XS750AU
Coast to Coast
Hi
Recently I have finished rebuilding the engine in my XS750-2D. Did not have to do too much, but I did go to 1st oversize pistons using scheuerlein pistons. Ironic that it is easier to get German pistons to fit a jap bike! Plus is was skipping second gear, which is not unusual for this bike. It turned out that the PO had put the circlip with the wrong face against the gear and the circlip had been pushed out of its seat while remaining on the shaft. That bike is now on the road and has been rejetted for pods. The mains went from 130 to 140 and the pilot jet went from 42.5 to 45. All running well now. During this process I acquired another XS750SE that was a wreck and in pieces for spare parts. Fortunately the PO did not make much effort to get decent photos and I picked up for less than AU$100.
The engine moved for less than a revolution on the kick starter and then stopped rotating. The PO had started to pull the engine down but got cold feet at breaking the cam chain, and had left it for years with the plugs out and the cam cover off. When I bought it, it was encrusted in mm of dirt and crap, so I am hoping that there is not too much wrong inside. When I have inspected the cam journals, the bearing surfaces were better than my other bike and I don't think the generator cover had ever been removed before. As this bike was not complete and at some stage had had a side car fitted I felt it was a clean slate that I could modify to my hearts content!
On Ebay there was a 896 big bore kit for under $200 which is a third of the cost of new German 750 pistons, the catch being that 750 cylinders cannot be bored out from 68mm to 74.5mm, you must use 850 cylinders. I have searched for over a year globally to find a set of 850 cylinders, seems like there are a lot more 750's around than 850's! Finally I tracked down a set of 850 cylinders out of North Queensland - same day I ordered the 896 piston and head gasket kit.
The head on the XS750SE was the same as the head (including cams) on the XS850 so I do not have to change anything on the head. The carbies are Mikuni 34mm series II which I believe will be OK. The other benefit of fitting the big bore kit is that the compression ratio will immediately change from the 750's 8.5:1 to the 896 having 10:1, and that should be OK.
The drive line on the XS750 was totally over engineered and is the same as used on the XS1100 so it will be able to cope with the considerable increase in HP and torque.
I am hoping that there is someone else on the forum that has completed this conversion before me and confirm if I have missed anything before I start building?
I am going to use pod filters and have a triumph 955 header that I am going to use for a very free flowing 3 into 1 exhaust. If the stand main jet is 130, any idea as to what main I should start with, I am thinking it is going to be 150+? On the primary jet side it would go from the 42.5 to 47.5? Would the primary air vent also need increasing?
Thanks for any help.
Regards
Tim
Recently I have finished rebuilding the engine in my XS750-2D. Did not have to do too much, but I did go to 1st oversize pistons using scheuerlein pistons. Ironic that it is easier to get German pistons to fit a jap bike! Plus is was skipping second gear, which is not unusual for this bike. It turned out that the PO had put the circlip with the wrong face against the gear and the circlip had been pushed out of its seat while remaining on the shaft. That bike is now on the road and has been rejetted for pods. The mains went from 130 to 140 and the pilot jet went from 42.5 to 45. All running well now. During this process I acquired another XS750SE that was a wreck and in pieces for spare parts. Fortunately the PO did not make much effort to get decent photos and I picked up for less than AU$100.
The engine moved for less than a revolution on the kick starter and then stopped rotating. The PO had started to pull the engine down but got cold feet at breaking the cam chain, and had left it for years with the plugs out and the cam cover off. When I bought it, it was encrusted in mm of dirt and crap, so I am hoping that there is not too much wrong inside. When I have inspected the cam journals, the bearing surfaces were better than my other bike and I don't think the generator cover had ever been removed before. As this bike was not complete and at some stage had had a side car fitted I felt it was a clean slate that I could modify to my hearts content!
On Ebay there was a 896 big bore kit for under $200 which is a third of the cost of new German 750 pistons, the catch being that 750 cylinders cannot be bored out from 68mm to 74.5mm, you must use 850 cylinders. I have searched for over a year globally to find a set of 850 cylinders, seems like there are a lot more 750's around than 850's! Finally I tracked down a set of 850 cylinders out of North Queensland - same day I ordered the 896 piston and head gasket kit.
The head on the XS750SE was the same as the head (including cams) on the XS850 so I do not have to change anything on the head. The carbies are Mikuni 34mm series II which I believe will be OK. The other benefit of fitting the big bore kit is that the compression ratio will immediately change from the 750's 8.5:1 to the 896 having 10:1, and that should be OK.
The drive line on the XS750 was totally over engineered and is the same as used on the XS1100 so it will be able to cope with the considerable increase in HP and torque.
I am hoping that there is someone else on the forum that has completed this conversion before me and confirm if I have missed anything before I start building?
I am going to use pod filters and have a triumph 955 header that I am going to use for a very free flowing 3 into 1 exhaust. If the stand main jet is 130, any idea as to what main I should start with, I am thinking it is going to be 150+? On the primary jet side it would go from the 42.5 to 47.5? Would the primary air vent also need increasing?
Thanks for any help.
Regards
Tim