Author Topic: Flat spot between 4-6k rpm (Read 4780 times)

sp2monkey · « **on:** February 23, 2007, 07:15:11 PM »

I've just got my 1st Bandit 4 and it has an annoying flat spot between 4 and 6 where it really hesitates and bogs down. As soon as it hits 6 it's like someone's lit a fire under it's backside and it seems to fuel ok from then on. If you are really tentative and let the revs rise gradually from a closed throttle you can move through it but snap the throttle too early and it coughs and splutters. Is 4-6 around the time when the fueling moves from pilot into main? Do you reckon this is a pilot / idle fueling issue.

I pulled the carbs off today and observed the following:

1) Pilots and mains appeared clear
2) Float bowls were a bit cruddy so I thoroughly cleaned.
3) Floats and needles looked good although I didn't measure anything
4) Two of the pilots had the rubber plugs over them and the other two had wooden dowels

forced in to block them.
5) The float bowl o-rings looked a bit worse for wear and one had split.
6) The drain screws were stiff and chewed.
7) There are no leaks when everything is together
8) Diaphragms and needles looked fine
9) The inlet and outlet rubbers are soft and pliable and do not appear to be leaking.

I haven't checked the plugs yet

I've ordered 4 new o-rings, 4 new drain screws and 2 new rubber plugs from my local Suzi dealer, should be here Tuesday.

The bike has the standard air filter and a 50mm stainless race slip-on.

After putting the bike back together, the problem is still there.

Any suggestions as to other things I can try in the meantime to iron out this hole in the fueling?

Thanks
Chris

sp2monkey · « **Reply #1 on:** February 23, 2007, 07:24:13 PM »

Forgot to mention:

It a 93 model on standard jetting 102.5 main, 32.5 pilot

Didn't check air screws, will do that tomorrow.

gsxr400 racer · « **Reply #2 on:** February 23, 2007, 07:40:26 PM »

there is 8 float oring 4 float bowl orings 4 fuel screw orings 4 rubber pilot plugs 4 orings under the emulsion tube , need to check emulsion tube wear needle wear too
carbkitcapital on ebay does the best and cheapest oring kit !

PitterB4 · « **Reply #3 on:** February 24, 2007, 01:15:37 AM »

A slight flat spot at 4k is pretty typical... even with a jet kit. It's a lean spot - wose in colder weather. Yours sounds worse that that, though.

pmackie · « **Reply #4 on:** February 24, 2007, 01:53:26 PM »

You already moved the needles to as rich as they will go, but you can try a couple of other things...

1. Air Screws as discussed. If you can't get into the range with the air screws, go up one size on the pilot jets.

2. You can increase the float bowl level slightly, say 1 or 2 mm over standard.

3. How's your ignition timing? If timing is too advanced, you can get a hesitation at low revs with a harder hit a higher revs.

4. Syncronize the carbs.

Thief400 · « **Reply #5 on:** February 24, 2007, 04:58:06 PM »

if you can raise the needles

pmackie · « **Reply #6 on:** February 24, 2007, 11:24:43 PM »

Oops...I just re-read your post and my response. I thought you had already raised the needles via adjustable clips...

Likely, you need to richen up the needle jet circuit. Raise the needles (lower the clip) if you have adjustable needles, if not, raise them with some shims. Best option is likely a jet kit. That in addition with the other items should help.

duane · « **Reply #7 on:** March 04, 2007, 01:25:43 AM »

Or...
Buy a jet kit from Factory Pro and be amazed how much it helps. The main jet is even leaner than the stock, but it's a good thing, hell, it's even a great thing. The Factory Pro kit has a different tapered neelde than the stock, that's something you cant change by stacking washers. The needle is what controls the all important midrange.