Sputtering when under load

My '80 1000 ltd Starts and runs good except when i get on it-somewhere around 6-7k it sputters like crazy. It will do this every time i get on it for the first time after starting up. After i do this once or twice it works like it should, then does it randomly. am i running lean/rich?

I have 15 pilot jets and 135 mains, no filters(pods coming soon) and v&h 4:1 with no baffle

also i have to have my idle very low, almost to the point where it stalls. if i have it any higher than 1k, it takes forever to come down in rpms.

No filters?

yea it was like that when i got it, havent had it too long. I have a '73 z1 and i took the pods off and put it on the 1000 to see if it made a difference, and made no difference.


by the way the 1000 has the 28mm's with accelerator pump

Sounds like the carbs could be dirty (sticking slides, partially clogged jets), and/or may be running lean and have an air leak. I'd clean the carbs first and then make sure nothing is causing the linkage to stick (i.e. lubricate and adjust cables), be sure the slides are closing fully and smoothly on their own. Examine the carb boots carefully for cracks. If no cracks are visible, mount the carbs being sure to evenly seat them on the intake boots as far back on them as they'll go, tighten clamps securely. Pull your spark plugs and check to see if the cylinder(s) are running lean or rich. Adjust air screw in the appropriate direction. If motor still takes a long time to drop back to idle, check for air leaks at the intake boots by spraying wd40 or carb cleaner into them. RPM will change if the boots are not completely sealed.
Hope this helps.

ive already had the carbs off 3 times, and they are spotless. New throttle cable, not leaking at the intake. ive tried the air mixture screws between 1 and 1 3/4 turns, and hasnt solved my problem. i havent checked the plugs, ill do so and adjust properly. It only does this when the idle is set around 1k or higher.

The main thing that bothers me is the sputtering, i can live with having a low idle for now.

Some carb jet needles have only one clip position, while others may have typically five clip positions.

If carbs at hand have multiple clip positions, what is current setting?

Good Luck!

Im not positive, next time i take them off i will look, but im pretty sure it only has 1 position. It acts like it is not getting enough gas, but there is fuel in the lines.

135 main is large step up from 102.5 oem main, but if bike performs well at wot, pulls redline in 5th with standard gearing (15/35), and doesn't foul NGKB8ES plugs, the 135 would seem okay.

As pilot circuit mostly influences lower rpm performance, it's likely not contributing to the mid-range sputtering where jet needle largely governs mixture.

Kawasaki.com seems to show 5 needle clip positions, but the image isn't clear, and I don't know. But earlier years' large fours had 5 clip positions with middle clip being the norm.

Could perform throttle chop during sputtering, with immediate plug reading. Meaning chop throttle, simultaneously disengage clutch and kill ignition. Coast to stop and read plugs. Carry a short length of tubing along that fits snugly over the plugs to remove them without burning fingers.

If sooty, suspect needle clip too low (maybe one clip below middle) which has raised the needle in the slide and resulted in too rich mixture. Would return the clips to mid-position.

If whitish, would first suspect fuel starvation for whatever reason, but where ample fuel is accessing carbs, then suspect needle clip too high. Would lower the clip one position, which raises the needle and enrichens mid-range.

Imo, the plug readings are best evidence of what's going on inside the combustion chamber under any given conditions. Otherwise, it can be mostly a crap-shoot.

Would assure plenty of fuel in tank, and test run with fuel cap ajar to assure no fuel starvation due to clogged cap vent. With bike parked, would also remove carb drain screw to assure steady full flow of fuel into carbs. Objective being to rule out fuel starvation as reason for a too lean running condition.

While at it, if not already done, would assure valve clearances being to specs, and double-check ignition timing and correct functioning of auto advance, and visually observe plug spark (for healty, fat blue spark).

Good Luck!

Another test, when sputtering, is to apply some choke to see whether enrichment improves or diminishes performance.

Does bike ever get past the mid-range sputtering to perform satisfactorily at wot? Or once getting to sputter, just can't overcome it?

Good Luck!

try a #20 pilot and see what happens...no filters/pods and an open baffle, 20 pilot is the place to start...you are probably wayyyy lean on pilot, that might explain idle hang up......if carb to motor boots are of unknown age and advancer for ignition hasnt had some attention for a while, you might want to rule them out.....good luck


oh, and those accel pumps might need attn......

If not already done, would also verify correct service floatbowl fuel level via clear tube test.

Otherwise perfect carbs may run lean with too low level and rich with too high level.

Good Luck!

well for one i am big on baffle rap and air filters they help monitor intake volume and exhaust back pressure to help keep a constant even pressure in the combustion chamber for even and smooth running. another thing is i am not sure if this has electronic ignition or points???? if points i would strongly recomend that you check the points to make sure good there and then check the clearance then get it running and check the timming. i have had this problem on my kz 650 and the left point plate was way out and the points and plugs where shot i have came to the conclusion that great spark and proper air flow should be checked off before going straight to fuel... let me know and as with the others good luck