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Discussion Starter #1
I need to teardown and clean the carb on my sons Raptor 350, I have a shop manual on a CD and also found a site that had a good write up and photos on cleaning and rebuilding this carb. The manual makes a special note that you should check how many turns out the pilot screw is from fully seated. My first question is, where is the pilot screw located? The breakdown diagram doesn't show or list it, and the photos in the article don't show it. .

Next, if you flip the carb upside down you will see the air/fuel mixture screwor the plug covering th screw, turning the carb so the air/fuel mixture screw is towards you while holding the carb, there is a threaded bore in the casting to the left of the air/fuel mixture screw. My son took the carb off and tore it apart before I got a chance to work with him on it and he can't remember what went in there, but there doesn't seem to be any extra parts (he did a good job of labeling everthing as he took it apart and swears he doesn't remember taking anything out of there). The breakdown in the manual doesn't have a bottom view. I found a photo of the bottom of the carb in the rebuild article that identified the jets and air/fuel mixture screw, but not what this other bore was for. It seems odd that it would be threaded if it wasn't used.

Last of all doesn't the 350 raptor have a fuel filter? If it does where is it?

Any help would be appreciated, THANKS.
 

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As for fuel filter no ,not that i know of its just pipe from fuel tap to carb
 

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Discussion Starter #4
Thanks quadz, I can't believe Yamaha would not put a fuel filter in the system, well it will have one when it goes back together. I tried the link for the carb but it's not working for some reason. I will try it again from work tonight. Thanks again.
 

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Discussion Starter #7
Thanks Kaper that answers one of my questions. That photo of the bottom of the carb is the one I was refering to, that was a real good write up on how to clean and rebuild the carb. BW228 that was a good lesson in carb operation thanks for the link. Still stumped about the pilot screw unless they mean the air/fuel mixture screw (I thought they were 2 different things).
 

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In the image that I posted it points to a Primary jet. That is also know as the Pilot jet. I am guessing that is what you are referring to as the Pilot screw.

Here is another reference image that may help....

 

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Discussion Starter #9
I know the jet is supposed to be turned all the way in and seated firmly. I'm beginning to think what Yamaha is calling the pilot screw is reallly the air fuel mixture screw. It is the only screw adjustment on the carb as far as I can tell. There is a screw in the bottom of the float bowl cover that screws in horizontally, but from what I can find out that is just a drain screw and gets seated firmly also.
 

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Discussion Starter #11
It's pretty bad when Yamaha themselves calls it by 2 different names in the service manual. they probably do it on purpose to confuse people so tthey will take it to the stealer. Thanks for all the help everyone.
 

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Discussion Starter #13
There is a main jet, a pilot jet, and a pilot screw which is also called the air/fuel mixture screw on this carb. Don't get jets and adjusting screws mixed up jets are not adjustable they are screwed in and seated firmly and not turned again until they are removed again, the only thing you can do with a jet is to change its out with another jet of a different size. Not trying to sound like a jerk here sorry if it seems that way.
 

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The fuel screw is often called the pilot screw because it is used as a valve that adjusts fuel flow through the pilot jet. The jet controls the max flow allowed, the screw adjusts from that max all the way down to zero when bottomed out.

The pilot circuit (pilot jet valved by pilot screw) is simply the air/fuel mixture adjustment from idle to 1/4 throttle. It has little effect above 1/4. The needle and needle jet affect mixture from 1/4 to 3/4 throttle (controlled by engine vacuum) and the main jet from 3/4 to wide open throttle.

The fuel filter is a fine mesh screen built into the fuel petcock's intake tube... you must remove the petcock from the tank to clean it.
 
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