Help: Engine cutting out after sustained high speed

[Rallyfan]

Hello all,

GS500F 2006 California model.

Carbs cleaned and synced, valve clearances checked, plugs, air filter.

Frame petcock replaced.

Bike starts great, idles well, drives great except after 10 minutes at high speed (5k or higher in 6th). It then "runs out of fuel" and bucks.

I suspect the fuel cap and/or the breather vac line from the carbs.

I've found the thread on how to clean the cap, and I've done it a few years back so I can repeat that (I'll troubleshoot by riding with the cap open I suppose).

However, I can't find a picture of the breather I'm supposed to be looking for.

Any help? Many thanks.

[Watcher]

Do you have an in-line fuel filter?

Ditch it.  My 97 behaved the same way, clogged/old/fouled filter was the culprit.
It would be fine at around town speeds and in stop and go traffic but a short jog on the interstate would kill it.  Was burning fuel faster than it could flow.

[Rallyfan]

Thanks for the response.

No inline fuel filter.

Do you now where the hose I'm looking for is supposed to be? I wonder if it's pinched or missing. Thanks.

[Watcher]

The breather on the carbs comes out of the upper "rail" and should be routed to go over the air box and down near the suspension.

The vacuum comes off, IIRC, the left carb on the inside (towards the center) and runs to the frame petcock.
It's POSSIBLE this has a pinhole in it causing an intermittent vacuum leak.  This line controls the petcock, and might be shutting off fuel flow at higher RPMs.
It would be easy to diagnose by going for a ride with the petcock on the PRI position.
Could even be a faulty petcock.  Was your replacement new?

[Rallyfan]

Thanks.

The problem occurs even on PRI.

So, the fuel cuts off at high sustained speed whether the petcock is on RUN, RES, or even PRI.

(Petcock was used).

Thanks.

[Watcher]

Yeah, make sure your breather isn't catching wind.  I've got a hose routing diagram somewhere around here...

[Rallyfan]

Aha!

Wow you've been TREMENDOUS help, THANKS!

So the hose labeled VENT HOSE FROM UPPER T CONNECTION is the one we're talking about? In the diagram I can't tell where it originates.

[1018cc]

I'd pull the hoses off that connect the tank/petcock/carbs together and make sure you can blow through them easily if you're going to be pulling stuff apart anyway. I have come across a clutch hose (on a car) that has failed internally. The outside looked fine but the inside had just about swelled shut. Totally different fluids I will admit........but yeah, check for kinks in the routing etc using the diagram Watcher posted.

[Watcher]

So the hose labeled VENT HOSE FROM UPPER T CONNECTION is the one we're talking about? In the diagram I can't tell where it originates.

Between the carbs are two rails, an upper and lower rail, each with a T-fitting.
The lower rail is the one you plug the fuel line into.  The upper rail is where the vent hose originates.

If you take off the fuel tank you'll be staring right at it.


#6 here.

[Rallyfan]

Thanks!

I had a quick look (tank on) and don't see it. I'll have to pull the tank later tonight.

I appreciate this very much! I'll post back with my finding (and frankly I suspect I'll have further questions... sigh...). Thanks!

[Bluesmudge]

I 2nd watcher's thoughts on this. The one time this happened to me was when an actual Mechanic worked on my bike. They routed that vent hose up towards the front and the bike would bog down and die after driving at high speeds for a few minutes.

I think it leans out the mixture because my bike also ran really hot when that happened.

[Rallyfan]

I'll post a pic ASAP but I suspect that's my issue. I'm hoping you are all correct. Please keep fingers crossed, I'll post back. Thanks!!!

[Rallyfan]

 The round object seems to be a breather. It's T-ed form the top rail of the carbs as described. It faces the side of the bike, outwards, and does not extend backward to the battery. Is this my problem? If so, do I lengthen that hose and route it to the battery box? Will the round thing even fit some where there? (Please pardon my naïveté). Thank you!

[Watcher]

It's hard to see what it is I'm actually looking at.  A wider photo would help that.

But I'm not familiar with that round thing.
Typically they have a plug thing on the end to allow liquids to come out but nothing to come back in, but it's fits inside the tube so the diameter is the same if not smaller...

If that's for sure the breather I'd run to an autoparts store and have them cut a length of fuel/vacuum line to replace that.
Sorry, but I don't recall the diameter of the hose you need.

[Rallyfan]

The plot thickens. Please look where I'm pointing. Is THAT the missing hose origin?

[Rallyfan]

[Watcher]

Yessir, that there is your breather with nothing attached to it.

The other thing must be part of the emissions system on the CA model, which would explain why I'm not familiar with it.

[Rallyfan]

Aha! OK I've attached a hose thusly. It's pouring rain so no way to test... I'll post back when it's dry. THANKS!

[Rallyfan]

My issue now is the fuel hoses. Why can't I get both on their barbs?! Reserve leaks...

[ShowBizWolf]

Ohh that is something I've struggled with too... why oh why couldn't there be just a little bit more space there?? Very frustrating!!!

I've seen a lot of different recommendations around the site for what fuel lines to use. I had some success with clear fuel hose from AutoZone or Advance... can't remember which... in the small engine section. It's thin enough to allow room for the clamps. A few years ago I thought it was the hoses and when I changed 'em I realized it was the fuel valve itself in/on the tank that was leaking.