Hi, guys!
I`ve had some problems with my ride lately - it tends to die on one cylinder at middle rpms when accelerating hard - if you just slam in the full throttle, at about 4000-5000 it begins to stutter and won`t go much faster if you just stay at full throttle - to accelerate you must quite gently increase the throttle to get over to 8000 w/o issues. If it dies or stutters, you just release the throttle and it kicks in again. It`s especially annoying and noticable when accelerating fast in 4th gear. This has been a problem of my bike since i have it, but as the time goes, it has become worse and worse. The carbs are clean and the valves are in specs. I`ve changed the sparkplugs, ignition coil wires, switched coils in place (eletrical resistance of both coils is 4,4 ohm, if it does matter) - nothing changes, the same thing (left cylinder stutters). I tend to think it is the electrical problem and even more, i think it could be the igniter block at fault - it is solid age and the contacts might have got unreliable and etc.  

So if i`m right, would it be possible to replace it with gs500 igniter? As the engines are quite similar (except for the head)? Or maybe i should carefully take the old block apart and look if it can be fixed? What do you think? Any ideas or conclusions welcomed!

Oh yeah, excuse my bad bad bad english! I`ll try to explain more if something is unclear.

Thanks!

Quote from: tres^if you just slam in the full throttle, at about 4000-5000 it begins to stutter and won`t go much faster

I have heard of a similar problem when the carburetor slide rises too fast.  It's possible that the mixture becomes too rich, too quickly, and causes the plug to gas foul.  If that were the case, then the problem may be related to the pair of holes in the bottom of each carburetor slide.  When that is the problem, it may be fixed by putting a nylon screw in one of the two holes in the bottom of each slide.  This should slow-down how fast the slides rise after you slam in the full throttle, by a little bit.  That may not solve your problem, but may hide it, and the bike may ride better.

The real problem is why it happens only on one cylinder.  I would look for anything which makes one cylinder run richer during sudden acceleration.  For example, the carburetor float levels may not be identical.  You can check them against each other using a pair of hoses, one hose connected to each carburetor drain screw.  If the problem cylinder has higher float level, then that could be part of the problem.  Also, if the idle mixture screw is giving more fuel to the problem side, then that could cause the problem to affect the "bad" cylinder more.

I would start with comparing the float levels of the two sides; then check the carburetor slide holes for obstruction; while you have the slides out, check the diaphragms for pinhole leaks (hold the diaphragm up in front of a lightbulb and look for light coming through).

For the electrical system, I would check the spark on each side using a tool with 9mm gap:



...and see whether the spark looks weak on the bad side.

If all else fails, I would try running a little leaner on the "bad" side, such as by setting the float a little lower there; or try using a hotter sparkplug, and see if the problem is changed at all.

(Sorry if I am only suggesting things you have already tested).

EDIT: PS-Does the GSX400e have 4 valves per cylinder, or 2 valves per cylinder like our GS500s?  There are many GSX users on the http://thegsresources.com website, who may also be of help.  I think most of them have the 4-cylinder GS or GSX.

Hi, Rema1000!
Thanks for your reply. Actually, your suggestions are very worthwhile! I wasn`t aware, the float level has so high impact on riding performance and can cause such behavior. It for sure could be out of balance, as i have taken apart carbs for several times and probably adjusted something wrong. As i remember diaphragms were perfectly ok. I`m not sure what you meant with the holes in the slides, can`t think which exactly.
I`ll definitely check and adjust the float level if necessary.
I tended to think it is an electrical problem, because of one morning after rainy night i had huge problems starting my bike. It stays outside covered, cause i have no space in garage which is being rebuilt for some months already. After i started it by pushing, it ran very weak. I rode to work with rpms below 3000 -4000 (by feel, cause i have my tachometer destroyed in accident), because anything higher and it would die on one cylinder. When i got to work, i took off the igniter block, regulator and coils. Dryed them all on electrical battery (thing to make room warm ) for some hours. And put them back before going home. Now it would run quite ok if not accelerated quickly. When accelerating fast it stutters (not so bad, you can still speed up quite quickly but anyway) and sometimes (not so often) dies on one cylinder. I prolly should have mentioned this in my original post. I`d really like to get this problem solved so i could enjoy my ride much more.

And also i have noticed, my top speed has decreased over time. When i bought it ib summer last year it was about 160km/h on speedometer (more like 170 -175 in reality), but now it`s more about 140-145 on o`meter. :/ Riding in 6th gear after 110km/h is quite vibrating, too. This could be related to THE problem i think.

Yes, gsx400e has 4 valves per cylinder. Very nice bike for city riding and some fun if ambitions are not too high.