Hey guys.
For the past month my GS has been acting strange.
Symptoms: It starts fine, and after 10-15 minutes, the left cylinder will stop firing. Intermittently, the cylinder will re-light again, but it's rare. upon restart, if the engine is warm - it fires on 1. if the engine is cold, it will start on 2.
Troubleshooting: Spark is present, plugs gapped OK. Carbs may need to by synched, but when it runs on 2 cyl, it runs very well....
Recently, I disconneced what I think is a vacuum line from the fuel petcock, leaving it still connected to the left carb (the carb that controls the mix for the cylinder that keeps dying). #53 in the pic below is the line I'm talking about:
http://houseofmotorcycles.bikebandit.com/partsbandit/showschematic.asp?dept_id=724806
When the bike was running, I put my thumb over the opening in the line (that is usually connected to the fuel petcock) and the cylinder starts firing again. Remove thumb and the cylinder dies.
I used to think it was an ignition prob, but now I think it may be a diaphram in the petcock or something....
Advice? If i remove the petcock, and fabricate my own fuel setup - what do I do with this vacuum line..., if indeed that would solve the problem?
Thanks guys and gals,
Matt
The intermittent nature of the problem sure tempts me to label it "electrical". But it's hard to argue with reproducible results like you're getting by tweaking the vacuum line. The funny thing is ... I thought that the diaphragm in the petcock worked because of the vacuum pressure exerted on it. Now I'm hearing that it (sometimes?) works better without the vacuum.
:? The mind reels.... :?
Theoretically, running the engine with the petcock in the PRIme position will take the whole vacuum question "out of the loop". Have you tried this before? The results you get when running on PRIme should give you a fairly good idea of how a petcock-less, home-grown fuel delivery setup will perform.
Meanwhile, if you still suspect electrical problems you might look at the thread Narrowing down the problems to a broken bike (http://www.gstwins.com/forum/viewtopic.php?t=5500). Sorry if you've already waded through it....
If there is a leak in the diaphram or the fuel switch body, either fuel or air could get sucked down the vacuum line from the carb, and really mess up your mixture. If taking that vacuum line off, and putting your thumb over the end fixes the problem, than I would suspect that is what is happening.
For the short term, you can just disconnect that vacuum line and plug it. A bolt with some goop on it works well. You will have to ride with the bike on "Prime", and you won't have a reserve. If you don't turn the valve to "Run" or "Reserve", and you happen to have a leaky float valve, you could have gas running into the air box and out on the ground.
You can replace the fuel switch, or put two simple petcocks in the two lines, one for run and one for reserve. The fuel would not shut off automatically when the engine stops though. Or find a better vacuum operated fuel switch from another bike, that actually flows enough fuel for the engine.
Cool, thanks guys. I should have mentioned that I always run with the petcock in prime, as it seems to not give me the dreaded stall out problem on the freeway if I do that.
I think I'll try to plug the vacuum line as a temporary fix, I guess I don't need it with the petcock in prime anyway it sounds like. Then, I'll try to rig up my own hardware and just get rid of the pesky petcock, since it has caused so many problems allready.
Thanks guys!
:cheers:
It'll be nice to have one less problem to worry about. :)
You can cap the vacuum port at the carb as well, and get rid of that tube entirely. Something similar to the vacuum caps on the top of the carbs works well.
Mizen,
What you have found is the same cause of my wife's GS playing up. About two weekends ago whilst returning from a mountain ride her bike started to miss badly and the right cyclinder had died. As luck would have it just before we got home the bike came good again and I couldn't get it to play up once in the garage. We too assumed that it was electrical and I cleaned all the contacts in the system and checked resistances - but all was good.
Then yesterday whilst riding the bike over to our mechanic for a service the bike played up again. The mechanic also assumed it was electrical related. After running the bike on high idle for a while it started to miss again, he checked all the components and swapped coils etc. to try locate the fault to no avail. In the end he found that the petcock was causing the problem as when he removed it and connected up an aux fuel supply direct to the carbs and blocked off the vacuum line the bike would run just fine. So touch wood we have found the problem.
Cheers
Conrad
Awesome, I'm glad to hear that you also got the problem solved.... I've been pondering what mine could be for a month or so. I can't wait to plug that line and just get back and ride for now.
This weekend I'm gonna ditch that petcock with an extreme vengence. Thing has caused me so much headache.... especially since I run on prime anyway.... should have done it long ago.
Thanks! :thumb:
I run my fuel line straight from the tank to the carbs. I have a simple on/off valve on the hose. I connect it to the reserve spigot on the tank petcock.
You need a fuel valve to shutoff the gas when you're not running the bike.
Don't trust the float valve to do the job. They will eventually let gas leak past into the cylinders or on the ground. :nono:
well at least it is not sounding TOO bad, im guessing on a leak somewhere
isnt it weird, when running on one, it behaves like a gz250? :roll: , i know mine did :dunno:
Cool - then I'll definitely be picking up a fuel valve soon.... just need a chance to work on the temporary fix of plugging the vacuum line and running on prime.
yeah - nothing is worse than riding around on a really heavy 250. In LA traffic. :)