Low Speed Mixture - Snowblower Forum : Snow Blower Forums
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post #1 of 13 Old 02-24-2018, 01:31 PM Thread Starter
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Low Speed Mixture

Ariens 8/32 from 1975 here. Trying to get a better understanding of how to properly set the low speed fuel mixture. It has a new carb about 2 yrs ago. Runs solid under load and is a mule. With no load it surges so I think it needs adjustment somehow on the low speed fuel circuit. Is there a method for adjusting the main mixture and the low speed mixture on full load vs no load or how is this done properly?
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post #2 of 13 Old 02-24-2018, 01:56 PM
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Originally Posted by 59ctd View Post
Ariens 8/32 from 1975 here. Trying to get a better understanding of how to properly set the low speed fuel mixture. It has a new carb about 2 yrs ago. Runs solid under load and is a mule. With no load it surges so I think it needs adjustment somehow on the low speed fuel circuit. Is there a method for adjusting the main mixture and the low speed mixture on full load vs no load or how is this done properly?
I would suggest YouTube videos. DonnyBoy (think that is his handle ) has good videos on adjusting mixture screws. Some may be on a chain saw, but for the most part, the process is the same.

Not rocket science once you watch the video. Basically, clockwise turning of the screw limits the fuel, which will make it run leaner, and the opposite does the opposite ! Kind of fun once you get the hang of it. You'll be looking for engines to work on !
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post #3 of 13 Old 02-24-2018, 01:57 PM
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idle muxture screw 1 1/4 turns out base setting
high speed screw 1 1/2 turns out base setting
warm it up set hi speed mix screw turn in until it runs ruff then out till it runs ruff then set it in the middle
you can adjust slighty to your conditions warm= a lil less rich cold a lil more rich
idle mixture should be close
then adjust idle speed
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post #4 of 13 Old 02-24-2018, 02:06 PM
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depends what your replacement carb has for adjusting . Original would have a low speed . Assuming that it's a tecumseh?
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post #5 of 13 Old 02-24-2018, 02:23 PM
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Set the basic setting. Screw the needle in all the way, not tight, just until it stops. Then 1-1/2 turns out. Same for the high speed adjustment under the carb.

Start and warm up the machine, at full throttle adjust the high speed mixture until rpms peak at their highest. Adjust slightly in and slightly out then settle in the middle.

I then raise the idle by turning in the idle screw to around 2400rpms. I use a hand held tach that just needs to be held close but by ear is fine.

Then adjust the mixture screw in or out until the engine rpms peak their highest. You should adjust the screw in and out and settle in the middle.

Then drop the idle to around 1800-2000 by screwing out the idle screw. (I think that’s spec)

To test the low speed mixture, idle the machine and move the throttle quickly back to full speed. If it doesn’t choke and ramps up in RPMs immediately then you’re good. A momentary stumble isn’t a problem.

If it chokes then make a 1/8 of a turn adjustment at a time until it accelerates properly.

In practice it take me under a minute.

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post #6 of 13 Old 02-24-2018, 02:27 PM
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you know he doesnt have a tach if he did he would know how to do this
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post #7 of 13 Old 02-24-2018, 02:31 PM
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post #8 of 13 Old 02-24-2018, 02:32 PM
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Donít really need one, just stating how I do it. The idea is an elevated rpm, not idle, not full throttle.

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post #9 of 13 Old 02-24-2018, 02:44 PM
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right i didnt say to raise idle 1st before adjusting as he might raise to high tuff to know by ear
i use a tach myself
better to use the slow to fast as a guide without the tach imo
as jt said make sure nothing is clogged or you will be doing all this again
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post #10 of 13 Old 02-24-2018, 02:53 PM
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easy way, on warm engine, adjust high idle, wide open throttle, until it sounds good as too far in or out engine sounds like crap.
then lower throttle lever to just before kill switch is engaged, adjust low idle air screw, not the idle butterfly set screw, adjust until engine sounds good, then bring throtle lever back to wot and adjust the low idle air screw until engine sounds good.
on wot engine uses both low and high speed air mix screws.
this assumes carb is cleaned and has good fuel flow from tank.

Bought a dead but now fixed 1980ish craftsman II 10/28....ITS ONE HEAVY BEAST

MY VIDS ON FIXIN HER UP

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