# Lawnboy



## Rentahusband (Aug 25, 2008)

Working on a Lawnboy #7350. Starts and runs fine for about 15 minutes. Then it starts to run rough and smoke. If I take the air filter off it clears up. Put it back on and it acts up again. Filter is clean, carb is clean. What am I missing??
Thanks


----------



## 30yearTech (Sep 14, 2006)

Did you check the exhaust ports and muffler? Back pressure could cause a similar issue.


----------



## Rentahusband (Aug 25, 2008)

If there was build up in the ports or muffler, would'nt it run poorly from the start? The owner said after about 15-20 minutes it would loose power and die. They had a hard time getting it restarted and when it did, it would do the same. I ran it for 25 minutes before it started to loose power, but never died. There is more blue smoke when it is loosing power, but when I remove the air filter it clears up and runs as it should. But why is it only doing this after running for awhile? When I take the filter off I notice a little fuel spitting out the carb until it clears up and gets back to normal. Seems like it is getting to much fuel after it has been running for awhile. I did notice there is some oily crud on the deck in the lower crank seal area. Is it possible the lower seal is leaking when warmed up?
Thanks for you reply 30year!!


----------



## 30yearTech (Sep 14, 2006)

Partially restricted exhaust will cause more back pressure and spit back through the carburetor. Since this engine utilizes a reticulated foam air filter, it can become saturated with fuel after it has run for awhile until eventually it causes the engine to start running richer. This will in turn cause the engine to slow down and loose power. When you remove the air filter, the mixture leans back out and the engine starts running better. 

Excessive back pressure can cause a discharge through the seals due to increased crankcase pressure. The rich running mixture can allow unburned fuel oil mixture to condense in the muffler causing a thick black oily discharge. Old weak fuel can also cause this type of discharge in 2 cycle engines.


----------



## Rentahusband (Aug 25, 2008)

Ports were clean. Took the propane torch to the muffler and burned out whatever crud was in there. Seemed to have done the trick. Mowed for 1/2hr with no issues. Thanks for your input 30yr!!


----------

