96 M900 dies with 1Gal left in tank

[sunbum]

Hi all,
  I've recently acquired a 96 m900 from a good friend who owns several other Ducs (this is my first bike, but I've ridden it a few times in the last couple of years).  There are ~29K miles on the odo, the top of the airbox has been removed and it has D&D slip-ons.  The emissions canister has been removed, but the problem surfaced twice before its removal.  I have searched on several other boards as well and the mention of a similar problem prior to today hasn't given me a solution.
  The basic problem is that the bike acts like it's running out of fuel when the tank gets to around 1 gallon left. It sputters and dies if I twist the throttle both while cruising and after moving up from first gear.  It has happened a few times -- the first time, I had 70 miles showing on the trip meter and was riding in slow traffic, ambient temps in the upper 60's.  I added another gallon to the tank from a jerry can brought to me and was able to motor along normally for a fill-up.  The next time, I had 109 miles on the trip odo, temps in the upper 70's.  Added 1g of fuel again and was able to get to a gas station with no further sputtering/dying for a top-up of two more gallons of premium, just like every other fill-up. 
  Initial troubleshooting: While changing my rear shock, I looked at the fuel hose that comes out of the filter on the bottom of the tank and saw that it's length might allow it to kink a little, so I shortened it to relieve the kink that may have been the problem.  I could probably shorten it another couple inches, but I don't want to limit my ability to raise the tank all the way up.  In the process of shortening that hose that goes to the vacuum petcock, I drained the tank, confirming that gas will readily flow out until nearly completely empty.  I had thought maybe the fuel light wasn't working, but a trip around the block with only 1/2 g. in the tank lit the lamp and it stayed lit all the way to the gas station a mile or so away.  The bike performed normally all the way to that fill up so I thought I'd fixed the problem for good.  I have tried different gas stations, so it shouldn't be fuel-content related.
  On Tuesday afternoon, I got caught in a torrential downpour 5 minutes from home.  Air temp was in the low 70's.  On the run into the driveway, I could just feel the same sputter thing happening, but attributed it at that time to the rainy conditions.  I immediately set about drying the bike off once out of the rain.  I don't give the bike any more washing than a dry-off if it gets wet, but I do keep it clean with bike polish.
  This morning (air temp 73), as soon as I got out of the neighborhood, the same thing started happening.  In 2nd gear, the bike did a little sputter, and in 3rd felt like it was running out of gas.  I thought that if I went to 4th, the revs would be lower, but the engine cut out as soon as I got off the clutch and gassed it.  I restarted while coasting and limped in 3rd to get enough momentum to get into a gas station.  2.99 g later and I started normally and pulled out.   This time, the bike never seemed to recover to it's normal range of power as I moved up through the gears to 50mph and I had to take neighborhood roads back to my house so I could cruise in 2nd while having a little choke applied the whole way to keep it from dying.
  Now I'm really stumped since a fill-up seemed to 'fix' the problem until this morning.  I'm mechanically inclined (I've upgraded the rear shock and done the emissions canister removal mod), and I'm not afraid to carefully tear into things to fix whatever the problem may be, but I don't know where to start troubleshooting.
  Any and all suggestions will be greatly appreciated.  Thanks,
Myron

[Howie]

Two possible reasons I can think of:
      Fuel pump removed.
      Water in fuel.

[Norm]

I'd check to see if the fuel pump is blocked or damaged. No fuel pump wouldn't matter. Also check the filter, it could be clogged to the point where it only dribbles fuel thru via the pressure above it and when it get's to 1 gal, there isn't enough pressure to pass.

[sunbum]

  From my experience removing the excess fuel line during troubleshooting trial #2, gas flows *very* freely from the fuel filter outlet (as noticed by the large puddle on the floor when the tube slipped out of my gas container).   I'll take a look at the fuel pump when I get home today.   I can affirm that it most definitely is still attached in its stock location.  Is it safe to assume that the fuel pump input line won't flow fuel to the pump if the bike is not started?  I ask in an effort to avoid more inadvertent gas spills on the garage floor. 
  When I filled up this morning at a typically busy station, the bike started and idled just fine.  That leads me to think 'water in the gas' may not be highest on the culprit-list.
Myron

[erkishhorde]

I'm no expert but I've had something similar recently. Here's what I did.

One way to see if your fuel pump is working properly is to bypass it. If the bike runs fine, you're pump is likely bad. You should be able to get up to about 120mi without pushing it hard with the pump bypassed but you should be finding a gas station soon. You'll loose some mileage since the outlet for the tank is lower than the inlet for the carbs. Also be careful about leaning into any turns really aggressively when you're low on gas since you're counting on gravity feed. Ask me how I know.

If it's the same pentagon (hexagon?) vacuum fuel pump as on my '95 m900 then it can dribble gas even with the engine off. Fuel can still pass through it sort of if it's not running but not enough for the monster to run properly. If you fuel pump has kicked the bucket or you'd just like to rule it out all together without thinking about it, CA-cycleworks has an alternate (same brand/specs but different shape) pump.

In my case, I think that there might have been something floating in the tank like a scale of rust which has a higher chance of clogging the fuel outlet when your low on gas. I've yet to get my bike back from the shop to find out if I'm right about this diagnosis but I sent it in for a POR15 treatment (anti rust coating) for good measure.

[sunbum]

Well, I lengthened the line using clear fuel line from my kart spare parts bin and gas is definitely making out of the tank/filter in a kink-free path.  I have even bypassed the fuel pump just now, and on a ride around the neighborhood, it sounded like it was running way lean/stumbling/out of gas.  This is with close to a full tank of gas.  I used clear line from the vacuum petcock to the line that normally is at the exit of the fuel pump and there are no big air bubbles to indicate that the fuel isn't flowing. 
  The bike starts and idles just fine, and responds to choke just like a carb should.  I'm pretty sure the fuel pump is working because I forget to cap it off before starting it after bypassing the pump and got a good dose of residual gas spurting out and onto the frame/engine/my leg.  When it cools down again, I'll hook the pump back up just for grins.  Keep the suggestions coming, no matter how trivial they may sound.
Thx,
Myron

[sunbum]

Update:  I put the fuel pump back into the mix to replace the gravity feed that just wasn't working much at all while riding.  Leaving the unkinked clear fuel hose from the filter to the petcock and putting the airbox back on again, the big wouldn't stay running at all.  Arrghh.  I came back the next day and as I was taking the coil bracket off to get to the airbox again, I found one of the wires had come unplugged from the coil.  Everything went back together and the bike ran but wouldn't hold idle too well.  The left carb's drain tube was weeping a fair amount of gas and that had me worried.  I took the bike out and romped on it and throttle response was great again -- even around 4-5k RPM, I wasn't feeling the same lack of power any more.  I rode it into work this morning and on the way home this afternoon, the fuel warning light came on (first time I've seen it come on while riding).  I'm taking that as a good sign.  I'll pipe up again should the problem resurface.  Thanks to all who contributed!

[dlearl476]

Two possible reasons I can think of:
      Fuel pump removed.
      Water in fuel.

One more, albeit a long shot:
Clogged vent tube.

This is more evidenced in full tanks than empty, but these are classic symptoms of a clogged vent tube:

It has happened a few times -- the first time, I had 70 miles showing on the trip meter and was riding in slow traffic, ambient temps in the upper 60's.  I added another gallon to the tank from a jerry can brought to me and was able to motor along normally for a fill-up.  The next time, I had 109 miles on the trip odo, temps in the upper 70's.  Added 1g of fuel again and was able to get to a gas station with no further sputtering/dying for a top-up of two more gallons of premium, just like every other fill-up. 

The reality being that it has more to do with opening the tank and equalizing the pressure than adding the gas.  A lot of '99-2000 BMW F650s left the factory with their vent line an the charcoal cannister line reversed and this exact thing would happen every time the fuel got low.  Open the filler, all better.

The left carb's drain tube was weeping a fair amount of gas and that had me worried. 

I'd run a good injector cleaner/fuel additive through it (I hear NOS makes a good one, available at a 7/11 near you.   )  Seriously, BG 44K, Techron, or something similar.  That leak may be indicative of a sticky float bowl or valve.


I generally run a bit of 44k through all my vehicles once a year and use "Supercharge II" about every fifth tank full. 

[Drunken Monkey]

My money's on you either fixing a kink (despite the fact that the fuel lines are supposed to not collapse when kinked, they can) or it being a vacuum issue in the tank.

So if it happens again, wiggle the lines and/or pop open the gas cap and listen for a "fooosh" sound.

[dlearl476]

My money's on you either fixing a kink (despite the fact that the fuel lines are supposed to not collapse when kinked, they can) or it being a vacuum issue in the tank.

So if it happens again, wiggle the lines and/or pop open the gas cap and listen for a "fooosh" sound.

Yeah, when I first got my '99, the PO warned me that if you weren't careful when you put the tank down, it would bend the line.  The symptom on mine though was either it wouldn't start, or it would start and only fun for about 30 seconds (until the float bowls ran dry) then die.

One of my best moments ever:
I was really busy and going out of town so I took my bike to the (very good) dealer here to have the valves adjusted and the belt tension checked.  When I went to pick it up, it wouldn't start.  The techs were worried.  I lifted the tank, adjusted the hose and, with three of them watching scratching their heads, I hit the starter and it fired right up.   



Now, when I go the shop,it's all "MR" Earl and 


If they only knew.

[dropstharockalot]

One more, albeit a long shot:
Clogged vent tube.
.... 

This was my thought, too... my uncle had an Audi that did the same thing he got down to around two gallons in the tank.  He'd hop out, pop the gas cap off, wedge something in the filler neck to let it vent, and we'd be on our way once the tank had a chance to breathe.

If it was a fuel feed issue or kink, you should probably have the problem regardless of the tank level.  Ditto for a carb or mixture problem...It sounds like once the pump sucks out a couple gallons, the air isn't getting in there and filling the vacuum and the pump can't overcome the pressure.  Pump struggles to beat the pressure vacuum in the tank so you get sputter, until the vacuum's just to strong and you get no gas.

Did your PO mod the gas cap with anything aftermarket?  Coulda f'd up the tube in the process... that, or coulda crushed/pinched/obstructed the vent line when de-emissioning it.

My S.W.A.G.  Don't buy anything expensive or work on the bike with anything sharp on the basis of my completely unqualified advice.

Good luck.

[dlearl476]

that, or coulda crushed/pinched/obstructed the vent line when de-emissioning it.

For that matter, could have just thought "oh, I'll plug this line that went to the cannister."  Wouldn't be the first time.