Bike quit while running harder then normal

[Big Red]

Hey folks, was out for a little ride this afternoon about a 20km tour. On my way back found a newly paved and open flat road so I decided to open it up. I had been cruising at 100km/h went then twisted the throttle. Got up to 145 then it stopped accelerating. Hardest I have pushed it this year. But had it up to 170 last year with no issue.

At that point I decided to slow down anyways but the bike decided it had enough. Pulled in the clutch and it died. Let the clutch out and it would start right up but no power and would die right away again. Stopped at a buddies place and called the wife to bring the truck and tools.

Tried to the starter. Could see fuel going to carbs. But not trying to turn over. Pulled plugs 1 and 4 dry as a bone both of them. Decided to roll it down the driveway so we can get it in the truck so popped the clutch in 1st while rolling just to test and it tried to roll over. So tried again and it fired up. Let it idle for a bit and after some rough idle it was running fine. Shut down let sit for another 10 minutes then tried the starter and it fired right up. Rode home with no issues. Got home check things over plug look good now. Any ideas?

Did a 200km tour last week no issues but didn't push it hard either just a nice cruise.

Thanks

[1948man]

Hey folks, was out for a little ride this afternoon about a 20km tour. On my way back found a newly paved and open flat road so I decided to open it up. I had been cruising at 100km/h went then twisted the throttle. Got up to 145 then it stopped accelerating. Hardest I have pushed it this year. But had it up to 170 last year with no issue.

At that point I decided to slow down anyways but the bike decided it had enough. Pulled in the clutch and it died. Let the clutch out and it would start right up but no power and would die right away again. Stopped at a buddies place and called the wife to bring the truck and tools.

Tried to the starter. Could see fuel going to carbs. But not trying to turn over. Pulled plugs 1 and 4 dry as a bone both of them. Decided to roll it down the driveway so we can get it in the truck so popped the clutch in 1st while rolling just to test and it tried to roll over. So tried again and it fired up. Let it idle for a bit and after some rough idle it was running fine. Shut down let sit for another 10 minutes then tried the starter and it fired right up. Rode home with no issues. Got home check things over plug look good now. Any ideas?

Did a 200km tour last week no issues but didn't push it hard either just a nice cruise.

Thanks

I am absolutely not an expert but it sounds like it was starving for fuel when put in high demand. Do you have an in-line fuel filter? Is the main jet maybe not up to it?

[fbody_mike]

I was going to say the same thing, fuel. Inline filter will cause those symptoms, so will a bad petcock, or plugged tank cap. The vent tubes from the carb can also cause the bowls to empty at high speed if they are not routed properly. Try to replicate it again, and it if dies out, open the drains on the carb bowl with something to catch the fuel, see how much pours out, it might be just a little.

[Brendan W]

Restricted fuel flow would be my first check as well.

[hannibal]

Low carb float level?

[Big Red]

I had a similar issue a few years ago and removed the inline fuel filter and it stopped. It was definitely starved for fuel. Going for a ride this weekend make sure the floats are full and give it and see what happens. Thanks for the ideas... If I have the same issue I will check the float levels and also petcock. The tube are routed properly I have confirmed already.

Thanks

[Gorminrider]

Turning the tap to "prime" on hard steady run may fix it too, if it persists.

Vacuum petcocks can be fine at normal riding but don't forget your engine vacuum is a variable determined by throttle plate and load...Up a long long hill at a highway speed, (On my 650) opening to prime makes all the difference. Check the vacuum line too.

[salty_monk]

And make sure the gas tank is venting properly... next time it dies try taking the cap off and listen for a “whoosh” as air rushes in...

[BigD_83]

Turning the tap to "prime" on hard steady run may fix it too, if it persists.

Vacuum petcocks can be fine at normal riding but don't forget your engine vacuum is a variable determined by throttle plate and load...Up a long long hill at a highway speed, (On my 650) opening to prime makes all the difference. Check the vacuum line too.

I've experienced this on my 650 as well. Thought it was a fuel level issue (perhaps getting near reserve) but I would put in nowhere near half a tank worth of gas when filling up.

[Grimly]

I had an odd fault, caused by the in-tank strainer being partially clogged in the pores.
It would run fine when the entire strainer was submerged, as enough fuel was oozing its way through, but at around the half-tank mark it would start to die, then pick up again, and would be fine if I parked it up and restarted it.
I replaced the strainer with a new one from the cheap-ass petcock that wasn't much use - at least that part worked.

[Gorminrider]

^^Yes, and of course the strainer above the float needles in the carbs ..but bear in mind that technically, a partial obstruction in a fluid channel does not affect flow at each end...like a river with boulders and canyons, flow speeds up through obstructions...

I've experienced this on my 650 as well. Thought it was a fuel level issue (perhaps getting near reserve) but I would put in nowhere near half a tank worth of gas when filling up.

fuel level does make a difference- there's a change in the gravity pressure against the petcock's vacuum diaphragm spring ...and then too, the increased pressure flows faster even where the vacuum "piston" is not fully open

(cheapo ebay "hopeful" replacements taught me these lessons-I can't say it's their fault where intended for different bikes but i am thinking about relearning the skill of winding my own spring some rainy day...)

It shouldn't be an issue if the petcock is properly designed but...I note the default replacement petcocks all look the same and while they work very well on my Two-carb GSX400s, on the 650, maybe keeping up with 4 carbs/on a larger engine is a strain on vacuum....? especially as the manifold suction declines with an opened throttle on a lugging engine...?

I'm ok with the vacuum petcocks but there's certainly something to be said for simple on-off ones if you have good float needles and seats...-which (IMO) are important on both varieties...

[Guest]

When you run that hard from what I learned, your vacuum drops accordingly and can't keep the diaphragm open on the petcock, the spring over rides the vacuum and starves the bike for fuel. This happened to be a couple times. One time my vacuum hose was collapsing down shutting off the vacuum. Put a stiffer hose on. The other time, the petcock spring seemed to be way to strong for some reason, kept starving the bike around 80. New petcock. So far so good, haven't had any problems for several years now.