Pls help, i have problem with one cylinder of My gs500

[Richard NW]

hello, recently i took my bike from service. They have change jet needles, cleened and tuned up carburetors. Also they changed my air filter, oil, tightened cam chain, and cheked valves. From then, my bike is runing like new, but only for 10 minutes  > First time when that happend, i check ignition coils, and sparks plugs, Left coil was dead, than i changed 2 coils with spare ones that i have. Everything was ok but only for 10 - 20 minutes, again left side - no spark. If i turn off the bike in that condition, and start again, some of times he s working normaly, but if i leave bike for 3 or 4 hours, and start him, he s working fine, but again for 10- 20 minutes than one cylinder trouble is coming back. PLS Help me 

[SkyBob]

is there oil on the spark plug of the misfiring cylinder?

[Richard NW]

No Spark plug is perfectly clear

[Janx101]

Heat related? ... maybe a cable somewhere is loose/worn/pinched... engine heat starts problem again each time, ...

Multimeter to check resistance of wires... bike workshop manual wiring diagram to know where to check!?

Or the contact 'clamp' inside sparkplug connector.... maybe loose and heat cause expanding clamp so then bad contact with plug?

[gsJack]

Sounds like a coil problem when it happens 10-20 minutes after startup and is OK again after cool off.  You changed ignition coils but did you test signal generator pickup coils?  There is one for each cylinder on a 97 model.