hesitation below 3k rpm

[gallant_pilot]

hey guys!

bandit 400 gk75!

after fixing my engine and setting the carbs to stock setting !

the bike hesitates to take off below 3k, i must open the throttle and pass 3 k and then release the clutch lever and then it goes fine.even while i am riding in other gears it does the same!

any idea?

[greg737]

that's not much information, probably not enough to make a sound or helpful (internet forum type) judgement of your problem.

but... if you have to rev the engine way up to get it to produce enough torque to motivate the motorcycle, then it sounds like the engine is way down on torque (in an engine that doesn't produce much torque to begin with, especially in the lower RPMs).  So the issue of possible low compression (in 1 or more, or all, cylinders) is what comes to mind here.

(the description of your problem sounds very similar to another forum member's experience with trying to ride his Bandit 400 at very high altitude.  same result, having to rev the hell out of it then release the clutch just to get it going.  the high-revving Bandit 400 engine is very sensitive to low O2 and atmospheric pressure at altitude, which has the effect of greatly reducing its torque production.)

[gallant_pilot]

i rebuilt the top end recently and checked the cimpression. its 850 Kpa on all 4.

i am luving at 4100 ft. is there any other reason, like carbs perhaps?

[greg737]

Well, living at 4,100 feet above sea level but tuning your carbs from instructions provided for sea-level operation could be your problem.

Running over-rich air/fuel ratios will give you that "down on torque" feeling. 

The truth is that your Bandit 400 just isn't going to be capable of producing the manufacturer's listed amount of horsepower and torque at 4,100ft elevation.  First, there's less O2 at that elevation and second, the atmospheric pressure is much lower which is a significant issue when your engine has very small, high-revving cylinders.  The atmosphere is much slower to react to the pull (vacuum) of the tiny cylinders (example: a single cylinder 400cc bike will be much less affected by altitude than a multi-cylinder 400cc bike).  You're just not going to make 53 horsepower at 4,100 ft and tuning your carbs for sea-level is just going to hurt the power output even more.

In your situation I would want a wideband oxygen sensor on the exhaust so I could do some data-logging and diagnostic work.  I have installed this setup on my Bandit 400 fuel injection project bike.