I just finished up the project of swapping the high compression pistons into the 900 motor in my bike.  It fires, but won't run unless I give it a bit of throttle, and won't continue to run unless I keep it above 2300-2500 RPM.  I've double checked the cam timing, and swapped a couple different maps into the PCIII, but that hasn't helped any.

Any suggestions?

Does the motor sound fine?
what was the piston to wall clearance?
did you check/set squish?
piston ring end gaps?

how does it turn over by hand? tight or normal?
If this all is good look at what you are doing when you give it what it wants . more throttle =more fuel and more air. try adding one and then the other and see if one improves it.

Everything was within spec, and the motor turns over easily.  It seems like it was running really well in the upper RPM ranges, although with new parts I didn't get too crazy revving it.  I did just pull the plugs and they're really black.  I also noticed that it seems to pop back into the intake a bit when the motor dies.

If it's running rich, and removing a signifcant amount of fuel via the PCIII doesn't seem to help, how do I add more air without just opening the throttle plates more?

I think the next step would be to figure out why it is so rich as installing hi-comps alone would not do this.
any chance the power commander is not grounded or a sensor unplugged from the work being done?

Looks like I may have a more serious problem.  I'm getting oil on the spark plug from the horizontal cylinder, and after running it a bit I'm getting an oil leak from the head gasket as well.  The oil leaking out is really black, as opposed to the nice clean oil in the crankcase.   I'm pretty much done for the day, but I'm thinking a compression test is in order.

Just finished the compression test, 185psi on the horizontal cylinder, and 182 on the vertical.  I tested each cylinder three times, and the results were identical.

I guess I'll be pulling the cylinder head this week for a closer look.

Oil huh?  Compression's good so that's got to be a relief. 

Think your valve guide(s) are at fault? 

They better not be, I just got the heads back from the local duc shop.  They were supposed to inspect them and adjust the valves.

The oil leak at the head/cylinder surface makes me a little suspicious, so that's the first thing I'm checking.

Valve guides do not USUALY leak that much. lets hope they did not fall out/in.

Quote from: ducvet on June 02, 2008, 05:33:02 PM
Valve guides do not USUALY leak that much. lets hope they did not fall out/in.

oo, not that's an interesting idea

I have seen a guide shift in its bore and it is not pretty. Most shops do a fine job, it all boils down to who is doing the job.  I have also seen a car shops version of guide repair where they knurled the (outside of a) guide and it made the hole oversized so much ducati wanted to scrap the head.

With work, I still haven't had time to tear into it.  I'm hoping it's just an issue with one of the two oil o-rings, but I'm not sure how oil would get into the cylinder.  Unless of course oil isn't draining out of the head properly, but again, I won't know what's up until I tear into it.

The guides might not be bad, but maybe they reused the old seals and there leaking now

I would hope they would replace this when they did the guides, but ya never know anymore.

For the oil problem he is describing they would have had to left the seals off. seen it done.

My larger concern is that he is saying the fluid coming out is not the same as the fresh oil in the crankcases.
Could be carbon mixed with fuel (over rich condition)
             assembly lube (moly paste)
             or aluminum lets not go there.

I'm starting the tear down in about 20 minutes, so I'll find out.

The oil leaking is very black, something I associate with contamination from combustion.  There wasn't any moly used on assembly, I lubed everything with engine oil, and primed the oil system before I ever attempted to start it.