2001 Gs500 Running on one cylinder

[HungaryMVP]

Hello all. This is my first time posting so please let me know if I need to change anything. As for my motorcycle! Recently I noticed my bike has been running on one cylinder and I am not sure what the problem is. I have checked all the the fuel lines, taken off and cleaned the carbs multiple times, and has spark. I am trying to get my hands on a compression tester because I think that will be the problem. I was just wondering if anyone had a similar problem with compression and what would the cause of it be and also what did you do to fix it? Personally I'm thinking carbon build up on the valves or blow by. Please let me know. Thanks

[ajensen]

Usually, if a valve is burnt or not seating properly, the cylinder will begin to run as the engine speed picks up. For example, when I had a burnt exhaust valve on my 500 single, there was not enough compression to kick start the engine. However, once I bump started going down hill, the engine ran (although not very well) as long as I kept the revs up. I know that people ridicule the finger over the spark plug hole method of checking compression, but the technique does give you a rough idea. I have a compression gauge, but before I screw it in, I use my finger just to make sure that something is not totally wrong. Does anyone on the forum use a strobe light to check timing and if the spark is working on both cylinders?

[mr72]

As for the cause of bad compression, in order of likelihood on a GS500:

1. tight valves (insufficient valve lash, need to reshim)
2. bent or burnt valve(s)
3. carbon build-up on valve(s) (about to become bent or burnt!) - personally I don't think this actually happens, so I will also list:
3. Blown head gasket
4. Otherwise bad/worn valve seats
5. Rings shot

#1 and #3 can be fixed without a complete top-end rebuild. The rest deserve a complete top-end rebuild.

[gsJack]

I had an 02 with the same problem, spark and compression both checked good but it was running on one cylinder.  I finally grabbed the plug wires and one pulled right out of the coil and that was the problem, a bad connection.  Fixed by cutting off a half inch of wire, putting on a dab of moisture sealer, and screwed it into the coil tight. 

GS plug wires are screwed into the coils and bonded tight in place, you can't turn them or pull them out.  I had previously discovered that on my 97 GS I bought new and it was sitting there in the garage so I then went over and grabbed the plug wires and they were both loose at 80k miles on the bike.

[The Buddha]

The other possibility is the auxillary ground could be bad.
Cool.
Buddha.