One cylinder not firing, GSX R 750 W

Question

What could be possible reasons that one of the four cylinders (the left or first one) is not working? It was working before, than it did not, then it did again and now not again. I was able to start the bike, but only the other 3 cylinders were firing, after driving few hundred meters, the bike went out. I guess it was flooding.

This is what I considered so far (updated list):

• spark plugs (OK)
• cable to the spark plugs (OK)
• it is not wet in the corresponding slot for the spark plug

update:

• there is a spark
• after cleaning the gas cap it works again. Maybe there was too little air going through, such that low pressure in the tank prevented that enough gas was used. I am not sure though, if this really solved the problem.
• I could imagine that the gas petcock is not perfectly working

I know it may be a problem with the carburetor, but I have no idea what to check for.

(apologies for bad language, this is not my standard vocabulary)

Answer 1

Background

The GSXR 750 has the following attributes.

• Carb and FI versions depending on year.

• 4 Carbs or 4 throttle bodies, depending on year

• Two coil packs, 1 for cylinder 1 and 4, 1 for cylinder 2 and 3

Troubleshooting

Possible causes

• If a coil were bad you would have an issue with two cylinders more than likely. Coils going bad on high energy lead connection to the coil is very rare.

• A single bad fuel injector is possible

• A single bad carb is possible

• A single high energy lead failing to a sparkplug is possible

• A single sparkplug bad is possible

Possibilities

• A sticking float bowl on a single carb. Check needle and seat and ensure the needle is dropping down

• A tear in the CV diaphragm at the top of a single carb is possible. This would create a very lean condition that would be more pronounced when your choke is engaged. When you go off choke the vacuum is reduced and the lean condition is less evident. While riding, downshift and go off throttle, if you get popping in your exhaust check the diaphragm. This could be a source.

• As another poster indicated, you could have an oil fouled plug. Do you have oil smoke coming out of your exhaust? Take your finger and wipe it in the exhaust pipe exit. If it's really black and oily then you may have a bad valve guide or rings. If it's just black and sooty then your too rich. If the color is not black but a bit brown, that's better and indicates a more normal mixture and lack of oil in the exhaust.

• Bad high energy lead. Check the resistance of the lead to ensure it has very low ohm reading using a multimeter. Validate spark by putting a sparkplug into the lead and turn the engine over while grounding it on your valve cover or other conductive and grounded component.

• Bad spark plug. Make sure it isn't black and sooty. Carbon is a conductive material. If it's built up with black carbon it can ground the insulator and there will be no spark. You can clean it with carb cleaner and a toothbrush and test again for spark as above

Conclusion

You might have multiple issues, you might have one. Provide more information and I can edit this to reflect the data given.

Answer 2

Your description is making me question your diagnosis so far, in terms of is it one cylinder affected or all. Because a GSXR should be able to run (badly) on 3 cylinders, and cleaning the fuel cap shouldn't make a difference to just one cylinder.

From your description i'd start by replacing the fuel and ensuring it flows freely to the carburettors. (is it possible that it has old/dirty fuel?) disconnect the fuel line to the carb and drain it into a bottle and see if it runs freely. Drain the carb float bowls.

If you're certain that this just affects one cylinder then i'd suggest you remove the carbs and clean/inspect and look for blockages. Make sure you can blow air through each fuel line, jet etc.

Does the bike run on that cylinder at all? (at idle? half throttle? full throttle?) does choke make a difference? Those things might indicate a blocked jet.

Has anyone made any changes to any of the adjustments on the carb? screws etc?

There's a few microfiche diagrams to help you identify parts: http://www.suzukipartshouse.com/oemparts/#/l/suz/50d3c45ff870021958f27633/1993-gsx-r750w-parts

Answer 3

Peter's on it, all the way across the board. If all those checks test out, then check for a sticky valve on that one cylinder. In fact, adjust valve lash on all cylinders.

Then check compression.