Author Topic: 920 Jonsred  (Read 344 times)

0 Members and 0 Guests are viewing this topic.

Offline Eggiessouth

  • pruner
  • *
  • Posts: 2
  • Karma: 0
920 Jonsred
« on: August 24, 2015, 06:18:34 pm »
When my friend brought me this saw, he said he could not get it to run. I checked it over, good compression, getting fuel, no spark. I found the two piece ignition modual at ChainSawr. Got it, installed it, now it has spark. It then started, but it ran lean. I pulled the carb & rebuilt it, replacing the welsh plugs & diaphram/gaskets. Carb was clean! It still ran lean, almost to the point of running away to high speed. I pulled most everything apart again & found a previous person had not got the manifold back in place on a prior repair attemt. The manifold had also been damaged in the attempt. Back to ChainSawr & got a used manifold. Installed it & it starts & runs, but only from mid range to top end?! When rpm's get below midrange it dies. If I hit the throttle it takes off again. If the rpm's get to low it will stop &be wery hard to start. If I shoot a little (mixed) gas in the carb it starts & it does the same thing again. The impulse line has been replaced. It does have some scoring on the exaust side of the piston, none on the intake. Any ideas? 

Share on Facebook Share on Twitter


Online 3000 FPS

  • Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 4444
  • Karma: 273
  • Location: Carpenter, Wyoming
Re: 920 Jonsred
« Reply #1 on: August 24, 2015, 08:00:55 pm »
Well the scoring might be causing low compression if it is across the rings.  Also does it have this problem when running the power head only with no bar and chain.   
Do a compression test on it.   
PP 505, 475, 445.

Offline jmester

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 2046
  • Karma: 156
  • Location: MD
Re: 920 Jonsred
« Reply #2 on: August 24, 2015, 08:10:18 pm »
I agree sounds like low compression to me as well. Had a Stihl saw with a scored exhaust side of the piston do the same thing you are talking about. Ran great on top but would die on the return to idle and be hard to start.
FEAR NO TREE. FEAR GOD.

Offline Eggiessouth

  • pruner
  • *
  • Posts: 2
  • Karma: 0
Re: 920 Jonsred
« Reply #3 on: August 25, 2015, 08:14:44 am »
It has 120 psi. Does the same with no bar & chain.

Offline jmester

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 2046
  • Karma: 156
  • Location: MD
Re: 920 Jonsred
« Reply #4 on: August 25, 2015, 04:40:29 pm »
Seems low to me I would like to see at least 150
FEAR NO TREE. FEAR GOD.

Online 3000 FPS

  • Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 4444
  • Karma: 273
  • Location: Carpenter, Wyoming
Re: 920 Jonsred
« Reply #5 on: August 25, 2015, 09:13:02 pm »
Even if 120 psi is a little on the low side I do not believe it is low enouph to cause those symptoms.
I would do a crankcase pressure check at this point.   Sounds to me like it is starving for fuel at the low RPM's.
PP 505, 475, 445.

 

Related Topics

  Subject / Started by Replies Last post
9 Replies
627 Views
Last post May 03, 2013, 01:44:44 pm
by HMLT360Pro
21 Replies
1602 Views
Last post October 26, 2014, 09:28:29 pm
by David Young