View Full Version : Finally found fix for old problem on Stihl FS450K

Tom M King
07-15-2016, 6:42 PM
I bought it new for a job in 1999. It got used occasionally, but the throttle cable kept breaking. I could never figure out why the cable didn't last long because there is probably less than a 1/2 ounce for full pull on the carb linkage.

Some years ago, Stihl stopped selling that model of replacement cables. The dealer couldn't help, but did call and let me talk to a rep at Stihl. He said the assembly from the handle to, and including the carb had been changed, and that the new cable wouldn't fit, and for some reason even if I bought the new style carb that it wouldn't work.

I cobbled up something that worked for a short while, but when that broke it sat for years.

Just browsing ebay last week, I found a new old stock cable. I ordered that. I also found a handle grip with throttle cable attached and ordered that. I figured between the two, I might be able to rig up something that would work.

The NOS cable was the right one. When I was inside the grip putting the new end onto the trigger, it was odd that there was such a weird layout for the springs for the trigger and safety trigger. All the springs were rubbing together as well as on the end of the cable.

Then I looked at the other end of the cable. It continued out through the swaged on ball that activated the throttle on the carb, and was to be put under a screw going into the block.

I had looked at the grip with attached cable, and the end to attach to the carb was different. The cable did not continue on to become the ground for the kill switch. There was another wire with a female clip on it that stopped near a turn the cable sheath makes under a clip that holds it in place. On the old model like mine, under that hold down clip is a male clip on a wire that goes to the coil. It looks like the new style wire will work fine by just taking that male clip out and plugging it into the female plug.

If I hadn't bought both pieces, I would have overlooked exactly how the old wire worked, and not only that, but WHY THE CABLE HAD BEEN BREAKING. It wasn't breaking. It was BURNING IN TWO.

I decided to just use the choke as the kill switch until someone doesn't remember to, and burning the cable in two.

I see why they changed the design, but the young guys didn't know.

I'll bet there are many of these FS450K's sitting in shops all over the country, and nobody knows what to do with them. I paid $1100 for mine in 1999. If you can find one cheap that doesn't work, buy it.

Jim Koepke
07-15-2016, 6:52 PM
If I hadn't bought both pieces, I would have overlooked exactly how the old wire worked, and not only that, but WHY THE CABLE HAD BEEN BREAKING. It wasn't breaking. It was BURNING IN TWO.

Many years ago my ride was a 1957 VW bus. For some reason the clutch cable kept breaking. Turns out fixing the ground strap to the transmission fixed the problem.

Some cables are made to be conductors, others aren't.


Jim Becker
07-15-2016, 7:31 PM
That was a good discovery, Tom!

Tom M King
07-15-2016, 7:45 PM
Just almost pure luck. I didn't even realize what was going on until I was standing in line at Subway for lunch that morning and it came to me. If I hadn't bought the grip and cable that turned out to be "new style", it would have slipped by me again.

The circuit went from the kill switch, through two touching springs, and down the throttle cable on one side of the swith. The other side used the coiled metal sheath over the Teflon lining that separated it and the cable that slid inside. The new style cable had two wires from the switch. One simply plugged in, and the other needed to be grounded to the crankcase. If I hadn't had the new cable in hand, I would have had no idea what the new design was.

We have a lot of volunteer Pine trees that I need to get rid of that I can't get to with the bushog. This came at the perfect time.

Mike Henderson
07-16-2016, 9:31 AM
Wow, that's quite an insight - I'm sure it took you a while to figure it all out. I'm glad you were able to do that. Send a note to Stihl. Maybe they'll post it to help others - you never know.


Tom M King
07-17-2016, 11:27 AM
It turns out that this was a fairly common way that kill switches were routed on string trimmers. I think the problem here was the cable is the same size as used on regular string trimmers, but the engine is so much larger and more powerful, that I expect the coil puts out a lot more current that they didn't allow for in engineering.

I figured I could find a youtube video of someone running one. Just skip to about 3:00 in this one: https://www.youtube.com/watch?v=IghpSvZXxIA