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Just picked up an 03 KLX400R. Cleaning the carburetor and have some questions.

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Hi All,

I recently picked up an 03 KLX400R (street legal version) with 1776 miles on the bike. The bike has an FMF Q4 exhaust with a rusty ass stock header pipe. The bike has the stock airbox unmolested.  I pulled the carburetor out to do some cleaning and noticed that it was very dirty. I pulled the jets out and saw that the two smaller jets are unlabeled and the main jet is a 142.5. Also, the air cutoff diaphragm in the carburetor was very worn out and looks like its about to give any second. I am about to pull the trigger on a carburetor rebuild kit but wanted to know if the previous owner had the right jets installed or if I need to purchase another size. I live in south Texas where it is constantly hot and humid and the elevation is about 700 feet or so.

Any specific carburetor rebuild kit recommendations? Also, I want to replace those japanese industrial standard screws (those that hold in the float bowl, needle valve assembly, etc) with something that is a little more accessible/ less prone to strip out. What size screws do you guys use for this?

 

Thanks for the pointers.

Edited by maelstrom93

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Make sure you replace the little o-ring that is hidden under the float valve seat. Most kits don't include this and it is a well-known problem for the BSR carb. When it hardens and fails it causes the engine to flood with fuel and hydro-lock the cylinder. Happened twice to me before the great fellows on T-Talk set me straight on the issue. If you do a search or read the FAQ above you'll find the size of o-ring required.

 

The carb works well with the 142.5 and a 22.5 PJ or even a 25. The needle/spring is where the real benefit is found and there are a few aftermarket needles available. I used the DJ kit but many recommend the JD kit.

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Oops, disregard everything I said, I thought your bike had the Mikuni BSR that my 2003 DRZ400S has and it appears that the 2003 KLX400R has the keihin FCR carb installed. Sorry!

 

Maybe you should include a pic of the carb body or ck to see if it is a Mikuni or a Keihin. That kit you referred to is for the Mikuni BSR

Edited by shuswap1

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OK, I checked the OEM parts diagrams at Rocky Mtn ATV and they show a FCR. Goofy!

I'm not aware of any kit coming with this o-ring, can't be certain without more info. Personally, I don't see much in that kit that you would likely need. I'd spend the $ on a JD kit or DJ kit, get the NEEDLE and source the O-ring separately. The needle mad a very nice difference to my bike.

The screws aren't a big deal, I just run a hacksaw blade over the head and convert them to a slot-type screw driver. Takes 15 min. Or, get hex head screws.

 

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+2 on the James Dean jet kit. I'd also get the stainless fuel screw, used to fine adjust the idle mix.

James Dean can probably also supply the oring and ACV diaphragm also inspect the slide diaphragm while you have the carb off. Give the float needle SEAT a nice polishing, check but do so according to the manual, float height, chances are it is fine, do not move the tang unless you are positive it is incorrectly set.

Note: The starter jet and main jet look identical but are different sizes.

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