026 Surging

[J Beard]

Heres the deal, working on a saw here at the firehouse.
will not throttle up only surges.
have already rebuilt carb.
replaced fuel line.
replaced fuel filter.
regapped magneto.
have good spark.
idles great.
fires on second pull.
was going to replace impulse line but dealer gave me the wrong hose.
carb to impulse line does not look like it seats far enough in, but there is no way to adjust the fit.
impulse line appears good on inspection.
piston looks like new through the exhaust port.
adjusting high idle screw can make it bog out, but can not achieve WOT.

OK saw doctors lets hear your ideas?

 

[Lakeside53]

Carb metering diaphragm/gasket in the wrong order?

You can hook on a piece of fuel hose to the impulse nipple and carb to see if it is your impulse hose.

 

[J Beard]

Carb metering diaphragm/gasket in the wrong order?

You can hook on a piece of fuel hose to the impulse nipple and carb to see if it is your impulse hose.

Double and tripple checked, assembled as it came apart. Had never been apart before.

Will try it next shift.

Thanks

 

[tommymacher]

surging is usually a sign of a lean condition isn't it?

 

[J Beard]

surging is usually a sign of a lean condition isn't it?

Cant say, this saw will barely come to half of what WOT should be.

 

[Justsaws]

Surging or missing. Does it shoot out lots of un-burned mix. Is the plug and or muffler wet after running it wot?

Surging=fast then slow/fast then slow, repeat ...

Missing= saw will not spool up to wot, tries to goes faster and just cannot, it will however run with trigger held wot for a long time at a faster speed than idle but not high speed. Sounds like it is missing half the strokes and that it is running rich so people will try and tune it leaner.

Brain sleepy, but a bad coil will sometimes miss. Rare on those Stihls but possible. More common with points and condensers and earlier electronic ignitions.

 

[Lakeside53]

Pressure test your carb - it might be flooding...