2001 Monster 900Sie, Help troubleshooting hard starting backfiring and stalling

[bigbrotherjohn]

Hoping for some help here, I'm the new owner of a 2001 M900Sie with 8000miles, I've put about 100miles on it since I bought it.

From the beginning the bike would occasional have small pops or backfires (sometimes through exhaust, sometimes intake) at light or partial throttle. Last night though after a longer than usual ride (about 1hr) the bike started to backfire more frequently and would die at idle or barely hold idle.  I let the bike rest overnight, when I tried to start it in the morning it would start and run roughly for a few seconds and then die. I charged the battery for a few hours until my charger said it was full, then the bike started slightly more easily but still died after a few seconds. If I hold partial throttle sometimes I can keep it running for longer but it pops and backfires a lot (exhaust and intake).

What are the likely root causes for this kind of issue?

Currently my plan to check/replace is:
New timing belts (it's time to do this anyway)
Oil change
New Spark Plugs
New Air Filter
New Fuel Filter
Check operation of Engine Temp Sensor

Anything else I should be looking at? Does this sound like a common issue?

Thanks so much for the help!

-JC

[Howie]

Yep what you want to do is maintenance, but, unless you are overdue on the belts, diagnose first.  My guess would be a vacuum leak or throttle position sensor.  TPS can be tested with a voltmeter (digital).  Key on, back probe the wires to the sensor.  Black/green is ground, brown/green is TPS signal.  The signal should increase to 5 volts as you open the throttle.  Better yet is a scan tool, which you need to reset it anyway.  Before even testing, disconnect it and look for corrosion.  New sensors are available at a reasonable price from our sponsor http://ca-cycleworks.com/

[bigbrotherjohn]

Thanks for the suggestions Howie, I will try this in the morning.
I did notice that there is some kind of rubber nipple under the fuel filler cap that looked damaged, is that part of the vacuum system?

[Howie]

OOH!  Tank vent!  Cheap fix and likely cause.  Open cap and see how it runs.  Also check the tank vent lines for kinks.  Bike have a charcoal canister on it?

[bigbrotherjohn]

Ok great, thanks, I will try that too. Is the vent intended to prevent vacuum in the tank which would result in low fuel pressure?

[ducpainter]

That rubber nipple is a seal to allow the evap system to draw fumes from the tank.

If the charcoal canister has been removed the rubber piece serves no purpose other than to block the vent if it gets damaged. You can remove it.

[Howie]

Ok great, thanks, I will try that too. Is the vent intended to prevent vacuum in the tank which would result in low fuel pressure?

Yes, more correctly, fuel starvation.  As dp stated, no canister no need for the nipple.  Is this bike a US model?

I just realized, 01 should have a TPS that can be adjusted with a volt meter.

[bigbrotherjohn]

Howie and Ducpainter,
Update from this morning, I tried to start the bike, it cranked fine, popped once or twice but wouldn't run.
Then I took off the seat, raised the tank, wiggled/unplugged and replugged the TPS, then set the tank back down and opened the filler cap. Tried to start the bike again, cranked fine, popped a few times and after trying a few times it ran for about 3 seconds then died. Couldn't get it to start again after that.

Random note, the R line on the tank looks like it's folded in half when the tank is down, maybe I can try running the bike with the tank up so the line won't be so pinched. Bad idea?

Btw, as far as I know the bike does have a charcoal canister, I haven't removed anything.

[ducpainter]

R is return. If it's folded in half that would not be good. You can run the bike with the tank raised. Just be gentle so as not to stress the hinge and create a leak.

It would be best if you had a rear stand and have the bike vertical.

[d3vi@nt]

Currently my plan to check/replace is:
New timing belts (it's time to do this anyway)
Oil change
New Spark Plugs
New Air Filter
New Fuel Filter
Check operation of Engine Temp Sensor

Anything else I should be looking at?

Good idea to check the valves while you're at it, too.

[Howie]

Don't use the tank prop rod that came with the bike, find a board and support it from the center.

[bigbrotherjohn]

Haven't had too much time to work on this during the week, but got a few minutes today to check the TPS sensor.

I turned on the bike, put one multimeter lead on the battery (-) terminal and the other on the sensor output. The voltage output started at 0.43V and increased up to 5V as I turned the throttle. I don't know if those are the right values but at least it is giving some output.

Any idea roughly what the output Voltage should be at 0% throttle?

Thanks,
-JC

[Howie]

I don't remember the beginning voltage range, but it is more than 0 since closed throttle is partially open.  Ah, all about your TPS  http://bikeboy.org/ducati2vthrottleb.html

First I would worry about the fuel tank venting and fuel return hose Cheap and easy first!

[greenmonster]

Your TPS voltage is normal, see Howie`s link.

[bigbrotherjohn]

Thanks for the bikeboy link, thats a great write up. So yeah it seems like the TPS is in the right range.

I'm gonna spend some more time on the fuel delivery system, fuel filter and fuel pump and venting. The fuel pump also seems a little quieter than it used to be, but that might be my imagination.