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Interesting finding

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jchesshyre
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Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 12:13 pm

I've had a slightly more free-flowing exhaust, namely a Fuel, for a years. I love it but found that if I also put a K&N air filter in then the bike was down on power a bit, especially at the top end - presumably the combo made the mixture too lean. 

A few months ago I finally got round to slightly richening the mixture via an extra shim under the needles and a step up of one size in the main jets. As I wrote in the thread about it, the difference was delightful so as I'd suspected it must have been a tad lean even with the Fuel exhaust plus stock air filter. 

Today I thought I'd try the K&N filter in the bike with this richer carb setup and affraid I'm amazed! It revs more smoothly up through the revs and pulls noticeably harder at all revs. Looks like I've found the sweet spot. 

I'll see how fuel consumption is after I've been for a long ride as opposed to the ring-road hoonage I've done today...in the rain...
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eternally_troubled
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Re: Interesting finding

Post by eternally_troubled on Tue 26 Jan 2016, 12:44 pm

(I know it's all in the other thread, but to summarise....)

Is that:

Fuel can no baffle

K&N air filter

125 main jets

1 extra shim to raise the needle (what thickness is the shim?)

or have I got it wrong?
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 12:51 pm

All correct, except the baffle is in. There was a thread from another member - alexibrow I think his name is - who set his CB up like all this but had the baffle out. I occasionally take it out for fun, and do quite like the increased audibility when filtering etc., but find it's less tractable at low revs, and also think that it results in a bike whose bark is worse than it's bite rather than the other way round ;-)

The extra shims are just another of the stock shims, taken out of my retired bike. I can't say I know how thick they are.

I think it's also worth noting that it's a Fuel 'midi' (400mm) exhaust - I believe the 'mini' (350mm) one, which I ran for a good while, results in ever so slightly leaner running still. I haven't verified this absolutely scientifically, just looked at the plugs every so often and noticed a touch more tan after swapping to the larger can. If one was being ultra-detailed with all this then I think it's worthy of consideration. I also happen to think the midi one suits the look of the CB better.
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Beresford
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Re: Interesting finding

Post by Beresford on Tue 26 Jan 2016, 1:02 pm

I've run my bike now with 3 different cans, The standard black one, a slightly modded production stainless steel Yamaha 600 can and a 2" straight through.
The bike ran best with the Yamaha can and was also nice and quiet at low revs but would really howl high up.
I'm now experimenting with baffles in the straight through to tame the noise a bit, but I have found that the mid range is much improved with a (approx 50%) baffle in place. Not so sure about TWO running though as I haven't had a chance to test this yet.
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Re: Interesting finding

Post by eternally_troubled on Tue 26 Jan 2016, 1:09 pm

jchesshyre wrote:All correct, except the baffle is in. There was a thread from another member - alexibrow I think his name is - who set his CB up like all this but had the baffle out. I occasionally take it out for fun, and do quite like the increased audibility when filtering etc., but find it's less tractable at low revs, and also think that it results in a bike whose bark is worse than it's bite rather than the other way round ;-)

The extra shims are just another of the stock shims, taken out of my retired bike. I can't say I know how thick they are.

I think it's also worth noting that it's a Fuel 'midi' exhaust - I believe the 'mini' one, which I ran for a good while, results in ever so slightly leaner running still. I haven't verified this absolutely scientifically, just looked at the plugs every so often and noticed a touch more tan after swapping to the larger can. If one was being ultra-detailed with all this then I think it's worthy of consideration. I also happen to think the midi one suits the look of the CB better.

Excellent stuff. I guess you might be able to measure the size/thickness of the existing shim and find a washer that was about double that thickness.
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 1:16 pm

According to 'Jets R Us', the shims in most Keihin carbs are 0.5mm thick.
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Re: Interesting finding

Post by eternally_troubled on Tue 26 Jan 2016, 3:13 pm

jchesshyre wrote:According to 'Jets R Us', the shims in most Keihin carbs are 0.5mm thick.

That's good - finding a 1mm (ish) thick washer shouldn't be too hard!

I've got my bike apart currently (still fixing the exhaust!) and I'm half tempted to take the carb tops off and try raising the needle a bit - assuming it is just as 'easy' as taking the carb tops off?

I haven't changed the jet size but it might be interesting to see if raising the needle helps at all if you keep the standard jet.
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 3:19 pm

Yes, you can do that without removing the carbs. Changing jets does require removal. 

I've just been for a blast on my lunch hour and I think this is the deal: raising the needle richens the mixture at part-throttle running, and I think this was responsible for the difference I felt before changing the air filter. I had been beginning to wonder whether I should have kept the main jets as 122 as full throttle didn't feel all that different. 

But now, with the K&N air filter, it's full throttle where I'm really feeling a difference with this latest change, as if the less restrictive air filter has enabled the larger main jet to make its presence fully felt. 

It'll be interesting now to look at the spark plugs next time I take them out.
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geewhizz
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Re: Interesting finding

Post by geewhizz on Tue 26 Jan 2016, 3:47 pm

Great post,  thank you both.  I've been thinking about this for a good while. I like running it with the baffle out mainly unless on a long run.  And I've got the k&n filter in.  Is there a theoretical ideal for this set up based on your current experiences?  It seemed on other posts that keeping the main jets the standard and adding a shim would be the deal but I've not experienced this set up
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Jameshambleton
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Re: Interesting finding

Post by Jameshambleton on Tue 26 Jan 2016, 4:39 pm

I'm running a very strange combination that a couple of people might run, K&N, 35KW restrictor, standard jetting (as far as I'm aware), de baffled beowulf exhaust. 
The bike pulls and revs really well from 2K rpm, having the baffle fitted has dramatically changed my engines power and it feels seriously underpowered. When I have the baffle removed (always) the engine runs so much better and it's noticeably more powerful it accelerates so much faster and just feels better overall.
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 4:57 pm

What kind of restrictor is it? The Honda one has restrictive carb rubbers *and* replaces the 122 main jets with 125s.
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Jameshambleton
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Re: Interesting finding

Post by Jameshambleton on Tue 26 Jan 2016, 5:51 pm

Mine's just a washer restriction in the inlet rubbers, these are them on "the bay" no change of jets or anything else just. 
In all honestly I need to check my spark plugs to see how she's actually running  since I haven't checked them since I fitted them 4.6K miles ago but the bike still starts on the touch of the button but has needed a little bit of choke recently due to living outside and air temps.
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ashcroc
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Re: Interesting finding

Post by ashcroc on Tue 26 Jan 2016, 6:05 pm

Interesting findings.

Think I might have to look at doing the same to my stead instead of just waiting to see what the plugs tell me next time I whip them out.
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jerryfudd
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Re: Interesting finding

Post by jerryfudd on Tue 26 Jan 2016, 6:21 pm

....maybe someone could rustle up a few pics for those carb novices - myself included Smile

Dan
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 6:30 pm

Although I've been working on my CB ever since I got it (bar tyres and headset bearings), I too was a carb novice before this, which was partly why I put off doing it for so long. I was wary and nervous and didn't want to screw it up.

But the Haynes manual came up trumps and it was an absolute piece of cake. The only thing to be very careful of in addition to the guidance in the manual is that the screws holding the carb bowls on are rubbish and you need to use a bit of WD40 or similar and the best fitting screwdriver you can possibly find. Even despite all this I had to hacksaw a new slot in one of them.

I'll be opening up the carbs again sometime fairly soon as one of my pilot screws needs removing with some unconventional method as the head has broken off. I'd happily post some pictures but honestly Haynes has all the information you need.

It would be worth investing in a set of gaskets for the carbs. I have some but was so excited about trying the bike out with the new setup I didn't change them! I don't have any leaks but that's just luck - I easily could have done.

It's a good idea to clean the outsides of the carbs thoroughly before opening them, and make sure the space you're working in is well lit, clean, and doesn't have anywhere for little bits to disappear down if you drop them.
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Re: Interesting finding

Post by jerryfudd on Tue 26 Jan 2016, 6:35 pm

thanks, looking at the pic from Lings which part is the shim to which you need to add an additional one?

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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 6:38 pm

Part number 3. That little circle below the needle is a washer. You just add another of them.

The thing I found is that looking at a diagram like that made me think it was an immensely fiddly job. When it's actually there in front of you it's really, really not. Promise! If I placed every task I've ever done on the bike on a scale of 1 to 10 with 1 being adjusting the clutch cable and 10 being adjusting the valve clearances, I'd rate this as maybe 5 or 6.
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Re: Interesting finding

Post by jerryfudd on Tue 26 Jan 2016, 6:40 pm

thanks, did I also see that you have different jets - which part is that and where do you get the replacement jet? Honda?
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jchesshyre
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Re: Interesting finding

Post by jchesshyre on Tue 26 Jan 2016, 6:50 pm

I did change the main jet (responsible for fuel at 80-100% throttle), which is part number 29 there, up one size from 122 to 125. Again, I was lucky in that I had some lying around as my bike came with the Honda restrictor kit which includes these. But it shouldn't be too hard to find the right ones if you ask at a Honda dealer or look here http://www.allensperformance.co.uk.

Read this as well http://www.dansmc.com/carbs2.htm and the other pages on there about the carb components. It's really well explained and that whole site has helped me hugely over the years.
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ashcroc
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Re: Interesting finding

Post by ashcroc on Tue 26 Jan 2016, 6:57 pm

A long time ago I was advised if stripping carbs down to do it in one of those disposable foil roasting dishes (the sort you get at crimbo for the turkey).  Not only does it provide a clean area to work in but no little bits get lost if when you drop them.
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Re: Interesting finding

Post by eternally_troubled on Tue 26 Jan 2016, 9:06 pm

All good advice on here! Having taken apart other carbs on other bikes I can definately second the idea of a clean workspace that will (hopefully) catch lost screws/spring etc. Also make sure that if you pick things up you do it over the tray so when an unexpected bit falls off it lands in the tray rather than in your lap or (more likely) on the floor!

Also +1 for having some well-fitting, quality small screw drivers for this kind of work.

As jchesshyre says, I reckon that carbs aren't that difficult to take apart and clean etc. You can start to get into problems if you start radically (more than a few jet sizes) changing anything and/or if the o-rings/rubber in your carbs has deteriorated. Often the old rubber can be fine and then your disturb it (after 20 years off being in the same position) and it fails, so as minimum you might have to buy a new float-bowl gasket - you will notice if this starts leaking Smile (petrol on the floor!)

The carbs on the CB have diaphragms (which you will find while add the washer to your needle) - reiterating what Haynes says - be careful with them! The bike won't run well if you put even a small hole in one.

Anyway, if I *do* manage to fit my extra washer then I'll keep you updated...
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liverpool_f_
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Re: Interesting finding

Post by liverpool_f_ on Wed 27 Jan 2016, 8:27 am

Excellent tip on the baking tray. I do most of the disassembly of bike/instruments/electronics on some carpet tiles so the little bits you drop don't bounce of to the land of little dropped parts. It also saves the counter top from getting wrecked with heavy objects and you can take them outdoors and keep your knees dry if you need to work and the ground is wet.

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