Question for you small engine experts

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09-30-2010, 7:54 PM
Louis Brandt

Question for you small engine experts

Hello,

I have a Craftsman 2 cycle gasoline string trimmer that’s a few years old, and I’m having no success in starting it. I did get it started earlier this summer, and I did in fact start it today, but only after about thirty minutes of working with it, and after it stopped, I haven‘t been able to start it again. This time, I tried for hours, with no success.

I’ve replaced the fuel filter, the air cleaner, the primer bulb, the hoses and the plug. I know that it’s getting gas, but it still won’t start.

My next step (tomorrow) will be to remove the plug from the cylinder and, leaving it connected to the plug wire, see if I‘m getting a spark across the terminal. Remember, it’s a brand new plug (gapped correctly).

I’m beginning to suspect that the problem may be the ignition module, so here’s my question, and I think that the answer to it may tell me whether the module is good or not.

If the ignition module is bad, will I NOT see a spark? (or can the plug still fire even with a non-functioning ignition module)?

Thanks,
Louis
10-01-2010, 6:41 AM
Chris Parks

Quote:

Originally Posted by Louis Brandt

Hello,

I have a Craftsman 2 cycle gasoline string trimmer that’s a few years old, and I’m having no success in starting it. I did get it started earlier this summer, and I did in fact start it today, but only after about thirty minutes of working with it, and after it stopped, I haven‘t been able to start it again. This time, I tried for hours, with no success.

I’ve replaced the fuel filter, the air cleaner, the primer bulb, the hoses and the plug. I know that it’s getting gas, but it still won’t start.

My next step (tomorrow) will be to remove the plug from the cylinder and, leaving it connected to the plug wire, see if I‘m getting a spark across the terminal. Remember, it’s a brand new plug (gapped correctly).

I’m beginning to suspect that the problem may be the ignition module, so here’s my question, and I think that the answer to it may tell me whether the module is good or not.

If the ignition module is bad, will I NOT see a spark? (or can the plug still fire even with a non-functioning ignition module)?

Thanks,
Louis

The carburettors are adjustable for both slow engine revs and fast engine revs. If the settings have been changed then it might be difficult to start. An air leak will also make it difficult to start, make sure the carb is tightly attached. The ignition module can still spark and the motor may fire or momentarily fire and the module will still not have enough energy to make the spark strong enough. I had a motor recently where the plug sparked every time I looked at it but the module was weak and the spark sometimes wandered around at the electrode as the motor was cranked. A broken ring or hole in the piston won't help either though it seems that the piston is still in one piece but the ring can break. Hold your thumb over the plug hole and pull it with the throttle wide open and see how much compression it has. it should be hard or impossible to hold it there. If there is no effort required the ring may be broken or the piston is damaged.
10-01-2010, 7:58 AM
Lee Schierer

Also check the exhaust ports for carbon build up.
10-01-2010, 8:38 AM
Chris Parks

Also check the air filter is clean as this will cause flooding. The other thing might be the needle and seat in the carburettor or the pump diaphragm in the carb could be shot. The carb pump relies on compression supplied from the crankcase by a short hose, this must be connected and undamaged. Also the seals in the motor can go hard and leak air and that requires expert advice to fix unless you are very handy. Generally on a cheap two stroke it is dead at that stage.
10-01-2010, 4:19 PM
Dave Ogren

2 cycle catalic converter

This has happen to me on a lot of 2 cycle motors. The catalic converter gets plugged. It is really a screen at the exhaust port. It gets plugged up with carbon. Just take it out and throw it away. The manufacturers say it is also to keep sparks from starting forest fires.

Good Luck,

Dave
10-01-2010, 7:03 PM
Chris Parks

Quote:

Originally Posted by Dave Ogren

This has happen to me on a lot of 2 cycle motors. The catalic converter gets plugged. It is really a screen at the exhaust port. It gets plugged up with carbon. Just take it out and throw it away. The manufacturers say it is also to keep sparks from starting forest fires.

Good Luck,

Dave

We don't have that stuff on motors here. It is really a spark arrestor to prevent fires, clean it or get rid of it as Dave says. Also a blocked muffler will have the same effect. If totally synthetic oil is used the carbon build up is minimised.