Ducati Monster Forum

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.

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.

Ok, so I pulled the cylinder head off, and I'm more stumped then I was before.  There's a little oil in the combustion chamber and I've got quite a bit of unburned fuel in the cylinder as well.  With the valves open, there is no noticeable play in the guides.  The valve seals look fine as well.   [bang]

I'm not sure if the oil caused the misfire, and as a result the unburnt fuel in the combustion chamber.  Or, I've got a fueling issue, and it's washing down the cylinder wall and allowing oil into the combustion chamber.

Does anyone know if a set of throttle bodys off of a 620 are interchangeable with the 900?  if so, I'll swap out the ones off of a known running motor and see what happens.

While you have the head off I would pull the cyl. and check to be sure the oil control ring did not get broken during assembly. Much easier right now.

The rings look fine, the hardest part was getting the correct orientation of the end gaps.

What year is the 900 swap?  Carbie or Fuelie?

The motor is a 2000, the harness and computer are from a 2002.

Not sure if the throttle bodies are the same.

Which ECU are you running?

The ECU is from a 2002 900.

Ok, so tonight I changed the throttle bodies, injectors, and regulator from a known running 620.  It didn't make a bit of difference.

The oil in the cylinder is clearing up, so that may have simply been the rings not sealing 100% initially.

This whole problem is especially frustrating since at about 2800-3000 RPM it sounds oh so good.   It revs quickly with no hesitation, feels smooth, and has no misfires or smoke to indicate any problem.

Just for the heck of it, I'm going to replace the fuel filter tommorrow.

The filter was really gross, and definitely the original one in the bike.  That however wasn't the problem.  It still very much feels like a timing problem, but unfortunately I don't have anymore time to work on the bike this weekend.

Just got done pulling the flywheel and verify the gears driving the timing shaft were timed correctly, and that wasn't it.

I tried asking the local Duc shops about looking at it.  One is a month away from being able to take a look, and the other won't touch it because it's not stock.

Where do you live?

Someone here may have another suggestion of a dealer or indie wrench.

Anchorage Alaska, my options are pretty limited.  I did talk with Mark at DucShop who suggested a TPS adjustment, and trying to record some air/fuel ratios.

Hmmm...Anchorage. Limited options indeed.   :-\

Perhaps a sticky injector.
Maybe the ECU is whacked.

I wouldn't think it's an injector problem, as I've swapped throttle bodies/inectors/regulator.

Anybody got a spare ecu/gauge cluster/key set laying around?

Yeah, you swapped TB's, I forgot.  :P

Is it dead on one cylinder at low rpm, or both?
I'm thinking it's just dead on one, or it wouldn't start.

All your electrical connections tight?

Grasping at straws here... :-\

Both cylinders are firing as the rpm drops, but if it gets below about 2200 they both cut out.

Is it the spark or the fuel that's quitting?

Dunno how much that helps, they're both controlled by the ECU.

Fresh out of ideas now.  :(

TPS voltage checks out fine.

Does anyone know of any incompatibilities between 2000 sensors and 2002 computers?

The only other thing I can think of doing, would be to swap all the 620 stuff back onto the bike and attempt to tune it for the extra displacement with the PCIII.  If I were to do so, does anyone have a ballpark as to how much extra to add via the fuel tables?  Specifically, are the values in the tables a percent of the duty cycle? or some arbitrary value it uses?

Around 25-30% more fuel above 10% throttle, not so much difference below 5% according to base maps I have.
Values usually milliseconds injectors are open.

Thanks, I'll give it a whirl for a baseline.  If it's enough to get it running I'll worry about dyno tuning.  If it's not the answer, I'll keep scratching my head.

Ok, so with the 620 ecu, gauges, etc. installed it definitely ran better below 2500 rpm.  It was obviously lean above 3000, so I added 30 to the PC3 tables.  At that point it would run down to about 1800 rpm.  I took the 2500 and below area of the table and removed 10 from the tables and it was enough to run down to approximately 1400-1500.  Adding or removing fuel below that point seems to make no difference

I'm hoping I've got it running well enough to get it onto a dyno and get some AFR's and find out exactly what's going on with it.

Just picked it up from the dyno, AFR's are a touch lean, but nothing weird.  Some misfires at low RPM, but the powerband is real smooth.  We only ran it up to 5k rpm, but made 61hp, and 90ft-lbs of torque.

I'm still getting a lot of oil in the horizontal cylinder, so that's coming back apart this weekend if I've got time.  Didn't find anything last time, but it still indicates a problem to me.

Was the light flywheel on (and the bike running well) before you changed the pistons?

90ft-lbs of torque with just hi-comp pistons(and a PCIII and dyno tune)?!  That's amazing! I am impressed! Good work.

It wasn't tuned yet, I was just getting air/fuel logs to try and diagnose the problem.