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Ok, I have a 92 Suzuki Bandit 400. Just recently noticed the bike lurching a small amount at mid range rpm's and some trouble stating and maintaining idle. Thought maby since the bike is stored outside there might have been some water that made its way into the tank. Added dry gas, did nothing, so we pulled a spark plug and it looked like it was running a little lean. It has quad mikuini(appologize if mis-spelled, me no good at english) carbs. Wondering if fuel mixture is something that often or ever comes out of adjustment on carbuorated bikes, and if so how should I go about adjusting? Any tips will rock.
 

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Kawpuke Extraordinare!
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Yeah possibly. If its surging at moderate rpm and light throttle settings and hard to start. There are fuel mixture screws under the bottom of the carbs near the float bowls. Most have an aluminum plugs that cover the screws. U will have to look under somehow and see if the plug is still there. If so your gonna have to take off the carbs and carefully/gently drill the plug and take a screw, screw it in a little bit and then use pliers and pull the plug out. Then tighten the screws down and count how many turns it takes until they seat. Then unscrew them and start with 1/2 turn more out than they were to begin with. Then go ride it and see if it helps. If not try a half turn more and see. If not you might have something in the pilot jets and in that case your gonna have to take carbs apart and clean them.
 

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if you haven't done any mods to the bike and it just started doing this, then after 12 years your carbs might need cleaned and synchronized. the cleaning will get rid of the varnish which will help the mid range sputter, and the synch will help out the idle. throw in a clean air filter and new plugs too. make sure the plugs are properly gapped. put in a new fuel filter too
 

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second chimp in space
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What KZ said.

Test the water: the bottom of the carb bowl will have a drain. My Mikuni carbs on my '82 GS550 had just a bolt, take the bolt out and you're left with a hole for the fuel to come out with. My current bike has a nipple you can put a tube on then a screw to let the fuel come out. Either way, drain the bowls into a dry and look at what comes out. If you see some separating in the liquid, you have water. My kawi once got at least a quart or two of water in it, and the stuff that came out looked like water, smelled like gas, and you could see something like putting water on a greasy pan. The bike didn't want to start at all. I took my carbs apart for cleaning, they were filthy. You might be able to just put some cleaner into the fuel and not have to take the carbs apart. You can get some at auto parts stores. If that doesn't help, you'll need to take the carbs apart and fully clean them. Then synch them.

It's possible that the idle mixture screws loose their adjustment after a while. Do what ZXLNT said to get at them. I think yours might be on top of the carb, not on the bottom, though. My Mikunis off my Suzuki had them on top, and the Keihins on my Kawi have them on the bottom. The ones on top are easier to get at. What you want to do is turn them so you have the highest idle. A 1/4 turn might affect the idle by 50 rpm or so (if you're close to what it should be), and it can seem unstable, but if you stare at it long enough and listen carefully enough you can tell if it's going up or down when you turn it a certain direction. Play with it until you have the highest idle, as that will be your most stable idle.
 
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