1994 M900 "hesitated"?

[mostrobelle]

I have a 1994 M900 Monster with about 68,000 miles on it.  The other night as I was riding home on the freeway at about 70 mph, constant throttle ( think, but I was going through a large sweeper so perhaps I was letting off the gas a very small amount), the bike felt like it wanted to run out of gas.  I thought it was going to stall out, so I began to pull over and then it kicked back in again at full power--had another brief episode of stalling--and then ran it fine after that.  I was about 50 yards from my exit anyway, so I pulled off the freeway and babied it the last couple of miles home through town going < 40 mph and keeping the rpm's below 4000. 

I had a top end rebuild back at about 38,000 miles and that's when I put in a big bore kit.  A couple of valve guides failed and that's what necessitated the rebuild.  Everything else motor-wise is stock-ish.  A ton of stuff has been replaced on the bike over the years--too much to list.  The fuel filter was replaced about 7000 miles ago.  It's been a long while since the carbs have been cleaned. 

Any thoughts on what this might be before I take it into the shop?  I'm very concerned that it's motor trouble.  I did a valve check a few weeks ago and one of the clearances on the horizontal cylinder closing shims had tightened up on me--my clearances really don't change much on this bike anymore.  I was getting ready to take the bike in for a compression test anyway, and now this new issue comes up.  I'm hoping they're not related and that the new problem is just a booger in the carbs or a fuel line/filter thing.  Those were a couple of suggestions from Ducati friends that I spoke with last night.  The bike has been backfiring just a tad more than usual, too.  That's been the case over the past several months.  It only does that on starts and deceleration.  My throttle grip has been not wanting to snack back as quickly as I like either.  Sorry...just listing everything that I can think of that is going on with the bike.  There's usually a small laundry list of stuff that needs fixing.  Even though I'm going into the mechanic for this one I like to focus his attention rather than just letting him go nuts chasing stuff down.

Thanks in advance.   

P.S. All of my searches brought up carb issues. 

[ducpainter]

I'd do the obvious stuff first.

Fuel filter, adjust clearances, carb synch, and a leak down test.

It also may be something as simple as a little water in the ethanol fuel.

IME vehicles that are run regularly don't require carb cleaning, so I'd skip that.

[64duc]

I'd do the obvious stuff first.

Fuel filter, adjust clearances, carb synch, and a leak down test.

It also may be something as simple as a little water in the ethanol fuel.

IME vehicles that are run regularly don't require carb cleaning, so I'd skip that.

   +1  I would add to that, check the connections on the ignition coils and the plug for the wires  coming off the pickup coils. Disconnect and reconnect. Any corrosion on these connections could cause a misfire.

[Ddan]

Maybe check that the vent tubes from the diaphragm are still in the pods.

[mostrobelle]

Good thinking on the pods.  Checked them and all seems OK.  The throttle is definitely weird though, so the hubby was nice enough to pull it apart for me and get it all cleaned up.  We'll see if that makes an improvement.

edit - I'll bring up the coils thing with the shop.  One of the pick-ups failed about a week after the engine re-build and I know that's not something I can repair myself.  The failure wasn't intermittent though--it just died and the bike was running on one cylinder one morning.  I'm not sure how often they need to be replaced but I'm going to guess that if there's anything original on the bike at this point that it might be getting ready to go on me.    

[mostrobelle]

The problem is back.  Bike was definitely running on one cylinder this morning.  Started up OK and ran fine for a few minutes, then it cut way down on power.  It's probably a pick-up or a coil.  <crosses fingers> 

[mostrobelle]

Confirmed: bad pick-up.  Compression test came back good...   

[The Mad King Pepe']

Someone with more experience than me please correct me if I'm wrong, but in your first post you mention a closer on your horizontal cylinder getting tighter. Now could that lead to suspicion of deposits on the valves, or is that me thinking too far ahead? Would a compression test prove or disprove that?

[mostrobelle]

Someone with more experience than me please correct me if I'm wrong, but in your first post you mention a closer on your horizontal cylinder getting tighter. Now could that lead to suspicion of deposits on the valves, or is that me thinking too far ahead? Would a compression test prove or disprove that?

No idea here...I do know from the number of times that I've seen bikes yanked apart that engines tend to get pretty dirty--even in the places that you'd think would be more pristine.  My bike had some sort of crusty black stuff all over the place. 

[64duc]

No idea here...I do know from the number of times that I've seen bikes yanked apart that engines tend to get pretty dirty--even in the places that you'd think would be more pristine.  My bike had some sort of crusty black stuff all over the place. 

  That is carbon. If it is dry, it's caused by running rich. If it is a thin crust it is relatively harmless.  If wet then it's oil getting by the rings or the valve seals.

[mostrobelle]

It was dry--a bit over a half a mm of stuff. 

[ducpainter]

Someone with more experience than me please correct me if I'm wrong, but in your first post you mention a closer on your horizontal cylinder getting tighter. Now could that lead to suspicion of deposits on the valves, or is that me thinking too far ahead? Would a compression test prove or disprove that?

It was dry--a bit over a half a mm of stuff. 

I would think a loose opener would accompany a tight closer if carbon was the culprit.