Stalls at highway speed - looking for direction

[a747freak]

Hey everyone,
I'm having an issue with my GS250 and I think it's fuel related, I'm just not sure where to start. What happens is at highway speed, say 70-75mph with throttle wide open and pushing hard, my bike tends to just stall out. It happened today and took me about 5 minutes to start up again. It would start to catch and then die, and finally it started and idle'd fine, and I rode it home without any other issues. It performs perfectly fine at lower speeds, and I drive it around town frequently and short hops on the highway at lower speeds without issue. It has never happened outside of 6th gear pushing hard.

I've only had the bike since February, and the first thing I did was clean the carbs which were atrocious. I didn't soak the carbs or replace any seals or o-rings though, just cleaned with carb cleaner. The petcock has a slow leak, but I thoroughly cleaned it and it has been better. Any ideas for the exact cause, or where I should start? I'm guessing a more thorough carb cleaning or petcock replacing but I don't want to just jump in and start spending money/time blindly. Thanks for all your help, this forum rocks.

[kinnet]

Thoroughly and correctly cleaning your carbs is never time wasted.

[Nessism]

Sounds like the petcock may be fuel starving the carbs.

[Crescentius]

If the petcock is original, it needs to be replaced (not rebuilt-unless you absolutely cannot get a replacement). If you don't know when the carbs were last cleaned, tear them down in to tiny little pieces and clean and dip everything and replace all the o-rings. If that isn't causing your problem, it absolutely will cause other problems, so start with that. Both these things are relatively inexpensive to do anyway.

[FlyingSteve]

Sounds like the petcock may be fuel starving the carbs.

Only problem with that is it shouldn't take 5min to restart. It would stall, then you'd go to restart, bowls would fill up (since he says it rides fine at lower speeds/engine loads) and it would fire right back up.

I'm wondering if it isn't overheating when you are doing extended periods of WOT. Then once it cools off a little, it starts back up.

Since it doesn't want to restart for a little bit, if it is overheating, it may be due to valve clearance issues. If the clearance is a little too tight, then when you get that motor good and hot from running it hard (WOT, 6th gear) the clearance will close up even more as the valves/cam, etc, expand.

Is it always about the same amount of time of WOT 6th gear cruising to stall? OR does it seem to be worse/better on a hotter or cooler day?

Could also be the spark plugs. My GS550 was stalling at weird times during warm-up and then wouldn't restart for 10 or 20 minutes. One day it stalled after running for only 2 minutes and wouldn't restart. I bought new plugs on a blind hunch and viola, it started right up and has given me no issues since.

So I would check/replace the plugs and check the valve clearance first. Relatively easy and cheap/free. Also, pull the petcock and check the filter. When you are running the engine hard like that you are moving a lot more fuel and so bits of sediment and crap could be clogging up in the petcock filter. That theory is much less likely though as it would happen more frequently than just when you are at WOT on the highway. From what you say about running the bike hard, it is more than likely an issue with something overheating and failing until it cools.

[a747freak]

Only problem with that is it shouldn't take 5min to restart. It would stall, then you'd go to restart, bowls would fill up (since he says it rides fine at lower speeds/engine loads) and it would fire right back up.

I'm wondering if it isn't overheating when you are doing extended periods of WOT. Then once it cools off a little, it starts back up.

Since it doesn't want to restart for a little bit, if it is overheating, it may be due to valve clearance issues. If the clearance is a little too tight, then when you get that motor good and hot from running it hard (WOT, 6th gear) the clearance will close up even more as the valves/cam, etc, expand.

Is it always about the same amount of time of WOT 6th gear cruising to stall? OR does it seem to be worse/better on a hotter or cooler day?

Could also be the spark plugs. My GS550 was stalling at weird times during warm-up and then wouldn't restart for 10 or 20 minutes. One day it stalled after running for only 2 minutes and wouldn't restart. I bought new plugs on a blind hunch and viola, it started right up and has given me no issues since.

So I would check/replace the plugs and check the valve clearance first. Relatively easy and cheap/free. Also, pull the petcock and check the filter. When you are running the engine hard like that you are moving a lot more fuel and so bits of sediment and crap could be clogging up in the petcock filter. That theory is much less likely though as it would happen more frequently than just when you are at WOT on the highway. From what you say about running the bike hard, it is more than likely an issue with something overheating and failing until it cools.

You know I was wondering about overheating too. The spark plugs are brand spankin' new, I was actually on a test ride after having just replaced them when this happened again. Each time it's happened has been after roughly 5 minutes of highway driving, and it did seem like it didn't take as long today (probably the hottest of the few days in which it has happened). So, I will check the valve clearances, then replace the petcock, then plan to clean/soak the carbs and replace o-rings.

[FlyingSteve]

I'm betting it isn't the carbs... But like others said, it doesn't hurt to clean them and will only do you good to replace the o-rings on the carb and the intake manifold boot gaskets/o-rings, whichever your bike uses.

What you should do is good out for a ride again on the highway. Take a few tools with you like a spark plug socket and ratchet. Get it to stall, pull a plug and see if you still have spark or not. If you have spark, then that eliminates the ignition system. While cranking it over with the plug removed, see if you are getting fuel in the cylinder. You should either have some gas spraying out of the spark plug hole or a strong smell of fuel coming out... Just something that tells you there is fuel going into the cylinder.

If you have fuel and strong spark and no starty... Well then it's probably your valve clearance

[Nessism]

Valve clearance doesn't make a bike stall at freeway speeds (although you should check them anyway). Carrying a spare plug is a good idea to check spark, but I still think the carbs may be sucking dry. If the gas tank vent is not breathing properly a vacuum can develop in the tank and restrict fuel flow so that, and the petcock, are where I'd look first. Oh, and doing the carbs properly is never waste as already mentioned.

[salty_monk]

You could also double check breather in gas cap is clear. If partially blocked you could be pulling a vacuum.

Next time it dies try removing gas cap and see what happens...

[FlyingSteve]

If the breather in the tank is plugged up causing a vacuum to be drawn in the tank, causing fuel starvation, then it would happen a lot more frequently then just when he gets on the highway and is cruising at WOT for 5 minutes. And it wouldn't just clear up in 5 or 10 minutes allowing the bike to restart and operate again at a lower speed/less throttle with no issues, and work fine like that all day long. He states that the bike runs fine when going around town and cruising at lower speeds/less throttle.

When he gets on the highway and is cruising at WOT in 6th gear, that is a lot of load on that little engine. If the valve(s) are tight to begin with, when the motor gets good and hot (like when he is cruising at WOT in 6th gear...) the tight clearance turns into too little clearance and the bike stalls. It doesn't restart for a period of time because it needs time to cool for the metal to contract and open the clearances up.

I do believe that valve clearance issues are a culprit in hot restart issues, right?

If he was having issues with the bike all the time, then I would agree more with fuel flow theories. However, he only reports having problems when running the engine at wide open throttle in 6th gear. He also stated that on a hot day (today it was 90F at his location) it seemed like it stalled out quicker.

[Fizzyhair]

As a thought, what ignition system does the 250t use? I had a similar experience with a gsx750 last year. It turned out to be the crank sensor that fed the CDI/eCU ignition box. Exactly same symptoms! But if it's points or distributed firing this may be irrelevant.

I'm actually not sure why it would have been the problem. I was tipped of by a forum user that it should be checked as t can give this symptom and so I took a look.

[a747freak]

Update

Ok today I ran it again till it would stall. It didn't actually feel like a stall, but more like one cylinder dies and I can give it throttle but at that speed, one cylinder just doesn't do anything. So I was able to squeeze the clutch and pop start it, and both cylinders were back. I stopped on the side of the road and it idle'd fine for me. But on the way home I took back roads, and she did the same thing in 5th gear on a hill, and I was able to pop start it again without interrupting my ride. So, any ideas? I'm not sure why it was behaving differently today, I tried pop starting it yesterday when it happened with no luck. Also, it occurred about .5 miles away from the place it did yesterday.

On a side note, on the way home from this test ride I came up to a yield sign for the highway and waited for traffic, and some blond idiot in a convertable rear-ended me. No injuries or damage, I didn't even drop the bike, but still.

[Larry D]

Seems to me your bike is running fine while tooling around town and cleaning the carbs properly and a new petcock wouldn't be throwing money at it blindly......

There are a few basics that MUST be done to ensure a solid baseline. Clean carbs, valve adjustment, carb sync, sealed airbox, good spark and charging well.

Stalling while at highway speeds appears to fuel starvation to me. I'd get some of basic maintenence completed before you go much farther.

[FlyingSteve]

Seems to me your bike is running fine while tooling around town and cleaning the carbs properly and a new petcock wouldn't be throwing money at it blindly......

There are a few basics that MUST be done to ensure a solid baseline. Clean carbs, valve adjustment, carb sync, sealed airbox, good spark and charging well.

Stalling while at highway speeds appears to fuel starvation to me. I'd get some of basic maintenence completed before you go much farther.

Rebuilding the carbs barely costs anything anyway... So might as well do that.

If it was a fuel starvation issue, it should be starting right back up once the float bowls refill. So why does it restart right away if he pops the clutch, but not if he pulls off the road and tries to crank the engine?

[Larry D]

Rebuilding the carbs barely costs anything anyway... So might as well do that.

If it was a fuel starvation issue, it should be starting right back up once the float bowls refill. So why does it restart right away if he pops the clutch, but not if he pulls off the road and tries to crank the engine?

It's not filling the bowls when the petcock is "ON" and the bike is not running, the bowls will only be filled when the bike is off if it's in the "PRIME" postion. After restarting by popping the clutch, it's not at highway speeds and gives the bowls and chance to catch up.

As Ed, said, valve clearance will not cause a bike to stall, unless you bend a valve at the same time...I imagine that would cause a stall, permanently.....

Are you running an extra in-line filter ?