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Old August 8th, 2020, 07:31 PM   #1
Macd7919
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Rough running at low rpm

Hi everyone, my first post here and I’m hoping I can get some help, or confirmation, on what I think is wrong with the 2011 250 I just picked up. I did some searching and I’m pretty sure this is what my problem is but wanted to confirm the symptoms I’m having match my suspicions. The previous owner had left the bike sitting (indoors) for at least a few years. She said it ran fine before that (which I doubt at this point) so I got the bike already knowing I would be rebuilding the carbs. First thing I did was drain all the old fuel out and refill with fresh. I got the bike to start but it ran very roughly and you couldn’t give it any throttle. Fast forward to today - I rebuilt the carbs with all new jets, needles, etc... and reset the idle air screws to 2.5 turns out. The first thing that made me think the bike hadn’t been running right before I got it was that the idle air screws were nearly all the way closed (not to mention the o-rings and washers were on the wrong side of the spring). Anyways, got it back together, went to fire it up, ran for about 30s and died. Cranked it over again and nothing, then a big backfire. Did it a few more times and it was the same thing. Pulled the plugs and they were wet so I grabbed two new plugs and she fired right up and idled, roughly. So now the bike is running roughly but will stay running on its own. If you slowly feed it throttle it roughly revs up until it hits about 3k rpm and then it runs great. Above 3k, it’s perfect. Let it fall below that and it’s rough, I would consider rough to the level of unridable. My question is, when I was in the carbs doing the rebuild, I’m 99% sure I did NOT see the needle jets in either carb. These would be part number 16017-1417 in the Kawasaki Microfiche. I’m going to pull the carbs back apart tomorrow to confirm but can anyone confirm that these are the types of symptoms I would see if those pieces were missing? Also, is there anyone who has a pair of needle jets they would be willing to sell me? It looks like there is quite a wait to get them from any of the normal sources and I was hoping to get this thing on the road sooner then later. Thanks for any input you may be able to provide!
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Old August 9th, 2020, 11:49 AM   #2
Macd7919
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Pulled the carbs out this morning and confirmed what I thought. Looks like I’m missing the needle jets. Can anyone confirm this would cause the symptoms I described above or should I be looking elsewhere for additional issues? Thanks!
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Old August 9th, 2020, 11:52 AM   #3
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@ducatiman should be able to help if he's around.
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Old August 9th, 2020, 12:59 PM   #4
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Absolutely will not run properly as is.

You need needle jets - no doubt.
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Old August 9th, 2020, 02:03 PM   #5
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DIY is often accompanied by do overs and trial by fire. OP should have determined critical parts missing in 1st go around.

Sorry but I can't accept the comment "running great" without needle jets, an integral component of the main mixing chamber.

Predicting the need for further actions, beyond needle jet replacement, is impossible.
Replace them, then reevaluate performance based on real world riding conditions.
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Old August 9th, 2020, 02:21 PM   #6
Macd7919
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Quote:
Originally Posted by ducatiman View Post
DIY is often accompanied by do overs and trial by fire. OP should have determined critical parts missing in 1st go around.

Sorry but I can't accept the comment "running great" without needle jets, an integral component of the main mixing chamber.

Predicting the need for further actions, beyond needle jet replacement, is impossible.
Replace them, then reevaluate performance based on real world riding conditions.
Well, it’s scary to say the previous owner (PO) had all prior service done by a shop. I know as I have the receipts for all of it, including said “carb rebuild”. Also, I’m the one going back in and “fixing” things. I have a sneaking suspicion the shop who did the work last time dropped the needle jets, possibly didn’t realize it, and could never get the bike running right, and then it sat. I also found the springs/washer/o-ring on the idle air screws backwards when I took it apart. That was corrected but I wasn’t familiar enough with the carb on the initial disassembly to know there were needle jets missing but I know that I rebuilt the carb correctly (not my first rodeo) with the exception of not knowing these carbs had a needle jet and with the resulting poor low rpm w/clean running up top I knew there was something more going on, which is where I found out about the missing needle jets looking through other posts and the Kawi microfiche.

With all that said, my main question is IF the needle jets were left out, is that the type of result one would expect (low rpm stumble with clean running in mid-high rpm range)? Unfortunately I have nothing to compare to as I’ve never had a ninja 250 or ridden one before. I’m sure I’m not the first person to have tried running one without the needle jets and there should be some sort of idea what stage of fueling they affect. Lastly, does anybody have any laying around the would be willing to sell? I can get them through my normal parts source but shipping is something like 3 weeks out and I was hoping to get this thing back on the road sooner then later. Thanks for any info in advance!

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Old August 9th, 2020, 06:49 PM   #7
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I'm not sure of the compulsion to discuss what the exact running ramifications of missing needle jets entail, they absolutely, automatically need to be replaced.
I'd dissuade envisioning some sort of a "workaround", if thats where you are going with this?
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Old August 9th, 2020, 08:09 PM   #8
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Well, the first question regarding what that particular circuit in the carb affects is for my own personal knowledge, and, also because I like to know that I’m more or less OK to leave the remainder of the carb as-is and not go digging deeper for “other” possible issues while I have it out. It seems to be a relatively straightforward answer as carbs are relatively simple contraptions but maybe there is something I’m missing that makes it more complicated.

Your second question I’m not quite seeing where I was asking for a workaround. I’ve asked multiple times in this thread if anyone has a spare set of needle jets they would like to sell. To me, that’s painfully obvious that I’m planning on replacing them and even went as far as to explain that they are 3 weeks out from my parts distributor and I’d like to get the bike back on the road by then. In my first post I said it was unridable as is, so putting it back together just to be in the same manner really wouldn’t do me much good.

So, again, I’d be interested to hear what that circuit (the one with the needle jet) affects so I have a better understanding of what I’m working on with this particular carb. Also, if anyone has a couple needle jets available they would be willing to sell I’d be happy to buy them from you. Thanks!
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Old August 9th, 2020, 09:33 PM   #9
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https://www.ebay.com/itm/Kawasaki-20...75.c1#viTabs_0

Found a listing on ebay for what looks like a US stock of this part. Says 3 in stock. I'll poke around some more if you want.
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Old August 9th, 2020, 09:54 PM   #10
Macd7919
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Quote:
Originally Posted by Emu View Post
https://www.ebay.com/itm/Kawasaki-20...75.c1#viTabs_0

Found a listing on ebay for what looks like a US stock of this part. Says 3 in stock. I'll poke around some more if you want.
Thanks for checking into it but (to my location at least) they want $15 shipping so the jets would run me close to $100 for the two of them. From the dealer they are about $57 (for two) so I was hoping to maybe find someone with them in hand that would take somewhere around that neighborhood for them. Worst case I just suck it up and order them then wait the 3 weeks. I do appreciate your effort checking though!
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Old August 10th, 2020, 11:19 AM   #11
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needle jet = spray nozzle of sorts, placed prominently smack center of venturi. If its missing, proper atomization and spray will be compromised. As the throttle plates are opened, venturi velocity increased, slide rises, needle taper determines clearance...normally creating an atomized fuel "spray". But without the needle jets, the sunken emulsion tube is then the next surface exposed to venturi. The ID of the (now missing) needle jet and the ID of the emulsion tube differ, as well as their placements.....resulting in unmetered fuel entering the venturi.

Think of your garden hose with spray nozzle on, then removed.

As the presence of needle jets (all parts, for that matter) is confirmed both in receiving from user and final shipping of finished carbs within my service...never an issue, nor ever needed to become one.

I'll now yield to other members further comments.
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Old August 10th, 2020, 01:02 PM   #12
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The reason it’s worse at idle is due to variable AFR due to change in air-flow volumes at idle versus high-RPM/WOT. Without needle-jets in place, idle AFR is way too rich given full-flow from emulsion tube. With more air-flow, this large amount of fuel isn’t as overwhelming, so it appears to run better. But is still too rich. Less bad is still not good or perfect.

Yeah, shops all suck at working on carbs. Mine sat at shop for 3-days before they called me asking how to plug in OBD-scanner!
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Old August 10th, 2020, 05:38 PM   #13
Macd7919
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Thanks guys, that’s the info I was looking for. I suspected it was running way rich on the bottom end and then once it got past the point where that circuit was having a large effect, in my case, about 3k rpm, it got back to a reasonable AFR and ran clean. Well, I bought the bike knowing it needed a carb rebuild so overall it’s not a huge deal but now the picture is much more clear as to why the bike was sitting. I understood, or they knowingly let me believe at least, that they just stopped riding it for personal reasons and it sat until they were moving to Chicago and didn’t want to take it with. They conveniently forgot the part about it running like crap prior to parking and not being able to fix it. My first inkling something was wonky was the idle air screws being turned nearly all the way in (like, 1/8 turn from bottomed out). Oh well, in the end not a huge deal. Thanks again for the info!
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Old August 11th, 2020, 10:05 PM   #14
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Never ever believe anything bike-sellers tell you! There’s ALWAYS something to hide.

Oh, BTW, when those needle jets come in, be careful not to install them upside down. Tapered end faces needle!
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Old August 14th, 2020, 07:09 PM   #15
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Quote:
Originally Posted by DannoXYZ View Post
Never ever believe anything bike-sellers tell you! There’s ALWAYS something to hide.

Oh, BTW, when those needle jets come in, be careful not to install them upside down. Tapered end faces needle!
I agree with Danno 100%. My buddy, who I know very well, said he was the only owner. I know for a fact he didn't to much more than oil changes, with 8,800mi on the clock that's like 2 oil changes, 9 if he did them once per year. When I started getting into the bike I found nearly all the carb hardware screws stripped out, gouging in both fuel bowls, nissin HH brake pads front and back, and lots of other evidence of someone getting under everything and half assed "fixing" something. He told me that the only people in it were my local shop and him and he bought it BRAND NEW.

It's taken me a little time and a little money but I am slowly getting the bike where I want it.
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