Bandit 1200 misfire

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Bandit 1200 misfire

Hello, I have a 1200 bandit year 2000 naked on a 'w' reg. The bike has a very slight misfire, only noticeable at low engine revs / little load. I have changed the plugs, air filter is fine (bike only done 9000 miles on clock), checked ignition coil resistance (fine), pulse generator resistance (fine), can't see any air leaks. I've had carbs off and cleaned all jets out also, but still no different. There is evidence of someone else (previous owner) been in carbs (due to condition of screws) which worries me. There is a scorpion end can on too. The jets appear to be standard. My next plan is to ballance carbs.(no gauges as yet)! Don't suppose it's a valve problem? Anyone got any thoughts which may help me along the way?

Cheers, Daws

If it's missfiring then it seems more likely to be a pilot jet is out than just the carbs needing balancing. You should balance the carbs before adjusting the pilot settings tho'. Once the carbs are balanced it's pretty easy to adjust the pilot screws by ear (well, apart from the burnt knuckles), at least so you can be sure whether this is causing the misfire.. I've also seen this on engines with either a valve problem or a damaged bore so I'd want to do a compression test first - it's a quicker job!

Hi,  A quick update, done a compression test this morning all 12 bar, or as near as damn it which sounds ok to me. Haynes manual says 12.5 Standard, with a minimum of 8 bar so I feel confident the head / valves / pistons are fine. When I stripped the carbs last night I noticed that pilot jet in carb 1 was a bit 'chavelled' (someone's been in before) and I also noticed that plug no 1 (all new a couple of days ago) still looked clean & new compared to other 3. Could this be due to this jet? I'm gonna renew it anyway. Tappy - do you think I'll be wasting my time balancing carbs, ie, would you expect it to run better than this if it just needed carbs balancing? I'll keep you informed of progress & thanks to Tappy for his thoughts.Daws

If it was just the carbs I wouldn't expect it to be miss-firing, but maybe I've just never seen a bike with carbs so badly matched - I guess it is possible, but it seems unlikely.You say you've had the carbs off to clean them - what have you checked? Did you check the position of the pilot screws? Float heights? Float fuel level?You wouldn't be wasting your time balancing the carbs - it's not a long job and it might also show other problems that could be causing the symptoms.The compression is reasonable and you say it's even, so if you balance the carbs you should be able to get all four carbs pulling the same vacuum. If you still struggle to get them to match then it could be that one of them is pulling air in elsewhere - possibly inlet stub, inlet stub gasket etc.If you get significantly more pulsing on one then there may be a problem with the valves (too much clearance - but if it was causing a misfire I'd expect a very noisy top end) or possibly the exhaust. As it's missfiring however you might find that you'll need to re-balance the carbs once you've cured the missfire. As always - absolute values or readings are not as important as trends or differences. The fact that plug number one is still clean is very significant - it sounds to me like there's just not enough fuel coming through to No1 at idle. To tune the pilot screws: Warm the engine (warm, not cooking itself) screw in the throttle stop slightly to give a fast idle (1600rpm) and adjust the pilot screw a half turn. Wait 30 seconds to see if the engine speed increases or the missfiring lessens. Then turn it another half turn and wait again. If 5 full turns hasn't cured it then turn it back to where it was and try going in half a turn etc. As the mixture improves, then engine will speed up. If you go too far it will start to slow, hunt or missfire. Find the limits in either direction, then set the screw to half way between those limits, then screw it in one half turn.Once you've done it on all the carbs, and burnt your knuckles, wait until the engine cools, then one at a time screw each one in until it seats, noting how many turns it took, and then turn it back to where it was. Compare the settings. If you want to be really finicky you can then even them out, rebalance the carbs, and adjust them again.Bear in mind that if you take too long then engine will heat up too much and you'll end up setting it too lean. And burn your hands even more.Apologies if I'm teaching you to suck eggs. 

Hi Tappy, I just noticed the time on your posting (around 1 am) could you not sleep!! Thanks for all the advice and I don't mind sucking eggs if it helps me out. I think I will try the pilot screws as you said. When I stripped the carbs I just blew all the jets out with the compressor. I have got some vacuum gauges on order (Morgan carbtunes) so I will balance the carbs through the week. If this doesn't work I will strip carbs again & check float height etc. I did try to determine whether the previous owner had tried jetting the carbs because someone's been in before. The pilot jets are correct at 37.5 according to Haynes, but I was puzzled with the main jets, they had lettering on which didn't  match the manual. I think manual says O-8 but mine had something else (can't remember now, 3 letters & I think one was a z?Again -  thanks Tappy for all advice  & get some sleep man!!Daws

You sure you were looking at the correct info for the mains?Every main I've seen is just numbers.  Don't know what carbs are on the bandit but Kehins I'd expect to see numbers in the range of 100-200, and Mikunis 300-400 odd. Don't be suprised to see different sized mains on the inner and outer carbs - my ZX7R as standard has 190 mains on no. 2 and 3, and 180 mains on no. 1 and 4.The needles can be allsorts of funky letters and numbers though - NOZH, N1EF etc.

Sounds like you need to get the bike on a dyno that will tell you if its the carbs.

Now this depends on what your definition of a misfire is, but wild guess here, based on experience of a 1200 bandit I had from new a few years ago is that it may be the emulsion tubes in the carbs are worn- they're the tubes that the slide needles move up and down in, very common on the earlier 1200s, and the needles in some TP  carb kits  exacerbate things, which from your posts, it sounds like yours may have-  mine wore emulsion tubes within a thousand or so miles with the Factory needles in.Have a good look at them, if they look even slightly oval, then it will make carburation from just off idle to approx 5k rpm pretty nasty , and no amount of chasing float heights , pilot jet sizes / needle heights etc will sort it. 

Hello TrickyDicky, That's an interesting point. Was yours the original standard tubes and if so how many miles on the clock. Also hows much to replace? Also hello to Shiny too, I will check out in more detail if I strip carbs again. Not done anything today (apart from a round of golf this morining). I was going to set air screws as per Tappy - might do it through the week when I get my vacuum gauges. Thanks to everyone for comments - will keep you posted.Daws

Yep, original std tubes, (99 model)  replaced first set around 5k miles, put 2 more sets in after that before 10k . Was a few yrs back, but seem to remeber they were  about £40 for the 4

Uprated emulsion tubes here: racing are the uk dealers for them.

As the missfire is only at idle & no throttle I'm sceptical that it's the emulsion tubes, or that a dyno would show anything - especially as it sounds like it's only No1 that's causing the problem. But if it's a common problem then it could be - I think it'd just be easier to do the other checks / tests first. But it sounds like it might well be worth replacing them if you have the carbs open again!! Don't forget that you can check the float height / fuel level without taking the carbs off (using a piece of clear tube on the carb drains).

Worth checking the Carb mounting rubbers to, they are prone to cracking and will let air in. Could explain why it is only on 1 cylinder and why the plug looks like it's clean (running lean) If it is and you need one let me know as I have one laying around the garage you can have.

Hi Gents, It's me again. I have just tried balancing the carbs, but to be honest i don't think they were out according to the manometer instructions / haynes. They were all within 2 cm/hg's of each other. I tried to improve but not any better I'm afraid. I've had enough for tonight (early rise this morning + a game of squash after work) so I'm knackered (getting too old for it)!! Tomorrow & plan to fiddle with my wife, err no, I mean the pilot screws & if to no avail I will be stripping the carbs for further inspection (float heights, emulsion tubes and a closer inspection of the Mains to ensure correct ones.)  Tappy - I notice you said you could check the float height by draining the carbs, could you explain? Is it just a case of comparing volume drained from each carb? I've not seen this method before.Thanks for comments & I will endeavour to keep you up to date.PS If emulsion tubes are worn will it be easy to see or will I need a magnifying glass?

A quick update, Carbs on the bench, stripped, can't see any evidence of worn emulsion tubes though i suppose it's difficult to tell. The holes look concentric to me and the needles themselves look / feel ok. What does concern me though is that I have a seized pilot air screw on No 2!! I cannot move it at all one way or the other, and now the heads just about knackered. Tried soaking in WD40 too. I guess this could well be my problem and I suppose the 'o' ring seal is chuffed and probably drawing air. Not sure how I'm going to get that out without a butchering job. The main jets are correct at 102.5.  Daws

Hmmm. Thought you said No 1 plug looked clean? What did number 2 look like? The seized in pilot screw might just be a red herring. Seems a bit suspicious tho' - especially as you think someone else has been in at these carbs before.Don't remember ever trying to drill out a jet from a carb - reckon it'd be a bitch of a job. Brass jets in cast magnesium. Unless you're close to a very good engineering shop I'd be thinking about picking up a second set of carbs off ebay...

Hi Tappy, I too think think it could be a red herring. I did try adjusting no 1 air screw, but it didn't seem to improve it. I've put carbs back on now, because it does run after all. Only other things i can think of which i haven't tried is measuring float height (couldn't think of an accurate method with carbs off. Is it possible the coils are faulty (maybe intermittent) even though resistances are good? Think I will try a 'spark junp test' as in Haynes manual - you know the one with a couple of nails in a piece of wood. Check how far the spark will jump. I can't see it been out but now I want to eliminate everything I can. Failing that, like you say it's another set of carbs.Daws

The coils can be dodgy with OK resistance "at rest". Almost certainly not the coils tho' - these would tend to be weak at idle, but also start to really fail when you get towards peak torque with the engine under load - giving a nasty missfire when you tried to accelerate etc. Plus the problem would be affecting two cylinders (coils are shared bewteen cylinders - usually 1&4 and 2&3).Rather than doing a spark jump test you could try removing one spark plug cap at a time to see if it makes any difference to the engine running. Each time you remove one the engine should audibly run onto 3 cylinders and slow down a bit. Don't remove more than one at once. And don't remove them for too long either - a few seconds should get the results. If you remove one and the engine note doesn't change then it may still just be a fuelling issue, but if the engine note changes for each one then it ain't ignition.Oh - and wear your bike gloves or use something insulated to pull the HT caps off. Modern CDI units can easily throw out 35K, which while it shouldn't kill you, will certainly let you know you're alive. To check the fuel height with the carbs on the bike, connect a piece of clear hose to the float bowl drain outlet, and raise the open end up above the carbs. Turn the fuel tap to "prime", then open the float bowl drain and the fuel will rise up the clear tube to the same height as it is in the float bowl. Clearly the bike need to be upright for this to work. Suitable tube is battery breather tube, or can be acquired cheaply form B&Q etc.

OK, it's been a while but I finally got the seized air screw out & replaced but it made no differance to the misfire. Today I have checked and reset the valve clearances & it still has the missfire.Beginnig to wonder if a valve is burnt (although a compression test revealed nothing).This is totally doing my swede in now. I have checked everything I can think of. Spoke to a Suzuki dealer today who said if the mixture screws were out it still wouldn't misfire. I don't like been beat but I am thinking of taking it to a shop to see if they can sort it. I have one last question - this bike has a scorpion end can & I don't have the original. Could this be the culprit?regards, Daws

I disagree with the shop - if the pilot screws are far enough out then it'll cause the engine to "phut" every couple of seconds. Fuel height could do the same thing. Is it this kind of a misfire?Have you tried adjusting them or just set them to the Haynes manual standard settings? Factory settings are pretty lean (for low emissions) so might be upset by a different end can.If you want to try adjusting them it's pretty simple, but you WILL burn your fingers (unless you've got small hands like me ):The only tricky bit is keeping the engine at the right temperature - too low and you'll end up setting the mixture too rich, too hot and you'll set it too lean. So get the engine warmed up, and if it's getting a bit hot switch it off for a bit.  Or use a big cooling fan in front of the engine - that can help too.While the engine is still cold, screw in each pilot screw one at a time until it's seated, and count the number of turns it takes to do this. Note it down so you can return to original settings. Once warm, adjust the throttle stop to give a fast idle ~ 1700rpm. Start with No 1 pilot screw and turn the adjust screw a turn outwards. Wait 10 seconds or so and see if the engine note changes. Keep doing this and counting how many half turns it takes until the engine starts to "phut" - at this point it's running way too rich. Then screw it back in a turn at a time so that you go back through where it was. Again listening for changes in engine note, speed, misfiring etc. Once you've found the two extremes, the best places for the pilot screw is likely to be somewhere in between.What you're aiming for is the fastest idle speed, and then usually lean it off half a turn. Depending on how much difference it makes you might need to back off the throttle stop slightly to bring the revs back down to 1700 rpm (you should never have to increase the throttle stop because if the revs are dropping you're moving the pilot screw the wrong way).Having said all that you should check the fuel level first. Fit a piece of clear plastic hose (B&Q do a range of diameters - battery breather hose is usually about right too)  to the float bowl drain. Form a "U" bend with the open end of the tube above the carbs, and tie-wrap or tape it in position. With the bike upright, open the petrol tap to "prime", and observe the level the fuel rises to in the tube - it'll be at the same level in the float bowl. You manual might give a setting for the height. If not, then it generally should be slightly lower than the float bowl / carb joint, and if one of them is significantly different to the others then that should tell you something.

Hi Tappy, I will try the fuel level when I get some pipe, this I have not done yet. Regarding the pilot screws, I have today put them back to 'haynes manual' 1 & 3/4 turns out.  I have fiddled with them trying to obtain the fastest idle with each one but I couldn't seem to improve it. I have realised though that when screwing out it is getting richer, not weaker as I first thought!! I checked the plug colours today (before I reset pilots) : 1&3 were very clean, as new but 2&4 very sooty. Probably pilots not set correct but I did wonder if the coil feeding 1&3 was faulty although primary & secondary resistance are within spec.I will try adjust again once I have checked fuel level.  Cheers tappy.

I would expect one coil to feed 1 & 4, and the other to feed 2 & 3. If this is the case and 2 & 4 are both sooty I wouldn't be suspicious of the ignition system. 

Hello, Yes tappy i will check that out, I may have got that wrong. I have tonight checked the fuel level as you suggested with the clear pipe. They are all 4 very similar height, at the joint of the float bowl. I did notice carb no 4 was slightly lower than the other 3 (maybe 3 mm). I fed all 4 clear pipes to the left of the bike so they were all side by side to make it easier to check. Would you say no 4 is ok as is?I have also checked all 4 spark plug caps (removed from HT lead) for resistance. I think they are ok:1) 11.25k   2) 10.85k   3) 10.5k   4) 12.5k. It doesn't give reading in Haynes manual for bandit, but compared to my FZR 600 manual which does I believe between 9-13k is good.I haven't had time tonight to fiddle with pilot screws. maybe Thurs/Friday now before I get chance.Daws

If they're all around the level of the float bowl joint then they should be about right. I wouldn't worry about 3mm at this stage. If tuning the pilot jets improves things then it'll be worth tweaking the No 4 float slightly, but if the pilot jets make no difference and the problem proves to be elsewhere then it would've been a waste of your time.

My 1200 mk1 does the same...  I suspect a leaky diaphragm in the carbs or an air leak at the carbs...



you may want to try don't get me wrong the lads on here know what there talking about but the bandit forum is full of guys who have the bike so may have seen and remedied the fault before.


DAWSDid you ever solve this? - just started happening to mine so am looking into it. It's a 2000 1200 s, apple of my eye stormer of a bike. Engine is not heavilly modded, but does have a stage 1 dynojet kit and a micron end can(e-marked)  added about 5 years ago.  Even when I had it new it was always a bit rough sub 2500 rpm, but it has been running beautifully for last few years but recently a slight creeping problem with this misfire on choke which got worse yeserday (I think affecting number 4 cyclinder (far  LHS). Fine at any rpm where the mains take over but a definite slow running problem with this ocaisional squeaky little missfire (like a loose carb with a small bit air getting in). Needs to have choke on or be under load to hear missfire. Went through usual electrical tests but all ship shape. Conviced it's carbs and will concentrate on slow runnign circuit. One thing - my bike is on original coils / HT leads and this did manifest on a very damp day - could be HT leads even though they check out (i.e. problems under load). Not going to renew coils / leads as a firsr step though as I still think it's carbs. These seem to be more succeptable to fuel going off and coating the carbs with varnish than any other vehicle I have ever owned - which is a good number by this stage! Will post here how I get on. Cheers, Guy

just aquired the same problem on my bandit 1200 k3,i can definitely rule out carb problems because i have changed the carbs for another set and balanced them,changed all coils with leads changed all the spark plugs and set all the valve clearences and the compression is 104 and the completely random misfire still occurs ....HEAD WRECKING....

 On tickover squirt a bit of WD40 around inlet tract..if it hesitates you got an air leak, also , have these got a potentiometer( throttle position sensor???) not sure , also one of them laser temp tools could be used to measure difference in exhaust temp...thats all i will add to this very extensive thread!!

I don't think you can "rule out" carb problems by just replacing them with another set. Maybe both your old ones and new ones have worn needle jets causing the rough running? Carbs do wear y'know...

Afternoon I have a 1200 SK6 and I have the same issue as the OP, @Daws, did you fix your slight missfire at idle..? ta.  

wow alot of chef's on this one so here's my ten penneth if your bandit has fresh air intake going directly into the cylinder head suzuki fitted minimum sized pilot jet to get through fuel immisions thus causing a slight misfire and hesitation on pull away which got worse as the bike got older,increasing the pilot jet size by one will cure the problem. regards  

@Corky, I assume you mean part "number 27" on the following diagram - - Can I also assume the stock PJ size is 15 so the next up would be 16..?  

yep part 27 and yes 16 i guess

I know that this thread is old but I'm having the same problem with my 1200 bandit and I'm wondering what did solve the problem?  

Hi folks,  I have the same problem also, on number 4.  Done all the usual also.  New plugs, clean air filter, new diaphragms in carbs, full carb strip and clean, compressions at 150 psi, balanced carbs, checked the rubber carb mounts, re-set valve clearances.  Bike is an 03, 6400k miles and well cared for. Pulling number 4 plug lead off on tickover does nothing, all others slow the engine down.  Checked spark on number 4 and it appears very strong.  Tried another coil on 1&4 (second hand though) still happens.  Now need a smaller helmet as I've pulled all my hair out. HELLLLLLLLLLP.  

150psi sounds very low to me for a bike with 6400 miles on it. Should be around 190. Were all the cylinders that low or just that one?

Hi Tappy,   All cylinders were more or less exactly the same i.e. 150 -152, and took exactly the same time to 'top out' at their max.  I noticed someone else earlier in the thread also had approximately the same figures. I had warmed the engine up first, so I'm going to check them cold later to see if there is a noticeable difference.  Obviously there may be a variance from one compression tester to another, but this was a brand new unit and as long as they measured the same, I had a comparison.  The annoying thing is that when on the road the bike goes very very well and shows o sign of a misfire hindering performance.  I have now ordered a brand new coil, albeit a pattern one, to see if that may cure it.

If you have no misfire out on the road then I don't think it's ignition - it's much harder for the ignition system to generate a spark in a cylinder full of dense, fuel-laden mixture than the barely filled cylinder that occurs at idle. It has the same ignition timing as #1 so that's not the problem. It has the same compression as all the others so that's not it either. So it really is looking like fuel. If it only occurs at idle then it's the pilot settings / airways or a minor air leak. When you stripped & cleaned the carbs did you blow through the air passages? Have you tried adjusting the pilot screw on that cylinder? If you have to adjust it a long way then it's probably not the long term cure, but if you can get it chiming in again then it would start to point you in a particular direction...

Hi, sorry been away for a while.  Yes, when I stripped the carbs every conceivable  orifice was opened, flushed and blown through with an air line.  I have since tried a new coil, even though in my heart of hearts I knew it wouldn't be the fault, but at least I have definitely put than one to bed.  I'm sure I have altered the pilot screw when running previously, but I will do it again to be sure.  I remember checking their position at returning them exactly after stripping them down, 3.5 turns out rings a bell. Thanks for your help, keep the suggestions coming.

Well once there's a bit of wear in carbs it's sometimes useful to adjust the pilot screws anyway for smoother running. Are the header pipes all happy and sealing correctly? And the 4-1 collector?

Hi guys, I just bought a 1998 gsf1200 with a race can (loud). I flushed out the tank and added new petrol mine kinda pops a little on the motorway between 2-4 thousand rpm. She,s only done under 11k.Do you think I should take off the carbs and clean them ? My mate says these race cans can impair the running if the carbs have not been dynojetted is this right and if so what kit would you guys reccomend?   cheers Dougie  

Have you tried blanking off the exhaust emission pair valve system? This can cause a misfire if the reed valve stops sealing properly.

I think my problem really is because of the race can, I did up the mains from 102.5 (stock) to 110 as someone on banditforum suggested and put the needle heights to 3rd one up from 4th but was told to put them back now I have put in bigger mains jets. Since moving the needle height to 3rd from top I lose power up to 2000rpm and its a little rough but bags of power there on up... On another point I had to put it on reserve the other day and it seemed to run a lot better despite cleaning out the tank when I got it could there be crap inside the main pipe in the fuel tap?

I am having a similar problem.
Although I can clean it up by opening the mixture screws 6 1/4 turns (too far as the spring is no longer pushing on it).

I have rebuilt the carbs and cleaned and checked everything over and over. The needle circlip setting doesn't seem to have any affect.

When opening the mixture screw are we richening it? If so I may have a vacumm leak between the carb and the cyl. (On all cyls. though?)

So... not sure if anyone is is watching this thread anymore but anyway... I think my float levels are off making all 4 carbs lean. I believe the pevious owner may have installed this kit : It says the float levels need to be at 11 - 11.5mm, I have them at 13.5-14mm (stock). Although it also says to measure them with the carbs upside down.  From everything I have read you are suposed to measure float height with the carbs at a 45* angle (floats just touching the needle valve).  That may be the extra 2mm right there.  Either way it is worth a try as I know I am real lean on all 4 cyls.

Hi folks,  sorry I haven't been on here to update things recently, but I do have some good news.  After exhausting every component to do with the ignition and fuel system, I decided to get the carbs off...... again.  Again I stripped them back to nothing, checked every component, which all seemed ok.  Cleaned everything out with carb cleaner and reassembled.....only this time I installed a dynojet kit as I had been talked into spending £120 by one of the many experts I had contacted.  Even as I was installing the carbs back on the bike, I was thinking "that's another £120 down the drain".  The bike is now sorted.  It goes like an absolute rocket, well as good as a standard1200 Bandit can anyway. Why??  I still don't really know as I remain suspicious about the wisdom of spending on the dynojet kit, and I do wonder if I inadvertently cleaned something out that I didn't notice, doubtful as I was meticulous in doing the same job both times.  As my bike is totally standard, including the exhaust, I fitted the nominated jets that came in the kit (you get 4 different sets of jets in the kit), the new needles etc, set the float heights as per the instructions (upside down, not at 45 degree angle) and hey presto! Bike is riding beautifully, clean throttle response, great acceleration and top end speed. So to end this sorry tale from my point of view, I still didn't find the 'smoking gun' type of evidence as to the cause of my problem, but it was cured at the time I installed the dynojet kit.  Coincidence?......I'll let you decide. Thanks to everyone on here that gave there assistance and advice to me.

That's quite interesting. A few years ago my mate fitted a dynojet kit to his otherwise standard bandit 600 and it made it quite fluffy and unhappy. In your case it sounds like the dynojet kit has compensated for something so if the exhaust is standard then that would suggest a problem with the air filter, housing or carbs etc. Still - as long as it's going like a rocket


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