Total Motorcycle Community Forums

Been doing a LOT of reading of the FAQ and the forum (and some googling) and I haven't run into a solution just yet. If this question's been answered, feel free to point me in the right direction to find the post.

I recently purchased an '01 Ninja 250 that was not running. The bike looked in pretty good shape.

I pulled out the carbs, cleaned them thoroughly with cleaner and a small copper wire, measured and adjusted the floats, put the idle mixture screws at 2.5 turns, reinstalled the carbs, and then used a jumper battery to get it started (bike battery was dead).

The bike starts strong, but idles around 3000 rpm, and then (after about 3-5 minutes of running) starts to die unless I open the throttle.

I thought I had adjusted the floats wrong, so I pulled the carbs again, re-measured (everything looked good), and cleaned a few jets again just to be sure. I reinstalled the carbs, and this time it wouldn't start and had gas coming out the carb overflow tube. I figured some debris had gotten under one of the float needles, so I pulled the carbs one last time, and cleaned again.

Now the bike is doing the same thing as I mentioned earlier. Starts, idles at 3k for a few minutes, and then dies.

Thanks,
Kyle

A little more information:

I thought the floats might have had a crack in them, so I submerged them in water and checked for bubbles. None.
The float needle is a regular cone with no visible cracks.

Is it possible there is an air-leak at the float bowl mating surface? The rubber gasket is unbroken, but whoever last worked on the carbs before I bought it used some blue RTV (I'm guessing) with the gasket.

I believe I adjusted the float correctly (17mm), but I've never done it before, so I can't be 100% sure.

Any help would be very appreciated.

I know it probably sounds stupid to someone who obviously knows what they're doing like you do, but check to make sure the choke isn't stuck open. If it's stuck open it'll do exactly what you're describing and end up fouling out your plugs.

Thanks for the tip. I will check the choke cable on the carbs when I start up next time.

I'm also going to try leaning out the idle mixture by screwing in a half turn and see what happens.

Check for leakage at the front of the carbs.

Checked the choke cable, everything looks good there.

By front, you mean the carb-to-engine boots? Should I use the ol' WD-40 and check for bubbles method, or do you have a better one?

I did a bit more work this morning. I adjusted the idle mixture screw to roughly 2.0 turns out (from seated), and she seemed to want to die immediately. So I backed out to about 2.25 turns, and that seems to be the best I've gotten out of her yet. She still wants to die, but right before the engine stumbles, it hangs around 1k for just a second or two.

Still at a loss.

While the engine was running, I sprayed starter fluid on the vacuum hoses and mating surfaces of the carbs, with no effect on the engine speed or sound. I sprayed a little into the intake, just to make sure I'd know what to listen for, and to my surprise, the engine LOST power. I thought ether would make it flare.

Hmmm sounds like you're running rich to me, especially with that last symptom.
Are you running the stock jets? (Yes this will sound stupid too, but are the pilot jets in the carb? Done that myself before.)
Are there any mods to the intake or exhaust? What altitude are you at?

Definitely rich. I can smell the gas on the exhaust. As far as I can tell, all jets are stock (and installed). No mods that I can tell to intake or exhaust. I am in Alabama, which doesn't see much elevation change at all. Can't be much higher than sea level.

I know the symptoms look like a misadjusted float, but I don't think that's the problem. I noticed the idle mixture screw is supposed to have a spring, metal washer, and o-ring, but when I worked on it, only the screw and the spring fell out of the body. Either the washer and o-ring are stuck in there, or previous owner took them out and forgot to replace? I'm going to tear it down again, and check.

I'm betting the O-Ring and washer are MIA, especially if you didn't have to drill out the mix screw cap. They're very small and easily lost. If you can track down a 90 degree screwdriver (goes out about a foot and then makes a 90 degree turn with a flat blade about an inch or two away from the angle) then use that to adjust the mix screws while they're on the bike to see if it messes with the idle speed at all. Fair warning, Craftsman doesn't make one, Harbor Freight doesn't carry one, only Snap-On and Matco make them, so you gotta track down one of those guys driving around in a truck to order one.