I have replaced the engine in my 907 with a 944ST2 engine. Not a straight fit but with some adjustements to the crancases and coolant lines it fits.
I will need to fix some niggles on the engine, it runs very bad at low rpm and low load. Coughs and splutters, even barks back in the intake when decelerating, throttle closed. Runs fine with under load. Idea's welcome, I think Ill start with rpm-sensor, TPS? coils, plugs?

Question on the clutch, does anyone know the diameter of the master cylinder on the 907, and is it different from the ST-2? Actuating the clutch on the ST2 engine with the master of the 907 is much harder than the 907 originally.
Cheers J

What year of ST2 engine have you fitted? I have ST2 cylinder heads and barrels and pistons fitted to my 907ie bottom half, so apart from the water pump housing is effectively the same as the 1997 ST2. I'm using the 907 P7 ECU and injection system and it runs very well. I suggest you carry out a full TPS set up and throttle body balance.
I'm surprised that the clutch has a harder pull as there is no difference in the clutch itself between the 907 and the ST2. They both use the same dry clutch, although when they went to the 3-phase engine with different crankcases in 1999 I think the size of the clutch slave cylinder was increased (the slave has a star shaped socket set into the outside of it). From about 2002 the clutch was changed to use alloy plates and basket but nothing else changed.

Thanks Derek,
I used a '98 ST-2 engine, I swapped the whoe engine, including wiring loom, ecu and all the sensors.
I agree that TPS set-up and balance is a good start, (will be mu first) but I cant help thinking that this is running so rough, there is more to it than just TB's and TBS being out of balance. I read that the rpm pick-up on these is sensitive to air gap and can benefit from "shimming" Not sure what the gap should be but I will aim for minimum without touching.

On the clutch, I was surprised about the difference, on my 907 the clutch was light. I swapped the slaves; 907 slave on the ST2, no difference. Maybe this clutch is using stronger springs? I can chack that tonight an swap them from my 907 engine

Cheers J

And maybe try the quiet clutch mod at the same time, this one needs it. (the basket may be at the end of its life)

Thanks Derek,
Clutch question solved, springs in the ST-2 are thicker wire, I swapped them and added the extra friction plate at the bottom.

Need to read up on JPdiag. I see info on the cables and hooking up, but not much on what it can do with an older ECU (IAW16M).
Can it check all the sensors and tell me if they have a bad spot along their range?
Cheers J

Hmm, interesting about the clutch springs.
I'm not sure that JPDiag will talk to the IAW16M , there used to be a version that did but it seems to be no longer available.
GuzziDiag should work though if you select a model that uses the same ECU. You should be able read and clear any DTC errors and read the values from each of the sensors. Download here -

Did the quiet clutch mod, funny result. Initially the clutch clattered when engaged, now it rattles with the clutch disengaged. Prefer the new situation, Rattle on demand It works fine, good action and no slippage at full throttle.

The rough running is now solved too, simple fix, The bike was running way too lean at small throttle openings. Adjusted the air bypass scews (inwards) and it transformed the bike. Really amazing difference, where it coughed an pluttered and hesitated on take-up, it is now perfecly smooth. (thanks for tip Derek)

Cheers J

Does the fuel pump in the 907 tank deliver adequate pressure to the newer ST2 injection system?

Phil

It should do. Both systems run at 3 bar.

Yes I am using the ST2 ECU.
Any advice on where best to buy the cables?

The fuel pump appears to work fine. Its the pressure regulater that sets the pressure anyway. On the 907 this is on the throttle bodies and on the ST-2 inside the tank. Using the ST-2 TB's and the 907 tank I ended up without a regulator. That didnt work Luckily I recognised the symptoms of low fuel pressure (from when the PO used normal fuel hoses inside the tank, soon ruptured)
So I took the regulator off the 907 TB and put it the return line under the tank. Didnt measure the pressure, but the bikes runs perfect.
Cheers J

got mine here




details can be found in this thread

and many others