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spudulike

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Here's the next one, a Stihl 038 Magnum, got an uneven idle - not even fired it up but the plug tells a tale - it is the white one on the end, the one in the middle came from the MS880 mentioned earlier and the one on the left from a hedge trimmer.

 

Note how white the two plugs are - a sure sign of a weak mix and possible bad adjusted carb or air leak:thumbdown:

 

Next step - pressure check:thumbup1:

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Right - the 038 magnum, pressure checked 100% fine, compression 150psi, carb cleaned, piston looked fine - the bugger didn't start - 15 pulls and the plug looked a little damp - no flooding so the carb isn't working right. Riched up both screws - the same, not even a pop - the plug is sparking fine.

 

Noticed the fast idle doesn't click off on opening the throttle and the carb throttle valve plate isn't being opened by the fast idle setting. Adjusted the throttle linkage and the spring that works on the black horizontal throttle/choke linkage and this mechanism works fine.

 

Tried starting tonight - 3rd pull a good pop, take the choke off - two more pulls and off she runs, just needs a tach tune for final setup:thumbup:

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Out of interest did you take a peak at the intake side of the piston?

Those wire mesh filters aren't the best! Especially if it is old, the mesh can warp and the spacing between the wires is greater in certain places than it should be. It usually doesn't hurt compression unless it is really bad but it will eat the piston skirt. A felt filter is available instead.

Unlike when the saw would have been released, Stihl now only recommends wire mesh filters to be used in extreme winter conditions i.e. falling snow.

 

Good diagnosis work though :thumbup:

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Out of interest did you take a peak at the intake side of the piston?

Those wire mesh filters aren't the best! Especially if it is old, the mesh can warp and the spacing between the wires is greater in certain places than it should be. It usually doesn't hurt compression unless it is really bad but it will eat the piston skirt. A felt filter is available instead.

Unlike when the saw would have been released, Stihl now only recommends wire mesh filters to be used in extreme winter conditions i.e. falling snow.

 

Good diagnosis work though :thumbup:

 

Yup - standard procedure, raise the piston, look at the exhaust side, lower it and look at the back of the bore - it is a four year old aftermarket P&C, thought it looked a bit clean and the owner confirmed - the compression is good - got two gauges with different one way valves and one shows good residual compression and the other with the schrader valve shows all components are 100%. On less good bores, the latter gauge reads low - in this case I had 150psi on both:thumbup:

 

Just tached it and it now runs well - slight variation at idle that I have tracked down to a very slight leak around the throttle valve pivot but not worthy of a new carb yet.

 

This was an interesting one!

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Here we go, another 357 with uneven idle - have had this one in before, pressure test is 100% as I have replaced the troublesome inlet boot. comp check a very healthy 160psi, pressure check fine, repeated by plugging AFTER the carb - airleak - it is leaking around the throttle pivot - have stripped and will see what I can do on rebuild but that is the route cause as the rest of the carb has been ultrasonically cleaned, checked and rebuilt.

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got an ms200 with the dodgy carb syndrome ,rang local dealer as expressed an intrest in the 201, he then told stihl didnt have any carbs in stock :sneaky2:but would keep trying ,4hrs later still no joy ,so swapped carb of a working sew hey presto good as new ,so rang again still no carbs ,so rang jonsie & guess what ,itll be in the post monday :biggrin:

so thats saved me £400 :thumbup1:

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