OPE: what would be too hot?

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Have an MTD weed whacker, 4 stroke, that I bought years ago. Fixed a fuel line this summer and fired it up for the first time in a couple of years. Ran good for nearly 10 minutes then lost power--would idle, but would bog when I hit the gas. Hit around the spark plug area with my new toy from HF, the laser heat gun thingie, and it showed a max of 288F. Any chance it just overheated? I haven't had a chance to try out again just yet.

Fresh gas, although plug and oil are getting old.
 
Aircraft air cooled engines have an aluminum cylinder head temp redline of about 475 degrees F. Some are 500 F and some are 425.

Even so, air cooled engines are intended to run quite hot. The high temperature differential between the ambient air and the "fins" results in effective heat transfer.

I'd guess that you have carb problems.

Just an FYI, the infrared non contact thermometer won't be anywhere near accurate unless the surface being measured is flat black.
 
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I'd say 75% of the weed eaters I had trouble with had crud in the carb - tiny carb does not tolerate much.
 
Originally Posted By: supton
Ran good for nearly 10 minutes then lost power--would idle, but would bog when I hit the gas. Hit around the spark plug area with my new toy from HF, the laser heat gun thingie, and it showed a max of 288F.


Put the toy thingie away and start diagnosing the problem. "Bogging" down when calling for power is a classic symptom of carburetor issues, especially given the history.
 
No need for rudeness; I was curious about temp.

But you are right, there was crud in the gas tank that I've been ignoring. If I get around to it today I'll see about flushing it out.

Thing gets 10 or 20 minutes of use a year, sometimes none. I ran it yesterday and ran out of time to mess with it, and didn't think about crud--it was running fine, right until not.

Gives me a good reason to tear it apart. For fun.
smile.gif
 
Originally Posted By: supton
No need for rudeness; I was curious about temp.

But you are right, there was crud in the gas tank that I've been ignoring. If I get around to it today I'll see about flushing it out.

Thing gets 10 or 20 minutes of use a year, sometimes none. I ran it yesterday and ran out of time to mess with it, and didn't think about crud--it was running fine, right until not.

Gives me a good reason to tear it apart. For fun.
smile.gif



Metallic type things don't give accurate reading with ir temp guns. The shiny metal affects the reading somehow.
 
Don't have the manual anymore, but I'm sure it's online. Seemed odd to overheat, but I had a 2 stroke moped that overheated on a hill--I had earlier fixed a split fuel line that had left an oil mess on the cylinder, so on a long hill it nearly made it to the top--then gave up. After scrubbing the fins it later made it up the hill. Hence the thought about it getting too hot. [In this case, no oil mess on the fins, so... not sure how it'd overheat. Probably just crud in the carb.]
 
I don't think upper 200s on an air cooled is anything to worry about. Unless you are running some 10 year old conventional 5w20 in the crank case. Its a trimmer: if it even starts, it wont run right. If it runs right, the line jams. If the line doesn't jam, the line runs out. They are all just problematic frustrating lawn tools, almost by design. I spent a ton on a nice Kawasaki 2 cycle and it still gives me some issues here and there.

Fresh oil and a carb cleaning should fix it until it wants to bother you again.
 
Does it run OK hot with the choke on or partially on? That would point to definite carb issues. Could be a plugged gas cap vent as well, if it runs OK for some times, then poops out. Many times just fresh from the gas station fuel will cure lots of problems. People often forget how old the fuel is in their OPE or storage cans. Fine for up to a year in a quality, sealed storage can. Less in others.
 
No choke. Good question on the vent. Gas is getting old, been in the shed all summer (since this winter?) but it does run the lawnmower ok.
 
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