'99 M900 Bogging down

[MonsterDave]

I have a '99 M900 with FCR41 carbs. When I installed them last summer, they worked perfectly and I had no problems for the whole riding season. Yesterday I took it out for the first time of the year and after a while, it started bogging down. Even to the point that it actually stalled when I came to a stop. I was having this problem originally, that's why I got the FCR's. And, for a while, they were great! What could be my problem?

I've replaced the plugs and checked and cleaned the fuel filter. The plugs were "whiteish" in color so I'm pretty sure my mixture isn't to rich to foul plugs. I get really good air flow through the fuel filter so that shouldn't be it. What else could it be? Could I possibly be getting some sort of vapor lock after the engine warms. I filled the tank with premium gas when the bike was stored for the winter and also used Stabil. Could it possibly be just bad gas?

My nearest dealer is 1.5 hrs away and I really don't want to take it there. (major pain) I also have a trip planned in two weeks that I was hoping to take this bike on but I don't want to end up having problems the whole time. That would totally ruin the trip

Everyone here has always been able to offer suggestions in the past for any issues I've had with it so I'm hoping you do now.

This is driving me crazy!!! (WTF)

Thanks everyone

[Speeddog]

Will it start and run OK for a little while, then falter and die?

If so, tank vent plugged/hose kinked/otherwise compromised vent.

[MonsterDave]

Yes, it starts perfectly and, for the first 20 min or so, riding is great. Then it starts with the bogging/bucking. It almost sounds like one cylinder is misfiring but it's hard to tell while moving. Today, it got to the point where it actually stalled on me. I pulled over at an intersection and it quit. I had to let it sit for a minute, then it would start up and I could go. (did it twice within 10 miles)

I was talking with my father-in-law (used to be a motorcycle mechanic) who thought maybe it could be a coil issue since it started and ran fine for a while. He remembers from years ago that he worked on bikes that after they got warm, it would effect the coil. I know technology has changed quite a bit since then but my bike is about as simple as it gets.

I've checked the fuel lines and hoses but nothing seems to be wrong. I've also looked at the tank vent but can't tell if anything is wrong. What would be a good way to test that?

[Speeddog]

Easiest to run it until it quits, then listen for it slurping in air when you open the filler cap.

There's two tube ends coming out the bottom of the tank, one leads up to the drain for the filler area, and the other leads to the small rubber seal boot near the hinge of the filler.

Try blowing in the end of each hose that is attached to those tubes, with the filler cap open.

[brad black]

ride it with a spare key in the cap, then crack the cap when it starts to die.

[Howie]

Is the EVAP canister still on it?

[MonsterDave]

Speeddog - I will check the tubes tonight when I get home.

brad black - Not sure I have a spare key but if I do, I'll try that.

Howie - The EVAP canister is no longer there. Was removed before I purchased the bike.

I'll take a photo of it tonight and post it so you guys can see what's going on in there.

What do you think about it being the coils?

[Howie]

If it is dropping one cylinder it could indeed be a coil, ignition module pickup or even the resistor in the spark plug cap on the ignition wire.  We are going by symptoms you are describing, which sound like fuel starvation.  Let's eliminate that first by trying what Speeddog and Brad are suggesting.

[memper]

Might be helpful to clean the jets and see if the float bowls are getting fuel in each one.
Would it be reasonable to inspect the electrical system? Battery, coils, rr? I know that in some situations one might be chasing an electrical issue guised as a fueling issue.

[SpikeC]

 How did you clean the fuel filter? This sounds like a dirty fuel filter to me. My K100 would do this when it needed a new one. As far as I know they cannot be cleaned.

[Howie]

Very dirty fuel filter is a possibility.  Ducati suggests changing it every 6k.  Clean a fuel filter?  A little like rinsing your toilet paper so you can use it again.

[MonsterDave]

OK, cleaning the fuel filter may be an overstatement. I drained the fuel and blew some air through it. No clogs. Good stream of air.

I just checked the 'venting tubes' by blowing some air through them as well. Good air flow coming out of the vent in the filler cap, no clogs.

Making the pics work is not going well. Click on the word "venting" in the link and it will take you to the flickr site. You can click the right arrow to see the next image. BTW what is that thing? (I kind of kidnapped my wife's account to post these.)


[/url]Venting by viatori, on Flickr[/img]

[SpikeC]

 Crankcase breather

[the_Journeyman]

Occasionally my M750 will do that.  It's usually on really hot days, in slow or stop & go traffic when the tank is less than half full.  The fuel lines are routed right over the vertical cylinder.  Turns out, my issue was the gas getting to hot and not refilling the carb bowls fully causing it to run poorly and even stall.

JM

[greenmonster]

Mine behaved like that when the membranes
in the fuel pump were semitoast.