# 2 cycle weed whacker not starting



## ccrider966 (Jul 8, 2006)

I have worked on many 2 cycle blowers, weed whackers, etc and occasionally I get one that just will not even try to start. Presently I have a Craftsman weed whacker that has 95 psi compression, good spark, good plug, cleaned carb, good filter, etc but will not even give a pop when I inject gas into the cylinder! I am pretty sure the carb is ok but even given that, it should at least pop when I squirt gas into the carb mouth or spark plug hole.
Could there be a timing problem or a blown crankcase seal or what? I imagine there is a key on the crank that times the spark and that is the best idea I have as to what would cause it to act this way. 
Anybody have similar experiences?


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## Sir Thomas (Dec 7, 2013)

Have you looked at the flywheel on this machine. I know a lot of Craftsman 2 cycle has the key built into the flywheel and they will shear off easily especially if it is aluminum. The key is so short and the slot on the shaft is shallow. You will get spark if the alignment of the flywheel is not right timing wise but it won't fire.


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## ccrider966 (Jul 8, 2006)

That is just what I suspected but it is a job to tear it down to inspect it. I will have to do it I guess! I have seen that aluminum key cast into aluminum hubs before and it is a lousy design, they just shear off too easily. I did not know Craftsman had that problem though......Thanks.


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## Rentahusband (Aug 25, 2008)

I just had the same issue with a Craftsman trimmer. I cleaned and rebuilt the carb, had 110 on compression, good spark, integrated flywheel key was good, exhaust was clean, air gap was good for the coil, fresh premium non oxy fuel. The dang thing would not even fire with carb or starting fluid sprayed in the carb or spark plug hole. I fought with trying to get it started for over 1/2 hour. It finally started, ran good and has started everytime now. I can not figure out what the problem was. Make sure to replace the filter screen in the carb. I have learned to always replace this screen when installing a kit. There is definatly not much of a flywheel key on these! I removed the flexable shaft and 4 screws off the front flywheel shroud to access the flywheel.


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## Sir Thomas (Dec 7, 2013)

Do you have a piston stop? Good to have. The problem with some machines with these type keys is that there is not a bolt directly attaching the flywheel to the shaft. The Craftsman Blower I worked on had a washer, extension, scroll which you have to attach to the stock, washer, peller mount and peller, washer and finally a nut. By the time you add all that, the flywheel may move, especially if the magnet is too close to the coil, and you can't lock it down where it belongs. The stop holds the shaft about 1/4 turn before the magnet reaches the coil so there is less danger of the flywheel jumping off the slot.


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## 30yearTech (Sep 14, 2006)

Sir Thomas said:


> Do you have a piston stop? Good to have. The problem with some machines with these type keys is that there is not a bolt directly attaching the flywheel to the shaft. The Craftsman Blower I worked on had a washer, extension, scroll which you have to attach to the stock, washer, peller mount and peller, washer and finally a nut. By the time you add all that, the flywheel may move, especially if the magnet is too close to the coil, and you can't lock it down where it belongs. The stop holds the shaft about 1/4 turn before the magnet reaches the coil so there is less danger of the flywheel jumping off the slot.


That is exactly correct. You don't want to hold the flywheel while tightening down the retaining nut. That can cause the flywheel key to shear, a piston stop works great for this. 

Another thing to look at for this type of issue is a massive air leak into the crankcase, many times the engine will not attempt to start even with a prime.


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## OptsyEagle (Jul 17, 2007)

How do those stops work. Do they screw into the spark plug hole. Wouldn't the torque of the flywheel break this thing or break something else?


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## 30yearTech (Sep 14, 2006)

OptsyEagle said:


> How do those stops work. Do they screw into the spark plug hole. Wouldn't the torque of the flywheel break this thing or break something else?


It screws into the spark plug hole and the piston is stopped by it. If you were to over torque the flywheel retaining bolt/nut I guess it would be possible to break or otherwise damage the piston / crank / or rod. It's never happened to me.


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