950 Cutting Out / Backfiring. Why?

I've got an '04 950 with 14k on it. I purchased it in May of this year with 11k, and have put 3k on it since then. Last week (around 13k on the engine), it started 'missing' every once in a while. Seems to happen every 2- 20 miles sporadically when it's happening. Sometimes it does it, sometimes it doesn't. I went 350 miles on the way to WY this week, and it didn't do it once. I stopped to fill up gas, and it started doing it. Both trail riding, and highway riding. I tried unplugging the ignition curve under the seat ~ no difference. Tried running an octane booster, still doing it. Valves are set correctly, just set them 1500 miles ago. Replaced the air filter, and cleaned the prefilter ~ still doing it. Replaced the spark plugs ~ still doing it. Seems to be worse when the air cools quickly (such as climbing in elevation or getting ready to rain). Seems to do it anywhere from 3500 ft to 9500 ft in elevation.

Happens most frequently around 3500 rpm to 4000 rpm when climbing a hill (putting a load on the engine), but can also happen at 6000 rpm in a flat (doesn't seem to be much consistency to it).

Comes and goes ~ it's not always there, and it'll go away from a hundred miles at a time (or more).

Any ideas on the cause? Carb sync? Fuel pump?

I purchased some Seafoam, to see if it'll help, but I highly doubt it'll make a difference. I also purchased some octane boost, and will run in through the engine on the way home from WY next week (about 1000 miles) to see if it'll help to use it on a consistent bases... but I'm always putting in the highest octane fuel from Shell or Chevron, so I doubt that's the issue.

Thanks,

RWC

It's done it since the valve check?
My guess is that the carbs aint seated correctly thus leaking air.When i did my valves myself the first time,it ran like a 2stroke. A quick text message to Pyndon and all was sorted.....it was the carbs not seated correctly although it seemed like they were when i put them back on.

Nope. Ran perfectly for 1k after the valves were done. Did the valves around 12.3k, and it started doing this around 13.3k.

Good idea, though... because that's what if *feels* like ~ a lean surge or pop. There's no way, though, as my mileage is still in the low 30's on a regular basis (so I doubt it's running lean?)

Sounds to me like you are losing ignition. I hit the kill button the other day by accident and got the backfire. I'll bet it was a nice flame out the back too.
Causes for ignition loss could be:
Clutch safety switch
Sidestand safety switch
(both are disabled on mine)
Dirty Kill switch
Dirty/bad ignition switch

Saw something from Pyndon about an electrical gremlin. don't ususally go to the OC. I'll look for it.
Also RWC nice idaho ride report!

Have you checked the battery terminals.?

Not sure if the 04s had the emissions stuff on them but my SE did something similiar to what you described when the crap vacuum caps on the rear cylinder started leaking by. It would do it....then run fine. The cap finally fell of and it ran like crap all the time until I put a new cap on.

Mine was the sidestand switch.
It would cut out even on smooth paved roads, but disabling the switch cured it.

Funny thing,... I've been having this infrequent "misfire" knocking situation since 3500 miles or so. Almost 8000 miles so far on an 06 950.
Lately, the "knock" or periodic low RPM hesitation/ misfire was more frequent, especially after cold or just warmed up.
Anyway,... I looked for a while in all the forum searches that seemed relevant to the problem you described. Ignition, plugs, fuel, and carbs....
The most easy for me on a Sunday afternoon (no shops open) was to check out the possible air-fuel components.
Sooo many different explanations from various inmates.
I removed the air filter and noticed a wee bit of dirt on the slides of each carb.
The air filter was probably due for an exchange since I had it cracked apart,... but really not too bad. A few squirts of Gumont Carb cleaner and then I reassembled everything. I could not locate the right fuel filter to add onto the petcock so the minor carb cleaning and wiping down of internals was all I accomplished as far as I was concerned.
Yesterday and today I rode with no incident of the said problem!
The only thing I can guess is a few crumbs in the air-fuel system that caused this... Or maybe a loose seal? don't know...

For what it's worth.
The carb related forum feedback made sense to me... although the descriptions were certainly more gross than cleaning with a few squirts of solvent.
Check it out if you have the time.
At a minimum you will get to know your bike better by the nakedness.
What she doesn't do for you,... you can get done elsewhere.

I've caused that problem when the heel of my boot made contact with the side stand.

Also if or when you get to removing the carbs check out the carb boots for cracks. When mine did it it wasn't as sporatic as your experience but it could still be cracked boots.

DW

Float levels?

Cleaning the kill switch is a good idea.

I know the sidestand is disabled, but not sure about the clutch ~ I'll look into it. Thanks for the advice.

Thanks. It was a great ride, indeed.

Yep ~ that was the first thing I thought about too. Pulled over and checked them, and they're solid.

The PO pulled the emissions off it. Think I should check it anyway?

I'll check it out ~ thank you!

OK ~ I'll examine the boots. Thanks.

Why would it start randomly if it was float levels? I can see if it'd happened right after I'd worked on the bike and messed with the carbs ~ but not 1k afterwards??

Another one - Water in the fuel .

I had some problems ages ago my bike was missing and sometimes cutting out turned out to be with water in the fuel , mine had blocked overflow drain holes in the filler rim under the cap in the tank and the fuel cap wasn't completly sealing would allow water inn . Just another thought and something to watch out for .

Removed and drained the tanks and fitted a inline fuel filter .

I don't know... but mine did the same thing and the float levels were just slightly low so I was just throwing it out there as a possibility.