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.