# toro string trimmer wont stay running



## bw1 (May 25, 2010)

Hello all. I have a toro string trimmer model 51974 310042961. I rebuilt the carb and put in new denso plg and will not stay running. The carb is walbro wyc-7-1. 

I did the following:
1. rebuild carb making absolutely sure new gaskets and such went back on the exact way they came off. Removed old ones laid them down in order removed paying attention to what side is up etc. Screen applied correctly. Carb totally cleaned as far as I can tell

2. Clean and blew out the carb at about 25 or so psi air pressure

3. Put in new gas line x3. the line with the filter which does blow air bubbles when primer bulb is compressed went to the bottom nipple on my primer bulb as it was before. The line into the tank for gas flow back to tank went to correct nipple only one on opposite side of carb so it is straight run down to tank. the last very short new fuel line went from top nipple of primer bulb to nipple coming out of carb on the side towards trigger control.

The primer bulb will not prime unless I turn unit upside down so I assume it is filling via the line where gas returns to tank. 

Unit will start on second pull or so and will run anywhere between 5 seconds up to a minute. During this time primer bulb stays full so I assume it is sucking gas

It is as if I put fuel lines on primer bulb backwards but I am sure I did not. Going to home depot today to look at new toro gas lines to make sure and will report back in a few hours.

This is not my first rebuild but I will admit I have never has this happen before. Strange indeed. Primer bulb is brand new with no apparent cracks or pin holes. Tried two just to make sure. All gas line is brand new.

This one has me stumped fellows. Any suggestions. I write notes when taking stuff apart and take pictures and video. Cannot figure out what in the heck I did wrong. 
If the holes where the fuel line goes into tank x2 have become even a tiny bit and invisible to me enlarged would that cause my symptoms

thanks
brad


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## bw1 (May 25, 2010)

*update*

checked new unit and i have fuel lines correct. the longer nipple on primer bulb on the bottom is going to gas tank. shorter nipple on top of bulb going to left side of carb if u are looking at carb installed. return line going from right side of carb straight down to full tank.

could the gas cap be the issue. i just bought one and will install shortly. very strange what is going on at least for me
filter removal did nothing and i made sure line was submerged

lets say u have a gasket and identical thing but is more flimsy and rubbery unlike the gasket material and thinner. obviuosly these go together and assume the thicker gasket goes to metal and then the identical looking thinner rubbery piece goes on top of that. I will check that I did that and report back. starting to second guess myself. Am I correct on this?


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## paulr44 (Oct 14, 2008)

Whoa, hold your horses. You have to invert it for it to prime? That suggests the fuel filter isn't sitting down in the fuel, or there's a leak someone in the system and it's sucking air. Sometimes we'll see this when there's a pin-hole in the fuel line.

The inversion issue alone tells me if it runs, it's running on what's in the carb. and feed line and then stalling out from starvation. That make sense to you?

Is the tank above or below the carb.? This makes a difference.


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## bw1 (May 25, 2010)

paulr44 said:


> Whoa, hold your horses. You have to invert it for it to prime? That suggests the fuel filter isn't sitting down in the fuel, or there's a leak someone in the system and it's sucking air. Sometimes we'll see this when there's a pin-hole in the fuel line.
> 
> The inversion issue alone tells me if it runs, it's running on what's in the carb. and feed line and then stalling out from starvation. That make sense to you?
> 
> Is the tank above or below the carb.? This makes a difference.


the tank is below the carb. I guess new bought today fuel line could be bad. changed the cap and primer bulb and no luck. Im thinking a small hairline crack in tank. it seems not to hold pressure. starvation theory is dead on. but why? got to be a crack in tank. im going to get more fuel line in am tomorrow and try again. Im also thinking about forcing compressed air into take from a fuel line say at 25 psi and see if I get a tank leak. Is 25 psi enough? I thinking one of the kids dropped the trimmer and tank has crack. Tank is plastic

thankyou Paul


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## 30yearTech (Sep 14, 2006)

It sounds like you have the fuel lines hooked up wrong. 

The fuel line with the filter, should not "blow" bubbles into the tank when the primer is depressed. This line should be attached directly to the nipple on the bottom of the carburetor.

The line coming from the side of the carburetor should be attached to the suction side of the primer bulb, and the return line coming out of the primer, should be attached to the short line returning the fuel to the tank.

You do not need to pressure test the fuel tank for leaks, or you may create a leak you don't currently have.

The "Primer" is actually a purge pump, used to charge the carburetor with fuel to reduce starting effort. The system *does not "PUSH"* fuel through the carburetor, but rather "DRAWS (sucks)" fuel from the tank through the carburetor. Then pushes the fuel back into the tank.


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## bw1 (May 25, 2010)

30yearTech said:


> It sounds like you have the fuel lines hooked up wrong.
> 
> The fuel line with the filter, should not "blow" bubbles into the tank when the primer is depressed. This line should be attached directly to the nipple on the bottom of the carburetor.
> 
> ...



Thank you for your reply. I took carb off and got me a little tub for some fuel. I changed fuel lines around until I got bubbles to go away, then I swapped fuel lines until I was pulling from line with filter into car, out of carb to primer bulb and from primer bulb back to fuel tank. Bulb primes right up, machine fires on second pull and will idle and keep going as it should. Now it dies instantly when I try to run WOT on half choke and dies even faster when running WOT on no choke even after 3 minute or so warm up, This carb has only idle adjustment, no high and low adjustment. I have brand new cap so I assume cap is not blocked. Can i rule out plugged filter since it was blowing bubbles out before or does this make no difference and it could still be plugged when trying to draw gas?
Fuel lines are brand new so I dont think they would be restricted. carb just rebuild and no screws are loose, ruling out dirt or debris as lines are new, and diaphragm is new also. Spring for needle is not distorted or binding as far as I can tell as it appears to work properly when depressed. 

I am thinking it is plugged fuel filter now that I got the fuel lines correct.

thank you


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## bw1 (May 25, 2010)

*update*

Ok put on new fuel filter and new fuel and have very slight improvement but still wont run wide open throttle.


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## 30yearTech (Sep 14, 2006)

Unfortunately getting one of these newer rotary valve carburetors to work correctly after a rebuild can be very difficult, even for the most seasoned pros. They have passage way's and check valves that are not serviceable. I have spent way too much time in the past working to get these carburetors to work correctly and have been unsuccessful many more times than I have been successful. 

I would recommend finding a new replacement carburetor for your trimmer.


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## bw1 (May 25, 2010)

*FIXED toro string trimmer wont stay running*

Thank you all for your suggestions. I got the line strimmer running strong on WOT. Took the carb apart again, simply put it back together with no additional cleaning except a little sea foam instead of carb cleaner this time around and also bent the fork that lifts the needle so it would lift the needle a little higher and for what ever reason it now starts on first pull and screams at WOT.Perhaps debris fell out, perhaps it is only temporary but I'm running with the good luck and will take it for as long as she works. It is seven years old so I'm not expecting miracles but for now all is good.

Thanks again everyone

Brad:thumbsup:


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## 30yearTech (Sep 14, 2006)

bw1 said:


> Thank you all for your suggestions. I got the line strimmer running strong on WOT. Took the carb apart again, simply put it back together with no additional cleaning except a little sea foam instead of carb cleaner this time around and also bent the fork that lifts the needle so it would lift the needle a little higher and for what ever reason it now starts on first pull and screams at WOT.Perhaps debris fell out, perhaps it is only temporary but I'm running with the good luck and will take it for as long as she works. It is seven years old so I'm not expecting miracles but for now all is good.
> 
> Thanks again everyone
> 
> Brad:thumbsup:


That's Great, sometimes things just work out... :thumbsup::thumbsup:


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