ninjette.org - View Single Post - New 250 owner. Idle hangs at 4,000 rpms. Carb issue?

anarchyx34 · August 31st, 2015, 05:19 PM

OK. So I created a few videos showing what it was doing. Sorry if it's hard to hear me I didn't realize how noisy everything was.

https://vid.me/mDoj
https://vid.me/UfvQ
https://vid.me/mo6j

So then I decided to dive in a take the carbs out. Pretty easy actually except for that motherf&CKing airbox. Anyway, as far as I can tell, the carbs are spotless, as they should be considering I have paperwork showing they were recently rebuilt. Here's what I checked:

-Pulled pilot jets, I can see through them. They look perfect.

-Squirted carb cleaner down pilot jet hole, and it flows easily into the throttle bore through the tiny holes. I don't have a piece of wire small enough to fit in there but I'm satisfied it's clear.

-Checked air mixture screws. One was 3.5 turns out, the other was 2.5. I reset both to 2.5.

-Checked float bowl height. Seems to be about 17-18mm, exactly the same on both.

-Visually checked carb sync. They seem dead on, and I generally have an eye for things like this. There's also a yellow paint mark on the screw which tells me that it was either never touched or set and marked meaning don't mess with this.

-Checked vacuum slides (what do these things do exactly?). They move smoothly, return closed quickly and there's a satisfying sucking sound from the diaphragm.

Here's what it looked like:

So I decided to put it back together just enough to get it to run and see if anything changed. I couldn't get the airbox boots on (anyone got any pointers here?!) but I figured it shouldn't be a problem to run it without the airbox. Kinda normal to do it on cars when you're in the diagnostic process.

It won't start. I definitely have it primed as I opened the float bowl drain that I could reach and fuel was coming out. I'll assume that's the case for both of them. I get sputtering with the choke fully on, but nothing with the choke off.

I exhausted the battery, so I grabbed the battery out of my scooter (losing the terminal nut in the process) and hooked it up and kept cranking. Nearly exhausted that battery too so I gave up for the evening.

Could the airbox not being connected cause it not to start? Are these generally that much of a pain to get running again after servicing the carbs?

Edit: Some added questions.
I've done a bit more reading on how these carbs work. If I understand it correctly, the vacuum slides act as a secondary throttle? Meaning, that when the engine is off they're closed. Engine is idling (full vacuum behind the butterflies) they open, but what happens when you go full throttle and lose all vacuum? They close again? Or does the tapered edge cause the air flowing through the carb to force them open?

Also, does the enrichener (choke) completely override the pilot jet & air-screw setting? Or is it a combination of the two? In other words, could my setting of 2.5 turns out on both actually be too lean for it to even start, even with the choke fully engaged?

August 31st, 2015, 05:19 PM	#11
anarchyx34 ninjette.org member Name: Joe Location: Brooklyn, NY Join Date: Aug 2015 Motorcycle(s): 04 EX250 Posts: 30	OK. So I created a few videos showing what it was doing. Sorry if it's hard to hear me I didn't realize how noisy everything was. https://vid.me/mDoj https://vid.me/UfvQ https://vid.me/mo6j So then I decided to dive in a take the carbs out. Pretty easy actually except for that motherf&CKing airbox. Anyway, as far as I can tell, the carbs are spotless, as they should be considering I have paperwork showing they were recently rebuilt. Here's what I checked: -Pulled pilot jets, I can see through them. They look perfect. -Squirted carb cleaner down pilot jet hole, and it flows easily into the throttle bore through the tiny holes. I don't have a piece of wire small enough to fit in there but I'm satisfied it's clear. -Checked air mixture screws. One was 3.5 turns out, the other was 2.5. I reset both to 2.5. -Checked float bowl height. Seems to be about 17-18mm, exactly the same on both. -Visually checked carb sync. They seem dead on, and I generally have an eye for things like this. There's also a yellow paint mark on the screw which tells me that it was either never touched or set and marked meaning don't mess with this. -Checked vacuum slides (what do these things do exactly?). They move smoothly, return closed quickly and there's a satisfying sucking sound from the diaphragm. Here's what it looked like: So I decided to put it back together just enough to get it to run and see if anything changed. I couldn't get the airbox boots on (anyone got any pointers here?!) but I figured it shouldn't be a problem to run it without the airbox. Kinda normal to do it on cars when you're in the diagnostic process. It won't start. I definitely have it primed as I opened the float bowl drain that I could reach and fuel was coming out. I'll assume that's the case for both of them. I get sputtering with the choke fully on, but nothing with the choke off. I exhausted the battery, so I grabbed the battery out of my scooter (losing the terminal nut in the process) and hooked it up and kept cranking. Nearly exhausted that battery too so I gave up for the evening. Could the airbox not being connected cause it not to start? Are these generally that much of a pain to get running again after servicing the carbs? Edit: Some added questions. I've done a bit more reading on how these carbs work. If I understand it correctly, the vacuum slides act as a secondary throttle? Meaning, that when the engine is off they're closed. Engine is idling (full vacuum behind the butterflies) they open, but what happens when you go full throttle and lose all vacuum? They close again? Or does the tapered edge cause the air flowing through the carb to force them open? Also, does the enrichener (choke) completely override the pilot jet & air-screw setting? Or is it a combination of the two? In other words, could my setting of 2.5 turns out on both actually be too lean for it to even start, even with the choke fully engaged? Last futzed with by anarchyx34; August 31st, 2015 at 07:31 PM.