Newbie really confused - carb questions

Hi Gang, I am sooo new to this thing and I know so little it's embarrassing. :thumbsup:

Yesterday, I was prepping my new-to-me 2004 wr450 for my first ride tomorrow. I don't know what mods were done to it but am sure the throttle stop was done given the way this thing rips.

When I first got the bike in January I was turning what I thought was the fuel screw to adjust the idle speed. Well yesterday it was b&^ch to start and when warm, the idle would fluctuate - high one minute, low the next.

After doing a few searches I learned I am a noob and I discovered I wasn't turning the fuel screw but the black knob on the carb. The best picture is from ARin

where I can now clearly see the fuel screw (red knob bottom of carb) and the black knob.

OK, my questions,

What the heck was I turning (one picture in the manual says is the throttle stop screw)???

Would it be responsible for it being hard to start and the fluctuating idle speed?

And finally, where should this knob be set (open, closed)?

The black knob is the idle speed adjustment. Set it so the idle is where you like it. I think the book says 1800-2000 rpm or something like that but you can just do it by what sounds right. The red screw is the idle mixture screw. Clockwise = leaner and CCW = richer. Surging idle is usually a sign of a lean idle mixture. Try opening the mixture screw. It has a range of about 3 turns. Above that you should go to the next richer pilot jet. What elevation are you at and what jets are in the carb?

Thank for the info PDBblue,

Whew, so that was the idle speed knob I was turning. Man, I was worried there for awhile.

We are at about 2300 feet in elevation and to be honest I have no clue what jets are in the bike. I will see how it does tomorrow on a ride and tinker with the idle mixture screw a little and then determine if I need to tackle the jetting question.


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