# Walbro carb adjust



## jackson (May 6, 2008)

My Sears Craftsman chainsaw 358.352090 uses a Walbro carb. In addition to the throttle adjustment there are two adjustment screws in the carb body marked “L” and “H”, presumably used to adjust air for low and high speed. Before I disassembled and cleaned the carb the Low screw was set 1/2 turn out from full in, and the High screw set 1 full turn out. The engine runs fine at these settings. But I find if I screw in the Low screw, the idle speed increases a lot. Is this an indication that the fuel/air mix is too rich? 

What determines the best setting for these screws?


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## geogrubb (Jul 28, 2006)

You can go to the Walbro site below, select Service/Aftermarket tab, they have a lot of info about their carbs. Have a good one. Geo

www.walbro.com


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## pyro_maniac69 (Aug 12, 2007)

when you screw the screws in, you are actually leaning out the mixture.

The way I adjust carbs is after I get it running, I hold the throttle wide open and set the H side to where its running at its fastest speed, but not bogging out. then I let up on the throttle and adjust the L side as necessary to where it will idle good, but as soon as you pull the trigger it will be at its high speed without much bogging


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## phillipmc (Jan 27, 2008)

pyro_maniac69 said:


> when you screw the screws in, you are actually leaning out the mixture.
> 
> The way I adjust carbs is after I get it running, I hold the throttle wide open and set the H side to where its running at its fastest speed, but not bogging out. then I let up on the throttle and adjust the L side as necessary to where it will idle good, but as soon as you pull the trigger it will be at its high speed without much bogging



You need to watch the RPM's of these engines you can get them to fast and burn the engine up. Its best to get the factory specs of the max engine speed and use a tack to adjust. Just my 2 cents


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## jackson (May 6, 2008)

Thanks for the source on the Walbro manuals, very complete. The carb is a Walbro, marked WA, though it is different than shown in the Walbro WA book. The book is dated 1994 and the saw is 1979.

All the Walbro books say to initially set both the idle screw and the high speed screw at either 1 1/4 or 1 1/2 turns out, which the books say will be a bit rich. For the idle screw, turn it in so idle speed increases and stop when the speed starts to drop, then back out a bit. OK, but that point is only 1/2 turn from full in. I’m concerned that only 1/2 turn out may be too lean and won’t provide enough lubrication. 

I also notice that every time the saw runs out of gas, the engine speeds up a lot. It runs at this very fast speed for about 10 seconds and then dies. Obviously it is running very lean as it is sucking out the last few drops of gas from the tank and fuel line. But why would it run so extremely fast? Does that indicate it is not normally getting the proper fuel/air mixture except when the tank is running dry?

Any thoughts?


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## hankster (Jan 1, 1998)

Start at 1 1/2 turns out. Go to full throttle. The high speed screw is then turned clockwise to reduce fuel (clockwise reduces fuel). As the fuel mixture is leaned out, the saw will run faster until it sounds as if it is screaming. At this point, turn the high speed screw to the left to allow more fuel until a "flutter" is heard. This is the proper RPM for your saw. 

For the low speed setting screw in until the RPM starts to drop... note position. Screw out and the speed will increase again, keep going out until the speed starts to drop. Setting should be the middle of these two settings. Now quickly pull the trigger, the saw should accel. smoothly... if it hesitates, open about 1/8 turn and try again.

Recheck high speed setting again.

Always make adjustments with a properly adjusted chain on the saw. You can not properly adjust the carb by RPM only.


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## 30yearTech (Sep 14, 2006)

No, 2-cycle engines when properly adjusted to not run particularly smooth. When you have a 2 cycle adjusted to provide good power they tend to sputter slightly. New closed ported engines are designed to run much leaner and the carburetors should be adjusted to the engine manufactures specifications and not the carburetors mfg specs. This adjustment generally requires an electronic tachometer such as described by phillipmc. Your saw being almost 30 years old should work fine when adjusted as described in the carburetor manual, if the carburetor is working properly the final adjustment should be more then 1/2 turn out from seat, I would think there may be a problem with the metering diaphragm or inlet needle / seat.


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