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Possible carburetor issue with Craftsman gas trimmer

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Blueshark New Member Total Posts : 1 Scores: 0 Reward points: 0 Joined: 2025/04/30 12:33:23 Status: offline 2025/04/30 12:43:32 (permalink) 0 Possible carburetor issue with Craftsman gas trimmer Hello. I’m new to the forum and need some advice. My son got a free Craftsman gas trimmer model C459.51212 (MTD 41ADZ20C899) that didn’t start and asked me to see if I could do something with it. I noticed that the spark plug cable was defective and fixed the issue. I installed a new spark plug and filled the tank with new 40:1 gas. The trimmer was difficult to start, did not run well and stalled after about 30 seconds. This occurred time after time. I took the carburetor apart and noticed that the diaphragm and gaskets were not in the best of condition. I cleaned everything with carburetor cleaner and reassembled. I also cleaned the vent on the gas tank cap. The trimmer still did not run smoothly and fast enough on full throttle. I could not order a carburetor repair kit for this model from the repair shop but I found a very cheap kit from Walmart.ca that included a carburetor, gaskets, fuel hoses and fuel and air filters. I installed the kit. Now, the trimmer starts somewhat easier but doesn’t run fast enough and stalls as soon as I release the gas throttle. I haven't done any adjustments on the low-high speed screws, really not sure how anyway. Should I buy a more expensive and (possibly) better quality carburetor from the repair shop, now that I have new gaskets, fuel hoses and filters? Any advice would be greatly appreciated. Thank you. Quote #1 1 Reply Related Threads
SRTsFZ6 Super Member Total Posts : 2097 Scores: 74 Reward points: 0 Joined: 2018/11/18 07:20:58 Status: offline Re: Possible carburetor issue with Craftsman gas trimmer 2025/04/30 19:34:10 (permalink) 0 You don't need another carb or anything else. I believe you have (besides the IDLE STOP SCREW), both a low speed and high speed adjustment screws. You'll need to buy, on Flea Bay (or Amazon), a kit of various carb adjusting screw drivers Their cheap, maybe $10.00 for all... The screw closest to the engine is the LOW SPEED screw The screw closest to the air filter is the HIGH SPEED screw. Get the engine to temp, and then adjust the high speed screw to get the RPMs to rise as high as possible. A little richer is better than leaner.. It may be need to go inward, (clockwise) to lean or outward to richen. Once that's in the ball park, go after the low speed screw setting. With the stalling, it likely needs to be richened up. Get a good solid idle, a one pull start once hot, then fine tune the HS screw. Both screws often affect the other so some back and forth will get it running correctly.. . Scott Quote #2

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Blueshark

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Total Posts : 1
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Joined: 2025/04/30 12:33:23
Status: offline

2025/04/30 12:43:32 (permalink)

Possible carburetor issue with Craftsman gas trimmer

Hello. I’m new to the forum and need some advice.

My son got a free Craftsman gas trimmer model C459.51212 (MTD 41ADZ20C899) that didn’t start and asked me to see if I could do something with it.

I noticed that the spark plug cable was defective and fixed the issue. I installed a new spark plug and filled the tank with new 40:1 gas.

The trimmer was difficult to start, did not run well and stalled after about 30 seconds. This occurred time after time.

I took the carburetor apart and noticed that the diaphragm and gaskets were not in the best of condition. I cleaned everything with carburetor cleaner and reassembled. I also cleaned the vent on the gas tank cap.

The trimmer still did not run smoothly and fast enough on full throttle.

I could not order a carburetor repair kit for this model from the repair shop but I found a very cheap kit from Walmart.ca that included a carburetor, gaskets, fuel hoses and fuel and air filters.

I installed the kit. Now, the trimmer starts somewhat easier but doesn’t run fast enough and stalls as soon as I release the gas throttle. I haven't done any adjustments on the low-high speed screws, really not sure how anyway.

Should I buy a more expensive and (possibly) better quality carburetor from the repair shop, now that I have new gaskets, fuel hoses and filters?

Any advice would be greatly appreciated.

Thank you.

Quote #1

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SRTsFZ6

Super Member

Total Posts : 2097
Scores: 74
Reward points: 0
Joined: 2018/11/18 07:20:58
Status: offline

Re: Possible carburetor issue with Craftsman gas trimmer 2025/04/30 19:34:10 (permalink)

You don't need another carb or anything else.

I believe you have (besides the IDLE STOP SCREW),
both a low speed and high speed adjustment screws.

You'll need to buy, on Flea Bay (or Amazon), a kit of various carb adjusting screw drivers
Their cheap, maybe $10.00 for all...

The screw closest to the engine is the LOW SPEED screw
The screw closest to the air filter is the HIGH SPEED screw.

Get the engine to temp, and then adjust the high speed screw to get the RPMs to rise as high as possible. A little richer is better than leaner..
It may be need to go inward, (clockwise) to lean or outward to richen.

Once that's in the ball park, go after the low speed screw setting.
With the stalling, it likely needs to be richened up.

Get a good solid idle, a one pull start once hot, then fine tune the HS
screw. Both screws often affect the other so some back and forth will
get it running correctly..

.

Scott

Quote #2

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