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Old September 9th, 2019, 11:15 PM   #1
LordVardamir
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Name: Jeremiah
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Question Is my carb beyond hope? Main jet looking odd...

As I mentioned in another thread, I have been trying to identify why my new-to-me EX250 is running like crap. It runs with somewhat bouncy idle at half choke and dies with too much throttle or the choke is released. Spark plugs showed me it is running lean (white tips). So... what gives?

Took the carb out again and compared it to another I had laying around. The main jet emulsion tubes sit way lower on my carb (right in picture) than the spare carb (left in picture).
I swapped the main jet emulsion tubes from the different carbs back and forth. The carb on the right always has the emulsion tube sitting lower than the other one.

My running theory is that the lower emulsion tubes and jets means wayyy less fuel is getting picked up by the main jet because it sits higher above the fuel when installed on the bike. But does this really have an affect at idle? Is there any reason to have the main jet sit so low?

More food for thought: The carb with the low main jets had the idle screws set to around 4.5 turns out. Has anyone seen this before?

I may be having a chat with ducatiman about cleaning my spare carb up....

Thanks for reading!
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Last futzed with by LordVardamir; September 9th, 2019 at 11:22 PM. Reason: Clarity
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Old September 10th, 2019, 05:47 AM   #2
jkv45
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Is the Needle Jet installed on the carb with the lower emulsion tube?

Marked "Collar" in this photo -

https://faq.ninja250.org/images/e/eb/Jim_carb_2.jpg
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Old September 10th, 2019, 06:09 AM   #3
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^ Bingo! Gone missing, no doubt

And reset both your pilot screws to 2.5 initial start position. At 4.5... evidence likely of desperate attempt trying to compensate for missing part.
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Old September 12th, 2019, 08:21 AM   #4
LordVardamir
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Update: I'm dumb. As you can see in the picture, I simply put the needle jet in from the air intake tunnel rather than under the emulsion tube. The previous owner had the needle jet there and I never checked to see if that was right until it ran like crap. After fixing that, the bike runs much better. Idle still bounces around and the bike seems like it's running lean (rpm's hang after rolling off throttle) but she runs now. Not to see if some light tuning can make her run better.
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Old September 12th, 2019, 09:46 AM   #5
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Glad you found that, but there also looks like corrosion around the opening for the air bleeds (not sure exactly what they are called) that would suggest the carb needs a thorough cleaning.

Once it's totally clean, the things to adjust would be the idle mixture, idle speed, and carb sync.

Hanging rpms usually point to a vacuum leak somewhere.
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Old September 12th, 2019, 09:51 AM   #6
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^ traditionally known as "air correction jets" as far back as I can remember. Note factory press-in install, non removable important little buggers.
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Old September 12th, 2019, 09:58 AM   #7
LordVardamir
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Yup, I did a soak in some water/Pine-Sol for a couple of days and BAM corrosion. Rookie mistake. What I learned: Don't soak carbs in too much water. I could have a leak somewhere. Either way, I'm going to send it off to ducatiman to set the carb back to a nice and clean baseline.
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Old September 12th, 2019, 12:49 PM   #8
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I've had the rpm hang high when all that was wrong was the idle mixure. A little richer with the idle mixture screws and it behaved.

That's not to say your carbs don't need to be absolutely clean.
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Old September 13th, 2019, 09:51 AM   #9
LordVardamir
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So I have been testing the bike with the gas tank off and just have a funnel of gas hung at the side. I never thought to close off the vacuum port that normally goes to the tank petcock. Leaving it wide open is just one HUGE vacuum leak! Good call jkv45. After closing that off the idle became much more stable and the engine seems to rev more normally. Awesome! Thank for all your help! I'm still going to have a carb cleaned to have as a back-up or to put on the bike and see how she does.
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