Ugh...the 900 let.me down...

Was heading up to the Yesteryear Farm Show on the 900. Perfect day for it with cooler weather. Cruising down the highway when all the sudden it started to falter a little. Like it was running out of fuel. I had just filled up though, so I know it's not out of gas. Then it started getting worse losing power, then finally just died. I barely made it to an off ramp.

Managed to get it pushed off the highway on to a bike path and tried some roadside diagnosis. Fuel seems ok. I can see it in the filter. Pulled the plugs to check spark...and as near as I can tell, there is none. Dang it!

So, here I sit waiting for my buddy to get here with a trailer. At least I found a spot in the shade.

And suggestions on where to start looking for a cause?

 

Fusebox......

 

Would that allow the slow degrading of power??

 

Probably not, but whenever electrical-related issues arise that's the 1st place (well, the battery is the real first place) I start, if for no other reason, it's the simplest way to start eliminating possible sources (which can be just as important as finding the actual culprit....).

Could also be a block fuel cap vent/"vaccum lock" issue.....open the fuel cap and listen for a "whoosh" sound as the vacuum lock is resolved.

 

Its safely back in my garage. Still doesn't start.

Checked the fuses. All seem OK. I get power on both sides with the switch on. Voltage is a tad low, but probably because I was cranking it so much trying to get it to start. I'll throw it on the charger tonight.

I had pulled the tank this morning. Hoping maybe something just got knocked loose putting it back on. I'll have a closer look in the morning.

 

The gas cap was one of the first things I checked on the side of the road. Didn't help to remove it or put it on prime.

 

Aftermarket fuel filter?

 

Good news! Now that its back in the garage instead of in broad daylight, I can see it IS getting spark. Not a super fat spark, but a spark nonetheless. With that information, I turned back to fuel.

First, I raised the tank up with a block of wood so I could see better. Then I cracked one of the bowl drains, and fuel flowed out. The petcock was on, so I could see the filter had run dry since there was no vacuum to open the petcock. I set it to prime and I could see it fill. Then I tried to start it again, and after some reluctance, it did start!

I had tried essentially the same thing on the side of the road with no luck, but I think I might know what is going on. The routing of the fuel hose with the filter in place is a little wonky. It has kind of a flat spot where it runs more horizontal. I think maybe when I reinstalled the tank this morning, it ended up in a place that compounded this problem, essentially vapor locking the line. By lifting the tank it angled the hose a little more downward and fuel flowed more freely.

Still a little odd. I had left it on prime for quite a while, so you would think at least some fuel would have flowed while I was sitting there. And I did lift the tank at one point, so why didn't that get me going? Also, I had ridden about 20 miles since fillup. Why did it suddenly decide to stop flowing fuel?

Still more investigating to do before I fully trust it again, but at least it starts.

 

This might be a stretch, but is your in-tank filter (attached to the petcock) clear? Depending on the condition of the inside of your tank, that filter could get compromised and slow your fuel flow to the external filter and the carbs.

 

Happened to me that the vertical gauze inside the petcock was blocking up with varnish. On a full tank it was ok, enough was getting through, but when it dropped to a half tank it wasn't passing enough.
Weird fault, as I knew it had plenty of fuel.

 

I'm pretty sure it was essentially "vapor lock" in the fuel line. When it happened, I had just gotten on the highway. The trip up to that point had been mostly flat ground and < 60mph speeds, but when it started cutting out, I was doing closer to 75 and up a light grade. Probably sucking a lot more fuel to the point where it overran the fuel flow in the poorly routed line and let an air bubble in. After that there wasn't enough gravity to get it going again and the bowls eventually ran dry.

I suspect the reason that I couldn't get it going again when I lifted the tank on the side of the road was because I didn't really have it on prime. My old eyes aren't so good any more and I was turning it the way I thought was prime. But when I was back in the garage with better glasses, I realized I was turning it to reserve instead. I don't remember for sure which way I set it on the road. I thought I tried both, but if I had done the same, I can see why it never was able to refill the bowls. Then of course once I thought I wasn't getting spark, I stopped pursuing fuel.

That's my theory anyway.

It's been fine since I got it back home and filled the bowls, though I haven't taken it out of the garage yet. I did cut the fuel line a little shorter so it had more of a downward slope to it. I'm still not thrilled with the way it routes, but I don't know what else I can do without pulling the carbs again to get better access to the line...and if I do that, it will no longer be possible to change the filter without pulling the carbs, so that's not appealing either.

I'm headed out on the KLR for a few days tomorrow morning so it'll have to wait until I get back for another road test.

 

Have fun with the thumpper, have owned a few of them. Great bikes too.