XS750 to XS896 big bore

XS750AU

Coast to Coast
Hi Dave
Starter are a world of their own!! On my 750 the electric turns it over easily when cold, but when hot not a chance, have to kick it!

Ryan - the 2nd gear on my 750 started popping out so that was the final straw which made me rebuild the engine. Turned out the only problem with second was that the PO had used an old circlip and had put the radius edge facing out. So the gear had pushed the circlip out of its seat and down the shaft so the gear could not engage properly!! So try to get the end cover off and have a look, there are some other fixes you can do once you get the cover off. Check out the triples site.
Mikuni series 2 carbies are not too bad, easy to get jets and parts. Once I got new mounting rubbers and throttle spindle seals they are working beautifully on the 750. Cleaning and seals are much cheaper than any alternative carbies.

Today was in the bush on the Husaberg FE550, that bike really does go. Almost as much Hp(62) as the XS and weighs less than than half @ 105. So no progress on the 896 build this weekend!!
Cheers
Tim
 

datadavid

Over 1,000 Posts
XS750AU said:
Hi Dave
Starter are a world of their own!! On my 750 the electric turns it over easily when cold, but when hot not a chance, have to kick it!

Ryan - the 2nd gear on my 750 started popping out so that was the final straw which made me rebuild the engine. Turned out the only problem with second was that the PO had used an old circlip and had put the radius edge facing out. So the gear had pushed the circlip out of its seat and down the shaft so the gear could not engage properly!! So try to get the end cover off and have a look, there are some other fixes you can do once you get the cover off. Check out the triples site.
Mikuni series 2 carbies are not too bad, easy to get jets and parts. Once I got new mounting rubbers and throttle spindle seals they are working beautifully on the 750. Cleaning and seals are much cheaper than any alternative carbies.

Today was in the bush on the Husaberg FE550, that bike really does go. Almost as much Hp(62) as the XS and weighs less than than half @ 105. So no progress on the 896 build this weekend!!
Cheers
Tim
Mine wont turn when cold, but will start the bike when hot! Had the same thing on the last one, starter just needed a good cleaning..
 

XS750AU

Coast to Coast
Productive day. Brought the engine back to my shed and stripped it down. As I said earlier the PO had started and thankfully lost interest, but he had left it open. The reason it would not turn over was due to the cam timing being completely out, causing a valve & piston clash :eek:. No damage done ;D. The crowns of the pistons had a layer of crud on them, but it had not gone beyond the compression ring. What is clear is that this engine has not done much work, if you look on the cylinder you can still see the original hone marks ;D ;D ;D.
It took about an hour to pull it down and four hours cleaning. The original owner had bought it for speedway and there was plenty of dirt built up on the outside to get off. I used a wire brush by hand so as no to ruin the silver engine paint. Not all perfect though as there was a thin layer of gunk in the bottom of the sump, and the carbies had some dusty build up in them. I guess the original owner did not have a great air cleaner for his speedway racing. The carbies must have blocked up before he did any internal damage to the engine.
The head on this engine is definitely the high compression version. Have a look at the photo and you can see the complicated machining to create 2 dome areas. I could not save the base gasket off the 750 cylinders so I need to get another one before reassembly the 896 so I can lower the compression a little from the 11.4 calculated.
Quick video of Saturdays work https://www.youtube.com/watch?v=JkRFqIKB5ls

Photos of bits - the gudgeon pins in the pistons look like they have been hot especially the centre one.
 

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datadavid

Over 1,000 Posts
Mine runs just fine with big bore and hi comp glad me and the machinist decided not to skim the cylinders at all! It will run like hell even on standard pump gas, only problem is starter engine cant turn it anymore not too hard to kick though.
 

datadavid

Over 1,000 Posts
Ryan Stecken said:
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.

Thank You! :) The mikunis dont suck at all, they are just old. And if they have been sitting chances are all seals have been dry rotted. If they are low mileage carbs with no mechanical damage or wear they are well worth repairing. Mine were not! Triumph carbs were just the cheapest option + its nice when you calibrate them and they Stay calibrated! :D
 

2_DONE_THE_TON

Over 1,000 Posts
DTT BOTM WINNER
datadavid said:
Thank You! :) The mikunis dont suck at all, they are just old. And if they have been sitting chances are all seals have been dry rotted. If they are low mileage carbs with no mechanical damage or wear they are well worth repairing. Mine were not! Triumph carbs were just the cheapest option + its nice when you calibrate them and they Stay calibrated! :D

Lets see what they do when I mount them on the old bastard :) may i ask you what type of triumph carbs you installed (searched for t900 carbs but they are all 4 cylinder banks...)

thanks!
 

datadavid

Over 1,000 Posts
Yes first gen new triumphs were all fours. Look for trident, legend or thunderbird carbs.
Preferrably not the first mikuni carbs as they wore out needles and needle jets. Keihins are superior. You can achieve stoichiometric mix across the range, they burn so clean you can run catalytic converters on these bikes..
 

datadavid

Over 1,000 Posts
Ryan Stecken said:
thank you!are there any 3 cylinder flatslides models :)?
My slides are flat! But I guess you mean proper mechanical flatslides? Nope, dont think so. It would probably cost you as much to get three of those as if you would install a daytona Fuel injection, not to mention installing and tuning ☺
 

XS750AU

Coast to Coast
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!

https://www.youtube.com/watch?v=Sw1mt2daakA

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
 

datadavid

Over 1,000 Posts
XS750AU said:
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!

https://www.youtube.com/watch?v=Sw1mt2daakA

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.."
 

XS750AU

Coast to Coast
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
 

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XS750AU

Coast to Coast
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
 

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XS750AU

Coast to Coast
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.
 

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teazer

Over 10,000 Posts
DTT BOTM WINNER
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?
 

XS750AU

Coast to Coast
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
 

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teazer

Over 10,000 Posts
DTT BOTM WINNER
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.
 

XS750AU

Coast to Coast
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
 

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