possible ignition problems?

[Guest]

completely new here and to owning a gs series bike. i've got an 81 gs750l and did run about a month ago. started to spit and sputter and now when trying to start it'll backfire only on the #2 cylinder and not even try on any other cylinders. The plugs aren't too old and don't look too bad "atleast to me" i was wondering what tests i can do to see what might have gone wrong possibly with the ignition system. the timing on the bike is good valves look good. im planning to do a compression test on it as well and checking carbs for debris just to cover all bases. i appreciate any and all help

[tom203]

Since it sorta ran "a month ago" , suspect the further consumption of fuel to have created this problem. Do you understand petcock positions? Have you tested it?
Figure it's way behind on maintenance,so peruse this link...

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

If bike has sat idle for months, carbs will likely need a thorough cleaning, thanks to that ethanol fuel that has been forced on us.

[Gsnewb]

thanks for the reply. when the bike is sitting idle i like to have the fuel valve shut off and run the carbs empty. have done this my entire life. i did happen to find out last night that the coils had somehow shorted out on me. i found an old manual and did some testing with the electrical system and found the coils to not have any resistance vs needing to get 3 ohms.

[tom203]

"when the bike is sitting idle i like to have the fuel valve shut off and run the carbs empty. have done this my entire life. "

With the stock suzuki vacuum petcock, there is no "off" , you got on ,res,and pr. If engine is running, fuel flows in first two spots. In "pr" it flows all the time. Left in "pr" spot, carbs can eventually overflow ,dumping fuel in crankcase which is bad news when you next sttempt to run it. ( The spit and sputter stuff)

It would be hard to short out the ignition coils with 12 volt dc - they are robust. Do some reading at this link- it's loaded with info regarding gs suzukis

http://members.dslextreme.com/users/bikecliff/

[Gsnewb]

I have an extra shutoff on the fuel line to fully shut off all fuel going to the carbs for when it sits. I did also happen to find that manual and perform the resistance test it says for the coils and how I need 3 ohms resistance and all I got was infinity/open reading

[tom203]

Do your ignition coils have connector plugs like in this link??

http://www.alpha-sports.com/spst/1981%20GS750L/15.htm?q=suzuki-parts

If so, when you unplug a connector and measure across a coil's connector terminals with your meter probes (meter on lowest ohm setting), you should see about 4 ohms. But you see infinite? Is your meter auto ranging?

[Gsnewb]

Yes my coils look exactly like that with same connectors. My meter is a fluke 115 and use it all the time for work