Model 10415 Carb questions

[22R]

Hi All,

After acquiring a couple junk lawnboys I have just got one running with a rebuilt short block from ebay. F series engine all new seals, bearings, and rings. Walbro LMR-10 Metal carb. When I first started it the air vane had no tension and it idled real low and sounded cool but it wouldn't rev up so I adjusted the air vane thumb wheel increased the tension and now it is revving up and running but the idle while lower than run speed is still higher than the minimum if I push the airvane back while it is running to the minimum throttle opening it will idle down and hold the idle.. Seems like I can have low idle and no high end or good throttle with high idle but not both low idle with high revs. Is this normal or should it wind up and idle down. I have no tach just by ear but I am not over revving cause I can still push the air vane open while running and make it increase RPM. The mixture screw on the side of the carb ? What does it do ? I have it open at 3/4 out. I guess I need a quick rundown on the proper tuning of the metal walbro carb if anyone wants to assist me. I am looking into getting a tach. Appreciate any insight. It runs and cut fine I just want to make sure that I have it revving and idling right too.

Thanks,
22R

 

[dewguy1999]

If you don't already know this, you can download a service manual for your mower from the Lawn-Boy Support Center.

 

[beg]

just got one last night.your govenor spring is not set right.the screw you mentioned is the altitude adjustment but you have to get the air vane set right first if it idles too high you have too much tension on it.excuse the dirty condition I have not cleaned it yet

 

[Phototone]

Hi All,

After acquiring a couple junk lawnboys I have just got one running with a rebuilt short block from ebay. F series engine all new seals, bearings, and rings. Walbro LMR-10 Metal carb. When I first started it the air vane had no tension and it idled real low and sounded cool but it wouldn't rev up so I adjusted the air vane thumb wheel increased the tension and now it is revving up and running but the idle while lower than run speed is still higher than the minimum if I push the airvane back while it is running to the minimum throttle opening it will idle down and hold the idle.. Seems like I can have low idle and no high end or good throttle with high idle but not both low idle with high revs. Is this normal or should it wind up and idle down. I have no tach just by ear but I am not over revving cause I can still push the air vane open while running and make it increase RPM. The mixture screw on the side of the carb ? What does it do ? I have it open at 3/4 out. I guess I need a quick rundown on the proper tuning of the metal walbro carb if anyone wants to assist me. I am looking into getting a tach. Appreciate any insight. It runs and cut fine I just want to make sure that I have it revving and idling right too.

Thanks,
22R

You actually don't want the air-vane to be fully closed or fully open at any speed setting while the engine is running. Of course the vane should hold the throttle fully open when the engine is stopped. You achieve this goal by adjusting the tension spring that holds the vane and throttle butterfly open. The "idea" is that if the mower encounters a heavy load (heavy grass) the slowing of the rpm will cause reduced airflow across the vane causing the vane to open up the throttle butterfly a bit, giving more gas to keep the rpm constant. This concept works at low speed or high speed "IF" you have some wiggle-room for the vane to work. So, even at the lowest or highest throttle lever setting, while the engine is running, the vane should not be fully open or closed. The altitude adjustment screw you mentioned is for leaning or enriching the overall mixture. You want the mixture rich enough for the engine to run at low speed, yet not get bogged down with too rich a mixture at high speed. You adjust this screw to give satisfactory results at both high and low rpm, and easy starting. Of course any carb adjustments should be done on a squeaky clean carb, and after the engine has had time to warm up.

 

[22R]

Appreciate the comments Guys. I have a induction tach coming so I can see my RPM's. I think that I have it tuned pretty good by ear as it does exactly as Phototone stated, It will increase RPM's if it hits thicker grass. I will be interested to see how close I am to 3100 with the tach. And Beg mine looks just like yours but while I had mine down to install the short block I removed the engine brake and installed a kill button. So nice not to have to hold handles to keep it running.

22R