dirt in engine?

I would love some advice, if there are any kinds souls out there...

I have a 4-cycle Troy-Bilt gasoline trimmer (model TB425CS) with only ten hours of use on it. The device is now extremely difficult to start. If I manage to get it started, it only runs for five minutes and stops itself. Also, if I get it started, I cannot stop it; the off switch does nothing.

I have been told the problem has to do with dirt in the engine. This may be because my wife emptied out a can that contained diesel and refilled it with gas. (Or maybe dirt has gotten involved some other way?) We filled the trimmer from that can, and there was possibly the residue of diesel that mixed in with the new gas.

The advice I'm looking for: is the device worth repairing? Shops in the area offer to work on it for $30-$36/hour, but won't give me a time estimate. Is the machine going to have any other problems down the road, after a repair? Should I junk it and move on? Should I attempt to clean the carburetor myself somehow? If I try this myself, is there an additive to put in the tank for cleaning purposes, or do I have to take the carburetor apart? What do I use for cleaning it out?

I'm good at tinkering and taking things apart, but mainly with computers. I've never gotten into gas engines, and am not sure if I should start here...

 

I Assume Its Still Under Warranty Where You Bought It.... The Kill Switch Has Nothing To Do With Dirt... It Just Shorts Out Spark To Ground..... I Would Take It Back...

 

Most trimmers have a filter attached to the suction line inside the gas tank. Form a hook in a piece of wire and pull the fuel line out of tank and inspect or replace filter. If you think diesel is mixed in the gas, empty tank and refill with gas. remove air filter and feed gas in carb throat with squirt bottle to get it to start and run out what is in the carb. If it still won't start, the diesel may have fouled the spark plug.
As another poster said, the kill switch grounds the ignition. Check to see if wire is connected to switch or wire is broken between switch and mag.
Hope this helps,
Mike

 

There's no way that having a small amount of diesel mixed with gas (even a cupful in a gallon) would create the problem you describe. It appears you have two problems and they really don't seem related but may be. If the machine stays running when you shut it off the kill switch is not working properly. THAT could also account for the other problem of very hard starting. If this is the problem, disconnecting the kill switch will make it start easily again.
I'm not familiar with your machine but I would remove both wires if it has two--if only one then remove that. Check for spark. If it starts you can always disconnect the plug wire with a pair of coated pliers or screwdriver to shut it off. If that fails there could be a shorted out portion of the wire from the coil--you'll have to visually trace it and inspect.

 

Has the fuel been mixed properly with the correct oil ratio? If so, I believe you probably have 2 unrelated problems. The kill switch is not working most likely because of a bad connection, or a wire just came off entirely. The hard starting and short run time may be a carburetion issue related to dirt. Does it run fine when it does run?

 

The machine takes its oil and gas separately. It has had an oil change recently, but after the problem developed. Prior to the oil change, it had about ten hours of service put on it.

When it last run, it sounded and felt unsteady, like it couldn't find its perfect idle speed. Time before that, it ran fine once I finally got it started.

I'll investigate the kill switch wires soon and post back.

 

he did say 4 cycle

 

Yes, I see it was mentioned. Thank you for pointing that out, although unnecessary.

predigested, sorry...I didn't notice that it was a 4 cycle engine the first time around. I have seen some of these with bad coils that wouldn't shut off. The coil worked fine as far as providing spark, but the terminal on the coil for the kill circuit was not making connection inside the coil. Check the switch with an ohmmeter to be sure it is grounding the kill wire when it's turned off. If so, it's good, and proceed to check the wiring and connections, then finally the coil.