I have a 4 cycle Troy Bilt Trimmer model TB425CS. This trimmer has always performed flawlessly for me. Starts on teh 2nd pull almost every time.
The last time I used it (2 weeks ago) I was trimming and the machine just stopped. I tried to restart it but it wouldn't pop.

Last night I took it out and tried to start it and nothing. So I tried to diagnois the problem. It is getting spark. So I put the plug back in, but I shot some starting fluid in the cylinder first. Pulled the string and nothing, no pop, no hint of wanting to start.
So I pulled the air filter assembly off and moved the choke, used starting fluid in the carb, and nothing. No popping no smoke nothing.
Now it had spark when the plug rested on the cylinder head so I can't see why it wouldn't have spark when I reinstall the plug. I wonder if the head gasket is blown or the cylinder is cracked?
My compression tester doesn't have an adapter for a hole this small so I can't check to see if it is leaking down or not. I was considering buy new head gaskets and replacing them but I don't want to go through the trouble only for it not to work.
Any ideas or suggestions?

 

Check for loose screws/fasteners and tighten as needed. Replace the spark plug. Let us know what happens.

 

The plug is new, not many screws to come loose on this machine. I don't know, I will by pass the cut off switch to see what happens. I find it odd that I have spark but with starting fluid it still doesn't want to start. Compression seems fine, it doens't spin over too easily, but I'm thinking that a gasket may be blown.

 

I mentioned the fasteners as a shot in the dark. The fasteners I am speaking of are primarily the four that secure the cylinder head to the crankcase. They can loosen and cause loss of compression.

If you do not have the 10 MM plug adapter for your compression tester, I doubt you have a leakdown tester with a 10 MM adapter. If you are not familiar with the leakdown tester, do a search to learn what it does. The only other thing I can suggest without proper tools is to adjust the valves.

Sorry I do not have time to write the procedure now. If you will PM me with an email address, I will send it to you tomorrow.

Good luck

 

I disassembled the cylinder head, checked the valves and piston rings and all is fine. There are no visible cracks or scratches on the cylinder wall. I reassembled and tried again with no luck.

I think the iginition module is malfunctioning. It seems strange put I get a spark when the plug is removed. If I use starting fluid, the trimmer SHOULD fire up if it is getting spark no matter what, but it does nothing, not even hints at starting.

I don't want to throw parts at this to fix it as the coil is $43. I feel that th eproblem lies in the ignition somehow because like I stated, the trimmer was running great while I was using it but it just cut out and died, not a slow loss of power but instant off. So to me it seems that it is the ignition module. Anyway to test it or perform tests. I do notice that it doesn't always spark when I pull the cord, but it seems to spark about 80% of the time.
I just don't know what to do, I used this trimmer maybe a total of 10 times since I bought it last year and it wasn't cheap either.

 

Have you tried a new plug. I have seen plugs fire when out of the cylinder but will not when compression is applied. If you put you finger over the spark plug hole and pull the engine over you will know if you have compression.

 

I'll try a new plug, it does have compression.

 

Send me a PM with an email address and I will send you a document they may help.

 

Hi, I have the same trimmer and am having the exact same problem. Spark on the plug when grounded but no pop when trying to start with plug installed. I know this was a long time ago but maybe Airman has the document he sent to MyMopar.

Thanks

 

I had the same problem,Take the spark plug out and put a I dropper of 2 cycle oil down the spark plug hole, make sure before you do this the piston must be at the top of the cylinder so the oil will not leak out the ports.This gives it more compression to help it to start.I did this to 2 of the same trimmers,even after I overhauled the carb.and they been running ever since,don't figure. Hope this helps.

Jerry

 

Thanks, I tried that but no help. Checked out the flywheel for timing and found the keyway on the flywheel stripped which made timing off. Who thunked that.

 

hey guys i have a 2 cycle trimmer that is the 27cc model...it was running fine and then stopped and wouldnt crank and then when pulling the starter cord it started making a horrible screeching sound and wouldnt even begin to start...i put a new spark plug in it out sound continues and no luck on starting.