I've had my GS500F for six months now, and today a new problem surfaced. Its the first hot day since I bought it (36 degree C in Sydney). Started the bike, rode it for 10 mins, then stopped it to do an errand. Came back 5 mins later, started fine, and rode off. Within a minute or so it started to splutter, particularly as I opened the throttle up. Idled ok, but after the first few seconds of acceleration it would feel like fuel starvation. If I kept the thottle open it would choke for a while, then surge, then choke a bit, then surge etc. This happened all the way home, but got progressively worse until it felt permanently starved. The bike never stopped though; it just felt like it was running at half power.
I have a few thoughts:
- vapour lock (really hot day, got even hotter sitting still after the first ten mins ride)
- blocked jets or fuel filter; maybe blocked jets in one carby only, explains the feeling of half power
- electrical fault, cutting the spark to one plug intermittently.
So - where should I look first for a solution? I'll let it cool and try it out later this evening, but I want to fix the cause as I don't want this to happen 200km from home!!
Thanks for any ideas
Quote from: jawntybull on October 30, 2008, 09:48:34 PM
I have a few thoughts:
- vapour lock (really hot day, got even hotter sitting still after the first ten mins ride)
- blocked jets or fuel filter; maybe blocked jets in one carby only, explains the feeling of half power
- electrical fault, cutting the spark to one plug intermittently.
Those are some good points to look for. What octane are you running? 91 is less prone to vapor lock. When did you last flush the carbs? Always a good step in maintenance. Only firing on one cylinder? I don't have any advice on that one :oops:
Maybe check the battery. I had a dying battery once that made the GS run good/not good alternatingly
Problem solved yesterday - so for anyone who has similar symptoms...
It was not fuel at all, nor was it hot weather. One of the terminals on the primary side of the left side coil had come loose; this meant one cylinder had no spark. It must have come loose over a period of time, explaining the intermittent surging.
Diagnostics - it felt that the bike was jumping between half and full power, which made me think of a problem in one cylinder. Easier to check electrics than fuel, so I started there. I took the HT lead off one side, and it ran (but poorly). Took the HT lead off the other side and the bike wouldn't start at all - so it had to be the still-connected cylinder that was the problem. Checked the plug - ok. Traced the circuit (required removing the fuel tank of course) and there it was.
Great details on the problem and the solution. Thanks!
May I suggest that you add a photo of the faulty connection point for the added future benefit of others? Or, since you've probably already reinstalled the fuel tank, maybe an arrow drawn on a schematic diagram/fiche?
I'll try and get a photo next time I have the tank off - no way to get one until then. BTW, I did a dumb thing when I put the tank back on - forgot to turn the fuel tap to open. I got 100m down the road and the bike stopped dead - I thought the problem had returned until I had my DUH moment. The good news is - the standard toolkit is up to the task - took me ten mins to undo the fuel tank, open the tap, then put it back again. If you did this you could get to the coils too (you don't have to disconnect the fuel lines; just rotate the loosened tank a bit) whilst on the road... they sit underneath the front of the tank. Each coil has two small wires connected to it; these provide the input charge to the coil - it was one of these connectors that had come loose.