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Jets for 400ex carb on a 250x

2517 Views 7 Replies 3 Participants Last post by  1972ct2
I am told I have a 400ex carb. No idea how to tell considering it has no stamp that I can find on it.

The two Jets that were in the carb are a 135 Main and a 38 Secondary (or pilot).

Question 1:
How can I find out if the carb is a 400ex or not?

Question 2:
Do I have the proper jet sizes for using a 400ex carb on a 250x (Assuming I do have a 400ex carb)?

Thanks in advance!
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I have no clue if the engine was modded. I am beginning to think it was. Based on this .pdf which I just found: - NEW/JETTING/JETTING-HONDA-TRX250X-300EX.pdf

(And is quite handy I might add, maybe something to save!!)

It suggests that if you were to modify your engine you should start the primary jet 4 sizes larger than stock and pilot jet 1 size larger. That would be my setup exactly based on their lists!

Looks just like a picture of the 400ex carb on ebay.. can't find a good pic of 250x carb yet.. still working on it.
Ok. So i have no clue. Here is a pic of the carb (i have already disassembled it.) the opening for air is about 2"...

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Clearing up the muddle....

Well, I figure since I have asked the question and found the answers I should at least provide this information for those who might search this thread in the future.

I am working on a trx250x from 91'-92' era. To identify your carbouretor there is a stamp on the side of the throttle body just above the choke lever.

It reads "QB" with some serial #s below it. Mine says "02A A GK" and some japanese symbol at the end. Based on my Clymer manual and bike bandit, I have a 93' Honda 300EX carb. Fyi, A stock trx250x carb will start with "QB01B A".

If you do not have a manual, go to search for the year and make/model of your atv, click on Fuel/Air and click on the image of the carb. At the bottom there is a parts list. Look for "Carb Assembly" and it will say "(QBXXXX)". This lets you identify a carb.

Proper jetting for the 300ex carb is 122 main and 38 pilot.

Hope this helps someone get the answers they need!
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