Stihl TS400

[alexcagle]

Ok. Now it sounds like an idle circuit problem on the carburetor. Did you set the idle mixture? A general setting is to run the idle mixture screw (L) clockwise or (in) till it stops. Don't over tighten it. Then back it out counterclockwise 1-1/2 turns. Also; if the blade spins at idle or when you are pulling the starter, then replace the clutch springs. They shouldn't engage until about 3,400 rpm, and the saw should be set to idle at 2,800 rpm. A broken clutch spring keeps the clutch engaged, and thus makes the saw lug the belt and blade at idle. On the carb; find out if it's a Walbro or a Tillotson carb, then get a kit with the welch soft plug in it. Take the welch plug that is in the carb out with a point carfully. Once it's out, take a small strand of wire and clean out the tiny fuel feed holes. Also remove the needle and spray some WD 40 through the holes. Don't loose the needle o-ring. Don't use compressed air, as this can damage the mylar check valve on the brass high speed nozzle. This nozzle is the larger looking plug, and has a check valve which under idle conditions, acts as a check valve. :bang:If it is faulty or not holding under idle conditions, will cause a bad idle due to letting air into the fuel supply inside the the carb that feeds the idle circuit. They can be checked by carefully driving the check valve out into the center of the carb and letting it fall out. The take a small clean hose that will fit over the nozzle end only, and leave the feed hole open. Then create pressure and vacuum by blowing on the other end of the hose. It should allow air one way only. If it doesn't, then you need either a new check valve, or just simply replace the carb. Confused yet? Hope some of this helps. Thanks

 

[HorseShoeInFork]

Thanks for your help axle. The clutch is good. Even though I've never gotten the saw to idle on it's own, I can idle it down slowly with the throttle and the blade stops turning. It just dies as soon as I let completely off the throttle. I did set the L screw at 1 1/2 off bottom.

The carb work you suggest is going to take me a few days to get time to do it all. I will look then to see if its a walbro or tillotson.

 

[HorseShoeInFork]

It's been a while since I talked about this saw and this will be the last time before it goes on down the road to someone else's garage unless I can get it to run right. If you aren't familiar with this I'll catch you up. Rebuilt the saw with new piston, cylinder, crank, bearing, all gaskets and various other parts. It should be a like new TS400 but I cannot get it to idle and it won't restart after it gets hot. It will start right up like any other Stihl saw when it's cold. Full choke, 4 - 5 pull to hit, 1/2 choke and it fires right off with 2 more pulls. It runs wide open and all through any throttle range except for low idle. It just smothers out and dies. If it's cold it will restart, if it's warm or hot it will not start back until it completely cools. Then it will fire right off again. I used it yesterday for 10 minutes without letting it die. It runs wide open under load and has tons of power. The second I sat it down it somothered out and died and wouldn't restart. It would hit every pull and almost run but wouldn't stay running. I came back 30 minutes later and it fired right up.

Can someone please tell me what could be the problem? I have too much time and $$$ in the saw to give up, but there is nothing that pisses me off more than a saw that won't start. Not to mention it is a real killer on my person yanking on a 35# boat anchor until I can't breathe.

 

[fearofpavement]

At the point you're at, I would try switching carbs with a good running one and see if you can move the problem. (there's lots of these saws around)

Sounds like a carb issue. It could possibly be an ignition issue. You've tried a different spark plug? Muffler screen clean (if present)?

Checked compression (recently)?

Confirmed timing correct? ie, flywheel in correct position? (key not damaged)

I was having a saw give me fits and it turned out it was a crack in a hose that only opened under pressure but not vacuum, so now if I check a hose it is with both vacuum and pressure.

Don't give up now. With help from the AS you will get it sorted out eventually. Keep in mind that these are relatively simple devices and there can't be that many possibilities.

I was working on a snowblower some years ago and it would idle all day but as soon as I gave it any throttle it would immediately die. I had that carb apart a bunch of times, checked everything else three or four times and in desperation called another mechanic friend over and he figured it out in about 20 seconds. The problem? The flywheel key was bent (slightly shifted). Put a new Woodruff key in it and it fired up and ran like new. Whodda thunk?

 

[HorseShoeInFork]

Yes on all of these items except switching the carb out. For all practical purposes it should be a "new" saw for what I've done to it. I used it Saturday and it started and cut like a dream for the 10 - 15 minutes I was using it - until I let it idle down and die, then it would not start back. Yesterday I walked by it after it sat all night and I thought what the heck I'll see if it will start. Full choke, one pull it was running - half choke one more pull and it was running like a top. I ran it long enough to get it warm and then let it idle down and it died and wouldn't restart.