Help: Engine cutting out after sustained high speed

[Rallyfan]

Got it to stop leaking but I M uninspired by the reserve hose. Is this normal, dangerous, or what?!

I should have disconnects the frame peacock instead....

So, now what?

[Watcher]

I've actually pulled the brass nipples out of the petcock while trying to pull the hose off, before.  You might want to make sure you have them seated nice and tight by tapping them with a mallet.
Or use the plastic handle of a screwdriver as a punch to tap with a hammer.

It's handy that they made the nipples two different lengths, but they are a bit too close together.
You might be able to use a hose one size smaller and really force it on, might even get away with no clamp doing it that way.
You can also sometimes get away with using a zip-tie as a hose clamp by pulling it really tight with a pair of pliers.

Also the screw type hose clamps, while not nearly as handy as those spring ones, do tend to be thinner and may work better in this application.

I can't remember how I did it mine, but on my first GS I did away with the reserve function.  Swapped the frame petcock for a simple on/off, and just capped the "on" nipple.
Murphy's law sure favored it, but I DID have to keep a closer eye on my mileage and make sure I zeroed the odometer every fill up.

[Rallyfan]

I've been eyeballing it for an hour and I've also looked online for pictures from other bikes, and I can't for the life of me accept that there's anything different I can do. As far as I can work out, with the stock hardware, this is the best I'm going to get...

If I'm mistaken and am going to have the bike burst into flames underneath me on the freeway, someone please chime in...

I've ordered the stock fuel hoses (perhaps foolishly; in any event, it was before this little fiasco) and they're en route. I'm tempted to simply leave well enough alone at this point. I *think* it's OK (?!...).

THANKS!!!!!!!

(and any further advice ALWAYS welcome and appreciated).

[Rallyfan]

[Rallyfan]

So now it's much worse...

I'm stumped.

Here is how I routed the hose. Battery is blue on the right. Hose is between air box and battery box.

Bike cuts out at speed.

Is the hose routed wrong?

[Rallyfan]

UPDATE:

1. Replaced RES and ON fuel hoses with factory hoses. Also tapped in the brass fitting for the ON hose on the frame petcock (it'd come out in my hand...).

2. Replaced the vent tube with a factory vent tube, routed via a clamp on the lower left bolt screw holding the air cleaner to the space between the battery box and the air cleaner. There is no fitting as far as I can work out; the rubber T off the carbs fits directly into the new tube. To do this I used dielectric grease on the inside of the new tube and a significant amount of pre-lenten profanity. A contortionist would have had an easier time admittedly.

3. Replaced the overflow tube to the tank with a factory tube, routed to the left of the bike clear of the chain and exhaust.

Rain permitting, I'll see how it goes. Meanwhile, am I missing something folks?

[Rallyfan]

Still no joy. Sustained speeds above 75mph make the engine stutter.

Any advice?

[Watcher]

Will it rev all the way up to redline at low/no speed?

Test each gear, as safely and legally as possible, to see if it's a speed issue, an RPM issue, or a throttle position issue.

[Rallyfan]

It will rev to redline from idle in neutral, and I've managed to do so in low gears (redline in higher gears isn't feasible on the roads I have).

I believe it is a speed issue, not an RPM issue or throttle position issue, because I can drive around at lower speeds with the engine at 9000 RPM. I believe there is something that happens if/when the bike's speed exceeds, say, roughly 75mph that leads to hickuping and the engine cutting out.

In all the excitement I have not had the clarity of mind to try pulling the choke (so as to enrich the mixture) because (a) the bike is lurching on/off at 75+ mph so I've got other stuff to think about and (b) I don't know if the choke lever has any effect beyond 5K RPM anyway. Would trying the choke enrich the mixture and thus tell me if I am leaning out? The plugs looked fine according to my mechanic, and when I inspected the previous set myself last year they also looked good.

I am tempted to add a "breather element" filter to the end of the carb vent tube but I don't think the stock setup is like that anyway. I am also tempted to start replacing each/every vacuum tube on the bike but that is quite literally a fishing expedition with no rhyme nor reason to do so -- it's a shotgun approach.

Thanks for your help! Any advice appreciated.

[jeZZa]

get rid of the vacume tap, i had the same issue and solved it by using the fuel tap from a RGT 250 suzuki, it also has dual fuel lines in and a single one out, its a manual tap so you need to blank off the vacume take off on the carbs. since i fitted it i can hang the throttle wide open and she just keps going til the tank runs dry

[Rallyfan]

Thanks for the tip! I've not been able to affect the issue at all regardless of which selection I make on the chassis petcock: ON/RES/PRIME all result in the same issue.

When you had the problem, was it temporarily solvable by selecting PRIME on the stock petcock (thus bypassing the vacuum anyway)?

Thanks!

[Watcher]

Say you drop a gear (or raise a gear) when stuttering at 75, what happens?

Also, totally try the choke next time it happens.  Never hurts to rule out improper size or clogged main jets.
I'm pretty sure the choke is impartial, and just offers what is essentially another jet right before the cylinder head.  It'll dump fuel at idle, at 5k, at 11k...
I've heard of people using them like pseudo cruise control.  Great way to foul some plugs, though.

[Rallyfan]

I will try the choke provided the rain stays away. I'll also try raising a gear since I'm uneasy to drop a gear at 75 with no throttle to blip and rev match - if I lock up I may never learn to play the piano.

[Watcher]

I will try the choke provided the rain stays away. I'll also try raising a gear since I'm uneasy to drop a gear at 75 with no throttle to blip and rev match - if I lock up I may never learn to play the piano.

You won't "lock up".  Just use your clutch like a clutch and you'll be stable.  No throttle while downshifting will engine brake fairly aggressively but nothing bad will happen unless you just let go of that clutch lever.

[Rallyfan]

OK so:

1. Choke has no effect. It still cuts out and jerks at high speed.

2. Gear selection has no effect. It'll do it at high speed in 5 or 6 (didn't try 4).

3. Shifting up or down has no effect. Only slowing down salvages the situation and the bike purrs along at under 70 or so.

I believe it is a speed issue, not throttle or RPM.

[Watcher]

In that case it means environmental air pressure is getting into the carbs somehow.
If you're sure the hoses are all routed properly, it could be that the airbox boots aren't sealing completely.

[Rallyfan]

Thanks for the patient and helpful responses!

If the airbox boots are not seated properly, wouldn't the idle creep upwards? I'll check the boots nonetheless and report back ASAP.

I love the bike nonetheless! Oh, what I'd do for fuel injection about now though... Sigh... OK! I'll post back when I get a chance to look into it.

Thanks!

[jeZZa]

Thanks for the tip! I've not been able to affect the issue at all regardless of which selection I make on the chassis petcock: ON/RES/PRIME all result in the same issue.

When you had the problem, was it temporarily solvable by selecting PRIME on the stock petcock (thus bypassing the vacuum anyway)?

Thanks!

nope, it would take slightyly longer to run out of fuel but would ultimatly run out and the bike would go lean, sometimes if you paid attention you could feel it starting and back off the throttle while yanking the choke to keep her alive

[Atesz792]

I've had this happen at sustained highway riding at about a 100mph.
Tank was half full, so not even close to hitting reserve, but I fueled up at the next gas station to full (bought about half a tank's worth of gas) and the problem went away. I'm thinking not enough hydraulic pressure in the tank with the lower level to account for the increased demand on the other side of the petcock. Sustained riding at those speeds happens so rarely though that I just didn't care after I had arrived so no troubleshooting has been done. I just make sure it's full on the rare occasion...

[Rallyfan]

nope, it would take slightyly longer to run out of fuel but would ultimatly run out and the bike would go lean, sometimes if you paid attention you could feel it starting and back off the throttle while yanking the choke to keep her alive

This does sound a lot like what I experience. I too can sometimes feel it starting and roll off the throttle to avoid it for a while. Thanks!

I've had this happen at sustained highway riding at about a 100mph.
Tank was half full, so not even close to hitting reserve, but I fueled up at the next gas station to full (bought about half a tank's worth of gas) and the problem went away. I'm thinking not enough hydraulic pressure in the tank with the lower level to account for the increased demand on the other side of the petcock. Sustained riding at those speeds happens so rarely though that I just didn't care after I had arrived so no troubleshooting has been done. I just make sure it's full on the rare occasion...

I'd trade this situation for mine because of the higher speed involved in what you describe. In my area one has to actually exceed 80mph to sometimes simply follow traffic, making the bike questionable to ride on the freeway as a result. Also, mine does it even with a full tank (and even when the tank is full and the tank cap is open, so I've excluded the cap vent). Thanks!