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#145979 - 09/11/19 02:50 AM Air/fuel mixture screw
redninja Offline
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Registered: 06/04/06
Posts: 512
Loc: SW CO and AZ
While I had the carb off, I drilled out the brass plug. Stuck the screwdriver down into the tube and found the screw was fully seated. It was extremely difficult to screw out, and it went only about two turns out. To make a long story short, I buggered up the head (is that even possible on a slot head ?). I think it was because I did not expect so much resistance, and the fact I wasn't actually looking at the head while turning. So I squinted down into the tube and could see a little bit of the head, but still couldn't turn it out past 2 turns.

So now I am concerned that if I need to adjust it, the head will totally strip. And, there is no way to get my usual TOOLS OF DESTRUCTION down into the tube. Is there a way to get the screw out with the head being messed up ?

So far, the bike seems to be running good, but now it wants to be started without the choke, whereas before the carb cleaning, it always required the choke, but did always start up right away. Is this a clue to a possible problem ?
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#145981 - 09/11/19 08:28 AM Re: Air/fuel mixture screw [Re: redninja]
#brer15 Offline
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Registered: 10/03/16
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Loc: Atlanta,GA
Maybe try using a larger screwdriver, that will still fit in there. Might be able to use one that is just a little too big by grinding down the flared areas just above the blade. And even grinding down the tip of the screwdriver to make the tip a little wider (trying to get a tighter fit in the screw).
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#145982 - 09/11/19 11:05 AM Re: Air/fuel mixture screw [Re: redninja]
Paul49 Offline
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Registered: 07/22/11
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Loc: High Peak, UK
I'd get some penetrant in there first, try & free it up.
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#145983 - 09/11/19 12:04 PM Re: Air/fuel mixture screw [Re: Paul49]
peejman Offline
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Registered: 06/03/13
Posts: 3289
Loc: East TN USA
Originally Posted By: Paul49
I'd get some penetrant in there first, try & free it up.


Yep, I'd try some penetrating oil and perhaps some heat on the boss to try to loosen it up.

Will it turn at all either way? If it'll go back in, I'd try rotating it back and forth, and carefully working it out. It's going to take a lot of patience to get it out without ruining the threads in the carb.

If its stuck hard, it might be best to take it to a machine shop and see if they can remove it with minimal damage to the carb. They're likely going to drill the screw out, so you'll have to buy a new mixture screw at the minimum.



Turning the mixture screw out adds fuel to the mixture, so it makes sense that the bike would start without the choke. 2 turns out is the normal starting point for adjusting mixtures screws, so in a way it's fortunate that's where it stopped. The fact that is was screwed all the way in before is more an indicator of a problem than it being 2 turns out now.

I suspect you'll notice a reduction in gas mileage as it's using more fuel with that setting. You may also notice reduced performance at higher altitudes due to the additional fuel. Both of those may force a need for 1 size smaller jets to restore performance, should you leave the screw where it is now.
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2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.

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#145984 - 09/11/19 01:33 PM Re: Air/fuel mixture screw [Re: redninja]
Muniac Offline


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Loc: Montrose, CO
I'd second the penetrating oil and heat approach. You've got a brass screw running in aluminum threads. Bad combination when heat, vibration and time are at work for galling. The unused threads are most likely corroded slightly. Heat on the boss will help expand the tolerance and WD40 will lubricate the threads. Hopefully enough you can "chase" out the remaining threads to remove the plug. Very delicate so go easy with forces and twisting. Just a little bit at a time back and forth is best. Good luck!
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#145987 - 09/11/19 10:00 PM Re: Air/fuel mixture screw [Re: #brer15]
redninja Offline
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Registered: 06/04/06
Posts: 512
Loc: SW CO and AZ
These all sound like good ideas. We have a grinder and plenty-o-screwdrivers.....I did put some penetrating oil on it when the carb was off the bike, but kinda half-heartedly; I was in a hurry to put it back on the bike. I have a bunch of other stuff to do right now, so it will have to wait a bit. At least I know how to take the carb off and on now.
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#145988 - 09/12/19 02:50 PM Re: Air/fuel mixture screw [Re: redninja]
Muniac Offline


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Registered: 01/16/04
Posts: 5828
Loc: Montrose, CO
There is something called a jet screwdriver. Its sides are perfectly parallel creating a square blade instead of a slight wedge. The idea is to get full contact on the jet's slot. Not just near the top edges. Most will grind a conventional screwdriver to fit exactly into a jet slot (depth, width and sides). Good luck.
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#145995 - 09/13/19 04:15 PM Re: Air/fuel mixture screw [Re: redninja]
Craig1 Offline
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Registered: 01/18/17
Posts: 35
Loc: GlenAllen, VA
Are you saying you can adjust the screw between all the way in and 2 turns out?
Since when all the way in the bike was hard to start, and two turns out the bike starts without choke, The correct adjustment may be between those two points. There may be no need to remove the screw at this time.
I have worked on many motorcycles carburetors over the years, and occasionally come across one with the screw turned all the way in from the factory.

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#146032 - 09/17/19 08:36 PM Re: Air/fuel mixture screw [Re: Craig1]
redninja Offline
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Registered: 06/04/06
Posts: 512
Loc: SW CO and AZ
Originally Posted By: Craig1
Are you saying you can adjust the screw between all the way in and 2 turns out?


Yes, it will turn between those 2 points, but is very hard to turn. So I don't dare try while the carb is on, for fear of damaging it further. I really need to take the carb off, and, using the suggestions found here, try to remove it, and replace.
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