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Rick, Small Engine Technician
Category: Small Engine
Satisfied Customers: 3844
Experience:  Outdoor Power Equipment technical trainer since 1990, covering eight states.
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i have kubota lawnmower 5hp petrol wont start backfiring when

Customer Question

i have kubota lawnmower 5hp petrol wont start backfiring when i trie to start it
Submitted: 3 years ago.
Category: Small Engine
Expert:  adamd-mod replied 3 years ago.

Hello there,

I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.

I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you and refund your deposit.

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Customer: replied 3 years ago.

continue to search for expert

Customer: replied 3 years ago.

ihave cleaned the carberator and its still the same

Customer: replied 3 years ago.
Relist: Incomplete answer.
Expert:  Curtis B. replied 3 years ago.
Good morning. How did problem happen? Could blade have come to sudden stop, that may have sheared the timing key on the flywheel, throwing the engine out of time? Is this a Kubota engine, or is it a Briggs engine used by Kubota? Model number of the mower?
Customer: replied 3 years ago.

its a kubota engine i dont know if it came to sudden stop i cant see aneything brokin on the flywheel number 103361

Expert:  Curtis B. replied 3 years ago.
Backfiring is sign that valve is open when the spark occurs. That means valve is stuck open, or the timing is off. But before doing that, can you drain the carburetor float bowl and see if there may be water in the fuel bowl? Pull the spark plug. and see if it shows moisture. If plug looks normal, and no water in the carburetor. I would want to remove the flywheel nut and check the key slot to see that crankshaft and flywheel are in perfect alignment. If not, the key is sheared and flywheel needs to be removed and key replaced.
Customer: replied 3 years ago.

the crankshaft and flywheel are in line no water in carburetor i have celend the carburetor stil backfiring wont start

Expert:  Curtis B. replied 3 years ago.
Remove the spark plug, and hold finger with rag over the spark plug hole to see if you have compression. If no compression, you have a valve stuck open.
Customer: replied 3 years ago.

there is compression it feels week

Expert:  Curtis B. replied 3 years ago.
It has to be at least 80 psi or it is not going to start. With weak compression, one of the valves is likely not seating fully. Can you remove the rocker cover and and check the valve clearance.? If one has excessive clearance, it is sticking open. Clearance should be less than .010 inch. 0.254 mm . The valves have to have some clearance also, or the will not close completely.