Unusually difficult diagnosis


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Old 11-02-14, 09:16 PM
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Unusually difficult diagnosis

I have a featherlite weedeater 25 cc engine or somewhere in that ballpark, not sure the exact size. To keep the post short I will just list what I have done to it. First got it, the thing would not start. Rebuilt the carb and it fired right up and ran great. Runs for 5 minutes then shuts off. It doesn't sputter, but shuts off hard.
Heres what I've done.
1. Replaced fuel lines and primer bulb when carb was rebuilt, cracked.
2. Replaced fuel cap, sounded like vapor lock.
3. Swapped ignition coils with another unit, runs identical.
4. Took off muffler to ensure no blockage, was wide open.
5. Checked for spark after it dies, strong blue spark.
6. Compression test, 105 psi after 4 pulls.

This is all done with fresh premium fuel, no ethanol blend, with 40:1 oil mix. I have not replaced the plug, but it is clean and the unit runs very well until it falls flat on its face. This has been going on for 2 years, so I'm trying hard to remember all I have done to it. It's a Zama carburetor. Perhaps the carb cannot keep up with the fuel demands?

If anyone has any insight, it would be greatly appreciated and very interesting. - Kyle
 
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Old 11-02-14, 09:49 PM
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Welcome to the DIY forum!

I have nothing to offer and I am posting this only for laughs.

Your problem is why I only have electric yard tools or, better yet, have the guy of Mexican heritage do my yard work. If only I could afford him these days.
 
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Old 11-02-14, 10:10 PM
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Originally Posted by Furd
Welcome to the DIY forum!

I have nothing to offer and I am posting this only for laughs.

Your problem is why I only have electric yard tools or, better yet, have the guy of Mexican heritage do my yard work. If only I could afford him these days.
Yeah, I've thought about it a few times, specifically for string trimming. Thing is, gas trimmers are so easy to come by, often for free. Plus I love the power gas offers the more power the better.
 
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Old 11-02-14, 10:18 PM
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I never had a power problem with my old Weedeater model 509. Unfortunately the spool assembly died and I can't get a replacement. Experiments with using a pair of washers to hold a piece of trimmer line, using heavy nylon zip ties and even 50 pound stainless steel downrigger line have all been qualified failures. I recently bought a ten inch "Renegade" blade but I need to get some arbor inserts and flange washers before I can try it. While that will be one wicked trimmer I won't be able to use it in the dirt like a string trimmer.

Juan, are you still working or have you retired?
 
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Old 11-02-14, 11:27 PM
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Will it start right back up or what does it do when you try to restart?
 
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Old 11-03-14, 11:57 AM
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Originally Posted by cheese
Will it start right back up or what does it do when you try to restart?
It is difficult to restart. Almost like it had to cool off. It has spark right after it dies.
 
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Old 11-03-14, 02:12 PM
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While it is running spray/dribble some carb/brake parts cleaner behind the carb and along all the mating surfaces if the engine tempo changes you have an air leak. Have a good one. Geo
 
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Old 11-03-14, 07:43 PM
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Could also be leaking air at the crankcase cover which is made of plastic and might be warping as it heats up.
 
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Old 11-04-14, 01:59 AM
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Originally Posted by cheese
Could also be leaking air at the crankcase cover which is made of plastic and might be warping as it heats up.
I took off the back cover to get the muffler off and noticed that the cover acts as the side of the crankcase. That's kind of bizarre. There was a piece of the gasket, which appears to be some type of rtv, was hanging off, but the gasket doesn't seem too bad. Maybe I will put some new rtv on if nothing happens with the carb clean.
 
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Old 11-04-14, 05:46 AM
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Stubborn Chain Saw

I messed up. Thought I was starting a new thread. Sorry.
 
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Old 11-05-14, 08:13 PM
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I put it back together and it did the same thing again. So I checked for leaks with the carb spray. No air leaks. I decided to switch the fuel lines around and see what happens, and now it runs really good! However it starts to bog down after about 5 to 10 seconds. If I crack the gas cap it starts running good again. But the thing is, it's a brand new gas cap. Plugged fuel filter? The filter was new not that long ago. Is the fuel pump weak and can't draw a little air through the breather on the cap? Pump was new when carb was rebuilt last year. Any thoughts? -Kyle.
 
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Old 11-07-14, 12:26 PM
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When it bogs down, shut it off and listen closely as you open the gas cap. If you hear air hiss when you crack the seal, the cap vent is bad or stuck shut.
 
 

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