Bandit 600 - weak midrange power - help!

[claytonia]

My 1999 Bandit 600S has developed a mysterious flat spot roughly between 4000-6000 rpm, where if i give it any gas under even a light load, it actually slows down. No missing, no strange sounds, just no power (although this morning when starting off cold, it was missing badly on 1 or 2 cylinders, eventually cleared out). On level ground or downhill, I can pretty much get it up well above that if I'm not trying to accelerate too hard - it will just lose power throught that rpm range and then pull stronger and pretty much normally from there on.

This has sort of come on gradually over the last 6-10 times I've ridden it, but become real noticeable the last 4 rides. Air temp, adding some choke don't make much difference. I though it might be a bad tank of gas, or maybe water in the gas, but its well into a second tank now. I'm thinking maybe the fuel filter, because it sort of feels like when you need to go to reserve. I've done nothing to it recently to associate this problem with (just changed the plugs, but no difference). I am running a Holeshot Stage 2 kit (pod filters, shimmed needles, fatter hi-speed jets, ignition advance), with a D&D slip-on. I've had this setup last summer without any problems. I think there are 3 shims on the needles, although it ran fine with 4.

Any suggestions would really be appreciated!!!

[tacoman]

I'm thinking you have bad gas.  My '97 B6 got sick a month or so back.  Ran real bad.  I filled the tank with fresh gas and dumped in a bottle of Chevron Techron.  I ran the bike a few miles to get the additive into the carbs then let it sit a few days.  Started right up.  It runs good now so I'm going to add some new gas and probably go with half a bottle of Techron.

[claytonia]

Thanks for the tip - I was thinking of trying that, before going to the trouble of cleaning the fuel filter. I'll give it a shot today.

[claytonia]

I tried the fresh tank of gas with a full bottle of Techron - no difference. Just yesterday I decided to try adding another shim to the carb needles (up to 3 now), and that did help quite a bit (its the only thing I could think of that would specifically affect the midrange). Its still there some when its cold, but when its wrmed up it isn't too bad, although there are still some hints of it. And I've had some mild pinging ever since installing the stage 2 kit and D&D can, and its still there, so I'm thinking maybe richer still. I may email Dale W. for advice - he always seems willing to help out.

[97RedBird]

I adjusted my floats for the same problem and it cleared up nicely.  I tried carb sync'ng, shims under the needle, A/F ratio, cleaning the filter, and new spark plugs.  The only thing that helped was the floats being adjusted.

my floats were measuring 18-19 mm, I made them 17mm.

Good Luck!

[claytonia]

Thanks for the suggestion! I was just pondering that possibilty today (and thinking that carb synching probably wouldn't make much difference), so its great to hear of your success with similar symptoms. I just wonder what causes them to get out od adjustment like that - it seemed to happen pretty suddenly, but maybe it was so gradual I didn't notice it until it got really bad.

As soon as it cools off some, I'm going to pull the carbs, clean them and adjust the floats. I'll let you know how it goes.

Thanks again!

[claytonia]

FYI - Its fixed and running great now! I did a quick cleaning/rebuild of the carbs (suggestion from Dale Walker - took apart, sprayed everything w/carb. cleaner, blew all the holes clear w/canned air); after installing them I checked the manifold bolts, and found one that was a good 1/4 turn loose (likely air leak there!); then synched the carbs (didn't need a whole lot of adjustment, but they were never done as far as I know). That was it - runs like a new bike now!