanking the baffle chambers....

Pod cone filters? Err... yeah. Pretty similar story. In the 50's/60's the 'thing' to aid aspiration was a big bell-mouth ram-stack. Provided a lot of air correction to smooth out flow going into the carb, and a volume upstream of the carb, where when you get 'stand off' effects, or reverse flow, through the carb, when a pressure wave or actual air-flow echo backwards from the closed inlet valve and caused a second suck through the carb-jets, and 'haze' of enriched mixture coming backwards out of the carb, the ram-stack would provide some space for it to linger, without being dumped to atmosphere, so it would get sucked back in again when the inlet opened again and started sucking, which was particularly critcal on two-strokes.

Cone filters started to become common in the 70's & 80's. Their flow capacity is usually pretty crap. Sat right on the end of the carb, they offer no air correction to smooth flow into the carb; worse, with a the filter element around the rim of the carb-mouth, they actually provide a restriction, making air turn a tight 90 degree bend inside the filter, where ther's bog all space for it, and generate turbulence, rather than air-correction whilst they are about it... do trap vapour stand-off, though and that was about all that they were ever much good for.

On highly tuned engnes / modded bikes where the air-box couldn't be ratained as the carbs had been swapped, and or the engine made to breath that much more to make so much more power than the air-box could flow, they were a convenience, and offered no gains in themselves, other than having to make a more effective hi-flo air-box, and often did more harm to engine performance than good; but were a acceptable compromise, if the whole worked better overall.

Many many other problems with the darn things, like in close set 4-carb set-ups the two outer carbs shrouding the air-flow from the centres, whilst the side-ways flow meant that adjacent carbs could be tryig to suck from thier nieghbours, screwing jetting... then rain or water-spray dampng the elements, causing curiouse runnng issues in the wet, and they clog quick, so flow drop off, occurs after maybe a few hundred miles not factry service intervals, and they are expensive so folk loath to chuck away defective pods, they are convinced are an 'upgrade'.

How many 'problems' do you want to make for yourself in this little project?

Identifying and blanking redundant air-bx plumbing, REALLY is the least of your worries here!
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martynmoore · L Plate Warrior Joined: 29 May 2017 Karma :

martynmoore · L Plate Warrior Joined: 29 May 2017 Karma :

Chris45 · Nitrous Nuisance Joined: 23 Oct 2016 Karma :

The crankcase breather pipe runs into the airbox on stock bikes, so not too certain where you could route it. Putting a filter on it may work, but then again, some MOT testers may not like what they see... a crankase pipe venting to atmosphere.

I guess older bikes, like the much bobbed CX500 didn't have that regulatory requirement back then...

Check this out, just wished I had kept my CX now... their handling was truly dreadful tho!

https://www.bikeexif.com/1980-honda-cx500
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martynmoore · L Plate Warrior Joined: 29 May 2017 Karma :

Teflon-Mike · tl;dr Joined: 01 Jun 2010 Karma :

Copycat73 · World Chat Champion Joined: 11 Jan 2013 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

I confidently predict it will run like an utter bagowank on pods. If it runs at all. Also that you will not be able to modify the carburettion to compensate for this.

From previous experience, I predict it will idle normally and rev reasonably well up to around 6,500rpm, then it will be like you've hit a brick wall and will go no further.

Keep the airbox.

Dynojet don't even make stage 3 kits (the one you'd use if you were fitting pod filters) for kawasaki 500 twins. I'm pretty sure that's because they couldn't get them to run right.

The crankcase breather on my enfield vents off the back mudguard and farts watery emulsion all over following cars, never been mentioned on the MOT. In fact, I'm not aware of the engine or engine componants being part of the MOT
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Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Chris45 · Nitrous Nuisance Joined: 23 Oct 2016 Karma :

Monkeywrenche... · Nearly there... Joined: 27 Mar 2015 Karma :

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

The only custom ER5 I've seen that tempted me was a 'military' job. The only images I can find are small ones from a defunct advert.

https://i.imgur.com/u5887jc.png
https://i.imgur.com/IFRdQEk.png
https://i.imgur.com/yodXmxd.png
https://i.imgur.com/YRnv8AA.png

Significant to this thread because it's retained the stock airbox. Lick of paint, some dickery with the rear subframe, you've got something distinctive but which might actually run decently.
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MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Can't be arsed to read the usual Tef text wall (He must just copy and paste, surely?) but my advice is to keep the airbox at all costs. Pods will run like @rse, and the airboxes on semi recent bikes are designed very carefully. Trying to remove it will just result in pain.
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hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

ive never had an er500,
but i have had a gs500 that i put pods on.
so id say it'll be near enough the same as far as results.

in my case, the gs500 had mikuni cv carburettors,
which like any cv carbs, they are known for being an arse to run with out an air box,

eventually after about 12 main jet changes, multiple needle clip changes,
and a couple of pilot jet changes, i managed to get it to run as good as it did pre airbox removal.

so it can be done. Very Happy

but i used a fuck load more fuel.
like an extra 50% more fuel!! which frankly is just rediculous,

i ended up going back to an air box in the end as i had quite a long daily commute, and it wasnt worth it.

if i was to do it again, id probably go for slide carbs, rather than a cv carbs.
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