# high mixture adjustment



## snowball (May 3, 2005)

Another ? . When adjusting the high end, am I doing this right? You set it at 1 1/2 turns out to begin with,then gradually turn it in until you reach the highest rpms before it stalls,then back off about a 1/8 of a turn or is this racing the engine to much? Also the high must be adjusted before the low can be, correct?


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## bugman (Aug 12, 2004)

one to 1.5 turns out, then fine tune till it slightly smokes on a 2 cycle. i never really saw if it mattered which first, but the low should just let it smoke just slightly, you may need a good light or good sunlight to see the smoke...


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## hankster (Jan 1, 1998)

OK, let see if I can explain how I do it. Starting at 1.5 turns is fine as long as you can get it to run and idle. If needed, increase the idle speed (and/or adj. the low speed mixture) until it will run. Let it warm up for a couple of minutes.

Now jamb the throttle quickly. If it hesitates then most likely the low end is too lean... back out the low end mixture 1/8 to 1/4 and try again. Keep adjusting until you get a smooth quick accel.

To test the high end you need the equipment at normal load. That means if it is a weedwacker, it needs string in it at the proper length. If a blower, it needs the tubes on it... or course a chainsaw would need a chain.

Give it full throttle and start opening the highend needle. At some point it will start to, what I call, 4-cycle. In other words it starts to run rougher like it is firing only every other rotation. Now close the high end until it just quits. I personally like to hear it go into 4-cycle mode once in awhile while running at full throttle... that insures you are not running to lean.

During this time I would suggest you don't run it more then 30 seconds at full throttle. While it's not a problem on blower, it could be a slight problem with weedwackers and can really torch a chainsaw engine.

Now drop back to idle and adjust the idle speed as needed... but it shouldn't have changed. Test the accel. again but it should be OK too. You should now be done.

You always want to adj. the low speed first and then high speed. A 2-cycle engine is always on the low speed circuit even when at full throttle... the low speed fuel port on the carb is on the engine side of the carb butterfly. The high speed circuit is on the air filter side of the butterfly and is only in use at high RPM (butterfly open). So any time you change the low speed mixture it will affect the high speed mixture but not visa-versa.

To experment get the engine running properly. Now open the low speed adjustment 1/2 turn. Run the engine at high speed and you will see it is now running rich.

Hope I explained the well enough.


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## hankster (Jan 1, 1998)

Oppps... forgot about setting the low end.

Once you can get it to idle properly, open the low end needle until the engine RPM starts to drop. Now close the needle... the RPM will rise and then start to fall. Set the needle about halfway between the two. Then do the accel. test and adjust slightly from there as needed to get good accel.


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## snowball (May 3, 2005)

Thanks for setting me straight on that guys.I'll do that the next time I'm in the garage.I've got a new carb kit to put in so all should go well , I'll let you know.


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## snowball (May 3, 2005)

hankster said:


> Give it full throttle and start opening the highend needle. At some point it will start to, what I call, 4-cycle. In other words it starts to run rougher like it is firing only every other rotation. Now close the high end until it just quits. I personally like to hear it go into 4-cycle mode once in awhile while running at full throttle... that insures you are not running to lean.


Hankster, after reading this part of the tread again, i'm a little confused, Don't take much.You said, I have to (open) the high end, thats (counter clockwise) right?Is this some kind of preset, that I must do before closing it?Then close it (clockwise) til it quits. By closing it, won't this make the engine rpms rev up and then quit?And when it quits,do I open (counter clockwise) it a little? Sorry for the confusion.
Also Hankster, Is there a site where I can get a good break down on the operational functions of the different parts of walbro carbs. I'd really like to know this info for my personal knowledge. Thanks


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## hankster (Jan 1, 1998)

With the engine not running close the needle all the way... now open in 1 1/2 turns and start the above proceedure. I don't know of any site that shows the operation of a carb... sorry.


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