Post by MCS on May 17, 2010 9:08:17 GMT -5
How to adjust a carburetor on a Homelite saw.
This subject comes up frequently and I've written the same answer several times so here is a general procedure that will work whether the saw has a Tillotson, Walbro, Zuma, or some other brand carburetor on any model Real Homelite.
Starting with the XL2 (1972), some smaller units do not have a high speed needle adjustment but they still work
A saw in good condition - no other problems - will exhibit these conditions when is is warmed up and the carburetor properly adjusted.
Note: If you are fussing with the adjustment and just can't find a sweet spot then there is something wrong other than adjustments.
Getting Started:
If you have a "chopping block" it will make a good spot to set the saw down when you have to make a change or adjust the idle speed. I don't like working on the ground. Make sure there is plenty of room so the bar and chain don't hit anything.
Start the saw and let it warm up. At these initial setting the saw should run half way decent.
All the adjustments are done "by ear."
Adjusting the idle: Set the idle speed so the saw runs just below clutch engagement then turn the Low speed needle for maximum RPM. Readjust the idle speed. Open the Low speed needle 1/8 turn as the low speed has a big effect on acceleration.
Adjusting the high speed: Before you can adjust the high speed you have to teach yourself to hear the "high speed miss." This setting is important because it ensures the saw is not running lean while it is working hard. A lean fuel-to-air mixture increases the combustion temperature and since that means less fuel it also means less oil. So run the saw slowly to full throttle. Just before it reaches full RPM you should hear it start missing slightly. Some call this "four-cycling." If you are not familiar with the sound take time
to learn to hear it. A slightly rich mixture is what causes it and that is what you want.
Close the high speed 1/4 turn and run the saw up to full throttle and repeat until you don't hear the miss. Once you find where the saw runs without missing, open the high speed 1/4 turn.
If you didn't hear the miss with the initial 1 turn open setting then open the high speed 1/4 turn and try it. If you get to 1 1/2 turns open and don't hear the miss either you don't have the knack yet or there is something wrong.
There will be some interaction between these adjustment so some additional fine tuning may be needed. Sometimes acceleration is the toughest one to get acceptable.
When you are out cutting and you wind up the saw you will hear the miss but as soon as you have a load on the chain the saw will smooth out and then just purr.
This subject comes up frequently and I've written the same answer several times so here is a general procedure that will work whether the saw has a Tillotson, Walbro, Zuma, or some other brand carburetor on any model Real Homelite.
Starting with the XL2 (1972), some smaller units do not have a high speed needle adjustment but they still work
A saw in good condition - no other problems - will exhibit these conditions when is is warmed up and the carburetor properly adjusted.
- It will idle without the chain turning.
- It will accelerate smoothly - no stuttering.
- It will have the distinctive "high speed miss" at full throttle and no load. This is important!
- It will return to idle without stalling.
Note: If you are fussing with the adjustment and just can't find a sweet spot then there is something wrong other than adjustments.
Getting Started:
If you have a "chopping block" it will make a good spot to set the saw down when you have to make a change or adjust the idle speed. I don't like working on the ground. Make sure there is plenty of room so the bar and chain don't hit anything.
- Set both the high and low speed one turn open. When you do this be gentle when you check for the closed position as the needle seats are just part of the aluminum casting. If a seat gets damaged the carburetor will have to be replaced.
- Adjust the idle speed screw so the butterfly is slightly open - you will have to watch the linkage to see it move.
Start the saw and let it warm up. At these initial setting the saw should run half way decent.
All the adjustments are done "by ear."
Adjusting the idle: Set the idle speed so the saw runs just below clutch engagement then turn the Low speed needle for maximum RPM. Readjust the idle speed. Open the Low speed needle 1/8 turn as the low speed has a big effect on acceleration.
Adjusting the high speed: Before you can adjust the high speed you have to teach yourself to hear the "high speed miss." This setting is important because it ensures the saw is not running lean while it is working hard. A lean fuel-to-air mixture increases the combustion temperature and since that means less fuel it also means less oil. So run the saw slowly to full throttle. Just before it reaches full RPM you should hear it start missing slightly. Some call this "four-cycling." If you are not familiar with the sound take time
to learn to hear it. A slightly rich mixture is what causes it and that is what you want.
Close the high speed 1/4 turn and run the saw up to full throttle and repeat until you don't hear the miss. Once you find where the saw runs without missing, open the high speed 1/4 turn.
If you didn't hear the miss with the initial 1 turn open setting then open the high speed 1/4 turn and try it. If you get to 1 1/2 turns open and don't hear the miss either you don't have the knack yet or there is something wrong.
There will be some interaction between these adjustment so some additional fine tuning may be needed. Sometimes acceleration is the toughest one to get acceptable.
When you are out cutting and you wind up the saw you will hear the miss but as soon as you have a load on the chain the saw will smooth out and then just purr.
