GSXR 400 Cylinder Issues

[Renton]

Can anyone suggest a few things to check as to why it only seems to be running on 3 cylinders and not 4?

Carbs have been cleaned, balanced, gaskets replaced, o-rings replaced and all sparks replaced.
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This is my motorcycle. There are many others like it, but this one is mine.
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[Timmeh]

If it's got a loud top-end rattle (even with the engine warmed up) then it could be a broken valve spring.

The only other thing I can think of is the rubbish OEM HT leads. The plug cap sometimes seperates from the wire causing the spark to happen between the top of the plug and the cap rather than at the bottom of the plug where it should be.

Replacement suzuki ones are about £22 each or something. I've had one go on my Gixxer and it gave me issues like your experiencing.

HTH
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GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
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[Renton]

Thanks Timmeh.

How would I know if it is the leads for definite though, (without buying new ones) would it just be a case of looking at them thoroughly?


One stupid question, what does OEM stand for? Have never known.
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This is my motorcycle. There are many others like it, but this one is mine.
Without me, my motorcycle is useless. Without my motorcycle, I am useless.

[Blau Zedong]

Buy some copper cored HT lead from a bike shop or motor factors for about £8, cut to length as required, replace the lot. The originals cause lots of problems as they are economical on length to begin with, then with time they turn as hard as steel.
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[Mudskipper]

[the grim reaper]

Check each spark plug against the block (whils using rubber handled grips and gloves and standing well clear of the bike) to see which one (s) aren't sparking. Check the contact in the cap between the HT lead and the Plug top and, if necessary, clean the contacts ect. Also measure the resistance of the HT lead and coil, you might not know the official figures but, if one is playing up, it should show up as different to the other 3.

Cheers

Grim
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[prawny1]

sounds like time for a compresion test, should be between 150psi - 220psi (with a minimum 115psi).

[Renton]

Thanks guys.

Will start with the HT leads and see where I go from there.


____________________
This is my motorcycle. There are many others like it, but this one is mine.
Without me, my motorcycle is useless. Without my motorcycle, I am useless.

[alun111]

Did you thoroughly check your carbs when you re-built them? Did you replace the dreaded o-rings? I'd loosen the drain screw on each carb to make sure fuel comes out...

Did you set the float heights correctly?

Does the missing cylinder kick in at certain revs?
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Summer: '00 Honda CB600F Hornet
Winter: '93 Suzuki GSF 400 Bandit VP Variable Valve
Past Bikes: Lifan LF100-5 Lifan LF125-A Honda C70

[Renton]

[veze]

i would do a compression test to be honest matey. have u tried to balance the carbs? i would check compression to be on the safe side, and you could rule out alot of possible problems by doing it to be honest. and if the test reads ok, at the presures stated earlier in this thread, at least you know you have a sound and good top end.
oh and it mite be worth popping on to www.400greybike.info
those folks are realy helpfull with imports.
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[alun111]

Did you get anywhere with the ht leads? I'd also replace the spark plug cap of the offending cylinder too.
____________________
Summer: '00 Honda CB600F Hornet
Winter: '93 Suzuki GSF 400 Bandit VP Variable Valve
Past Bikes: Lifan LF100-5 Lifan LF125-A Honda C70

[Creepin Moses]

I heard someone once say that a bike running whilst on the side stand can set the carbs off balance, which would I assume cause it to miss occaisionaly on the cylinder farthest away from side stand. Side stand has bike leen over to left side Causing a rush of fuel to left side carbs, thus starves the right side carbs of fuel.
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[Renton]

[nowhere.elysium]

A compression test is a test that determines that you're getting the same level of compression in all the cylinders: specifically, it is often used to check piston ring or valve seal integrity.

A compression tester is screwed into the sparkplug hole, and the engine is turned over, using the starter motor. If the tester reads below the normal pressure, then you know that there's something wrong with the cylinder in question.
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