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088 with an idle issue

Started by ELECT6845, November 02, 2013, 04:59:03 PM

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ELECT6845

Rebuilt this saw for a good friend on mine and I'm having an idle issue. Saw starts and runs great but the idle is all over the place. It ranges from 1800 to 2900 on the tach.  The saw has been pressure tested and the seals are good. Also has new fuel lines, impulse line, and intake boot. Could it be we need to vac. test the seals? Any other things to check?

sharkey

I would replace the seals because those saws tend to sit and get flat spots.  Did you use a gasket on the cylinder base?

It could also be the carb.  I have a Walbro that I just cant get the inlet needle to seat properly on.  When this happens you end up with fuel pressure on the needle jets and what works one minute wont work the next because the fuel level in the tank changes.  When you shut that 088 down is it hard (rich) to restart?

Saw Dr.

Did you do the pressure test or a local shop?  It must be pressure AND VACUUM tested to be valid.  How long did it hold press and vac?  Also, you MUST flex the A/V mounts to their limits while under pressure and vac to see if any of the rubber bits are leaking.  Often times the seals will only leak under vacuum, and not pressure or vice versa.  You also need to rotate the crank while doing the test.  If nothing else works, try a different carb.  I believe the main nozzle is replaceable on that carb, and a cost effective option as those carbs were big money last I checked.
I don't try to explain to others why I play with chainsaws.  For those who already know, no explanation is needed.  For those who do not, no explanation is POSSIBLE!

Super 250

ELECT6845

Thanks for the input. I have access to the pressure/vac tester so I will test it again and make sure to rotate the crank. I appreciate the help.

tlandrum

my bet would be the carb is bad. I ported one a while back for 056kid on as and his saw wouldn't hold tune either. I cleaned the carb and rebuilt it ,no help. I then used one  of my known good carbs on it and then the saw tuned and ran perfect.
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ELECT6845

Thanks Terry.  Its tuned to 12,250 right now with the port work. The plug is good and dark so I know I'm a little rich but better to be to rich than to lean.

jacob j.

Quote from: tlandrum on November 03, 2013, 10:40:06 AM
my bet would be the carb is bad. I ported one a while back for 056kid on as and his saw wouldn't hold tune either. I cleaned the carb and rebuilt it ,no help. I then used one  of my known good carbs on it and then the saw tuned and ran perfect.

Carbs are a major issue on the 088/MS-880. I have a whole box of them that are junk. One good option is finding an older carb in good repair from an 084.

joe_indi

You can never know till you replace it, the metering diaphragm might look perfectly fine, but might not be functioning properly. From stiffness brought on by age (its a 088) or a very minute puncture(you will notice a wetness on the normally dry diaphragm when you lift the metering cover)
We tend to think its some other problem and try to compensate by adjusting the L screw or bending the metering lever.
The only result is one moment it runs rich, maybe lean again or it becomes richer till it dies out.Mke it a bit lean and it goes from lean to super lean, then rich again and lean again.
Something like one of those diesel locomotive engines at idle.

ELECT6845

Quote from: jacob j. on November 04, 2013, 10:18:50 PM
Quote from: tlandrum on November 03, 2013, 10:40:06 AM
my bet would be the carb is bad. I ported one a while back for 056kid on as and his saw wouldn't hold tune either. I cleaned the carb and rebuilt it ,no help. I then used one  of my known good carbs on it and then the saw tuned and ran perfect.

Carbs are a major issue on the 088/MS-880. I have a whole box of them that are junk. One good option is finding an older carb in good repair from an 084.

Would you get a new carb or try to find an 084 carb? Will the 084 be the same as far as the linkage goes?

ELECT6845

One more note. It did hold pressure/vac while turning the crank.

angelo c

Quote from: jacob j. on November 04, 2013, 10:18:50 PM
Quote from: tlandrum on November 03, 2013, 10:40:06 AM
my bet would be the carb is bad. I ported one a while back for 056kid on as and his saw wouldn't hold tune either. I cleaned the carb and rebuilt it ,no help. I then used one  of my known good carbs on it and then the saw tuned and ran perfect.



Carbs are a major issue on the 088/MS-880. I have a whole box of them that are junk. One good option is finding an older carb in good repair from an 084.

JJ, what is the issue with that carb. Is it a constant failure point or a general failure. Just thinking about a repair ( thinking in terms of the pump repair on the 200t) and how to isolate the issue(s).

Ps. Good to see ya posting here too. 
wife,kids,dog,t-shirts to prove it

rattler

Quote from: angelo c on November 05, 2013, 07:23:16 PM
Quote from: jacob j. on November 04, 2013, 10:18:50 PM
Quote from: tlandrum on November 03, 2013, 10:40:06 AM
my bet would be the carb is bad. I ported one a while back for 056kid on as and his saw wouldn't hold tune either. I cleaned the carb and rebuilt it ,no help. I then used one  of my known good carbs on it and then the saw tuned and ran perfect.



Carbs are a major issue on the 088/MS-880. I have a whole box of them that are junk. One good option is finding an older carb in good repair from an 084.

JJ, what is the issue with that carb. Is it a constant failure point or a general failure. Just thinking about a repair ( thinking in terms of the pump repair on the 200t) and how to isolate the issue(s).

Ps. Good to see ya posting here too.
ELECT did you get it figured out?

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