Model 8671 Running rich then lean.

Canoester

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Model 8671 21" self propelled. Just replaced crank seals and have mowed with it a couple times this year. It ran very rich then I adjusted the needle valve to where it runs smooth it would not start until I back the screw out a bit. Then after about 10 minutes it runs too rich. Adjust and repeat...Can't find its happy spot. Any suggestions? (and yes I tried to sell it and give it away...:)
 

tom3

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This engine have a reed valve in the carb-to-engine throat? Might pull that out and check for something that would let crankcase pressure back to the carb. Need a good seal at those reeds.
 

Russ2251

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It's a 2 cycle model F with reed valve induction.
Sounds like sticky (or defective) needle/float.
 

Canoester

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Mowed last evening. True to form after about ten minutes the mower starts running rich and smoking. This is about the time I get to the steep part of the lawn. It ran great when I got off the incline. I'll mow up and down the hill next time and report back.
 

jp1961

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Hello,

From the Lawn-Boy mechanics handbook, here are areas to check for erratic running

Fuel tank screen partially clogged.

Fuel shutoff valve clogged.

Air leak in primer or hose

Improper float/float valve operation.

Incorrect carburetor float setting.

It's also possible the cork float has lost it's epoxy coating, allowing it to become the equivalent of being waterlogged.

To set float level, with bowl removed, invert carb with float arm resting on needle seat, the top of the float should be 7/16 to 15/32 above the housing/bowl mating surface. Adjust using needle nose pliers to float arm, do not bend by applying pressure to cork float.

Regards

Jeff
 

Canoester

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Go it running.

Update to the thread. The brass seat of the fuel mixture screw assembly had came unscrewed from the plastic carburetor housing and had backed out. It starts easily when cold but its still hard to start when its hot. Luckily I can get the part of the lawn I use this one for in less than 1 tank of fuel.
 

Canoester

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Go it running.

Update to the thread. The brass seat of the fuel mixture screw assembly had came unscrewed from the plastic carburetor housing and had backed out. It starts easily when cold but its still hard to start when its hot. Luckily I can get the part of the lawn I use this one for in less than 1 tank of fuel.

One year and four months later...Used the thing on and off over the summer. Driveshaft broke so I bought a new old stock off EBAY..It broke the first use. Old brittle plastic. Made a steel driveshaft and installed it, started mowing true to form the mower started running rich again. Shoved it under the canoe rack where it sat until today. Frustrated and tired of looking at it I took it to the curb but later retrieved it since I did not have the heart to let it go, Disassembled the carb and the brass seat had backed out again. This time I melted the plastic around the seat with a soldering iron after it was screwed in place. Assembled and it ran OK for the 5 minutes I used it.
 
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