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YB11 Carb pipes question

 
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Martin.T



Joined: 30 Aug 2015
Posts: 18
Location: Plymouth

PostPosted: Sun Nov 01, 2015 10:02 pm    Post subject: YB11 Carb pipes question Reply with quote

I`m reassembling my YB11 and have got to the stage of fitting the carbs.
As i didn`t take the bike and engine to bits i`m scratching my head, and i`m sure there is someone who knows the answer.
With the carb bank on the bench, looking at the top of the diaphram area there are 4 pipes sticking up 2 either side of the bank of carbs. 2 pipes have 90degree rubber ends on them, it looks like they may go into the bottom of the airbox. The other 2 have a large plastic knuckle on each of them, when the carbs are mounted on the engine these 2 knuckles point in towards the engine, are they connected to anything or do they just act as an air intake?
Any ideas would be very helpful.
Hopefully you can understand my explanation.
Is it possible to post a picture to show what i mean.
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brian



Joined: 22 Aug 2011
Posts: 3769
Location: Australia

PostPosted: Mon Nov 02, 2015 12:48 am    Post subject: Reply with quote

Easiest way to post pics here is to upload the pics to a host website like photobucket or similar and then post the direct link here. You need to click the img button above here at each end of the link. Or email them to me and I'll post them for you.
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2bims



Joined: 03 Apr 2010
Posts: 7289

PostPosted: Mon Nov 02, 2015 1:06 am    Post subject: Reply with quote

Have you looked in the YB11 workshop manual or spare parts Manual? Do you have these? If not I can email to you a link to download them...would just need your email address.......Not sure on YB11 pipes.....on Ducati carbs they have overflow pipes that route into spare cannisters, a pair of small boxes
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2bims



Joined: 03 Apr 2010
Posts: 7289

PostPosted: Mon Nov 02, 2015 1:17 am    Post subject: Reply with quote

Workshop manual seems to show that large pipes on top between carbs 1-2, and 3-4 are breather pipes that feed down, as drains/overflow....normally through the swingarm gap where the rear shock sits.....pipes to the outside of carbs one and four from underneath go to airbox, left and right to left and right...and main pipe in the middle is fuel pipe to tank
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who



Joined: 10 Nov 2010
Posts: 402
Location: Melbourne Australia

PostPosted: Mon Nov 02, 2015 3:23 am    Post subject: Reply with quote

Are you talking about the plastic filters that attach to the CV diaphragm breather hoses? These lines allow the diaphragms to work, if these lines are sealed or blocked the diaphragms are effectively in vacuum and will rupture when the vacuum force of the engine tries to pull them down, so they are breathers (to the back of the diaphragm) that allow the slides to move through their travel and then back again.

The filters face down, occasionally the foam inside the filters decomposes and can block the passage (see above) or grains of decomposed foam can be pulled into the carbs and do damage to the diaphragms. Some people pull out the old foam, some replace it with a small piece of new air filter foam, don't oil it, and they are good for another 20 years. Use tweezers. compressed air if it has decomposed. (do this with the hoses off the the carbs)

The other two tee pieces that sit between the two outer carbs, i'm not sure, but I think they are for warm air. The early genesis engines had a plate on the cylinder block that these connected to via a rubber hoses. The thunderace doesn't have this. Just point them downwards. You can attach some rubber pipe and run it out the bottom (downwards) of the carbs. Just make sure the hose doesn't interfere withe the carb action, and is clear of everything.

Hope this helps.
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bimotabob



Joined: 06 Jul 2013
Posts: 110
Location: New Zealand

PostPosted: Mon Nov 02, 2015 7:47 pm    Post subject: Reply with quote

Do all the Thunderace YB11 engines have heated carbs from the engine coolant circuit?
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who



Joined: 10 Nov 2010
Posts: 402
Location: Melbourne Australia

PostPosted: Tue Nov 03, 2015 2:25 am    Post subject: Reply with quote

No Bob, I don't think any of them do? Perhaps the EU models?

As I said some of the early black engined (genesis FZR's) had this feature, probably EU models where the weather is less kind. I've got at least 10 FZR engines here and although I have removed the feature from a couple of my race bikes, most do not have it.

This FZR1000 88 engine, from the EU has the feature fitted. You can see the fitting sitting over the water pipe, the hoses attached to the two nipples, and presumably benefited from the warm air the water circuit thermostat provided. It's right of the cam chain adjuster.

Also Martin.T via pm mentioned that bimota do their own thing with the diaphragm filters, they run them into the airbox (front of filter) on the right is YB11 airbox. (see lower photo)

Bimota use their own filters which are metal, not foam so should never give the same problems as the yamaha ones. You should always make sure that air flows freely through them, if it doesn't your motor will not run properly. If one is allowing less air through than the other your carbs will be effectively out of balance throughout acceleration, until they equalize in a cruze situation, so these little forgotten filters are more important than you would think! Rolling Eyes

This applies to ALL CV carbs, as they all have filters.



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Jonny B Bad



Joined: 05 Dec 2009
Posts: 555
Location: NE London

PostPosted: Tue Nov 03, 2015 10:38 am    Post subject: YB carb vent hoses Reply with quote

Who, the hoses that go into the fitting next to the coolant tube are the float bowl vents and I'm not sure that they take any benefit from the coolant tube, it's just a location from which they shouldn't hoover up too much crud.

It is interesting to see the diaphragm vents plumbed into the airbox on the 11. I suppose that these bikes breathing through the roughly forward facing holes in the frame are getting a ram-air effect. On full ram-air bikes both the float bowl and diaphragm vents need to be subject to the same pressure as the venture, so both vents are plumbed into the air box. On my 8 the diaphragm vents are plumbed into the hole in the frame that draws air into the air box (i.e. same pressure as venturi), but the float bowl vents were on a similar arrangement to the one in your picture (i.e. atmospheric pressure). I have recently re-located the float bowl vents into the air box and I think the bike runs better for it.

Sorry, bit of an anorak post - I'll get my coat!
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who



Joined: 10 Nov 2010
Posts: 402
Location: Melbourne Australia

PostPosted: Tue Nov 03, 2015 1:03 pm    Post subject: Reply with quote

Hey Jonny, makes perfect sense that the float chamber is vented as well! Put that coat down and enjoy a pint! You too Martin.T

I think if you look to the far right of the airbox picture above you can see the line running out that serves the float bowls, with a dodgy yamaha foam filter incorporated.

I would definitely get rid of the foam filter on the fuel bowl side, there are small metal fuel filters on ebay for monkey bikes etc.

So one of the great mysteries solved Very Happy
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Jonny B Bad



Joined: 05 Dec 2009
Posts: 555
Location: NE London

PostPosted: Tue Nov 03, 2015 1:55 pm    Post subject: YB carb vents Reply with quote

Nice to be appreciated Who and I'm never one to turn down a pint!

The thing that put me onto this was following Bimota's reported thinking in this regard. When the SB6R, which takes air from a snorkel at the front of the bike (unlike the 6), was tested, a factory spokesman said that the reason it went so well was that they had plumbed both carb vents into the airbox. However, in reality, some 6Rs had the diaphragm vents plumbed in to the airbox and others didn't. So they clearly didn't decide to plumb into the airbox until they were some way into production. The YB11 was contemporary with the 6R and they clearly applied the same thinking, albeit the 11 was only a development of the earlier YB8. Of course, when you look at it that way, they might have just been following a lead from Yamaha, which they applied to later production 6Rs.

Bottom line is that while it became accepted wisdom that with ram air the carb vents needed to be plumbed into the air box, it took them a while to come to that conclusion.
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who



Joined: 10 Nov 2010
Posts: 402
Location: Melbourne Australia

PostPosted: Tue Nov 03, 2015 3:07 pm    Post subject: Reply with quote

Yes Jonny, fuel bowls to vacuum, diaphragms to pressure, although if you want real time-real world ram air effect, you have to seal up the gaps (and everywhere else) between frame and airbox with some of that stick on foam between airbox and frame.

Back in 88 with the FZR750's they used to put heavier springs in the CV diaphragms for wet weather racing. An early form of traction control.

The later OW01 has quick release spring caps specifically for this purpose. It also allowed needle change and adjustment, within minutes, and with the carbs in place.

Sorry for the hijack, but a nice discussion. thanks.
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bimotabob



Joined: 06 Jul 2013
Posts: 110
Location: New Zealand

PostPosted: Mon Nov 09, 2015 3:11 am    Post subject: Reply with quote

I have heard people block one of the 2 frame air intake vents on the carb YB series as the CV carbs got too much air standard and run better like that
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who



Joined: 10 Nov 2010
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Location: Melbourne Australia

PostPosted: Mon Nov 09, 2015 5:25 am    Post subject: Reply with quote

Hi Bob, one of the early YB6's I worked on recently had the ram air hoses removed completely. Who knows whether they were removed for a reason or lost in transit!

The pre-thunderace exup engines had a really poor troublesome carb fitted, the BDST 38mm Mikuni carbs where problematic, hard to tune reliably, and wore needles and emulsion tubes out in no time.

They were not up to the job of WSBK racing on the OW01. This is the reason the RC30's were dominant, especially in domestic SBK championships, where you had to retain oem carburetors.

The thunderace BDSR38 Mikuni carbs, are the same beast as the early carburettored R1, (just smaller id and different spacing due to the cam chain being moved from center of engine to outside cyl) ).

A far more reliable and are less fickled and easier to tune carburettor, and very receptive to ram air, once rejetted about 4 hp shy of 39 mm FCR carbs at top end and better through midrange.
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bimotabob



Joined: 06 Jul 2013
Posts: 110
Location: New Zealand

PostPosted: Mon Nov 09, 2015 8:05 am    Post subject: Reply with quote

In case anyone isn't familar with the Northern hemisphere heated carbs on the Thunderace this is the setup, the bike was in miles in hour.
The large rubber hollow housing sits over the cam chain tensioner.







Looks like a rubber hose goes in one side and piping runs across between the carbs and exits another rubber hose. runs between the thermostat housing and the metal coolant outlet to the radiator. I'm not 100% sure what the inline plastic housing is for but i would take a punt its some sort of temperature valve. Carb warming is great for winters even here in NZ. Especially ram air bikes like 1990's kawasaki bikes which have major issues as the carbs freeze and the bike cuts out so they fitted a system like this.
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