Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: Demilus on April 30, 2008, 07:30:09 PM
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Alright. My 1992 GSF400N was running fine one day. The next day, I start it up and it is running very rough. It also didn't have nearly as much power as it used to. The exhaust is also much deeper. It seems like it is idling unevenly too. When I get into the lower rpms, it also started backfiring. I have no idea why it is doing this. It runs fine one day and then the next it pulls this crap. Of course I have a guy coming to buy it on Sunday. The day he checked it out it ran fine. I'm about ready to freak out right now. Any and all suggestions would be appreciated.
Thanks,
-Kurt
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dirt in the carbs. That's the first thing I'd suspect.
And did you let it warm up all the way and did it still show this behavior once fully warmed up?
Any smoke out the tail pipe and what color?
A
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I'm wondering if it's the carbs or the sparkplugs. Just took it for a spin and got it nice and warm. Turns out the left center cylinder isn't firing (cylinder second in from left side if you are sitting on the bike.) The header pipe was barely warm. The other three, however burned my fingers to the touch.
Any idea what it could be? I'm thinking fouled plug or dirty carb. Any chance it could be the timing? (I really hope not. That is one part of the bike that remains a mystery to me. I've yet to delve into the timing region.)
Thanks,
-Kurt
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surely not a timing issue. probably still most likely a carb issue followed by the plug. if those don't pan out, then move up the chain. Oh, check the spark plug wires and maybe it's the coil.
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How do I check the coil? And how do I check to see if the spark plug is working? Just take out the plug and try to start it? See if I get a spark?
Thanks,
-Kurt
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Well, what I would do is pull the tank and rig a temporary gas supply (be sure to close the vacuum line on the intake to cylinder 1), then start it up and start poking stuff. You can pull a spark plug wire (watch out, I always get a good shock) and see what happens. If #2 really isn't running, then pulling that wire will have no effect on the running of the engine.
So if you isolate it to one cylinder, then yes, check for spark (watch out... don't get shocked). You can pull the plug and examine it. You can stick the plug back into the wire cap and then hold it to the frame and check for spark at the plug. If you've got spark then it's likely a carb problem.
Did I mention it's most likely a carb problem? :wink:
Since you've got the tank off, it'll be straightforward to remove the air box. Then you can look down the barrel of the carb and see if it's pulling fuel (the plug should be in for this). You can stick your hand over the carb barrel and see if it pulls fuel (this will be obvious). Etc etc etc...
You may find that it's getting too much fuel (flooding) from a stuck float or fouled float needle. or maybe the pilot jet is plugged. etc etc etc...
If you find it's carb related, be prepared to tear down that whole carb: float bowl, float, pilot jet, main jet. cap, diaphragm, needle, clean it all really well, blow air through every orifice. run a stiff wire through every orifice etc etc etc.
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Alright, that's what I figured. I was just kind of hoping it was the plug so it would be nice and simple. I'm gonna tear down everything this evening.
Thanks again,
-Kurt
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this is worth a repost and a look for anybody wanting to dive into them carbs ; ; ;
http://forums.banditalley.net/index.php?topic=9697.0 (http://forums.banditalley.net/index.php?topic=9697.0)
Hope it hlps
Aid :bandit:
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Definitely check the simple things first. Due to the suddenness of this issue, I'd put about a 50% chance on a bum connection between the plug wire and the cap (pretty simple to check and fix - tons of posts here about it). The other 50% is on crap in the carbs...
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Alright, I took out my sparkplugs and the one in the second cylinder was fouled. I cleaned it up and got a spark out of it. then I put it back in the bike and tried it again. Still no firing in the cylinder. Took it out and it was soaked with gas. Wondered if my cylinder was flooded from before so I blew some air into the chamber and let it sit for a while. Blew on the sparkplug and got it to spark. Tried again and no luck.
I'm thinking stuck float in the carbs? Any ideas on how to unstick them if it is the floats?
I've pretty much resigned myself to tearing apart the carbs and cleaning everything.
Thanks,
-Kurt
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pull the offending float bowl, pull the offending float, look at the needle. sometimes the bit of dirt will be right at the tip and you can just blow it out. Sometimes it works down alongside the needle in which case you'll have to pull it apart to get it out.
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Change your orings if you have never done before :welcome:
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Theres nothing scary about pulling your carbs apart. Just work methodically doing one carb at a time making sure it is spotless.
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but always keep them connected as a bank of 4
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Alright, so I cleaned the carbs and now it won't start. I figured the carbs just didn't have any gas in them, so I just cranked, rested, cranked, rested, etc. That was last night. I tried the same thing this morning. Then I figured I'd look at the plugs and see if it was flooded. All the plugs were very wet. I blew on them and left them out of the bike for about an hour and a half. Put them in and tried again. Loud backfire followed by a fwooomph. Then it started making puttering sounds like it wanted to start. That brings us to now. Anybody wanna tell me what's going on?
Thanks,
Kurt
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Did you prime your carbs? Turn the fuel tap switch vertical (if there is a screw in the wait, remove it) for 30 seconds and try again. If this isn't clear search the forum. There's a good post somewhere on fuel tap operation.
It would take A LOT of cranking to fill the float bowls!!
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If there is a screw in the wait? There is a hole with threads between the res and the up positions, but no screw. Also, is there any way to see if my float bowls are full without taking the carbs off?
And I just checked my plugs again. They're soaked! What the heck?! Could My coils or something be bad? I get plenty of sparks. When my plugs are outside the engine.
Thanks,
Kurt
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THat hole with threads is where there would normally be a screw to prevent you from going from reserve to prime. I don't know why they do that, but whatever :annoy:
Anyway, you should be good without it in.
The single most important thing to remember when working on this stuff is... only do one thing at a time! Otherwise you'll never know what you did to fix something. WIth that out of the way, here's the primer on fuel flow.
The fuel tap works like this. Down position (all the way counterclockwise, 6:00) is normal "on" position. reserve position, a quarter turn clockwise from "on", or 9:00, should be avoided like the plague... seriously. it can suck the gunk from the bottom of the tank into the carbs with an ensuing disaster. The straight up position, prime, is one quarter turn clockwise from reserve, or 12:00. Only use this when the float bowls are dry.
The "on" fuel position only lets fuel run when the engine is pulling vacuum, that is running or cranking on the starter. This prevents fuel from accidentally just draining out all the time. Prime position just lets fuel run out all the time. If you've got a stuck float or float needle, it will just drain all your gas out through the carb and into the engine. Don't ever leave the bike in prime. Only use it for filling the float bowls when you need it and then switch back to "on". (caveat, there are times when prime is useful, like when you've got the tank propped off to the side so you can fsck with stuff with the bike running. Be sure to plug the vacuum line from #1 in this case).
So first thing to check is the operation of the fuel tap. Pull the tank and set it somewhere stable, fuel safe. With the tank sitting in it's normal configuration, and the fuel tap in the on position, there should be NO FUEL coming out anywhere. If that is the case, then good, otherwise, you need a new fuel tap. Put a tube on the vacuum inlet (small straight tube coming out of fuel tap). Suck on the tube a little bit :stop: (warning warning warning!! you may get fuel in your mouth!!! This is very bad advice! you have been warned!). Fuel should flow out the FUEL outlet and nowhere else. If you get fuel in your mouth, you need a new fuel tap, or at least a new membrane inside it. Go wash your mouth out and don't tell anyone you just gulped a bunch of gasoline. Gasoline is poisonous!! I am not responsible!! Don't mess around with this part!
If you want to, you can test the prime position. Fuel should just flow out the outlet.
If you've confirmed your fuel tap is working properly, then you can move down to the floats and float needles.
The floats move up and down as the fuel level in the bowls moves up and down. This pushes on the float needles and allows fuel to flow, or not, into the float bowl. The o-ring around the two tubular parts of the float assembly, where it plugs into the bottom of the carb body, prevent fuel from sneaking around the float needle. If they don't fit snugly, with no cracks, replace them. Probably smart to replace them anyway. The float needle must move freely in its plastic tube. It's a two part action. The float needle assembly slides in the plastic tube, should move freely. Then the needle itself moves in the assembly with a spring loaded action. That last little bit of movement is what closes the valve. If that doesn't move right, or there is any gunk in there, you need to fix it. You may have to actually pry the floats out of the frame and then pull the whole needle assembly out to get some of the grit out. Also make sure there is no grit in the fuel line or the passageways in the carbs themselves. Any grit there will eventually clog the float needle open. Finally, especially if you have to pull the floats out of their frames, you need to check the float level. With the float upside down and resting naturally under it's own weight, the top of the float should be 15mm above the flange where it sits in the carb. Google on adjusting float height for more details.
If you have wet spark plugs but are getting spark, you most certainly have a problem that will be solved by the above procedure. You are getting too much fuel, somewhere it is just running into the engine. If the above doesn't fix it, then you've got bigger problems or modifications that we don't know about.
good luck and keep plugging away.
A
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buy new plugs
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If there is a screw in the wait? There is a hole with threads between the res and the up positions, but no screw. Also, is there any way to see if my float bowls are full without taking the carbs off?
"Way" sorry typo... long week. If you plugs are WET you've probably got fuel in the bowls.
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One last question: After rebuilding the carbs, do I need to adjust them or have them tuned? This is keeping them in a block of four, not dismantling them completely.
Thanks,
-Kurt
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Well . i hate to tell you this but for me when my Bandit did the exact same thing it turned out to be the CDI box. Of course check out the simple things. Check coils, signal generator(off of crank)spark plug wires, spark plugs etc. After 2 months of looking it came down to being the CDI box inder the seat. Replaced it and walla.
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shudder....
it could be.
Demilus: often you'll need to synch the carbs after this kind of work. And the air-fuel always seems to need tweaking on mine.
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you havn't forgot anything from the carbs ? ?? ?
take plugs out, take away from bike, clean sparkys,
tap each carb on top with handle of screwdriver, not too hard this'll make sure the floats are not sticking.
press strater button MAKE SURE SPARK LEADS ARE OUT OF WAY. if you are worried about fire HAVE SMALL EXTINGUISHER AT HAND (CARBON DIOXIDE). as long as you take your time nothing will catch alight
suck on vacum pipe going to back of fuel tap, that'll fill each carbfloat bowel, use a pipe,
leave for few mins before putting sparkplugs in after checking gap (i think it should be 0.80 mm)
if it was working beforehand this will fix it,
i'm working on my carbs at the moment, before i removed them from the bikei ran out of petrol and because of the fuel tap needing a vacum it wouldn't quite fill the carbs up but did make for a expensive ciggy lighter