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The picture don't show much that is needed to see. But, it should be the main fuel mixture screw assembly you're about to deal with. It should be an easy job. There's the brass fitting that screws into the carb body and is sealed with a soft metal washer, or mebbie a real hard paper one. The brass fitting should have a straight hole part way thru the axis, with the inner part of the hole threaded the rest of the way to match the threads on the mixture screw. Between the head of the mixture screw and the threaded part should be a smooth and straight (no taper or wierd shapes) section. You need a new o-ring. Look around your pile of half used carburetor kits, or your O-ring box, and get one that the inside diameter fits the straight section of the screw, and the outside diameter fits the hole in the brass fitting. Just slightly snug on the o-ring fit. Next, clean up the fitting hole, the little spring and the flat washer that goes on the screw along with the o-ring. If you can't find 'em you've probably found the reason for the leak... Anyway, round up a spring and flat washer that will fit with a little clearance into the hole in the brass fitting, and a little clearance on the screw, both. One end of the spring should seat against the bottom of the screw head. Put it together as follows- Put the spring over the screw shaft.
Slide the washer on the shaft and against the spring.
Put the O-ring on the screw shaft and against the washer.
Give the whole works, including the hole in the carburetor casting, a shot of motor oil and make sure everything is all slicked up.. Put the soft metal washer on the fitting and screw them into the carburetor body.
Insert the screw in the fitting hole and gently run it in. You should feel some friction while turning the screw as it gets close to being seated. The spring should be pushing on the washer. The washer should be pushing on the o-ring. And the o-ring should bottom out in a clean hole. Spring pressure makes the O-ring swell a bit and that accomplishes sealing the fuel from leaking Do not force the screw against the seat! Use gentle force to find the bottom. Back the screw out one turn. This should get the engine started and let you make initial adjustments and warm it up. 1. Final adjustment of the main mixture screw is done with the engine fully warmed up and running at wide open throttle, or full governor speed (1750 RPM). 2. Run the screw in slowly and stop when engine speed starts to drop. Note the screw head position.
3. While counting screw turns, slowly back out the mixture screw and stop when the engine begins to slow down, or runs rough and makes exhaust smoke.
4. Return the screw to the half way, or best running, position. 5. Do this procedure several times and find the screw postion that gives maximum engine speed with smoothest running. Now, move the throttle to idle position and do it all again with the idle mixture adjustment screw. It's the smaller one just below where the governor shaft connects to the throttle arm inside the housing. If perchance the thing don't seem to run just right under load, try changing the main mixture screw 1/8 turn one way or the other. If that don't help, return the screw to where it was before you changed it. If it still don't run right check into ignition system needs. If it runs good, go have a cold one and gloat about your success and don't mess with it any further! Good luck, 450
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