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Hi everyone, My suzuki gsf400 is only firing in cylinders 3 and 4. I have new coils signal generator cdi is good new plugs had carbs checked out twice and told they were good. However i found number 2 carb had a broken tube on the side i thionk it is part of the start system as it goes up to the start plunger. I tryed to repair it by putting it back in place and used two park exposie. Please give help . Thank You Mark d. luton
 

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Three things needed to fire an engine.

Adequate spark at the correct time.
Correct fuel mixture.
Adequate compression.

You need to determine which of those is the problem and then systematically eliminate potential causes until you hit pay dirt.

I'm assuming that bike has two coils, one for cyls 1 and 4 and one for cyls 2 and 3. So off the bat the coils are probably okay. You could have something as simple as two bad spark plug leads or two bad spark plugs. With the number 3 spark plug removed from the head and stuck back in the spark plug lead with the threads held against the engine, metal to metal contact, turn the motor over and look for a nice fat blue spark. Re-install that plug and put the lead back on. Repeat the process for number 4. A word of caution, some ignition systems don't like an open circuit so be sure all plugs are connected during these checks.

If all that is well take note of whether or not the plugs on the affected cylinders are wet with fuel. If they're dry you've got a carb problem. If they're wet you've got either a carb problem or a compression issue.

A compression test can be done to verify adequate compression. All four cylinders should be close to each other on compression readings.

Look at the intake boots for signs of dry rot. If they look good remove the carbs and have a look inside. Remove the pilot and main jets and try to look through them. If you can't see daylight through them, you've found your problem and need to properly strip and clean the carbs to sort your issue.

If your bike is a 1991 - 1993 the link below shows the carbs. If you can, point out where the broken piece on no. 2 was, that might be helpful.
 
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