carb work

[james250ninja]

hey there,was wondering, Ihave a 2005 ninja 250. Can I shimm my needles on this model and if so how many washers should I use,I'm keeping the bike stock.

[kimboEX250]

yes, i used 2 4mm brass washers for each needle, my bike is stock as well

[JLinde1339]

I was doing carb work yesterday on my bike. My exhaust was heavily modified to about 7" off the exhaust header. Heard they've been called "chopped cans". Since I was getting some popping on decel, and from what I read, I assumed the bike was running lean. Well, I was right....and then some. Took the carbs out. The idle plugs where never removed, the valves were out of sync, and the jets weren't shimmed. So for a starting point, I pulled the mixture plugs, as the idle mixture needle was actually sticking up into one of the carbs, and not in the other. So I screwed them both in all the way, then backed out 2 3/4 (1/4 extra to compensate the pipes). I visually synced the valves, and left the shims out for now, to see if those minor adjustments would help. OMG, the bike came to life! It sounded great, fired up from cold without any choke, and didn't feel like a headwind would stall the bike when I rode it. Amazing. I now think the bike was idling on one cylinder, since the mixture screw was in so tight.

Now that the engine is running right, what would shimming really do to the bike? I couldn't really find an answer as to why you would need to shim. Just that you should.
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[kimboEX250]

the jet needles are for mid range power. a stock ex250 has a "power band" that hits around 9000rpms, by shimming the main jet needles it pulls harder from 7000rpms on up. the needle is tapered and basically plugs the main jet of fuel at idle, and raises with the throttle slide as you twist the throttle, shimming will allow more fuel at lower rpms, if you were way lean before you should be good, but i had to modify the snorkel because it was so rich it would load up and have no power until 3000rpm, hope this helps

[JLinde1339]

Yes, that helps immensely. I didn't have enough time to road-test it last nite, but hopefully tonite. I'll run it thru the rev range and see if it needs any further tuning. I guess my question is if shimming the needles affects all phases of the carb (idle, mid and high rpms) or just the mid range? From what I've read, you should do the needles first, then tune from there, but since my factory setup was so wonked, I wanted to get it running smoother before messing with the needles. At least now the idle mixture screws are set the same, so it runs way better at low rpms.
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[kimboEX250]

idle mixture screws: 0-1500k
pilot jet: 1500k-4000k
jet needle: 4000k-9500k
main jet: 9500k-13500k
i'm just guessin on the rpms, but you get the idea

[Jiggles]

Originally Posted by kimboEX250

idle mixture screws: 0-1500k
pilot jet: 1500k-4000k
jet needle: 4000k-9500k
main jet: 9500k-13500k
i'm just guessin on the rpms, but you get the idea

I believe they all actually overlap eachother

[kimboEX250]

sure, one in conjunction with the other, but as far as changing jets, shimming needles, etc, it will have different affects at certain rpms, that was just to give an idea of the rpm range that certain mods do, there is no "valve or switch" that kicks over to the next jet
"From what I've read, you should do the needles first, then tune from there" i'm thinkin they mean jetting, if you shim the needle too much it could bog or lug off a stock pilot jet, if you don't jet 2 shims should work, but i would consider jetting since the exhaust is modified

[choneofakind]

technically any changes to the amount of fuel delivered by the carbs is "jetting".

you start with the main jets, then go to the needles, then the mix screws/pilot jets

http://faq.ninja250.org/wiki/How_to_...e_your_jetting


JLinde1339: does your bike pull hard full throttle all the way to redline? If so, move on to midrange/ full throttle/cut the throttle, then roll on and off all the way from about 4k-9k. It should be smooth and strong and not backfiring or hesitating. Then use the idle mix screws to get the idle and off-idle response right.

you should be able to put it in second, cruise at 2500rpm, give it full throttle, and get to redline smoothly, strongly, without any lugging, hesitating, or surging on the way.

you can jet any exhaust/intake configuration this way.

[choneofakind]

http://www.factorypro.com/tech_tunin...m_engines.html

these are pretty general, and I've never had to mess with the floats, but these are good instructions for getting an idea of what you're looking for when jetting

[JLinde1339]

Very useful info. Thanks. Upon reading this, I realize there is a difference between the main jet and the needles. Didn't know they were different. That's prolly why I was so confused. Any idea where the main jet is found? I'm sure I'll be accused of asking the dumbest question ever after that one....
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[Socal5646]

Above the float bowls right next to the pilot jet and enricher jet

[kimboEX250]

nahh, we all had to ask the same questions at some point, just passin along the answers, here ya go
800px-Inside_carb_9.jpg

[JLinde1339]

Argh! Can't get attachments on my phone. Will have to check that after work, kimbo. Thx!

Ok, time to get my terminology straight. What are the names of the three jets, and what adjusts them? I think I have only half of the puzzle, and everywhere I read uses different terms. The idle mixture screws control which jet? I guess the enricher??? The 2 needles that you shim with washers are called the pilots?

I'm lost, cuz I've adjusted the idle mixture screws and my low-end is sooo much improved. They weren't even set the same from the factory. I've taken the needles out of the top, with the diaphragm and springs. Easy enough to work on. Maybe someone can clarify for me....
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[choneofakind]

The mixture screws control how much fuel gets mixed in from the pilot jets when it's idling/ at lot rpm's. The needles go in and out of the main jet (effectively closing/opening it depending on the thickness of that point of the needle) to control the flow for the mid-range when the bike needs more than the pilot jet can supply, but less than the main jets. Shimming the needles basically pulls them out of the main jet that much and allows more fuel out of the main jet for the mid-range rpm's.

The choke (enrichener technically) is a separate thing on itself. It simply adds more fuel when you open it. It only really affects the mix at low rpm's and mid-range because of the sheer amount of fuel the main jet supplies compared to how much fuel the pilot jets supply.

that clear anything up?

[JLinde1339]

Yes. Very much. Without any visuals, it was tough to grasp, but after some tinkreing and research last nite, I think I have a handle on it.

So I added a shim to the needle last night, and major bogging, till she hit about 5k. So I took it back out, and I'm still getting problems in the mid range that I can't diagnose. Of all the descriptions of whether its lean or rich, I can't tell if its bogging or stuttering. It seems to lose acceleration in the mids. Rpms hold firm, but the power isn't there, like it hesitates. But I'm not sure if its rich or lean in the middle. Could someone elaborate on the symptoms?
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[sombo]

Originally Posted by choneofakind

you should be able to put it in second, cruise at 2500rpm, give it full throttle, and get to redline smoothly, strongly, without any lugging, hesitating, or surging on the way.

That is exactly what I'm getting and this is after a shop I trust tried 2x to tune it. They admit they don't have any other exposure to 250's than mine and therefore aren't quite sure how it's supposed to feel at lower rpm's.

In the 2500-5500 (or so) range I get hesitating, coughing, hiccuping, and just general rough sounding. Between 6-8 is where I usually cruise at and it's good there except on decel from about 7k down it sounds off somehow. Not popping, but not smooth rpms if you can figure out what I mean. It just got a new exhaust from Area P put on and they used parts from a Sportisi Moto jet kit I got awhile back from ztrack to try out.

Another issue is unless the shop somehow lost about 1-2 gallons of gas when they did whatever they did, my mileage dropped yet another 10mpg down into the 30's. A few months ago a different shop tuned the carbs even though they didn't need it and that's when my problems started (this was a Kawasaki dealership btw) with sputtering in lower rpms and a loss of mileage from my normal 50-60 down to 40-50. Now with the latest work it's either gas was lost or it's now down to 30-40 mpg and that is completely unacceptable.

Just got done talking to the shop and they told me of the difference in needles that the jet kit came with being significantly different and bigger than what was in there (to my knowledge it already had a jet kit in it from a previous owner). They said that it came with a 40 and at first they used that and then put the 38 back in after the 40 proved to make it run worse. Now I'm thinking to get different needles and possibly not use this jet kit. Hmmmmmm, any suggestions other than putting it on the dyno (at $90/hr) to dial it in? Money is extremely tight atm and if I can (or a friend with proper tools and better know-how) do something w/o spending anything then I'm all for it.

[JLinde1339]

That sounds like my issue. And if your mileage is suffering (I haven't verified mine) then you're probably running too rich a mixture in midrange rpm's.
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[choneofakind]

Sombo, hesitating, hiccuping, and coughing sound like symptoms of lean conditions. Try one washer on the needles and see if that helps. Do you have the stock needles/whatever was in there before? try those instead of the sportisi moto needles, because if I'm not mistaken, the sportisi kit was intended for the current 250 and not the Pre-Gen bikes. If the sportisi is all you have, shim that out a little and see if that helps. If you don't want to pay for dyno, prepare to test-ride a lot and use the butt-dyno to decide which changes make it run best


JLinde1339, try tuning from the high RPM's down (main jet first, then needles, then mix screws). I think if it's bogging badly down low, turn the mix screws in 1/4 turn to lean it a little bit down low, then take it for a ride and see how it feels.

since you shimmed it, does it feel better or worse from about 5k-10k? is it possible that you aren't "feeling" the power as much because there's more power in the lower-midrange, and so the peak power doesn't feel as strong in comparison?

[choneofakind]

http://faq.ninja250.org/wiki/Ninja_2...le_Information

here's more info on the needles. Might want to take out your Sportisi needles and compare them.

[sombo]

It's not running lean. It's using WAY more gas now. Remember, my mileage also dropped from 50-55 when I got the bike, down to 40-45 after it was retuned (unnecessarily) from one shop, and now it's down to 30-35. There is absolutely no way that can be considered lean. It can also do that if it's not getting enough air in the mix cause it not burning right. Will know more when I can get some help tearing it apart to see the plugs. Remember, the kit put bigger needles with a different taper in to allow even more gas, not less.

[JLinde1339]

Originally Posted by choneofakind

JLinde1339, try tuning from the high RPM's down (main jet first, then needles, then mix screws). I think if it's bogging badly down low, turn the mix screws in 1/4 turn to lean it a little bit down low, then take it for a ride and see how it feels.

since you shimmed it, does it feel better or worse from about 5k-10k? is it possible that you aren't "feeling" the power as much because there's more power in the lower-midrange, and so the peak power doesn't feel as strong in comparison?

It was hard to get a read on the midrange. I finally got it back together later in the evening and it was dark when I tested it. And plus its really loud with the chopped pipes, and I didn't know if I'd make it to the highway to really test it. But on the residential streets, going from a full stop it was bogging and bucking, it honestly scared me so much, I didn't pay much attention to how the engine ran, just tried to keep it upright and moving. LOL. I do remember that it "woke up" around 5k-6k. I'm assuming that it finally burned off the excess fuel from the low-range flooding. Tomorrow, I may drop a shim in again and lean up the low end (which I didn't do the first time because it was dark), and see what results I get there. I now have it back to the way it was when I bought it, plus setting the idle mixture out 2.75 turns. And it has that hesitation in mid, and I can't tell if its rich or lean. But I'm guessing its prolly slightly lean overall because of the pipes.
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[choneofakind]

Originally Posted by sombo

kit put bigger needles with a different taper in to allow even more gas, not less.

bigger as in longer or bigger as in larger diameter? Larger diameter would close up the main jet more for the same needle height.

how many tanks have gone through it with terrible mileage? what size main jets are in it?

[choneofakind]

Originally Posted by JLinde1339

It was hard to get a read on the midrange. I finally got it back together later in the evening and it was dark when I tested it. And plus its really loud with the chopped pipes, and I didn't know if I'd make it to the highway to really test it. But on the residential streets, going from a full stop it was bogging and bucking, it honestly scared me so much, I didn't pay much attention to how the engine ran, just tried to keep it upright and moving. LOL. I do remember that it "woke up" around 5k-6k. I'm assuming that it finally burned off the excess fuel from the low-range flooding. Tomorrow, I may drop a shim in again and lean up the low end (which I didn't do the first time because it was dark), and see what results I get there. I now have it back to the way it was when I bought it, plus setting the idle mixture out 2.75 turns. And it has that hesitation in mid, and I can't tell if its rich or lean. But I'm guessing its prolly slightly lean overall because of the pipes.
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Try setting your idle mix screws at 2.5 turns if you think it's too rich. how many washers are on your needles now?

[JLinde1339]

I have none in it now. When I first pulled the carbs the other day, the idle mixture screw plugs were still on it. Looking into the carb chambers, one of them was poking up into the chamber, the other was recessed. So I removed the plugs, screwed them all the way in, and backed them out 2.75. Reinstalled the carbs, and tested it. Fired up beautifully, with no choke at all (always needed half choke since the day I first had it) and idled so smoothly. After a test run with that, found the mid still had that little hesitation. So I shimmed with a washer per needle, and that's where it started bogging on the low end. So I tried to lean it out with the idle mixture screws but had a real tough time with them still on the bike. So last night I pulled them off again, reset the idle mixture screws to 2.75, shimmed the needles with one washer each, and the low end was boggy again. So I pulled the shims out again, and it was fine, except for the hesitation in the midrange. I decided on 2.75 turns, because my pipes are really chopped, and from what I've read, that will make the engine really lean all around. So if I shim the needles, I think I'll have to reset the idle mixture screws to about 1.75, maybe 2 turns out and see if the bottom end bog is cured.
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[sombo]

Originally Posted by choneofakind

bigger as in longer or bigger as in larger diameter? Larger diameter would close up the main jet more for the same needle height.

how many tanks have gone through it with terrible mileage? what size main jets are in it?

I'm not sure the sizes of all the jets in it. I know it had 38's in it, the kit came with 40's and that made things way worse, they put the 38's back in and it got better but still sucks but is at least useable. As for the other jets I think of bigger as in numerical value and all I know is that they said these were tapered differently to allow more flow through.

Let's not forget that this bike has dropped almost 50% in mpg. Somehow I have a hard time believing running lean is the problem. They figure it was probably running close to lean when I first got it and it was running smooth. I can also tell you that it never needs choke and is easy to flood.

I've put 2 full tanks through with mileage in the 30's. First was with the 40 jets in, and second was after they replaced them but left the others. Also I got gas yesterday and when I looked in the tank it looked very likely to be at least a gallon used already.

[JLinde1339]

I just pulled out the carb and needles, and noticed that my needles have "N16I" stamped in them. I also noticed that the washers that I bought might be too big. They're 4mm, as I read somewhere, but while reinstalling them, the washers don't fit well into the little plastic seating at the bottom of the spring. I think that may be causing some problem. Not sure its the main problem, but I'm off to pick up some smaller washers. But I'm not even sure the needles are stock. Does anyone know if the stock needles are N16I? Knowing if they are or not will give me some insight as to where to go from here.
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[JLinde1339]

Got the smaller washers. Got them on (with some additional, unforseen side projects XD ) and there seems to be less hesitation in the midrange. I didn't get to give it a really good test, but hopefully later. I think I still need to dial in the low-end now, as it sounds the way it did when I originally bought it. Currently, the screws are out 1.75, and I may bring it out another quarter to a half turn to fatten it up a bit. Then again, I may hold off on that till I test further, in case I want to add another washer to each needle. Will update. But I'm starting to get the hang of these carbs.
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[JLinde1339]

Okay, settled on 2 washers per needle. Left the idle mixture screws at 1.75 and seems to be running like the champ that she is. Gonna do a test run today. Planned route is some highway and mostly back road thru small towns (30-55mph). So that should give me a good report throughout the whole range of revs. The lowend is so much more improved in sound and operation. Engine breaking below 3rd gear was originally very clunky, but now seems much smoother. It no longer sounds like a lawnmower when I'm sitting at a light, and much more like a sportbike. No more thin-sounding idle. I plan to run this setup for a while, and will check the plugs after the riding season ends to see what their verdict is.

Thanks to everyone who provided input throughout this process. I've learned a lot about carbs since I jumped on (read: hi-jacked) this thread. XD
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[choneofakind]

Sombo do you have the original needles or any needles that are intended for a pre-gen? I know people have run an Area P with stock pilot jets and shimmed needles successfully. That might be causing this problem, as I think Sportisi only sells needles for the current-gen 250

[sombo]

I think they gave me the needles that were in there prior to this. The reason me and ztrack decided to try this was because both generations of ninjette use the same carbs (Keihin CVK30). We figured it couldn't hurt to try the kit in the pre-gen because of that. Who knows, it still could work if we just play around with it. But I would rather run more on the lean side to help save gas and have smooth performance than to run on the rich side using up more gas and possibly flooding the engine at times.

My biggest problem is that I'm not a mechanic by hobby nor do I have the proper tools. I'm gonna try to get together with some of the local 250 rider/tweakers and see if they are willing to help.

[choneofakind]

They do not have the same needles. They have different part numbers.

http://cheapcycleparts.com/model_yea...semblies/25668

http://cheapcycleparts.com/model_yea...semblies/24701

Try a needle that is part of a jet kit that's made for a pre-gen, or get stock needles and shim them out. As far as I know, the only thing that's identical on both the current and pregen carbs is the slide/diaphragm assembly

[sombo]

Originally Posted by choneofakind

They do not have the same needles. They have different part numbers.

http://cheapcycleparts.com/model_yea...semblies/25668

http://cheapcycleparts.com/model_yea...semblies/24701

Try a needle that is part of a jet kit that's made for a pre-gen, or get stock needles and shim them out. As far as I know, the only thing that's identical on both the current and pregen carbs is the slide/diaphragm assembly

Yah, we didn't look at that part cause we "assumed" that by using the same carburetor it would have the same parts. You can see where our assumption might have come up short. Even with the same carburetors they are using different sizes of needles to get the different tuning that each has.

I already said I was considering just going back to what was in there when I got it. I just need help from someone that has the tools and knows what they are doing. If we are able to put it back to exactly how it was when I got it there shouldn't be a need for shimming. I was told it had a jet kit in it to begin with and the bike ran like a champ. Then Kissimmee Motorsports did something to the tuning a few months back and it hasn't been good since.

[JLinde1339]

Sombo, if all your doing is replacing the needles, its not really a major undertaking. I don't consider myself a "mechanic" but have been able to pull the carbs out numerous times this week and finally tweak it to where I'm happy with it. Ninja250.org has some awesomely informative DIY's and are worth checking out. And if it's just the needles, you won't even have to take the carbs off. The only tools you really need is a 10mm socket and ratchet/driver to pull the tank and some brackets, and a #2 phillips screwdriver to pop the tops off the carbs. I was so dreading this, as people were telling me "you don't wanna mess with the carbs" (not people on this forum, but people I know), but after the fact, I found it to be a lot simpler than I anticipated. Money, and being able to do what I wanted to MY bike were my motivators to doing the work myself. It was well worth it to me, and sounds like it will be to you too. Good luck.
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[choneofakind]

Yeah I definitely see how you made that assumption. In fact, that's likely the same one I would have made. No biggie

but seriously the needles are easy