Stihl TS 420 Won't hold idle unless primer bulb is pushed

Reply

  #1  
Old 09-07-12, 04:34 PM
Member
Thread Starter
Join Date: Sep 2012
Posts: 3
Stihl TS 420 Won't hold idle unless primer bulb is pushed

I was given a Stihl TS420 Cutting Saw to fix. It had pure gasoline run through it, and it would no longer start. I have so far replaced the piston, ring and cylinder assembly, spark plug, hoses, gaskets and carburetor. I have attempted to adjust the idle with the old carburetor, but not with the new one (assuming that it's set to factory standards). The persistent issue is that when it starts, it won't hold a low idle, nor will it stay running unless the primer bulb is pushed continuously. When pushed, the fuel will run the motor until the amount of fuel in the carburetor wanes, then if left alone, it will die out. This has occurred at every turn in the process, and still persists.

I'm not sure where to go from here. What could I be missing? What else can I check/change/repair/replace?

Is there a diagram anywhere that shows how the hoses are supposed to be routed (in case I have them backwards), because I think I have the hoses right, but I am only human. I have checked youtube for backyardmechanic and for donnyboy73, but neither address this issue with this particular saw. Any help or direction you can provide would be greatly appreciated. Thanks.
 
Sponsored Links
  #2  
Old 09-07-12, 05:04 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,728
It just sounds like the idle circuit needs cleaning. If you have a new carb for it and plan on using it, I would install the the new one and see where you're at.

Or you could dismantle the old one and clean it - it may work fine then.
 
  #3  
Old 09-07-12, 08:39 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,818
Sounds to me like the fuel pump in the carb isn't working, which could be due to leaking pressure in the crankcase, and the inability to idle goes right along with that diagnosis. When one gets run with straight gas, the crankshaft seals can get cooked. The bearings on the crank might even be cooked and allowing the crank to walk a bit. See if you can make it run better by spraying carb cleaner or starting fluid at each of the crank seals while it is running. If so, they are leaking.
 
  #4  
Old 09-21-12, 03:16 PM
Member
Thread Starter
Join Date: Sep 2012
Posts: 3
Thank you. I did replace the carb anyway. Where do i / how do i finx the idle circuit?
 
  #5  
Old 09-21-12, 03:20 PM
Member
Thread Starter
Join Date: Sep 2012
Posts: 3
Thank you. I replaced the carb since this post, and the problem continues. I will check the seals and see where that gets me. What are your thoughts on tge previous post regarding the idle circuit?
 
  #6  
Old 09-22-12, 12:11 AM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,818
The idle circuit is a passage in the carburetor.
 
  #7  
Old 10-19-13, 07:18 PM
Join Date: Oct 2013
Posts: 1
Stihl TS 420

I have the same unit, I have rebuilt the carb with the recommended carb kit, new plug, new fuel lines. What I found was a very tiny pin hole in the primer bulb allowing the system to suck air, I have yet to replace this to see if this solves my issue. I will keep you posted as to my findings.
 
  #8  
Old 10-19-13, 07:34 PM
Banned. Rule And/Or Policy Violation
Join Date: Apr 2013
Location: USA
Posts: 4,297
Changed the fuel filter In the fuel tank?
Tried running it without the fuel cap in place?
Done a compression test?
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes