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Chainsaw idles, goes to high speed for a few seconds but dies under load. Sometimes cuts half a limb before it dies. Changed gas and then changed spark plug. Still dies.
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My chainsaw was erratic. Sometimes it started and ran just fine and at other times it just refused to start or died as I raised it to cut a limb. What I finally realized is that chainsaws are different than other 2 cycles engine devices - they have to work at many different angles (including straight up). For that reason, the fuel filter that is in the gas tank is weighted to keep it at the bottom of the gas tank as you raise and/or lower the chainsaw.
On my Mccullough, the gas line broke right at the weighted filter, allowing the gas line to flop around. That's why it was erratic and died when I raised it to cut a limb. So, if you have erratic operation, take a minute to check your gas filter and be sure it's still attached to the gas line......
Two things. First, is the chain dull? Second, if it develops a "throaty" sounds when you're cutting instead of the "crisp" sound you normally get from a chainsaw or weedwhacker or dirtbike... then the carburetor's running rich - it's "four-stroking". Try fiddling with the two mixture adjustment screws; one should be for idle mixture, the other for high-speed mixture. Get the saw idling and turn one of those screws clockwise ONE-QUARTER TURN. If the saw's idle doesn't change, turn that screw one more quarter-turn. if the saw's idle still doesn't change, thats the high-speed mixture screw.
If the saw's idle changes while you're doing that, then you're on the idle-mixture screw - return it to exactly where it was and adjust the OTHER screw clockwise a quarter-turn. Now try cutting - see if you've improved the saw's performance. If it's still four-stroking, try another quarter-turn.
If you go too far, the saw won't want to run at all at higher speeds... so you'd need to back up the screw the other way. Run it at the richest (most counterclockwise) position where it doesn't four-stroke under load.
What engine. ? Did you try pressing on the gas a little to see if it will keep running ? You get no codes ? You know how to do the flash code test ? Clean the throttle bore an idle air control passages . Have you changed spark plug's & wire's ? Ever ? Fuel filter
Have you tried changing the gas you are using? Sometimes with the addition of ethanol, water condensation is attracted and builds up in the system, creating a fuel mix that affects performance. Also, make sure your settings for High speed throttle are correct. You may need to make a small adjustment on the screw marked H for running high throttle.
What I do with my stihl saws is after starting I let it warm up for a few seconds and then run it at full throttle for about thirty seconds. If your saw does not want to keep running I would check to make sure air filter is clean. Next you can adjust carb.setting for idle and hi speed,check your manual for instructions. Also I would remove and clean spark plug,check gap and reset or replace as needed. Make sure your gas oil mix is proper and gas has not been setting for a long time,no more than a couple of months without some type of fuel stabilizer. I use either STA-BIL or sea foam at a rate of 2 to4 ounces per gallon of gas. About the only other thing I might suggest is to check the feul filter. They usually are located on fuel pick up line inside gas tank and can be a pain to get to. Good luck and I hope this helps Thanks
mcdevito75 here, 3 seconds after the car stars I'll bet the idle goes way high, if so the fast idle swith / motor could be bad. Or if the idle goes way low, it could be the air Idle, sensor/ motor going bad. Either way have your local repair shop run a scan and see.
Check the air cleaner and muffler for plugging. One screw adjusts the idle stop (idle speed) position and the H and L jet screws set fuel mixture for high speed and idle speed mixture respectively. Turn both jet screws CW to stops (lightly) then back each out CCW 1-1/2 turns. This is a basic setting and should allow the engine to start and run. Start the engine and allow to warm up. Pull the throttle full on and adjust H CW until the engine starts to speed up, but 4-strokes. Correct adjustment is when the engine 4--strokes running free, but immediately 2-strokes when cutting. Release the throttle and adjust L needle CW until the engine idles fairly well, but allows the engine to 'follow the throttle'. Adjust the idle speed screw so that the chain stops turning, but the engine will continue to run. Hope this helps!
You need to set the mixtures for the carburetor. You will find a Low and High adjustment screw. At idle turn the screw in or clockwise until the rps starts to decrease. Then start turning it out till you hit max idle rpms. Turn screw back in a quarter to half turn and it should be idling smoothly. Be careful here and get someone to hold saw if necessary but hold in throttle to full speed and do the same with high adjustment screw. turn it in till rpm starts to drop then back it out until you get to max rpm and it won't go any higher then turn it back in a half a turn. If you have to change the high rpm jet a lot you might have to go back and readjust the low rpm jet again and set the idle speed. Never idle it high enough that the chain turns while at idle.
We used to have to do this a lot in timber business. You go up on the mountain to cut logs and the altitude has high enough that you had to adjust carburetor and then do it again when you got back to the sawmill.
Probably need to re-adjust the carburetor jets. They are very small screws in the base of the carburetor. They will be labeled with an "H" and an "L" . Set the low speed first by turning it in slowly until the rpm drops slightly then start turning it outward untill the engine idles smoothly. At that point you can also adjust idle speed. Then you need to be careful here but you need to hold the throttle wide open at the same time adjusting the high speed jet. Turn it in until the rpm drops then slowly turn it out. The rpm will keep increasing. Once you get to a point where it is max'ed out then screw the jet back in one half a turn. Changes in altitude like using your chainsaw in town versus going to the mountains for firewood can sometimes make it necessary to adjust the fuel/air ratio.
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