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Author Topic: XS750 to XS896 big bore  (Read 22934 times)

Offline Ryan Stecken

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Re: XS750 to XS896 big bore
« Reply #10 on: Jul 18, 2016, 10:59:53 »
Following along!might have an XS 750 soon too :-)

Online datadavid

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Re: XS750 to XS896 big bore
« Reply #11 on: Jul 18, 2016, 12:02:05 »
Did the same thing and with the right cams i think you will enjoy the power bump!

Offline XS750AU

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Re: XS750 to XS896 big bore
« Reply #12 on: Jul 19, 2016, 03:41:11 »
Did the same thing and with the right cams i think you will enjoy the power bump!
Hi David
Thanks for the reply. Can you give a bit more detail on the cams?
Thanks
Tim

Sent from my GT-I9506 using Tapatalk

“Engineering is the art of being approximately right rather than exactly wrong.”

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

Online datadavid

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Re: XS750 to XS896 big bore
« Reply #13 on: Jul 19, 2016, 04:01:17 »
Hi David
Thanks for the reply. Can you give a bit more detail on the cams?
Thanks
Tim

Sent from my GT-I9506 using Tapatalk
I dont really have great detail to give you but the earlier cams (77-78)are supposed to breathe a bit better. Web cams have a few profiles as well, to be welded on cores.

Offline XS750AU

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Re: XS750 to XS896 big bore
« Reply #14 on: Jul 20, 2016, 07:30:07 »
Hi Dave
What year model did you use as your base for the 896?
After your info on the cams I started to dig a bit deeper and had a Doh! moment. I had thought that all XS750's had the 8.5 compression ratio which when using the 896 kit would boost the compression to 10.5 which is not too radical. BUT the XS750E & SE which I am using had a compression ratio of 9.5 which means with the 896 kit it will be end up being 11.4, which is a bit higher than I would have liked. Anyone out there got an opinion on a 11.4 compression ratio on an air cooled 1978 engine???http://www.dotheton.com/forum/Smileys/default/huh.gif.

On the cams the XS750E appears to have the final design and the highest performance so that looks OK. Plus it keeps the valves open longer so I guess the actual compression will be a little less due to the swept volume with closed compression is slightly lower!!! The info I could find was per the attached image for the D and 2D and the following text for the E.

"Therefore the engine modifications were kept subtle and affect only the top end of the engine. For example the compression ratio has been upped from 8.5:1 to 9.5:1, which means it now requires premium fuel (at least 90.5 octane rating). The actual shape of the combustion chambers has also been altered and they now actually displace fewer cc’s than earlier XSs. Cam profile has been altered slightly, retaining the same lift but now having sportier intake timing. And intake breathing has been further increased by changing the venturi shape in the carbs (they’re still 34mm in size), modifying the main jets and adding on a, larger, better breathing air box.".

Guess if there are a couple of options on compression, think I will definitively use 2 cylinder base gaskets. If that is not enough there is always the option to swap heads with my other XS750-2D which has the 8.5 compression. That way I would boost the 750 to 9.5 and the 896 would end up at 10.5 (last option).
Cheers
Tim

“Engineering is the art of being approximately right rather than exactly wrong.”

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

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Re: XS750 to XS896 big bore
« Reply #15 on: Jul 22, 2016, 06:27:30 »
Since i built mine from scrap im not really sure what bike my head came from, but the starter wont turn the engine unless hot so either the starter needs a good cleaning or i got very high comp!

Offline Ryan Stecken

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Re: XS750 to XS896 big bore
« Reply #16 on: Jul 22, 2016, 10:44:15 »
Hey guys!

sorry for hijacking your post but I shortly before buying two complete XS750 (stock bikes).
is there any way to check for the famous 2nd gear jumping without riding the bike?
both bikes won´t start cuz they were sitting for years,need carb cleaning et cetera...

if the second gear issue will arise is it hard to fix?i guess it means tearing the motor down to the gears....?

thanks in advance and sorry once again?

Online datadavid

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Re: XS750 to XS896 big bore
« Reply #17 on: Jul 22, 2016, 13:38:14 »
Hey guys!

sorry for hijacking your post but I shortly before buying two complete XS750 (stock bikes).
is there any way to check for the famous 2nd gear jumping without riding the bike?
both bikes won´t start cuz they were sitting for years,need carb cleaning et cetera...

if the second gear issue will arise is it hard to fix?i guess it means tearing the motor down to the gears....?

thanks in advance and sorry once again?
Its not hard to fix, go to yamaha-triples.org for a few different methods. Only way to see if it slips is under load unfortunately.

Offline Ryan Stecken

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Re: XS750 to XS896 big bore
« Reply #18 on: Jul 22, 2016, 13:42:46 »
Thanks datadavid!
Youre xs project is awesome...

I guess I will need to look far better carbs too,got the mikunis 2's on it...but i heard that these suck hard.

Offline JadusMotorcycleParts

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Re: XS750 to XS896 big bore
« Reply #19 on: Jul 22, 2016, 16:49:03 »
Awesome project man.  Looking forward to seeing your progress :)