Strange long hang back to idle.

[DarkSyphonex]

I'm completely stumped here, anything you have for me I'll look into.

I recently bought a 2004 Ninja 250, one that'd been sitting for a long time with the tank full. Naturally, this necessitated a very thorough carb cleaning, which I carried out with no problem whatsoever. I also replaced the petcock with a brand new one, the old one leaked fuel. The bike has 6.5K miles on it.

The bike, once revved or blipped, will hover at around 4-5k rpm before taking an absurd amount of time to come back down to 1.3k. It does this without fault when coming to a stop at any stop sign or light. The bike responds to throttle inputs well and rev's just fine at all ranges, it just takes 8-10 seconds for it to come down to idle rpm's. The ONLY way I've found to get it to come down, is if I put it into gear and let out the clutch a little bit while holding the brake. Putting a load on the engine via the wheel is the only way to make it come down. Otherwise, when you're not giving it any gas or you've just slipped the clutch for a bit, it idles at 1,300rpm perfectly.

I'm not sure if it's normal, but the bike has never needed any choke to start up when completely cold, at any ambient temp from 60-90 degrees. Using any sort of choke, even on initial startup, will kill the engine.

Carburetor wise, both butterflies are visually synchronized. The mixture screws are turned out 2.5 turns. The throttle body is fluid and unobstructed. The cables are in great condition. There is no vacuum leak in the intake manifold because I sprayed the area on both the carb and head side while idling it and the idle never changed. The jets are all clean, both main and both idle jets.

I've no idea where the hell the engine could be getting air from when the throttle is closed, or why the hell it hovers at 4k rpm after giving it any sort of gas. Does anyone have any suggestions?

[maverick9611]

yup i had the same problem. pilot screws need to be adjusted. i just purchased a 2010 that sat for 7 seven years. after carb cleaning reinstall it was doing exact same thing yours is doing. i use ghostt pilot screw adjustment method
"Your initial setting should be 3 full turns out from the bottom, remember just slightly tighten them, don't go all Conan on them, as they are made of brass, which is soft, and can be damaged if over tightened.Then warm it up, slowly turn 1 side pilot screw in until the rpms drop, then back out till RPM's peak (and no further)* Twist throttle...see how it reacts...tweak to taste.
Repeat on other side... test ride. You're looking for best throttle response and transition from just cracked to 1/4 throttle opening or so.*

Thats a quickie, 10 cent tutorial on setting pilot screws."
oh and by the way welcome

[DarkSyphonex]

Originally Posted by maverick9611

yup i had the same problem. pilot screws need to be adjusted. i just purchased a 2010 that sat for 7 seven years. after carb cleaning reinstall it was doing exact same thing yours is doing. i use ghostt pilot screw adjustment method
"Your initial setting should be 3 full turns out from the bottom, remember just slightly tighten them, don't go all Conan on them, as they are made of brass, which is soft, and can be damaged if over tightened.Then warm it up, slowly turn 1 side pilot screw in until the rpms drop, then back out till RPM's peak (and no further)* Twist throttle...see how it reacts...tweak to taste.
Repeat on other side... test ride. You're looking for best throttle response and transition from just cracked to 1/4 throttle opening or so.*

Thats a quickie, 10 cent tutorial on setting pilot screws."
oh and by the way welcome

Well, after writing my post and feeling a bit restless, I went back to the bike and disassembled the entire carburetor again.

I re-cleaned every jet, pilot and main, and sprayed carb cleaner into every single circuit. This time, though, I did something new. I pulled out the mixture screws all the way, complete with the spring, washer and o-ring. Cleaned them all and stuck them back in. Instead of messing around with screw turns, though, I pulled them both back 2.5 times and fine-tuned both of them to be exactly the same by feeling the little nub that sticks out on the other end with my finger.

The bike still starts without the choke when fully cold, which I feel is odd, but holy **** it no longer hangs on the throttle! The choke circuits in the carbs are most likely gunked up still, but there's no way I can really clean them unless I put the whole thing in an ultrasonic cleaner. I feel this is probably the best tune the carbs are ever going to get unless I get an EFI conversion kit, but I'd much rather save for a new bike entirely. IT WORKS!

[maverick9611]

great job
intro yourself in new member section

[Racer x]

It sounds like the pilots might be a little tight. Even when cleaning they can still be restricted . It is a very tiny hole.
I say that because if you have a bike with the pilots very large. The bike will not stall cold with the choke off. You might want to go up a size on the pilots. Or try new ones.