Stihl 039 hard pull after replacing low and high carb screws

[smoking]

Hello,

First post here, but been referencing other threads for help. Hope someone might have insight into this.
My Stihl 039 wasn't idling right after I had a shop do a tune up. They had done a carb rebuild and replace the fuel filter. I decided to look at it myself. The L and H screws were bent and broken. I was annoyed, but I replaced them from an old spare carb I had. The screws were identical and the rubber washers looked good. I turned them to factory defaults (there are no limiter caps) as far as I can tell by the manual. However, I cannot even pull the starter rope any more. It feels exactly like it does when it is flooded. Took the spark plug out, and she pulls fine. Exhaust is clean. Looks good inside. I looked at other similar threads, but haven't found anything useful yet. I'm not sure why replacing those screws would cause this. Any thoughts?

 

[rupedoggy]

Try pulling it over with the ignition off.

 

[smoking]

Hello. I think I tried that, but I'll try again tomorrow.

 

[ozziechainsaw]

Maybe try with the plug out. Obviously it will be easier but just incase the rewind assembly has started to play up at the same time . I know that is unlikely but stranger things have happened.

 

[cookies]

mine take a couple pulls with the choke on to get some fuel/oil in the cylinder then their way easier to pull...little buggers have snatched the handle from my fingers on that first so I have learned to make the first pull or two slowly then once it gets easier pull like you mean it and it usually kicks over, flip the choke quick enough and it will go

 

[smoking]

I pulled it 20 times with the plug out just in case it cleared anything up. It pulls fine, but obviously doesn't run. I did notice, however, it started leaking gas mix out of the right side since my touch up.

Yeah, i tried giving it GOOD tug. It only gets harder to pull. She never did this before. Always ran like butter.

 

[ozziechainsaw]

Wow, that is different. So until you changed the L & H mixture screws, everything was fine ?

 

[smoking]

Yeah, she started up fine and ran with the trigger pressed. Just couldn't keep an idle without dying. Hence I looked to adjust the H and L screws.

 

[SteveSr]

I turned them to factory defaults (there are no limiter caps) as far as I can tell by the manual.

Once the limiter caps are removed the default screw positions listed in the manual or on the AF housing are NO LONGER CORRECT! If the saw runs at all you'll burn it up in short order from being too lean. Limited screws have a base setting (bias) that is set before the caps are installed. So the real setting is the base setting + the default (AF or manual) setting.

 

[smoking]

good to know. yeah i did play with them a bit, few turns this way, few that. nothing seemed to make a difference

 

[atpchas]

Is this how you adjusted the carb?

 

[cookies]

turn both jet pins all the way in until they stop (gently) rotate out one full turn, this is a general starting point on all carburetors. set the low first to set base idle then the high or secondary then tune for rpm.

 

[SteveSr]

good to know. yeah i did play with them a bit, few turns this way, few that. nothing seemed to make a difference

If the carb "L" screw is not having an affect you either have a carb issue or an air leak.

 

[smoking]

Hey folks. I appreciate the replies so far. I tried everything mentioned and no difference. Tried to start it in the off position. Try to change the adjustment screws on the carb. I even took the air filter off to see if that would help. I held the trigger down to see if that would make a difference while looking inside the carb and seeing the flaps open.

 

[smoking]

Update: following a YouTube video I took out the fuel line and inspected. It was leaking around gasket intersecting the gas tank. I'm not sure whether this would cause it to pull hard or not. However with the carb and everything out, it still is hard to pull. I'm sure to the experienced technician my statements sound funny. Live n learn. I continue...

 

[PV Hiker]

Hello,

First post here, but been referencing other threads for help. Hope someone might have insight into this.
My Stihl 039 wasn't idling right after I had a shop do a tune up. They had done a carb rebuild and replace the fuel filter. I decided to look at it myself. The L and H screws were bent and broken. I was annoyed, but I replaced them from an old spare carb I had. The screws were identical and the rubber washers looked good. I turned them to factory defaults (there are no limiter caps) as far as I can tell by the manual. However, I cannot even pull the starter rope any more. It feels exactly like it does when it is flooded. Took the spark plug out, and she pulls fine. Exhaust is clean. Looks good inside. I looked at other similar threads, but haven't found anything useful yet. I'm not sure why replacing those screws would cause this. Any thoughts?

So in most cases it is usually the last thing that was tinkered with that causes you grief. Meaning that it was running before you decided to replace the jets and now it does not. The jets you put in might not be a match causing wrong fuel delivery. Then there is the took it apart but just did not get it back together properly scenario that you may be overlooking.

Can put the old jets back in and set to factory settings. But there maybe too much fuel in the bottom of the crank case. That brings up the second issue of it not spinning easy with pull rope. Too much fuel can cause too much compression for the piston to travel around. When you had the spark plug out did you turn the saw upside down to see if fuel would pour out of the spark plug hole? When @rupedoggy asked you to pull it over with the ignition switch to off he was asking for feedback if the coil was delivering a spark and causing the hard to pull condition. I did not see where you had done this and reported back for further help. If you sheared a key on the flywheel you will get spark but at the wrong time giving you kickback with the switch in the on position but not in the off.

Suggest putting the old jets back in or try starting over with a new carb. As mentioned you could be having other problems but you need air, fuel and spark. So far you have not mentioned you have spark or proper fuel. It all has to come together at the right time and amount.

Back track to a know running condition and start over and watch what you bump, break or problem caused while doing it.

 

[Dennis Gauge]

Unless you screwed the mixture screws completely through the crankcase and into the piston, locking it in place, I can't see how just changing those would make any difference in how the saw pulled over. Something else has happened in conjunction with your mixture screw replacement. What that is, you haven't told us, quite probably because you didn't realize it happened when it happened.

Have you turned the saw upside down with the plug out? The only thing I can think of is the crankcase is full of fuel below the piston.

 

[SteveSr]

Hey folks. I appreciate the replies so far. I tried everything mentioned and no difference. Tried to start it in the off position. Try to change the adjustment screws on the carb. I even took the air filter off to see if that would help. I held the trigger down to see if that would make a difference while looking inside the carb and seeing the flaps open.

How about post a video of the saw exhibiting the problem... With the standard "1 & 1" stock settings on this carb the saw should run pretty well. If it doesn't something is broke and needs fixed.

BTW, how do you know trhat the replcement L & H screws were the same as the originals? Just because the threads happen to match doesn't mean that the geometry of the needle does...

 

[smoking]

I appreciate all the responses. I'm looking it all over. Just a quick message to say that today I replaced the fuel line and filter with oem parts and it stopped the leak. At least that is settled. I also replaced the spark plug just to rule that out. Will continue when I have the chance. I intend to post up the solution if I ever get there for posterity.

 

[Cycledude]

Hello,

First post here, but been referencing other threads for help. Hope someone might have insight into this.
My Stihl 039 wasn't idling right after I had a shop do a tune up. They had done a carb rebuild and replace the fuel filter. I decided to look at it myself. The L and H screws were bent and broken. I was annoyed, but I replaced them from an old spare carb I had. The screws were identical and the rubber washers looked good. I turned them to factory defaults (there are no limiter caps) as far as I can tell by the manual. However, I cannot even pull the starter rope any more. It feels exactly like it does when it is flooded. Took the spark plug out, and she pulls fine. Exhaust is clean. Looks good inside. I looked at other similar threads, but haven't found anything useful yet. I'm not sure why replacing those screws would cause this. Any thoughts?

how could they have bent those screws ?