August 30th, 2015, 07:07 AM | #1 |
ninjette.org member
Name: Joe
Location: Brooklyn, NY
Join Date: Aug 2015 Motorcycle(s): 04 EX250 Posts: 30
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New 250 owner. Idle hangs at 4,000 rpms. Carb issue?
So I just picked up a 2004 Ninja 250 for really cheap. The only issue with the bike is that it wants to idle at 4,000 rpms. Firstly it's a little difficult to start, and I need to use the choke all the way on. After it warms up if I try and completely disengage the choke, it wants to stall. So I played with the idle knob and got it settled to about 1200 rpms. If I blip the throttle, it'll hang at 4k. The only way to get it back down again is to play with the idle knob. Also there's a very fine line between it stalling and revving to 4k as I adjust the knob. I tried bogging the engine against the clutch to see if it would settle down to 1200 rpms by itself but it just goes right back to 4000.
I have a bill from a shop stating that the carbs were cleaned/adjusted and apparently re-jetted earlier this month. The PO said that this is how he got it back from them. He wasn't very mechanically inclined so I don't think he realized that it wasn't right. As far as myself, this is my first motorcycle but I've got over 10 years of experience as an auto mechanic. Unfortunately my experience with carburetors is somewhat limited. My gut instinct right now is to just buy another un-molested carb and throw it on and see what happens, but I'm hoping some of you might have some pointers for me. Thanks! |
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August 30th, 2015, 07:18 AM | #2 |
The Corner Whisperer
Name: Chris (aka Reactor)
Location: Northern KY
Join Date: May 2011 Motorcycle(s): 2010 250 (track), 1992 250, 2006 R6 (street/track), 2008 R6 (track) Posts: Too much.
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Welcome Joe!
I normally advise against just throwing parts at a problem. Check the airbox and air filter for anything that may not be right. But it sounds like the carbs didn't get cleaned properly. If you have 10yrs experience as a mech, then you're more than qualified to do this work yourself. Honestly, getting the carbs out of an 04 (pregen) is a bit of a pain in the behind, but not impossible. There is a great video somewhere here on the removal process. As far as cleaning the carb, it's not as hard as it sounds. Once the carbs are out, remove the bowls and then the jets and start ensuring everything is clean and clear. Also, do a search here for "hidden passages." These airways of the carb must be clean and clear as well.
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August 30th, 2015, 07:27 AM | #3 |
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Name: Joe
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Thanks for the reply. I'm also curious as to why they upjetted a completely stock bike. I might buy some stock sized jets just to have when I disassemble it. Those are at least cheap and will offer some assurance. Does the fuel tank need to be removed to remove the carbs? It kinda looks that way.
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August 30th, 2015, 07:28 AM | #4 |
in your machine
Name: Scott
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Pm @ducatiman for your carburetor needs, best part is he's located on Long Island.
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August 30th, 2015, 07:36 AM | #5 | |
The Corner Whisperer
Name: Chris (aka Reactor)
Location: Northern KY
Join Date: May 2011 Motorcycle(s): 2010 250 (track), 1992 250, 2006 R6 (street/track), 2008 R6 (track) Posts: Too much.
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Quote:
Yea, your gunna wanna remove the tank.
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August 31st, 2015, 09:14 AM | #6 |
Rev Limiter
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I would check that the slides rise and fall smoothly (engine off) by reaching from the airbox side and lifting them gently. They should feel smooth and drop without hesitation.
Also check for a vacuum leak around the intake boots between the carbs and the engine. What you described is typical of a vacuum leak. You probably would do well to remove the carbs and go through them. Make sure to study up on it first and be sure to remove the caps on the idle mixture screws if they are in-place. You'll want to be able to make adjustments later, but 2.5 turns out is a good starting point. Draining and cleaning the fuel tank is also a very good idea. |
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August 31st, 2015, 03:01 PM | #7 |
Lostcause enthusiast
Name: Graham
Location: Austin, TX
Join Date: Jan 2015 Motorcycle(s): 2000 EX250F Posts: 178
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Hey, that is the best way to buy a ninja, with gummy carbs! Its a super common problem on these as the passages in the carb are way small and prone to clogging. Sometimes you can do the old 'italian tune up' and ride the piss out of it and get whatever is clogging it to come through, but more often than not you've got to poke them crabs.
I'd check the air leak route first, all clamps are tight and all the boots are secured correctly, lots of crummy moto shops will screw that one up. Get yourself a big fatty lawnmower fuel filter for it, one of the clear ones so you can see if there is anything coming through. Worst case pulling the carbs isn't that bad, hardest part is getting the boots back on the airbox. Put the boots in boiling water and they'll get real soft and go on easy. Time to learn to rebuild a carb, the ninja ones are pretty easy, just don't be a ham-fisted doofus and you'll be fine. Next you can do a Quadrajet, it will make the ninja seem easy. |
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August 31st, 2015, 03:08 PM | #8 |
in your machine
Name: Scott
Location: Summer Shade, Ky.
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Personally Q jets are easy, tuning them is art I was well versed in, far superior to a Holley
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August 31st, 2015, 03:16 PM | #9 |
Lostcause enthusiast
Name: Graham
Location: Austin, TX
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ha you should teach me, the things are friggin' greek. its like the rube goldberg carb, rods and pulleys and i'm pretty sure mine puts a candle up to a rat's ass who pushes a cage to turn off the choke.
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August 31st, 2015, 03:27 PM | #10 | |
in your machine
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Quote:
The trick is playing around with the accelerator pump, the metering needles, jets etc....
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August 31st, 2015, 05:19 PM | #11 |
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Name: Joe
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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. |
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August 31st, 2015, 08:07 PM | #12 |
in your machine
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September 1st, 2015, 09:07 AM | #13 |
ninjette.org member
Name: Joe
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That helped a lot actually. So it seems to me that the pilot is still important when starting with the choke on. I'm going to try and get the airbox back on, and if it still doesn't start then I wonder if just backing out the idle screw one more turn would do the trick, because it sounds to me like it's just not getting enough fuel.
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September 1st, 2015, 09:38 AM | #14 |
Rev Limiter
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I would leave the mixture screws at 2.5 for now.
When you are cranking, open the throttle slightly - like 1/16 to 1/8 turn - and see if it fires up. You may need to adjust the hot idle speed or add some throttle manually to keep it running initially. It's also possible you are using too much choke (enrichener) - try backing it down. The idle mixture may be rich enough now that you don't need as much as you are familiar with. It does take some cranking to get enough vacuum for the petcock to flow, or you can apply vacuum directly to it to speed up the process (though I don't think that's the issue). |
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September 1st, 2015, 01:04 PM | #15 |
ninjette.org member
Name: Joe
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So I decided to give the shop that the PO had it at to see what kind of info I could get.
The guy remembered the bike and he said that they did pretty much everything they could to it but that was the best they could get it. He said that with this generation Ninja sometimes it's impossible to get them to idle correctly no matter what you do, whereas some of them are ok. I'm not of the mind to believe machines can be possessed by demons so I'm certain an answer lies somewhere. Oh and he also said that from what he remembers they had adjusted the valves in an attempt to correct the issue, although it doesn't say so on the repair-order. I'm wondering if I should pull the valve cover and verify the clearances. Lets see if I can get it running again first. |
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September 2nd, 2015, 07:35 AM | #16 |
ninjette.org member
Name: Joe
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Well sure enough when I put the airbox back on it started right up. Color me surprised. Still has the same issue though, or maybe slightly improved. I'd like to adjust the air screws while it's running but I don't have the right screwdriver. I can get a screwdriver bit on there but I can't turn it, so I'll have to hunt down the appropriate weapon.
I think something like this might work: http://www.amazon.com/T19086-4-Inch-...=finger+driver Last futzed with by anarchyx34; September 2nd, 2015 at 08:58 AM. |
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September 3rd, 2015, 05:14 PM | #17 |
ninjette.org certified postwhore
Name: Gordon
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a small flathead screwdriver bit, grind tip till perfect fit
if necessary cut it down in length, but shortys like this work perfect note the pilot screws should turn quite easily, no? |
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September 3rd, 2015, 05:22 PM | #18 |
ninjette.org member
Name: Joe
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Maybe my hands are weak? I was using bits just like in the picture you just posted but a little bit longer. I couldn't really get a good enough grip on them. I only tried the passenger's side carb as the driver's side one seemed even harder to reach. Did I mention that the engine is hot as hell too?
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September 3rd, 2015, 05:26 PM | #19 |
ninjette.org member
Name: Joe
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Another dumb question. How can it even get the air to run at 4k rpms with the throttle blades closed?
I can tune a standalone fuel injection system on a turbocharged car in my sleep, but this **** is like alchemy. |
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September 4th, 2015, 12:39 AM | #20 | |
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Quote:
turning pilot screws should not offer major resistance by any means, unless threads are spooged, orings deteriorated within, incorrect sized washers, etc. (in other words a parts problem within) RE: air and 4K....are you *certain* ALL your vac hoses are secure, no splits, ends tight and secure on the vac nipples? note there are 2 vac nipples *between* carb bodies (hoses come up between the bodies) and another shorty under the decel valve...check these all for cracks/splits/tightness as any leaks in any of these would cause issues. The 2 between may need to be checked by, sigh, removing the carbs yet again, impossible to properly check/view with carbs in place. Look for swelled ends (where they actually fit over the nipples) or general loose/sloppy fit which could cause leaks. There's some intense vacuum at those points when running. If you have the length to work with...cut them back to restore *tight* fit. Be precise here. I'll take for granted your throttle cables have been adjusted with adequate freeplay? |
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September 4th, 2015, 07:37 AM | #21 | |
Rev Limiter
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Quote:
2.5 turns out is usually very close, and most of the time a quarter of a turn either way is all that's needed for fine-tuning. If you are having running problems at 2.5 turns out, you need to look elsewhere. |
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September 4th, 2015, 07:39 AM | #22 |
Rev Limiter
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It takes very little throttle opening when not under load to rev the engine to 4000. I would say something is sticking or holding the throttle open sightly on one or both carbs. That, or there's an issue with the carb not being assembled or adjusted correctly.
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September 4th, 2015, 07:41 AM | #23 |
ninjette.org member
Name: Joe
Location: Brooklyn, NY
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The screws moved easliy when I had the carbs out. I just think it's a matter of getting the correct grip.
As far as vacuum leaks, I didn't closely inspect the hoses in-between but I did hose everything down with carb-cleaner while it was running with no detectable change. I'm not going to pull the carbs out again anytime soon though. I may just leave this as a winter project. It's not really that bad while riding, and the idle is either barely running at 1000 rpms or at around 3k with it fully warmed up. It does it at random as well. I'm sure I'll figure it out eventually. Either that or I'll put Microsquirt on it. |
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September 7th, 2015, 08:55 AM | #24 |
ninjette.org member
Name: Joe
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Ok, first of all the bike runs great right now.
Turns out all it it needed all along was to be richened a bit, and now it idles steadily at 1300+/- rpms, responds well to throttle snaps and falls to 2500rpms before settling back down to idle speed. Turns out I was trying to adjust the wrong screw. I was sticking my screwdriver bit in the recessed hole next to the idle air screw. I also had the idle speed turned WAY too high trying to compensate for such a lean setting. I set the idle speed to where it's just touching the throttle cam and gave it just half a turn. Then I adjusted the mixture and it's good. I have no idea how many turns out they're set to right now but I'm satisfied. Way to make a mountain out of a mole hill. Well, at least I learned a lot about my new bike in the process. I guess megasquirt can wait for some other time. |
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September 7th, 2015, 09:17 AM | #25 |
in your machine
Name: Scott
Location: Summer Shade, Ky.
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Glad you figured it out.
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