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McColough 1971 power Mac 6 wont run

Started by kj330, November 25, 2019, 07:42:21 PM

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kj330

New to me power Mac six. I had it running but messed up the adjustments . What should I set the adjustment screws to to start over . Thanks in advance

retiredmechanic

 some Mac shop manuals suggest 1 1/2 turns but I have discovered 3/4 turn for initial setting is best because it;s easier to screw out than in. then when saw is completely warmed up and chain is adjusted right, remember adjust the high side first ! in or out usually out to reach highest speed then slightly back off 1/8 to 1/4 turn depending on how sensitive it is responding then once satisified with High move to low side careful here because if used the 3/4 initial setting opening it up will also increase idle significantly if Idles speed adj screw was set to accommodate an idle set low side to get a smooth idle. then finally  set idle screw to assure chain isn't moving and saw doesn't stall. these are suggestive dependent on condition of carburetor and fuel lines and quality of fuel as well as ambient temperature. you might find that if this is done in a warm shop then a month goes by and you get outside in freezing temps it may require slight adjustment again also remember Mac's generally have a problem with cold starts before condemning the carb cause it refuses to start in the cold or after sitting throw a bit of primer in it first my old Macs always start 1st pull every time (after a primer shot)   
gunfire and chainsaws is a Sunday afternoon Lullaby in the country

retiredmechanic

Another point is what was the reason you felt it needed adjustment to begin with ? many times if the carb is just not responding well as expected a quick kit or minor rebuild and flush is all it takes  on the Walbro HDB series carbs meaning you dont have to mess with the needle and seat just a diaphragm and meter valve gasket and a few shots of carb cleaner through the jets and small holes and your back in business. but the base gasket under the carb is very   vulnerable and hard to find these days be careful with that one it doesn't always come in the kits 
gunfire and chainsaws is a Sunday afternoon Lullaby in the country

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