Bandit Carb issue!!

[mundgg]

2003 Suzuki Bandit 1200s 

Please help!! I bought this bike (bone stock) from a friend who was original owner. He put all of the 22,000 miles on the bike. He bought a Harley 2 years ago and this became the secondary bike. He still rode it, but it did sit more than before. It initially took a bit to warm up, so I figured I would inspect the slow jets eventually. (Turns out that could be common on these oil cooled bikes?)

Everything worked as it should when I bought it. The one problem I had was that I could hear the fairing "buzzing" MORE than I could hear the exhaust! I'm not ok with that, so I found a beautiful used Yoshimura slip-on (bolted right on to the 3 stock bolts!) Sounded great! Ran great! Rode it 150 miles with no issues except some popping on decel and gas smell (the "T" junction gaskets leaking a little) and figured it could be dialed in a little better with one size up jets to start, and new rubber seals on the gas inlet. 

This is where the issue started: my friend who owns a shop offered to break the 4 carbs apart and replace the gas intake o-rings and ultrasonic each one while apart. I have rebuilt many carbs (mostly Keihin) but I gladly agreed bc this is a royal pain! He took each one down the the core and soaked each one, (also careful not to soak the TPS on carb 4) since I got them back, no matter what jets (100 or 105 main & 15 or 17.5 slows) it has the same issue. 

Bike starts and idles fine, but bogs completely from 2k to 6k rpm, but then roars to life in the top range!? I have had the carbs out and tinkererd at least 30 times and no matter what idle air screw settings (1 to 3.5 turns out) or jet configuration, it is the same. (Re- cleaned carbs to double and triple check clean as well) The issue is the same with TPS connected or not. Also have tried at all levels of float height adjustment (12mm-14mm)

    I have figured out that if I ride it with the "choke"(enricher) lever slightly on, the low rpm is normal, but then that screws up the higher rpms. Also, if I remove the air filter, the original problem is magnified. (Falls flat on its face in low rpm throttle)

Sorry for long description, but I figured more info is better than less;)

- Jeremy. 

[TonyGee]

have you tried lifting the needles ? sounds a bit lean !!!!!  

as for the fairing noise, bin it and make it naked  

[fatblokeonbandit]

Have you got standard exhaust and air box???

[2scars]

FBOB is the go to on the Bandits.  But Tony's solution is the likely culprit.  I have found in my own tinkering that any change from factory will require some level of fuel adjustment.  Sometimes adjustment across all the circuits.  Pilot, needle, main.  It will be important to have a solid understanding of which circuit does what in the process of getting A/F correct, or close, across the rev range.

 

Good luck.

[TonyGee]

changing the air filter to a free flowing one can upset a 1200 Bandit, even pulling the rubber snorkel out will make a difference !!!!  

[fatblokeonbandit]

Just now, TonyGee said:

changing the air filter to a free flowing one can upset a 1200 Bandit, even pulling the rubber snorkel out will make a difference !!!!  

What he said........

[mundgg]

I have the stock airbox still fitted. I do have the original exhaust, but I really do not want to re-mount it. The bike ran well for at least 150 miles as soon as I fitted the Yoshimura slip-on, The problem arose when the carbs were split and ultrasonic cleaned (by a professional) 

I've been trying lots of different things. I even took the advice of taping off half of the airbox intake to "create more vacuum" in the airbox, it ran great down to the end of the street, until it proptly fouled the plugs out.  

Also, I've rebuilt, cleaned, and tuned many a Keihin carb in the last 25 years of riding and wrenching, but this set of Mikuni's is really driving me batty!!!

[mundgg]

We did raise the needles by moving the one shim from the top of the diaphragm (on the needle), to the bottom of the diaphram(on the needle. We bumped the slow and main jet 1 up (15 to 17.5 and 100 to 105) we did not mess with the middle jet (60) I have never seen a carburetor with 3 jets. Can anyone tell me what the purpose of the middle jet is for? My only guess is that it is for the "choke" or "cold start" circuit??

[Upshotknothole]

Sounds like needles to me, but that's just my internet guess. At this point I'd take the carbs back to bone stock settings and troubleshoot from there. Before you pull the carbs again, check and make sure that all your slides are still moving freely.

That bolt on muffler shouldn't have too much effect on the carbs, the stock bandit headers are pretty restrictive. Put the stock jets back in, AFR back to stock, and see what it does. Could be something wasn't put back together right, pinched diaphragm maybe. But chasing the problem with jetting on what's essentially a stock bike, is just wasting your time if there's something else wrong with them.

The later Mikunis had a lot of weird shit on them to get the bikes to pass emissions, and that TPS on the side of the carbs doesn't really do anything. You can leave it unplugged while working on the bike to troubleshoot it and it won't make any difference.

[Wee Man]

Worth a read.....

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

[DAZ]

Is it still on the original 20+ year old carb rubbers ? If so have you tried the spray of carb cleaner around them to check for air leaks either from the rubbers themselves or the o rings where they bolt to the head ?  It's quite possible that pulling the carbs disturbed/split something ,that would cause your lean spot and when you pull the choke it richens it up ...... ? 

Edited September 21 by DAZ
Bleeding predictive text

[mundgg]

 

We have sprayed starting fluid and carb cleaner on the boots with no changes in the rpms. (I wish it did! Then I could replace them!!)

Thanks for the carb tuning link "wee man" in that article, it would sound like my float levels could be the problem since it is from 2k-4500rpm where my bike falls flat on its face!!

[mundgg]

Also, good to know that the TPS is of no consequence and I can rule that out while tracking down the issue. I am hoping to have some time this weekend to pull the carbs again. (I'm getting VERY good at that at least!!!)

[TonyGee]

2 hours ago, mundgg said:

Also, good to know that the TPS is of no consequence and I can rule that out while tracking down the issue. I am hoping to have some time this weekend to pull the carbs again. (I'm getting VERY good at that at least!!!)

some people swear blind the TPS does make a difference but it does feck all !!!!  unplugged mine on my bandits and for the life of me can't tell any difference. 

[MrPositive]

On 9/19/2024 at 8:50 AM, mundgg said:

2003 Suzuki Bandit 1200s 

Please help!! I bought this bike (bone stock) from a friend who was original owner. He put all of the 22,000 miles on the bike. He bought a Harley 2 years ago and this became the secondary bike. He still rode it, but it did sit more than before. It initially took a bit to warm up, so I figured I would inspect the slow jets eventually. (Turns out that could be common on these oil cooled bikes?)

Everything worked as it should when I bought it. The one problem I had was that I could hear the fairing "buzzing" MORE than I could hear the exhaust! I'm not ok with that, so I found a beautiful used Yoshimura slip-on (bolted right on to the 3 stock bolts!) Sounded great! Ran great! Rode it 150 miles with no issues except some popping on decel and gas smell (the "T" junction gaskets leaking a little) and figured it could be dialed in a little better with one size up jets to start, and new rubber seals on the gas inlet. 

This is where the issue started: my friend who owns a shop offered to break the 4 carbs apart and replace the gas intake o-rings and ultrasonic each one while apart. I have rebuilt many carbs (mostly Keihin) but I gladly agreed bc this is a royal pain! He took each one down the the core and soaked each one, (also careful not to soak the TPS on carb 4) since I got them back, no matter what jets (100 or 105 main & 15 or 17.5 slows) it has the same issue. 

Bike starts and idles fine, but bogs completely from 2k to 6k rpm, but then roars to life in the top range!? I have had the carbs out and tinkererd at least 30 times and no matter what idle air screw settings (1 to 3.5 turns out) or jet configuration, it is the same. (Re- cleaned carbs to double and triple check clean as well) The issue is the same with TPS connected or not. Also have tried at all levels of float height adjustment (12mm-14mm)

    I have figured out that if I ride it with the "choke"(enricher) lever slightly on, the low rpm is normal, but then that screws up the higher rpms. Also, if I remove the air filter, the original problem is magnified. (Falls flat on its face in low rpm throttle)

Sorry for long description, but I figured more info is better than less;)

- Jeremy. 

New here but I have owned an ‘01 B12 (mk2) for about a decade and just rebuilt the carbs and threw on some pods. I switched over from your setup and enjoyed the bike like that for quite a while. Since you are using the original airbox, you should also use the stock air filter with a slip-on exhaust. Stock cv needles, with original donut sitting on five shims. If you’re using a cv needle with slots that would be somewhere near the fourth or third slot from top with the oem donut. You will also need to trim some length off the cv spring so overall it is about 109mm. Cv spring when you put it back in needs to be cut side down. You will want to go back to the 15 pilot and a 110 mikuni main jet, leave the 60 alone. Get genuine mikuni jets or you’ll create more issues. I like jetrus. Make sure your float heights are correct should be 13mm from base to top of float. Do not follow the way the book tells you to measure, or it will be wrong. You need to tilt the carbs just so the float comes off the needle. Set your screws to 3.5 turns out and go from there. This is all assuming your guy that broke them apart put them back together right. The bottom range is ran by the pilot and fuel screws until about 4k when the cv needles begin to lift. If you can get it to idle be sure the carbs are synced or that will mess up your other changes. Follow the book’s procedure for carb sync it, it worked well for me. 

Edited October 7 by MrPositive

[mundgg]

Ok, Thanks! Great advice from experience.  I have seen many other bandit forums where they struggled with the low end as well. Unfortunately,  no one has ever posted how they resolved the issue. A few have hinted that you should make sure the air filter is stock. Have you noticed that the air filter is crucial to making the bike run smoothly??  I've messed with many, many carburated motorcycles (mostly Hondas with Keihin carbs) and I would usually never even install the airbox or filters till it was running correctly! Are these Mikunis that sensitive to having the airbox and filter installed?

[MrPositive]

10 hours ago, mundgg said:

Ok, Thanks! Great advice from experience.  I have seen many other bandit forums where they struggled with the low end as well. Unfortunately,  no one has ever posted how they resolved the issue. A few have hinted that you should make sure the air filter is stock. Have you noticed that the air filter is crucial to making the bike run smoothly??  I've messed with many, many carburated motorcycles (mostly Hondas with Keihin carbs) and I would usually never even install the airbox or filters till it was running correctly! Are these Mikunis that sensitive to having the airbox and filter installed?

You should be able to sync the carbs at idle without putting the airbox on but i am not 100% certain because i only did that after i stepped up on jets. And before you start doing a sync it needs to be warm which can take a while with this bike.

Depending on where you live and elevation, people will have to make different changes. And even the bikes are all slightly different. You have to play around and make one change at a time and see what works. What i gave you should be really close to what you need to get your bike running well.

The problem you are describing is mostly due to your cv needle setup. You need to get the needle higher and reduce the spring tension up top so they lift sooner and richen up your mid rpm range. 

If you are running an unmodified airbox the stock air filter will outperform a k&n, uni or high-flow air filter. You will run too lean with a non-stock filter and you will not have smooth acceleration somewhere in the band.  

I am running a set of k&n ru-2922 pod filters on my bike right now. I did get it tuned pretty well but there is still a bit of a flat spot from 4-4.5k. Once you remove the airbox you need to make a lot of changes. I wanted to take mine off because it makes so much more room to work, but i may put it back on and do the setup i gave you because right now i don’t know if i can tune out the flat spot. If you want to simplify your life learn to live with the airbox and stock filter, it isn’t crucial but you need to go up on jets once you remove it due to all the excess air. I am running a 17.5 pilot, 150 mains, clips on cv needles at 4 with the stock donut and 3.75 turns out and idk the spring length inside cv but it is shorter than 109mm. And after all that, still have a flat spot, going to try 4 turns out and if that doesn’t work try a half or full step down to position 5 on needle. Or i might just buy a koso afr meter and install a bung on the midpipe to get it really right. In order to remove the airbox you will need to do a vent case breather and block the pair system off which is a bit of a nightmare but a doable one. I had to pull the exhaust off and the oil cooler and it was still difficult. 

Edited October 8 by MrPositive

[mundgg]

After being frustrated for most of the summer with this issue, I was able to find a decently priced set of carbs from a "running" B12 Bandit!! ($350! Not too bad since I have seen several selling for $600, $800, and some even asking $1200 for a "running" set!!) I popped the set in, and they worked fabulously!!! I am going to sync these when my Motion Pro sycronizer tool arrives,  but right off the bat, the low RPM issue is gone! I cannot imagine what was keeping the original set from working, but at least I now know that I am not completely crazy  

Now, I gotta make up for lost time and put some miles on this beast....

Thanks everyone who offered helpful advice! - Jeremy 

[McLean Racing]

Ive had this exact issue before on a bike that came in to my workshop after being worked on by another local bike shop, after alot of swearing and head scratching, it turned out that someone had put the needle seats in upside down before refitting the emulsion tubes. It rode like a brand new bike after that. Ive attached a picture of one. The tapered side needs to be the side that sits in the airflow. Hope this helps

Edited November 8 by McLean Racing

[Enjoythesilence]

16 hours ago, McLean Racing said:

Ive had this exact issue before on a bike that came in to my workshop after being worked on by another local bike shop, after alot of swearing and head scratching, it turned out that someone had put the needle seats in upside down before refitting the emulsion tubes. It rode like a brand new bike after that. Ive attached a picture of one. The tapered side needs to be the side that sits in the airflow. Hope this helps

Sadly i have done the same thing before-you live and learn.

[mundgg]

WOW! That is exactly why I posted on here, so I could find someone else who had the same issue! I knew it was something super simple or mis-installed!!! 

Thanks so much for sharing! I hope this thread helps someone else out who spends multiple hours (DAYS!) trying to figure out the same issue!

- Jeremy 

[mundgg]

Mclean! 3 of the 4 had the tapered side down!!! You were 100% correct!!! Thanks so much, and I hope this helps someone else that is just as frustrated!!!

- Jeremy 

[McLean Racing]

Just now, mundgg said:

Mclean! 3 of the 4 had the tapered side down!!! You were 100% correct!!! Thanks so much, and I hope this helps someone else that is just as frustrated!!!

- Jeremy 

No problem, theres not many carb issues i havent seen although im still learning new ones with this modern E10 shit petrol we have to deal with

[mundgg]

Agreed. I am fortunate to have non-ethanol fuel available at the gas station 2 miles away! I make sure to put that in anything with a carburetor!!!