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Calling The Carb Experts

954 Views 7 Replies 4 Participants Last post by  Goober
My buddy that i hunt with picked up a 05 Rubicon 500 TRX500FA around the same time i got my Rancher. The bike runs great and everything works. The only issue is a random idle issue, im sure cleaning the tank, shutoff valve and carb would fit the issue but would like to get your guys thoughts. The issue is the bike with crank up and idle fine and then after it warms up it doesnt want to idle, it will crank right up with applying a little throttle. He turns the little black adjustment knob on carb and gets it to idle again, he will go ride it and then it starts to idle high, adjust the knob again and lowers the rpms, after riding it again it doesnt want to idle. So basically he is fighting no idle/high idle. Its clearly a fueling issue and a simple cleaning would fit it im sure.

This is a generic carb pics off the interweb, not sure if this is the exact carb thats on his bike but it does have the 2 features that id like to get more info about.

What is that black knob adjustment for? Idle only?

Also see the other black handle just below the knob? When you pull that out with the bike running it kills. What is that?

Once hunting season is over im going to dive into it. Chances are hes going to want to just put a new carb on it($200) vs the down time of me rebuilding it. Regardless im going to rebuild it any tips?

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The carb is dirty—check out my TRX300 carb with chunks in it!

That black plunger is the primer bulb. It squirts fuel into the carb throat. The bulb rubber fails after so many years. Replace it and while you’re cleaning the carb, run some alcohol thru the lower half first and then attach the bowl and flush the upper half.

See the pinhole on the brass tube? This is why I am very careful to clean the carb with a brush first—so I prevent clogs in the channels.

I can tell the plunger is bad because the alcohol is only slightly coming out of the sprayer—the bulb balloons out the back of the plunger
I cleaned my neigbors carb on his pressure washer without taking it completely apart. I did remove the jets and floats to clean. I ended up using brake cleaner. This was the first time iver used brake cleaner and i was actually blown away with how well it cleaned. Put everything back together and we purs like a kitten now. So with that being said is brake cleaner spray safe for cleaning a carb? Also, besides the primer bulb what other must have parts should i get before even taking the carb off the bike? Is there simply a rebuild kit we could get that includes those must have parts(bulb, gaskets, seals, etc?

Also take the intake boot off to check for cracks in the rubber manifold or a leaking flange seal. Get the carb meticulously clean like @Goober does and reassemble following the manual all the way through and you'll be golden.

While ya got it apart you may as well adjust the valves too.
Thats a good idea, which also reminds me that i still need to adjust mine also.

You can’t rebuild the primer bulb or the starter valve.
But they can be replaced right?

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