K6 B1200 backfires through carb - how to fix?

[Octane]

Hello Everyone,
I'm new to the forum and have a burning question.
I have the following problem...
2006 B1200 Australian Spec bike (3rd gen - old SACS engine but new bodywork and suspension). 33,000km old.
Bike has just had the full tune up thrown at it. New plugs, new air filter, fresh 98 octane fuel, oil and filter change, thorough scrub down and polish. I have just finished balancing the carburettors at the specified setting of 1750rpm. They were out quite a way.
Brought them all into line and shut it down. That was last weekend. I started it today to double check my work. STarted first hit and idled alot better than it used to. Now it was still well under operating temperature but would still run okay without the choke out.
I increased the idle speed back up to 1750rpm to check my balancing efforts from the weekend prior and have noticed a random noise from cylinder 1 and sometimes 4 and even 2 & 3 occasionally.  :?:When this noise happens the vac gauge whould shoot back to zero and then back up again to normal type levels. Like an intenal sneeze inside the carb.
Running lean when cold? I hope that's all it is. I read that you can adjust the pilot screw to richen up the idle mixture to eliminate this problem but how do you know when you have it right? My carbs don't have the blanking plugs fitted either BTW.
The bike is standard except for a "Staintune" sports muffler and a K&N. No air box mod or anything.
I like to learn how to do things myself with guidance from others who know. I appreciate any help from other Members.
Cheers and thanks!

[rider123]

My guess is that the K&N filter and slip on without jetting is making an already superlean bike even leaner. The popping through the carbs is a sign of a lean condition. Do you have the mixture screw plugs drilled out? Turning them out a bit would help but you definatley will need to rejet or at the bare minimum put some shims under the needles for it to run well(still would be lean up top). You probably just lost some horsepower there. If you want to do it on the cheap (~10 bucks)try this:

You can drill the mixture screw plugs out(unless AUS bikes have them open) and turn them to 3.75 from lightly seated to start.

Put in 110 mains put the ORIGINAL filter in not the K&N.

ANd drill or cut a 1.5" hole in the top of the airbox cover.(The part you unscrew to change the filter) Keep the snorkle in

This gets you 90% of what a jet kit will give you and is a good starting point.

If you want to jet for a closed airbox and a K&N filter I would suggest starting around 105 at the minimum and at least a shim or two. Maybe 3.5 turns out?? The standard turns out on a stock bike according to the haynes manual is 3 turns from LIGHTLY seated(don't go crazy on those brass mixture screws) for Euro, Canadian and Australian bikes. THe poor US with their EPA just lists "Pre-set" :-)

If you want to do the bare minimum, popping in the stock filter, and setting the mixture screws out a bit and shimming the needles, until you have some jets will help alot. I've had a K&N filter and was trying to jet around it just for fun and with even with the extra 1.5" inch hole cut in half it was still a little lean on 110 mains, you're 4 steps leaner at 100 mains.

If it was my bike I would do this tommorrow: Pop the stock filter in temporarily, turn in the mixture screws untill they are lightly seated. Use a magic marker and a hand mirror so you can look underneath the carbs and make a line so that you can count the turns out precisely for each carb. I adjust the screws with a screwdriver bit and a cheap plastic dental mirror, it's tight but it works and its cheap. Count out 3 turns out for now so you are at the "stock" settings. It's going to be lean but be patient. Drive the bike until it fully warms up, at least 20 mins. Then turn the mixture screws out a 1/4 turn at a time untill the idle gets to the highest point before the idle starts going down again. For example you turn to 3.25 turns out, the bike idles higher, 3.5 turns out, higher still, 3.75 turns out, oppps idles less ok I'll settle at 3.5 turns out. Even though you will have more power at 3.75 turns out you are really just compensating for a lean main jet(or keep it there if you're happy with it for now). The correct setting would still be 3.5 turns out. Adjust the idle back to 1200 RPM. Another good test is when the bike is fully warmed up lightly blip the throttle if the RPM dips below set idle then recovers you are too rich on the pilot screws, turn in a 1/4 turn at a time. Alternatively if you lightly blip the throttle and the RPM hang for a bit then drop down you are too lean turn out the screws 1/4 turn at a time.

Even with the screws correctly set you will get some popping due to the PAIR emissions crap on the bike. Don't worry this is normal. Abnormally loud popping, or extreme amounts of popping will indicate a lean condition. For example my bike pops just a little but its more of a grumble and light little pops or burbling, if I turn the mixture screws in half a turn the popping gets a lot louder, cruise isn't as stable, etc. Every bike is different but my guess is with the stock filter in there and the slip on pip you have you'll probably end up around 3.25 or 3.5 turns out. You will still need to at least shim the needles. I got some from Dale but if there is a radio shack or a hobby store near you you can buy them. Depending on the thickness, I would put 1 or 2 shims on there as they will probably be thicker than Holeshots.

What shimming entails is putting shims underneath the needle seats to raise the needle(make midrange richer). I'm not sure if your bike has adjustable needles or not the Euro's do, Canada doesn't and the US doesn't. If you have a adjustable needles you lower the C-Clip a notch or two to richen up the midrange.

If you would like to have a quick look, and have a very small rachet set with screwdriver bits, you can take off number 4 carb cap without have to pull the tank off and lift the slide out of the carb and take a look at the needle. If the needle has a c-clip and indentations on the needle you can adjust it, if not you have to shim it.

BEFORE YOU TAKE OFF THE CARB TOP: WARNING

There is a little dinky o-ring at the front of the carb, under the carb cap, which gets lost very very easily. I highly recommend putting a rag or something up against the front of the carb to catch this if it falls off. Take the carb cap off CAREFULLY.





THis is what I have for reference:

17.5 pilots(stock is 15)

110 Mains (Little lean up top will go to 112.5's)

4 turns out on the mixture screws(may change with larger mains)

5 shims on the needles. (may change with larger mains)

Holeshot 5 degree advancer

I'm under 3000 ft altitude so I need it to be a little richer than most guys and I think my raggedly-ass hole I cut is a little larger than 1.5 inches and my Muzzy is a little more free flowing than the Holeshot can(2" vs 1.75").
I bought a jet kit from Holeshot which is great because Dale gives you tech support.
It's worth the $120 bucks in my opinion the bike just screams now.

If I find my jet kit as I need the 112.5 mains out of it, I could send you the 107.5's but its probably easier to call your local shop. Here are the part numbers for your pilots and Mains:

Mikuni Jets
Pilot: VM28/486 - 15's(stock)
Mains: N100-604 - 100(stock)

The second number after the first is the size they come in steps of 2.5. So my setup as I have 17.5 pilots(smooths cruise alot) and 110 mains would look like this:

Mikuni Jets
Pilot: VM28/486 - 17.5
Mains: N100-604 - 110


Addendum: Even with the pilot screws correctly set when the bike is fully warmed it may sneeze a bit when dead cold. THis is normal when the bike is cold. If you adjust the pilot screws to "cure" the sneeze when it's cold it's going to be super rich when warmed up. Do not attempt to adjust anything on the carbs until the bike is fully warm, at least 15-20 minutes of riding.

Also what octane grade is 98? If that's premium your just wasting money. The Air/Oil bandit series doesn't have enough compression to warrant premium gasoline. You should use the lowest octane available without pre-ignition or pinging. Using "Premium" is just wasting money on these bikes. I even have a 5 degree advancer on mine and while I can run well on 87 or regular when it is super hot out I get a slight bit or pre-ignition so I use 89 or mid-grade and get zero pinging and it runs great. Using premium for an engine that's not built for it could theoretically lose power and have more coke deposits from an incomplete burn. Premium gas doesn't mean you get more horsepower. Octane is an ignition inhibitor not a power rating.

[Octane]

Rider123, you are a Legend! I'm going to read this again after this post as I find it very interesting.
I will talk later on. Just for reference, we have 3 grades of petrol here. 91, 95 and 98. Depending on where you get your fuel, 91 USUALLY has up to 10% Ethanol added. I've seen pics of a bike in my local area which has had it's fuel pump eaten alive by that stuff.
Even when BP over here has stated that they are temporarily not adding ethanol to their standard fuel - sorry but i'm nut putting that acid into my fuel tank!. I agree 98 is overkill but the brand claim their fuel has a cleaning ingedient added - that's the only reason I used it. I usually just use the 95 - mainly to avoid the Ethanol of 91.
Pricing goes like this...
Last week 91 was $1.34 / litre. Add 10 cents per litre for 95 and add an additional 4 cents on top of that for 98.
Yes we are getting screwed over for fuel pricing.

Sneezing is considered normal when cold (for the bike that is) ? Well that's a relief.
Ok, so when adjusting the pilot screws, do you step through them say carb 1 thru 4 say .25 of a turn then cycle through again?

 

[rider123]

Yes, my pilot screws were all over hells half acre when it came out of the factory. One was 2.5, another 3, etc. What you want to do is make them all the same so you can unitize the mixture for each carb. So what I suggest is make them all 3 turns out for now. This is the quote "stock" setting according to the haynes manual. Now for you're setup it's going to be lean. Hell it's lean for a stock setup. Also For God's sake please put in the stock filter. The K&N flows way too much for the stock jetting and adding a slip on will only make it worse. Of course they won't tell you this at the bike dealership as they want your money. So when you start out at 3 turns for each carb. Turn out ALL the carbs 1/4 turn at a time. In fact I think it's safe to say you could probably start out at 3.25 turns out but its up to you. Wait until the bike is fully warmed up, at least 20 mins a short highway run will do it. Now turn out the screws 1/4 turn each time. It's a good idea to turn them out a 1/4 of a turn then ride around a bit so that it adjusts for the new setting and you can feel the changes. These adjustments are not instantaneous it takes a few secs for the carb to adjust. Also if you want to not burn your hand when adjusting number 2 carb screw stop the engine for a min or so and let the oil drain into the pan as there is a main oil line that your hand bumps up against to adjust the screw on the inner carbs.

As you turn the mixture screws out you notice 1 more power and 2 the popping will start getting less and less. If you do the little blip test like I suggested that will tell you if you've turned them out too much. If you are using the stock airbox and stock filter. Even with a slip on I don't think you'll need to go past 3.5 turns out but every bike is different. Put it this way if you are around 4 turns or 3.75 you've probably have gone too far. My guess, and this is only a guess is you will probably be ok at 3.25 or 3.5 turns out from lightly seated.

That's a bummer on the gas. In Canada we don't have Ethanol mandated by the government(at least my province). If you use ethanol(alcohol) you will need bigger jets. If you get some ethanol by mistake, don't fret these bikes don't have a fuel pump they are carbuerated not fuel injected. I have heard that ethonol used to eat through older carbs o-rings and such but I doubt it's a problem on newer carbs the main reason not to use ethanol for carbuerators is the jetting issue however minor. As far as "cleaning ingredients" go for gas it's mainly just marketing. IF you think your carbs need a bit of a clean just mix a little seafoam through the tank once a year.

Once ALL the carbs are set to where it's working pretty well you may want to then do a carb sync. Since you synced when the screws were God knows what, on a cold engine, they might be slightly out but this is totally optional as they will probably be totally fine for now until you get a jet kit or something. Once the mixture screws are were you want them then if you need to you could fine tune from there. For example my number 3 carb needed just a teeny more turn out probably less than 1/8th of a turn as it was slightly leaner than the other 3.

How did I know? Did I call Dion Warwicks Psychic Friends? Did JoJo Savard read my Tarot cards? Wiji board? Former Warsaw pact secret technology?

Nope this is where that ornery sneezing comes in handy and I had a little help from one of that infrared temp guage guns(On sale $29) When the bike starts up totally cold put a little pressure on the throttle(~1750RPM) with no choke on so you get the sneezing action you so love. Reach down with your other hand and feel the intake boots closest to the engine. As the cylinder "sneezes" you will feel the boot expand a bit in little puffs. If one of the cylinders seems to be "sneezing" more than the others a touch more out on that cylinders mixture screw will help that specific cylinder. Were talking like millimeters of travel(10ths or even 20ths) when turning. Don't go crazy and go "oh geez this carb needs half a turn". Another good way to see if you're either richer or leaner on a specific cylinder is one of those heat measurement guns.

When the bike is fully warm and idling, if a cylinder is running lean on a pilot the exhaust temp is going to be higher than a cylinder that is running normally. Alternatively a cylinder running rich is going to be slightly cooler than normal. So what you do is point the gun around 4 inches or less from the SAME point on each exhaust pipe, the readings will be totally useless if you take a reading from a different part of the exhaust. I like to take a reading from when the pipe starts to bend near the oil cooler. Now remember the inner exhaust pipes will be hotter as they also get a lot more heat from the engine. What you are trying to do is make sure the outer cylinders and the inner cylinders are within 20 degrees or so of each other.

So for example, I used the fahrenheit scale as the number of degrees are higher which gives you a more acurate reading. THe reading will jump around a bit on these things but you can sort of see what the temp is hovering around. My outer cylinders exhaust temp measured at the bend in the pipe hovers around 180F while the inner hover around 250F. Before I adjusted the screw Number 2 cylinder hovered around 250F and number 3 was 280F roughly. This combined with increased sneezing when cold, cruise plug condition give you an idea that maybe this cylinder needs just a squirt more gas on the mixture screw. And I do mean a squirt its probably like 1/10th of a turn. I hope this helps.

[rider123]

Actually this is important. I just checked out the Staintuned(bizarre name) muffler site and alot of the pipes there look like they have inserts. Is this exhaust you have free flowing or is it just schtick to pretend that you have a free flowing slip on? Measure the stock pipes exhaust hole, not the outer silver pretend exhaust, the actual hole that the gases come from. What is the measurement compared with the Staintuned?(What? Gizz stains from the power???) Make sure that it is actually larger because if it's closer to stock that will affect how much you richen the jetting.

THis is what I got from them but there is no clear picture of the exhaust aparture. From what I gather the insert is removable. Until you rejet I recomend you keep the insert IN, it will help a bit on the leaness of the bike. Looks like a nice pipe.

quote from "Staintune" This is the Bandit 1200 pipe They also have a 1250 pipe. WHich one is yours?

Performance:
In standard trim the Bandit pulls a maximum of 101 Hp.

Simply by bolting on a Staintune single system you will gain 10 Hp, pushing the yeild out to 111.7 Hp peak which on the dyno is reasonably impressive. But when you road test the bike you will be blown away by the responsive throttle and mid-range torque lift, or lift off in this case. There is no requirement for any engine adjustments, simply bolt on and enjoy the performance.

The Staintune also reduces those vibrations which are normally present through the pillion pegs, which is sure to please.

What about the noise:
The system designed for the Bandit has the Staintune removable restrictor system. The Staintune’s with the restrictors in put out a very nice deep note and with them out well…….. that’s a personal thing.

Restrictors in: 92 dba @ 4250 rpm
Restrictors out: 96 dba @ 4250 rpm



This is a little dubious:

"There is no requirement for any engine adjustments, simply bolt on and enjoy the performance."

111 Hp? Without jetting? I'd like to see the DYNO that proves it.

[Wrider]

Actually Staintune is one of the better aftermarket exhausts there is for street bikes.  It's meant more as Stay-in-tune.  Yes they have baffles, just enough to give the backpressure the stock cams on bikes need.
And as for backfiring through the carbs, that's not usually a lean problem (unless it's running super hot).  That's usually saying the valves need to be adjusted.

[rider123]

Nice good info. Yeah it looks like a good pipe. Hey I have a "Muzzy" which to me is kind of a wonky name, who cares as long as it works. As Wrider says until you get the jet kit it may be better to leave the baffle in there for now. You can always remove it later.

 I'm not sure I totally agree with the statement that the lean puffing is due to valves needing adjustment. I've had it puff after a fresh valve adjustment. My friends Bandit 1200 puffed when cold until he rejetted it. I can have Zero puffing when cold by simply turning out the mixture screws, if it was the valves the puffing would still be there. Many other Bandit Riders know about this behaviour. When my bike was brand new right out of the factory it would puff a bit when lean. I doubt every Bandit 1200 in the world has permanently out of adjusted valves that cannot be adjusted ever throughout the bikes lifetime. Since this puffing can be almost entirely cured with proper jetting I wouldn't go tearing up the engine just yet. Hell my bike is jetted and I still get a little bit for 30 secs or so, way less than stock for sure.

[Wrider]

I will edit that to say leave the baffles in there permanently.  One it will cut down on unnecessary noise, two it will provide better torque and horsepower everywhere except for the very top end, and three it will make it possible to tune the bike.  You have NO idea how hard it is to properly jet and tune bikes with straight pipes on them.

[Octane]

The bike is a new to me used machine. Unfortunately I wasn't given the baffle. I'd rather spend the $ on a Holeshot kit than chasing a baffle - unless there's one on ebay or something. I just had the Haynes manual turn up from the UK and have had a flip through.
I'm going to do the valves as soon as possible - just to make sure they're right. After that I'll recheck the balance and take it for a ride and start the mixture adjusting. I like this sort of tinkering except when I used to work on cars, you could buy a valve regrind gasket kit made by ACL (aftermarket). Can you get these sets for bikes too? I lost one of the vac plugs from the carburettors - looked EVERYWHERE for it. Spend easily 2 hours total looking for this thing. Gave in and bought a new one - $4.85 for one cap. 
I'll post pictures once she's tuned and polished out on one of our rides here. Gold Coast sounds nice.

[rider123]

You're probably going to need a 112.5 without an insert depending on how high you are from sea level. It's not a baffle its just a small insert which reduces the aperture of the pipe slightly. I received no noise DB killer on mine and I defiantly need more jet up top. I'm on 110 mains now and I'm under 3000 Ft altitude. The jet kit comes with 3 sets of jets, Dale suggests you start at 110 and then move up or down from there. Yes you can buy a gasket kit, I think it was about $130 for an OEM Suzuki one last time I checked, and aftermarket one will be cheaper. I would spend the money on Dale's kit first so you are all set up when you do your valve adjustment. I'm just waiting for the 112.5's to come in then I'm off to the races.

[Octane]

I'm at sea level or only a few meters above it. Average Winter Temp Low of 5deg C, top of 20deg C - Summer low of say 24deg C highest I've personally seen here was 42deg C. I just took it for a ride with a new Suzuki air filter fitted, mixture screws set to 3 and 3/4 turns. Once fully warmed up it's not too bad. Idles very smoothly at 1000rpm. When maintaining 60km/h (3rd gear) along a flat level road I can detect a bit of hunting or hesitation from the engine. Drop to second and pull the throttles wide open and the front end gets very light may have even lifted off - and it just hauls away. No complaints in that department.
Biggest complaint at present is the impossibly annoying loud buzz from the instrument cluster at between 3500 - 4000rpm. It's REALLY loud. If I press between the two clocks when its buzzing - it stops. I have check all the bolts and they are fine. Anyone with a Gen 3 bandit (2006) had this prob and fixed it?
I ride a 1250 Bandit also. To compare gen 3 to a gen 4 - the gen 4 is so much smoother and a whole lot less mechanical noise from the gearbox. The 1200's gearbox is VERY slick. Almost too slick. Sometimes cannot detect if I got neutral or not.

[rider123]

THe idle should really be set at 1200 RPM or so. At a 1000 the top end doesn't get much oil at that low idle. If you shim the needles a bit it should get rid of the hunting at higher rpm and improve cruise smoothness. If my FTP was up I could send you the shop manual. Do you have an FTP or location I could upload it to you? I have a 2005 but the engine should be the same. I had to take my fairing apart and put some rubber weather stripping to help kill some buzz on my fairing.

Also for the vacuum caps alot of guys here cut a few inches of vacuum hose and then cap them with an unused screw driver bit to make carb syncs in the future easier. Might be something you would want to try.

[Octane]

Well, I reset the mixture screws to 3 and 1/4 turns after last night riding it at 3 and 3/4. I feel that it now rides better. Did the whole blip the throttle thing and it returns straight away to the 1200rpm idle setting. No dipping or delayed return.
On a dead cold start thismorning it started first go and was none of the bad flatspots and surging it had with the K&N fitted. That really is interesting that a K&N in a standard airbox causes problems but a OEM filter in a modified airbox doesn't.
It now has a brand new OEM filter in. No signs of any sneezing when dead cold either  .
The vac tube idea is something I'm going to do. Once the Holeshot kit turns up I'll fit the tubes then. But first the valves must be done. Oh yeah - I filled up with 91 octane last night (apparently ethanol free) and it runs really well. No hint of pre ignition. We'll see in summer when it's freaking hot here. I swear people spontaneously combust some days!

[rider123]

Well no the K&N doesn't cause a "problem" per se, it just flows more than a stock filter. If you jetted your bike with a K&N filter it would be fine. But since the bike has the stock jets in there it's already lean as hell. Putting in a K&N filter only makes it worse. I imagine I could jet my bike for a K&N filter theoretically as I have one but the mains would have to be like 115 or 117.5 or something. And there may be a few flat spots to fix with the K&N filter.

[pmackie]

Carefull rider123...

here is the comment from Holeshot's website re: using K&N vs stock filter the the 2nd Gen 1200

"Note: We do not recommend any aftermarket air filter element with this jet kit. Extensive testing has found that the original Suzuki filter outperforms other high flow units in the new style air box. "

I believe that Ivan's Performance also recommends the stock OEM filter as well, and there are several guys on this board who have had problems getting the jetting right with a K&N filter installed. (However, there are some here who say that they have had success with a K&N.)

As Octane has observed, sometimes it seems that things just work better with a stock filter in a 2nd Gen Bandit.