Small Engines (Lawn Mowers, etc.)/Walbro Carburetor


I have an old Jacobsen snowblower with a 2 cycle engine that has a Walbro carburetor I want to make sure is adjusted properly.  It has only one adjustment screw encircled by a spring that is labeled "LO".  There is what looks like a screw in the "HI" position that I thought was adjustable, but it is either a preset and unadjustable screw or just a plug or something.  It has no spring around it and the head of the screw is tight to the carburetor body. So my conclusion is only the "LO" screw is adjustable but when turned doesn't seem to make much difference in engine response. The carb does not have a throttle and only runs at one high speed when started.  Exactly what does the "LO" screw adjust and how do I know when it is adjusted correctly?  What is that in the "HI" position hole. My concern is that I not run it too lean or too rich.  Any information I've found about Walbro has two adjusting screws.  Thank you for any details you can offer.

Check out these Walbro links:

I have a feeling the high speed is fixed on your carb.  You would not notice much of a difference adjusting the L "low" speed needle as this needle mainly adjusts the low speed circuit when the enigne is idling.

You could manually hold the throttle in the idle position to adjust the L needle.


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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