Small Engines (Lawn Mowers, etc.): 2 cycle carburetor adjustment, adjustment screws, screw out

Question
Hi, Eric,

I bought a Jacobsen/Homelite single stage snowblower 420E with a two-cycle engine very similar to one I had previously.  The man had rebuilt the carb and it starts and works good, but it seems like it runs at a higher rpm than might be appropriate.  I'm concerned that the adjustment is such that the engine may be starving for lubrication.  It has no throttle and runs only at the one high speed.  The person who worked on the carb had trouble keeping it running. I learned the problem was actually unrelated to carb adjustment, but I'm concerned he fiddled with it. I would rather the engine be running in the middle of the acceptable range than just on the edge.  The carb has both the H and L adjustment screws, and I would understand the H has primarily to do with high speed operation.  Can the H screw be adjusted slightly to reduce my concerns that the engine is receiving proper lubrication?  If so, which way?  What would the procedure be for verifying the carb is properly adjusted?  

Thank you for taking the time to respond to my questions.

Duane

Answer
You can turn the H (High Speed) needle out, just a little, to increase the fuel mix.  You should hear the engine RMP drop by turning the needle out.

The Walbro manual states to 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 engine 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 the engine.

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. Recheck high speed setting again.

Let me know if this helps.
Eric