Interesting issue that came up for me a few days ago.
I was riding home from work, and decided to take a different route. This led me to a road that I have been on before (in the evenings) that takes a steep incline for about half a mile. Usually when I go on this road, it is 50-60 KM/. However, in the middle of rush hour, it was stop and go traffic. For some reason, halfway up the hill while I was stopped, my bike just died. I was in first gear, back brakes on, clutch fully in. Tried starting back up, and it wouldn't even turn over for a second. After a second or third try, the engine turned over, and i revved the engine to keep it from balking again. But almost every time I stopped on the incline, the engine stopped.
Fuel was full, I just cleaned the carbs and the engine was running ok at speed and on level ground.
I read up on this, and there were some people who thought it might be the fuel vent hose, but I checked and there was no pinching in my hoses.
Could it possibly be a float level issue in the carbs? Has anyone else had an issue with this before?
I haven't had too much time to troubleshoot, or even check if I can repeat the issue.
Not sure how steep the incline was, but carbs certainly work best when level. If you go out to a good 4 wheeling spot (not a flat mud bog, but a rock garden) you'll notice that nearly every truck is fuel injected because carbs stall out at the extreme angles the trucks can obtain.
Too low a float level could exacerbate the problem.
Just checked, and it looks like the max grade is about 12.2%
checked the four-wheeler blogs, and it looks like that might be the issue
I'm trying to visualize it, but would an incline cause the float to think that it needs more fuel (putting more fuel into the carbs), or that it is already full (preventing any more fuel from getting into the carbs)?
I'm going to head back to a side street or parking lot that has a steep grade next week, and see if I can make the issue repeat, and get any further clues (wet spark plugs, fuel leaking out of vents, etc)
keeping the RPMs at 2000 might keep the vacuum high enough to not shut off. this can be done with throttle control or opening the choke a bit. that is if its the float levels going out of wack from the grade.
thanks for the suggestions. I'll try the choke thing.
Once the bike stalled, I tried starting with open throttle, and kept the throttle on at 25-50% at the stops on the inclines, but it still stalled out every time I stopped, even with throttle.
Quote from: danofthejungle on June 04, 2015, 11:15:45 AM
I'm trying to visualize it, but would an incline cause the float to think that it needs more fuel (putting more fuel into the carbs), or that it is already full (preventing any more fuel from getting into the carbs)?
Your making my head hurt :technical:
Then you have to figure out if the opposite would happen on a down hill :confused:
Honestly I can't visualize it right now, I just got off work and the brain needs a quick breather. I'll think about it in a bit.
The carb float pivots and needle valve are located towards the bikes rear in the bowl so going uphill the fuel would move towards the rear and tend to drop the floats increasing the available fuel. More likely to flood than starve?
Vacuum affect on fuel flow via the petcock diaphram could be eliminated by trying a run uphill with the frame petcock turned to prime. Worth a try.
Still the delay in cranking after it stalls would not be affected by fuel flow so there must be something else involved? Keep thinking, I'll probably worry about it all night now. :icon_lol: :icon_lol: :icon_lol:
At least if something opposite happens going down hill you have gravity on your side and bikes can be started by rolling downhill. :thumb:
I *think* the carbs would overfill and spill into the air filter/box on a steep incline. As long as your going fast enough to use the gas flowing down from the petcock, it won't flood. You could sit there and rev your engine :icon_rolleyes:
Think I missread the first post, when OP said the bike wouldn't even turn over I thought he meant it wouldn't even crank when he probably meant it would crank but not fire briefly?
I agree he was probably flooded and it would take a bit of cranking to clear the carbs and fire up again. I put 180k miles on my 2 GSs and quite a few of them in the mountains without ever touching the carbs and only had a couple of minor brief carb problems with them. Once I saw a puddle of gas below the air box drain tube of my 02 parked on side stand and it never happened again during it's 100k miles. After I bought the 02 I restored the wrecked 97 and it was parked in the garage and only occasinally used. Left it parked in prime once and when I went to use it again the oil had an extra quart of gas in it. In both cases just a fleck of dirt holding the needle valve open that flushed out upon restarting.
This case needs further investigation before messing with the carbs again. Never had any problems with mine parked on some pretty steep hills in the mountains. It does seem to me that the gas leaking thru carbs goes to the airbox with bike on sidestand and to the crankcase with bike parked on centerstand.
Sequence of events for clarification:
1. come to a stop on the incline, in 1st gear, rear brake on, clutch in
2. Engine bogs down, then dies
3. thinking "WTF??" in my head, try hitting the starter
4. no cranking or even clicking from the starter (or it might have and I didn't hear it), but definitely no cranking
5. take a second to put front brake on, release rear brake, shift to neutral, go back to rear brake
6. hit starter, engine turns, but doesn't take
7. turn throttle and hit starter, engine turns then finally takes
8. 50% throttle in first and clutch control to catch up to the car in front, about 20ft.
9. at the stop on the incline, engine bogs down and dies again.
10. kept throttle open with full clutch, to try to keep the engine going, but it still bogs down and dies
11. rinse and repeat about 5 or 6 times during the stop and go up the hill.
I would have to wait maybe 10 seconds every time to be able to start the engine again. I didn't want to turn around and go back downhill (2 lane road, and blind corner going downhill, so it would have been quite dangerous). I didn't smell any fuel at the time, but didn't get into detail on that. I did check the airbox drain hose cap a couple days later, but nothing came out from there.