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Author Topic: YZF750/1000R - The Fly  (Read 33147 times)

Offline canyoncarver

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Re: YZF750/1000R - The Fly
« Reply #180 on: Jan 02, 2018, 12:35:40 »
Prepping for the valve clearances.  I was able to get started last night.  You have to peel the onion to get the the valve cover. 
--

YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
65 Norton, My damn Shovelhead chop, and an 86' FXR
more YZF750R's, the KZ's, a Zephyr750...and the unfinished 75' CB550 cafe.
--

Offline canyoncarver

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Re: YZF750/1000R - The Fly
« Reply #181 on: Jan 02, 2018, 12:44:51 »
Last but not least.  I built two Raspberry Pi3's over the holidays.   This one will be a gateway to the internet for security cameras and a stateful firewall for the Wifi.  Fun stuff.
--

YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
65 Norton, My damn Shovelhead chop, and an 86' FXR
more YZF750R's, the KZ's, a Zephyr750...and the unfinished 75' CB550 cafe.
--

Offline XS750AU

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Re: YZF750/1000R - The Fly
« Reply #182 on: Jan 02, 2018, 18:21:26 »
Hoping you can help me understand the proper function of the Mikuni BST36SS carbies I am using on my triple. Understand that the YZF uses a different carb, but they appear to be similar.
There are 2 hoses coming off your carbies, just under the diaphragms, I have highlighted  in red in the photo.
It appears they would go into the airbox? Do you know what function they perform? Others have suggested that I blank them off, but I would prefer to understand their function before I do that.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline irk miller

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Re: YZF750/1000R - The Fly
« Reply #183 on: Jan 02, 2018, 18:45:26 »
Hoping you can help me understand the proper function of the Mikuni BST36SS carbies I am using on my triple. Understand that the YZF uses a different carb, but they appear to be similar.
There are 2 hoses coming off your carbies, just under the diaphragms, I have highlighted  in red in the photo.
It appears they would go into the airbox? Do you know what function they perform? Others have suggested that I blank them off, but I would prefer to understand their function before I do that.
My F650 comes with a pair of BST33's.  Those hoses are part of your power jet circuit.  It adjusts the mixture for high rpm delivery.  I don't want to claim credit as some expert on these, so here is a good article I recently read that does a good job explaining...

http://oldskoolsuzuki.info/archives/531

If they don't go to the airbox, then they could be a breather for the float chambers (explained at the end of the article).

Offline canyoncarver

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Re: YZF750/1000R - The Fly
« Reply #184 on: Jan 02, 2018, 19:59:05 »
Hoping you can help me understand the proper function of the Mikuni BST36SS carbies I am using on my triple. Understand that the YZF uses a different carb, but they appear to be similar.
There are 2 hoses coming off your carbies, just under the diaphragms, I have highlighted  in red in the photo.
It appears they would go into the airbox? Do you know what function they perform? Others have suggested that I blank them off, but I would prefer to understand their function before I do that.


I'm not sure this will help but on this bike, they are BDST38's and they do not go to the airbox and are used as bowl breathers.   These carbs lay flat on the bike rather than cv end up on a standard bike.  Likely the reason for the breather configuration.  They have a sort of screened check valve on them also.  In the pic you referenced I had moved them.  They actually lay like this and just out of the way:
« Last Edit: Jan 02, 2018, 20:00:55 by canyoncarver »
--

YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
65 Norton, My damn Shovelhead chop, and an 86' FXR
more YZF750R's, the KZ's, a Zephyr750...and the unfinished 75' CB550 cafe.
--

Offline irk miller

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Re: YZF750/1000R - The Fly
« Reply #185 on: Jan 02, 2018, 20:07:20 »
Moral of the story:  Don't block them off.  They serve a purpose.

Offline XS750AU

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Re: YZF750/1000R - The Fly
« Reply #186 on: Jan 02, 2018, 22:13:34 »
Quote
they are BDST38's and they do not go to the airbox and are used as bowl breathers.
Thanks, that is a great help. I guess the BDST is for the horizontal version of the BST vertical carbi - they look very very similar.
Quote
Don't block them off.  They serve a purpose.

That is exactly my thoughts, hence the question. I just wanted to know if they needed to vent or pick up a vacuum out of the airbox!
Next question  - there is one hose coming off the diaphragm cap (black plastic) on one carbie only. The other 2 carbies have the port capped off. It appear to route down through the choke and into the vacuum side of the venturi. Is this for carbi function or is it just supplying vacuum for some other engine control on acceleration?
If it is for carbi function then why are 2 out of 3 carbies capped off?
Thanks for your help.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline irk miller

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Re: YZF750/1000R - The Fly
« Reply #187 on: Jan 02, 2018, 22:56:25 »
Thanks, that is a great help. I guess the BDST is for the horizontal version of the BST vertical carbi - they look very very similar.
That is exactly my thoughts, hence the question. I just wanted to know if they needed to vent or pick up a vacuum out of the airbox!
Next question  - there is one hose coming off the diaphragm cap (black plastic) on one carbie only. The other 2 carbies have the port capped off. It appear to route down through the choke and into the vacuum side of the venturi. Is this for carbi function or is it just supplying vacuum for some other engine control on acceleration?
If it is for carbi function then why are 2 out of 3 carbies capped off?
Thanks for your help.
Did you see that link I posted up there in my first comment?  That's a write up on these BST carbs and explains all the tubes. 

Offline canyoncarver

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Re: YZF750/1000R - The Fly
« Reply #188 on: Jan 02, 2018, 23:54:25 »
Yeah, Factory Pro did cool stuff for the YZF. 

http://www.factorypro.com/Prod_Pages/prody73.html
--

YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
65 Norton, My damn Shovelhead chop, and an 86' FXR
more YZF750R's, the KZ's, a Zephyr750...and the unfinished 75' CB550 cafe.
--

Offline XS750AU

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Re: YZF750/1000R - The Fly
« Reply #189 on: Jan 03, 2018, 06:03:58 »
Quote
Did you see that link I posted up there in my first comment?
Sorry missed that!!!
Thank you both for your great help. I think I have now worked it out. It looks like all Mikuni BST carbies are not the same, as the Triumph BST's are different to the ones Factory Pro referred to.
Now for the explanation of how I think the Triumph BST36SS carbi Power Jet works.
The first photo shows the bell mouth, which has 2 air vents at the bottom, one for the pilot circuit and the other for the float bowl/main circuit. Up the top is the main vent for the diaphragm to lift the slide during acceleration.
The next photo shows the powerjet tube going from the float bowl up to the point where the fuel enters the air inlet between the butterfly and the cylinder head. The interesting point here is that the vent also extends up to the diaphragm cap to a hose barb. If the hose barb is not capped then the engine will just suck air and severely affect the carbi function.
The last photo shows the powerjet port coming in just behind the butterfly where there is max vacuum. By the way this also appears to be where the choke circuit also enters the carbi. The top highlight is the cap I have placed on the diaphragm cap hose barb. I guess Triumph had some kind of valve to control the vacuum at this point which I do not have on a 1978 XS750/896.
I am thinking that as the powerjet is pulling vacuum behind the butterfly that it will still function with the low impedance airfliter?
I think this is how they work - if I am wrong please let me know.
Canyon - sorry for highjacking you blog, but thanks for your help.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N