Runs lean?

[ilanidrac]

Hello,

I have a 2003 Ninja 250 that my brother will hopefully be using, but it seems to have an issue where it is very slow to come back down to idle. With the enrichener on, it starts to rev higher as well, so I assume it is running very lean.

I already replaced the manifolds and cleaned the carbs and all that basic stuff, but I am not sure what is going on. Everything seems to be in order.

I am wondering if its the jetting of the bike now. I tried to look it up, but I can't seem to find what the stock jetting of the bike should be. I will be taking the carbs off tomorrow to check them and want to compare against what SHOULD be in there. Bike is 100% stock. Semi related, are there specific jet sizes that are recommended here for the stock bike that might differ from the stock jets as well?

Aside from that, any idea what could be causing the slow to come down to idle/lean issue? I can't seem to find any air leaks either.

Thanks for any help/

[jkv45]

That's typical of a vacuum leak. Spray something around the intake boots (between the carb and the engine) and see if you get a change in RPMs.

As far as carb adjustments go, if you remove the carbs you will want to remove the caps on the idle mixture screws so you can make adjustments - http://faq.ninja250.org/wiki/How_do_...dle_mixture%3F A good base setting is around 2 1/2 turns out, but it's usually set leaner (less turns out) from the factory.

This section may have some answers - http://faq.ninja250.org/wiki/Intake

[ilanidrac]

Originally Posted by jkv45

That's typical of a vacuum leak. Spray something around the intake boots (between the carb and the engine) and see if you get a change in RPMs.

As far as carb adjustments go, if you remove the carbs you will want to remove the caps on the idle mixture screws so you can make adjustments - http://faq.ninja250.org/wiki/How_do_...dle_mixture%3F A good base setting is around 2 1/2 turns out, but it's usually set leaner (less turns out) from the factory.

This section may have some answers - http://faq.ninja250.org/wiki/Intake

I should also mention we backed those screws out probably 3 or 4 turns and they barely made a difference. I will check again for the RPM changes, but hopefully with the new boots it wouldn't be the issue.

[Ghostt]

How did you clean the carburetors? Did you verify all fuel circuits were clear with a air compressor?

Your initial setting should be 3 full turns out from the bottom, remember just slightly tighten them, don't go all Conan on them.



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.**

[jkv45]

Originally Posted by ilanidrac

I should also mention we backed those screws out probably 3 or 4 turns and they barely made a difference. I will check again for the RPM changes, but hopefully with the new boots it wouldn't be the issue.

That would suggest the passages are plugged or the o-rings on the idle mixture screws are deteriorated, ripped, or not in the correct position.

[choneofakind]

1) clean carbs thoroughly as suggested.
2) check for vacuum leaks by looking for broken hoses, spraying boot connections while running, etc.

Stock idle jet is keihin 38, stock main is keihin 105.

The enricher we have will raise the idle. It's supposed to do this. It is an enricher that draws both fuel and air, not a choke that just reduces air.