Suzuki bandit 1200 motorbike coughs when engine is cold. what could be causing it?

my suzuki gsf1200 bandit '02 motorbike has a problem where when revved at standstill between 1100rpm(idle) and 2000rpm it 'coughs' back into the carbs when the engine is cold and mildly warm. Only when it is fully warmed up will it rev without this 'coughing' back on itself.


I checked the carb balance this evening by attaching my morgan vacuum gauges and the carbs were only slightly out of balance, which i've now adjusted. But what i did notice is it coughs on all 4 cylinders, and randomly, when it coughs the gauge suddenly drops then returns to where it was.


Its done 10,000miles now, i've just bought the bike, and i know the valve clearances need checking/adjusting at 7,500miles so that is next on my list of things to do.


The bike had stood for a year before i bought it, but just these last few days i've done 200miles and it still does it. I have been told maybe the carbs are in need of a clean due to the fuel going off causing a residue to be left which affects the running.


Any help is appreciated.|||I know it's the expensive option (which therefore may not be an option) but take it to a Suzuki dealer for a full service - you've only just got the bike, you don't know it too well at the moment and it might be an easy fix for the service techs at a dealership.





It's what I'd do, anyway. Just get the whole bike checked out by those who know them. Then consider servicing it yourself from that point on.|||It turns out it is indeed because the mixture is lean. Because it's an old engine design they lean the mixture more and more to get it through the strict emission tests. I have done a huge amount of investigating and raising the main jet needle by 1mm has almost cured it. Can be done in situ.

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|||I checked and adjusted the valve clearances, new spark plugs, new oil and filter, genuine air filter, have removed the carbs 7 times in total, thoroughly cleaned and float height set correct. Jets cleared out. Carbs balanced. Still did it. The answer was to raise the needle to richen up the mixture

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|||Try replacing the spark plugs?


Good luck with adjusting the valve clearance of the Bandit. It is not for amateurs. Your will need special tools and tons of patience. If you plan to do it, get a repair or service manual.


Check the valve clearance for now, if not too much out of specs, let it be. Enjoy your bike first.|||Uh, the engine is cold and combustion is not as effective as it will be when it warms up. Let it warm up before revving it. Its not good to rev a cold engine.|||Mark is correct. usually means a lean condition, more choke, and let warm up some


before riding or ride easier till it warms up.|||Install new spark plugs and air filter.|||I'd bet money that if you can find the pilot jet screws on the sides of the carbs and richened the idle mix up a bit, that would stop the lean running carb backfire. The screws may be hidden under sealed tamper-proof plugs, although that doesn't mean they can't be removed. Neither can I tell you which way to turn the screws because while the screws on most control fuel, on a few they control air (like my '79 Kaw). See if you can find a yahoo owners group for your bike and ask someone who knows.





While it never hurts to tune a bike up and clean the filters, etc, a dirty air filter would only effect high speed running, bad plugs would either cause very hard starting or misfire under heavy load although at 10k miles, I'd go ahead and replace them and too tight valves needing adjustment will cause hard starting and sudden dying until thoroughly warmed up.|||This sound is old oil or wrong spark.or wrong oil.it can be electrice problem.so


1-change or clean air filter


2-change or clean the spark and make sur is correct one


3-change the oil engine and oil filter


4-check the battery.