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My lawn mower has suddenly developed this problem where it stalls while I am mowing. Once it stalls it won't start immediately but if I wait ten minutes it will start again (on the first pull usually). I'll mow another hundred feet or so and then it stalls again, and so on. I've got new gas, a clean air filter, and reasonably new spark plug. Any suggestions to troubleshoot this problem? Thanks!
Craftsman 6.6 hp 22" rear discharge, power propelled rotary lawn mower about 6-7 years old.
Answer -
Replace the spark plug and check the headbolt torque.
Let me know what you find.
Eric
I replaced the spark plug and checked the headbolt torque and the lawn mower still stalls out. When it fails it sounds very similar to an engine running out of gas. Almost like something is blocking the gas flow when the engine heats up. Any ideas - thanks.
Bob
Answer -
Do you have and overhead valve (OHV) engine? Have you ever checked valve clearance?
Let me know.
Eric
Yes, I do have an OHV engine, and no I have never checked valve clearance.
Bob
Answer -
You can check the valve clearance by removing the spark plug and rotating the engine to top-dead-center (TDC). TDC is when the piston is at the top of it's stroke. You can watch the valves or insert a straw into the spark plug hole to identify when the pistion is a TDC; make sure you are on the compression stroke when you check the valve clearance.
Let me know what the clearances are.
Eric
Eric
With the piston fully extended (TDC) the exhaust valve (top one) is fully closed and the intake valve (bottom one) is slightly open. I would say you could slide a business card between the valve and its seat.
Bob
Answer -
The valves should have .004 of an inch clearance. To be sure you are on the compression stroke, rotate the engine in the dirction it normally travels, should be clockwise direction, while watching the valves. As the piston moves down the intake valve should open to allow fuel to enter the cylinder. As the piston comes back up this should be the compression stroke. Once at TDC the piston should begin to go down again; power cycle. As you continue to rotate the piston should start to move up in the cylinder and the exhaust valve should open to release the exhaust gas. Once you are sure you are on the compression stroke TDC check the valve clearance again. The gap should be .004 of an inch.
Can you see an adjustment nut located on the top of the valve rocker assembly?
Let me know.
Eric
Eric
Sorry, I made a major mistake - there are no valve rocker assemblies visible so they are not overhead valves. When I look through the spark plug opening all I see are the tops of two values which open and close with the piston stroke. At the top of the TDC the exhaust valve is fully seated and the intake valve is slightly open as I said before. I have no way of measuring the intake opening through the spark plug hole but it could be 0.004 of an inch. Sorry about the mixup.
Bob
Answer -
Since you have an L head engine, the valve clearance is .008 on an inch for both valves.
You will have to remove the carb/manifold assembly to remove the valve cover on the side of the engine block.
Use a feeler gauge to measure the valve clearance with the piston at TDC on the compression stroke.
Let me know what the clearance is.
Eric
Eric
I removed the valve cover and could see a couple of valve lifters coming out of the block and the valves with springs and caps coming out of the head. There is no clearance between the lifters and the valve stems at TDC and the valves are seated in the head at TDC.
Hopes this helps.
Bob
Answer -
Just to make sure, rotate the engine over until the next TDC. Check the valve clearance again.
Another test you should do is to continue to rotate the engine 1/4 inch past TDC and check the valve clearance...mark a 1/4 inch on the straw.
Can you tell if you have a Briggs engine or Tecumseh engine?
Send me the model number and I can check.
Eric
The lawn mower is Model# is 917.377302
Bob
Answer -
Please check the model number again. I tried to cross reference with Sears but the website did not recognize the number.
You can go to Sears.com and enter the model number under "parts" and see the mower.
Let me know.
Eric
The number I gave you is the lawn mower model #. The other number is the engine number and is #143976600. I went to the Sears site and put this number into the parts search engine and it gave me a schmatic and a parts list. I emailed the parts department with the engine number and they told me that the manufacturer of my engine is Tecumseh.
Hope this helps!
Bob
Answer -
Engine model number worked. The valve clearance should be .008 of an inch, both valves.
How much clearance does each valve have?
Let me know.
Eric
The exhaust valve has about .006 of an inch and the intake valve has about .007 of an inch.
Bob
Answer -
The valves should be alright. When the mower dies, how long do you have to wait before it restarts?
Ignition coils can be difficult to troubleshoot because they will sometimes test fine when cold but under heat the coils of wire inside the module may expand and short out.
Do you have an inline spark tester?
Let me know.
Eric
From when I first start the lawn mower it takes about ten minutes to stall, after that I can start it in about five minutes but then it will stall again with two to three minutes.
I don't have an inline spark tester.
The lawn mower has a 'solid state ignition'.
Bob
Answer -
Since the carb has been cleaned, the mower starts easy when cold, the valve gap is alright, the spark plug has been replaced, intake gasket/screws are tight and sealing along with the headbolts/gasket, about the only part left is the ignition coil.
You can purchase inline spark testers at most auto parts stores for less than $10. Another option is to ask a friend who has a similar mower if you can borrow their coil and put it on your mower. These two methods are about the only way to test a defetctive coil that is affected by heat.
Does this make sense?
Eric
The carb has NOT been cleaned. Other than draining out the gas for winter storage I haven't done anything to the carb.
Bob
Answer -
Do you have an air compressor and any experience with carbs?
These carbs are fairly simple but an air compressor is needed to blow out all the orfices.
Let me know.
Eric
Yes I do have an air compressor and I have some experience with carbs. I also have the schmatic and parts list so I could follow along pretty well.
Bob
AnswerBig thing is to pay attention to how the carb linkages are connected before you remove the carb.
Also, when you blow out the carb orfices be careful not to blow out the inlet needle seat...no big deal if you do they are easy to replace but just don't want you to loose it right off the bat.
Since the mower starts easy I doubt the carb is at fault but it's worth a try cleaning it versus getting a new ignition coil.
Let me know if you find any debris in the carb.
Eric
