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Author Topic: XS750 to XS896 big bore  (Read 19846 times)

Offline datadavid

  • Posts: 1097
Re: XS750 to XS896 big bore
« Reply #30 on: Aug 05, 2016, 13:27:13 »
Beautiful morning today, so I took the XS750 to work. Great start to the day, I love that exhaust note, jetting seems pretty close, no coughs, flat spots or backfires!



It is pushing a bit of oil out of the case breather - any ideas anyone?

Was planning to valve stem seals and lap the valves this weekend on the 896 but I might have to look at the breather issue on the 750. Going in the "Distinguished Gentlemen's ride" in September so better off fixing it now.
Cheers Tim
If its like streams of oil you must have serious blow by?
Take the breather lid off and check for a yellowish plastic thingy, its an oil mist separator. Someone might have removed it to "aid breathing.."

Offline XS750AU

  • Posts: 290
Re: XS750 to XS896 big bore
« Reply #31 on: Aug 06, 2016, 04:08:09 »
Q.E.D.
No oil mist separator thingy!!! The 896 engine has one, so I took the measurements off it and turned one up in the lathe using nylon stock.
With the engine going there was absolutely no blow by, but the filter I have on the end of the breather tube was soaked with oil. Not sure if at full noise it was just shooting oil up and out without the the oil mist separator??? Just checked the manual and the schematic does not show one in the 2D engine - maybe they were introduced for the E???
The oil mist separator is in and we will see if that fixes the issue.
Spent the afternoon striping the head down, so I can lap the valves in and fit new stem seals (hopefully tomorrow).

Photos of the oil mist separator.

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

Offline XS750AU

  • Posts: 290
Re: XS750 to XS896 big bore
« Reply #32 on: Aug 08, 2016, 06:41:12 »
Had a few domestic jobs to do on Sunday, so progress was a bit limited.
Pulled the forks out, as the tubes need to be rechromed and then cleaned up the head and lapped the valves in, ready for reassembly.
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

Offline XS750AU

  • Posts: 290
Re: XS750 to XS896 big bore
« Reply #33 on: Aug 12, 2016, 09:01:07 »
Pushed the boundaries with my beloved to night and rejetted the carbies on the kitchen table.
Standard XS750 is 130 mains and 42.5 pilots
My XS750 with pods and perforated baffles is running 140 mains and 45 pilots
For the XS896 I am starting with 165 mains and 47.5 pilots

You will see in the photos that the mains that were in the carbies were the tall hex type. That is the same type I bought in the new sizes, but after fitting them I am not sure that they are correct as they don't screw down fully. The last photo shows the standard round Mikuni jets (137.5 which is too small) but it screws down full. Suspect the PO bought the wrong jets.
“Engineering is the art of being approximately right rather than exactly wrong.”

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

Offline Tune-A-Fish©

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Re: XS750 to XS896 big bore
« Reply #34 on: Aug 12, 2016, 09:18:42 »
The new are for Keihin crabs
"I didn't come here and I ain't leavin"  Willie Nelson

"love hard, live fast, die fun" Kacey Musgraves

"Like a Wreckin Ball!" Eric Church

Offline teazer

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Re: XS750 to XS896 big bore
« Reply #35 on: Aug 12, 2016, 11:03:41 »
I am pretty sure that those carbs use Large round main jets which have a different thread and are not sized the same way as large hex jets.  What needle jets are in those carbs?

Offline XS750AU

  • Posts: 290
Re: XS750 to XS896 big bore
« Reply #36 on: Aug 12, 2016, 20:43:37 »
Thanks for the replies - yes they appear to be wrong. The 165s are bound to be the wrong final size so next time I will get the large round design. Interesting though I bought the tall hex jets from Mikuni OZ, so there must be Mikunis out there that use them!!!!

Next question - in the generic "Engine gasket kits" there are six small black O rings in a sealed bag with the valve guide seals and the cylinder O rings (refer photo). It was the same when I rebuild the XS750, I cannot work out where these 6 small black O rings are meant to go. I left them out of the 750 and it is running fine. Anyone know???
Thanks
Tim
“Engineering is the art of being approximately right rather than exactly wrong.”

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

Offline Tune-A-Fish©

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Re: XS750 to XS896 big bore
« Reply #37 on: Aug 12, 2016, 20:55:53 »
I think those are for the head bolts.
"I didn't come here and I ain't leavin"  Willie Nelson

"love hard, live fast, die fun" Kacey Musgraves

"Like a Wreckin Ball!" Eric Church

Offline teazer

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Re: XS750 to XS896 big bore
« Reply #38 on: Aug 12, 2016, 22:42:23 »
Most round slide (VM series carbs use Large Hex jets.  Large hex jets are numbered to represent flow rates at 30cm of pressure IIRC.  Large round jets are measured in mm of diameter, so a 150 is 1.5mm diameter.

In simple terms double the size of a hex jet from say 90 to 180 and it doubles the flow, but double the size of a round jet and flow increases by a factor of 4, so a 180 round flows 4 times as much as a 90 in a large round.  There are tables on teh web that show a pretty close correlation for equivalent sized jets.

Offline XS750AU

  • Posts: 290
Re: XS750 to XS896 big bore
« Reply #39 on: Aug 12, 2016, 22:46:45 »
Found where the black O rings go = under the valve guides.
Did not remove the valve guides, so they will not be used.

Thanks for the explanation on the jet sizing. It will be back to the round jets.
Thanks
Tim
“Engineering is the art of being approximately right rather than exactly wrong.”

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