Author Topic: 5100S Problem  (Read 2069 times)

0 Members and 50 Guests are viewing this topic.

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
5100S Problem
« on: April 24, 2012, 05:52:48 pm »
First off I gotta say I'm probably working on the all time high hrs 5100. Used daily to cut firewood year round for 5 yrs.
Saw runs fine off idle but won't idle right. Is real irratic at idle and mostly just dies but will occasionally go lean before it quits. No air leaks that are easy to check for. Rebuilt carb, checked fuel line, impulse line, compression is 170+, muffler is clear, no scours on piston and ring and spark is great. I'm guessing its time to set up for a case vac check. Maybe he has plum wore out the crank bearings and seals.

Share on Facebook Share on Twitter


Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts
Re: 5100S Problem
« Reply #1 on: April 24, 2012, 06:58:41 pm »
Try checking tank vent, intake boot and seals.  Have you checked to see if cylinder bolts have come loose?  Had a racesaw do that to me once.

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
Re: 5100S Problem
« Reply #2 on: April 24, 2012, 07:47:03 pm »
Ran saw with cap loose no change. Intake boot just fine. Cylinder bolts all tight and sprayed brake clean at base with no change. Talked with Brad and he thinks it has to be an idle circuit plugged in the carb.
We had a Stihl 034 couple yrs ago that we couldn't get to idle right and that ended up being crank seals. Don't want to get steeered down the wrong road though.

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts
Re: 5100S Problem
« Reply #3 on: April 24, 2012, 08:21:57 pm »
Sounds like you need to pull a known good carb and test it on that saw.

Offline sharkey

  • Piped Saw
  • *****
  • Posts: 368
  • Karma: 37

  • Total Badges: 26
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Eighth year Anniversary Seventh year Anniversary Sixth year Anniversary Level 5
Re: 5100S Problem
« Reply #4 on: April 26, 2012, 01:00:26 am »
If it really has alot of hours, pull the muffler and try to make the piston move in the bore like the skirts are worn.  Use a screwdriver and try to push the piston back out through the intake.  If you get some play that is the problem. 

Here is a short video of a different dolmar that has alot of hours on it with the skirt problem.  The cylinder should be ok, its just that the piston skirts wear away.
http://www.youtube.com/watch?v=YoUMR7SKkxQ&feature=plcp
   

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
Re: 5100S Problem
« Reply #5 on: April 26, 2012, 06:11:13 pm »
Just put a new piston in last year.
Downloaded the Zama manual yesterday. Learned alot reading it. Talked about erratic idle caused by a leaky main nozzle check valve. Turns out both Zama and Walbro have a main ejector check valve. Without it atmosphereic  pressure is available on both sides of the diaphram when the throttle plate is closed. Checked it out per the maunal and sure enough no check action. Compared to another carb and it did check. Haven't proven this on the saw yet but got a donor carb from a shop that has other issues but the nozzle checks fine. Going to try and remove it and install in Earls carb. Supposedly its a service part but I doubt it can be bought outside of Zama.
Earl didn't start having trouble with his saws till he went back to pump gas. I've never had a fuel related issue on any saw. I only run AvGas.

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 23708
  • Karma: 664
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair

  • Total Badges: 53
    Badges: (View All)
    Tenth year Anniversary Nineth year Anniversary Level 8 Apple User Eighth year Anniversary 20000 Posts

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
Re: 5100S Problem
« Reply #7 on: April 26, 2012, 08:37:31 pm »
Here is the link to the Zama Tech Guide http://www.zamacarb.com/pdfs/TechGuide_2007.pdf where I got my info. I doubt very few people know the main nozzle has a check valve or what its function is. I'm guessing there must be rubber involved and therefore subject to ethanol deterioration.

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
Re: 5100S Problem
« Reply #8 on: April 29, 2012, 09:47:44 pm »
Well I haven't finished the saw but I put it all back together yesterday and tried to start it on a different carb. Do dice. Tried old carb with same results. Trouble shot to fuel pump not working on either carb. Installed new pump diaphragm and tested impulse line. All good. I'll know more in a few days when I get back on it but its looking like crank seals are shot. Noticed today pto side has quite abit of radial play. I hear these saws are famous for spun bearings.

Offline wkpoor

  • 4 cube
  • **
  • Posts: 61
  • Karma: 2

  • Total Badges: 12
    Badges: (View All)
    Third year Anniversary Level 3 Karma Second year Anniversary Combination Topic Starter
Re: 5100S Problem
« Reply #9 on: May 01, 2012, 04:29:57 pm »
OK here is the deal. PTO bearing is spun. Did crank pressure and vac test. Won't make any vacuum and if you blow into the hose attached to the impulse port is free flows out the bearing seal. I'm curious to see how tight a new saw is and good running older one for comparison.

 

Related Topics

  Subject / Started by Replies Last post
4 Replies
530 Views
Last post May 08, 2011, 07:20:52 am
by peppone
3 Replies
845 Views
Last post March 09, 2011, 07:47:49 pm
by hamish
2 Replies
1591 Views
Last post December 10, 2011, 10:38:37 pm
by 660magnum
1 Replies
769 Views
Last post January 19, 2012, 08:19:33 pm
by rgclmc
17 Replies
2546 Views
Last post June 07, 2012, 07:26:43 am
by farmboy
4 Replies
3855 Views
Last post February 20, 2013, 01:47:20 pm
by Cut4fun .
55 Replies
10851 Views
Last post September 21, 2015, 07:42:19 pm
by mikehonda
22 Replies
1595 Views
Last post August 29, 2013, 09:17:00 am
by fordfairlane78
3 Replies
471 Views
Last post September 10, 2014, 09:13:00 pm
by pigpen60
5100s air leak

Started by dolmar « 1 2 3 » Dolmar Makita

21 Replies
1373 Views
Last post January 16, 2015, 04:12:20 am
by dolmarfan