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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 29818
Experience:  Service manager and technician for all brands of engines with 40 + years of experience.
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small lawnmower engine running rich [plug fouled by carbon]

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small lawnmower engine running rich [plug fouled by carbon] and 'hunting'.I should be grateful for advice on cause[s] and remedies
Fouled plug is indication of too much fuel or too little air. Is the choke staying open when engine is running? Is air cleaner clean. Has carburetor been cleaned and the needle valve and float checked. If needle and float let in too much fuel, it can cause the rich fuel mix.
Customer: replied 3 years ago.

I can't answer until I have checked with the engine running. Unfortunately I can't do this until Sunday 1st June, when I shall let you know what I find out.

I should be grateful for your patience until then. As I am a new customer of yours, and am not familiar with how your system work, it also be most helpful if you would let me know how to get in touch with you then.



There will be an email in your in box that will have link to get back. Just get back when you can. Thanks
Customer: replied 3 years ago.

I find it difficult to answer because:


There doesn't appear to be a choke as such. There is a two-position manual control connected to the fan-operated speed governor (but not to the carburetor itself) by a large spring. I keep this in what I assume is the "run" position at all times because the engine slows or stops if I move it into the other position. The engine starts with only one or two pulls on the starter when primed by a few squirts from the bulb, and the manual control never needs to be used.


I can't report on any possible float chamber, because the carburetor sits largely submerged in the fuel tank, and I didn't have the time to remove it to examine what lies in the tank. I shall try to do this next weekend.


In the meantime, I had some photos taken (by my daughter, who e-mailed them to me) to show the carburetor and control configuration, and I shall try to attach them to this reply in case they help with your diagnosis.






PS:Sorry, I can't send the photos with this reply because I can't seem to convert them to a format acceptable to your system, so I shall send this answer anyway. It would help if you could send me a direct e-mail account so that I can simply forward my daughter's original e-mailed versions. In the meantime I shall try to convert them off-line.

In the meantime, any further advice from you would be welcome.

So carburetor is the tank mounted variety , here is link, very little can be done as far as adjustments, but rich burning and fouled plug are too much fuel or too little air. Be sure air cleaner is kept clean. Anything else may require a carburetor replacement!----

Customer: replied 3 years ago.

Thanks. I have downloaded and printed info from the link.

I have also managed to get the photos in the right format but your system tells me that they are too large (about 350kB over the 5000 max) to send you. I shall try to reduce their size but am not too hopeful.

I shall take your advice and clean the air filter again and remove the carburetor to see what I can see. However, you are probably right and I may have to change the carburetor. Any advice on where to get the best deal?

Not sure in UK, but PartsTree is my choice. Or Ebay!
Customer: replied 3 years ago.

Thanks. I'll explore and update you after next weekend

Ok, thanks.
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