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Old March 29th, 2024, 12:04 AM   #1
Maniakwu
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Name: Alex
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Carb jet questions?

07 Ninja 250 4500miles on odometer
Just bought and I'm trying to chase down idle issues and get it running properly.
Bike wont seem to start on choke. Will start without choke giving it a little throttle it starts pretty quickly. have to mess with the idle screw to open the throttle to keep it at 2000 RPMS, once warmed up the idle is finicky and will die at stops. '

Today I pulled the carbs off to clean and inspect, It definitely seems like someone was in here before/ maybe and aftermarket/Chinese carb? idk not sure.

First off the previous owner poked a hole in the top of the tank with a screw that was to long. thinking of trying to plug the hole with jb weld or something? any recommendations on that would be great.

Second.... looking at diagrams and other pictures, it looks like the enrichener pick up inlet is pressed in and doesn't thread out?? On my carb where the enrichener pick up is there are threads and whoever was in here last had a .65 main jet threaded into it. attached a picture of my carbs.

Third...PO installed pod filters (look cheap and had to bend to get them to fit) and they yanked the DB killers out of the exhaust pipes(so loud). That being said do I need to go up in main jet size? currently my carbs have a .98 main jet which I believe is even smaller then the stock?(1.05)

IMG_20240329_000016.jpg
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Old March 29th, 2024, 07:00 AM   #2
Triple Jim
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@ducatiman is the pro carb guy here.

In general, stock carbs run very well and don't need modifications... IF they're truly clean and the rubber parts and in good condition.

You would benefit from going back to the stock intake system. Again, it's well designed and doesn't need "improvements".

If your valves are out of spec, that will affect the running of the engine, especially when starting and warming up. They shouldn't need adjusting at 4,500 miles, but if there's a chance that it actually has more than that, it would be worth checking. The valve clearance tends to close slowly as the engine wears, and when they get to where they don't close all the way, trouble becomes obvious. A compression test will tell you if they're not fully closing. My 250 was finicky to start and ran poorly when cold. After adjusting the valves it was like I had a new engine.

I've had luck using epoxy to patch small leaks in tanks, but not specifically on a motorcycle. If the hole is above the fuel level it might be patchable. Clean the area with something like lacquer thinner to get any traces of oil and dirt off, and sand the area to rough it up before you apply the epoxy (JB or otherwise).

Until ducatiman shows up, this might be useful: https://n4mwd.blogspot.com/2013/10/s...-passages.html

Welcome to the board, Alex!
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Old March 29th, 2024, 07:25 AM   #3
ducatiman
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AFAIK...your carb lower choke inlet should look like this.........see pic

Either someone was in there prior OR these are not stock Keihin carbs (?)

IF you discover Far East copy carbs on there....I'd suggest purchasing Keihins.
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Old March 29th, 2024, 09:26 AM   #4
Maniakwu
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Name: Alex
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Quote:
Originally Posted by ducatiman View Post
AFAIK...your carb lower choke inlet should look like this.........see pic

Either someone was in there prior OR these are not stock Keihin carbs (?)

IF you discover Far East copy carbs on there....I'd suggest purchasing Keihins.
Is there any stamps or a way of identifying copycat Chinese carbs? I don't see Keihin stamped anywhere, I also see differences with the screws that hold the cover to the vacuum diaphragm that lead me to believe it is a Chinese copycat.

The choke inlet is what has me totally confused, it doesn't have to pressed in brass fitting like in the pic you posted, the inlet on mine is threaded and had a 5mm rounded jet threaded into that spot.(identical to the main jet BUT stamped with 0.65). This is obviously completely wrong right? I'll post a pic I took directly after taking the floats off that I was going to use as a reference when reassembling it until I noticed all of this lol.

IMG_20240328_190722.jpg

I guess if they are copycats I will have to track down
some Keihins carbs and possibly a stock air intake. In the mean time is there any advice on what I can do to make these useable until I can track a stock one down?
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