Toro 51974 String Trimmer Does not Rev Up

sranger941

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Oct 8, 2013
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Have a Toro 51974 power head with string trimmer attachment that I was using the other day which suddenly stopped running. Has always worked well. I was able to restart, but it would not rev up. Same on full choke, half choke and no choke. Replaced carb, new fuel lines and filter, changed spark plug, checked muffler and spark arrestor. Compression was above 160. Also removed the muffler, but no change. Gas is fresh and no problems with other 2 cycle equipment. Has spark and coil resistance was around 2800. Any suggestions on what I could have missed? Thanks
 
Last edited:

jp1961

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Jul 22, 2013
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Hello,

Anything binding the shaft? Not sure if it's a curved shaft or straight shaft. I guess you could remove the powerhead from the shaft and try to spin by hand.

My first guess would be a plugged muffler, but you've already eliminated that from the equation.

Toro mufflers do have a spark screen in the muffler that is prone to carbon buildup causing almost complete blockage.

Regards

Jeff
 

bertsmobile1

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Nov 29, 2014
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This is what happens when some one just throws parts at a tool before actually working out what the problem actually is.
So now we have absolutely no idea where to start because it could be any of the items you have replaced or all of the items you replaced or none of them.

So we go back to the basics
The engine starts so you know that the coil is working, no need to measure it and in fact with 99% of them resistance measurements are meaningless because of the trigger chip.
A secondary resistance will tell you if the plug cap is connected to the coil and that is about the only thing that you measure on modern coils.

You said it "just happened " .
What were you doing when it "just happened" ?
A sudden load or a very heavy load can rip the timing key out of the flywheel

Now you said you replaced items
Did you get them from an authorised Toro dealer ?
if no what sort of guarantee do you have that the parts are actually correct ( ebay said so ? ) or not a faulty second sold cheap on Amazon ?

We have no idea as you did not tell us .

Now how is the tank pressure ?
Does the pump bring the tank up to 5psi to 10 psi ?
If not how do you expect the fuel to get to the carb ?

Is the fuel system pressure tight ?

Have you gone to Toro and downloaded the service manual & IPL for your trimer , it is a free download ?
 
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