I put two stroke oil in the Lawn Boy 10640 and ran it briefly before it quickly became obvious what I had done. I have already drained the oil and replaced it with 4-stroke 10W-30 not just once but twice to make sure it's mostly gone. I also replaced the spark plug and the air filter. Yet when I run it, the exhaust still seems to 'smoke' after i turn it off... Like it's over heating. What do I need to do to fix it???

Curtis Sewell

• 7482 Answers
• Posted on Oct 10, 2010

SOURCE: I just bought the lawn boy 10640. haven't been

Sounds like you will need to clean the carburetor or replace your carburetor internal rubber parts like the diaphgram and O rings.
Be sure to use compressed air to blow out all the fuel and air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Sometimes you can get by with priming the carburetor or using starting fluid and letting it run a few times like that and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Keep in mind that the float for the carburetor must be level when you go to reassemble the carburetor or follow the instrucitons you get with the carburetor kit.
If the mower/weedeater is over a year old, then I also recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
When you clean your carburetor and remove the jet screws, you will first need to seat the jet screws.
But before you seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to seat them first and then turn them back out to their orginal position before you started.
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Curtis Sewell

• 7482 Answers
• Posted on Aug 21, 2011

SOURCE: Describe your Lawn-Boy 10640 20-Inch

Hi haystackcalh...

Sounds like you have dirt/debris in your caburetor jets,fuel passages or a diaphgram that is becoming non-flexible.
Check/Clean/Replace your Air Filter, a dirty air filter can make your engine run to rich with fuel.
Note: ALWAYS USE COMPRESSED AIR TO CLEAN YOUR JETS AND PASSAGES, VERY IMPORTANT.
Note:Before you disassemble the carburetor:
Mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you disassemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.
Sometimes you can get by with priming the carburetor or by using starting fluid and letting it run a few times like that, and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Check you fuel line condition after a while they will degrade and need replacment.
Check/Clean/Replace your fuel filter if you have one.
When you remove your fuel lines from the carburetor be sure to make a drawing to how the lines are connected to the carburetor.
Make sure you are using fresh fuel...and oil mix if your using a two cycle mower or weedeater with the oil to the right mixture and not too much oil as it can cause hard starting.
If the mower is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
The diaphgram may look good and flexible, but it can be deceiving and not act as a fuel pump as it should because it has become too hard and will cause hard starting,start and run and shut off, etc.
When you clean your carburetor, I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use COMPRESSED AIR to blow out all the fuel and air passages.The higher air pressure is needed to blow some of the trash/debris from the fuel or air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit, or you could also ask the parts man that you get your kit from.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Once you have your carburetor cleaned/rebuilt that should solve your problem.
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SOURCE: Lawn Boy 10641

see if the oil smells like gas the carb maybe sticking and gas gets into the oil washing the oil out this will make hard starting and smoke if so the needle valve is not sealing if you caught in time without major engine damage a sign is the oil being over full and smelling like gas