Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Stihl => Topic started by: Mark71gtx on September 29, 2015, 06:46:04 am
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https://youtu.be/-2clMPd4OBY
The saw runs like crap at high rpm. The carb has been rebuilt and I put a new coil and new seals on the crankcase. It still runs the same. Any ideas? Thanks!
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Sounds like an over rich high speed adjustment. Or the metering lever is set to high. Just a thought.
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I started it with the high adjustment at 7/8ths out and turned in and out it does not ever clear up. I have rebuilt many carbs for many saws and have never had this kind of trouble before. Maybe I need to check the metering lever though. Thank you for your input. Do you know the proper setting for the lever? It is a Magnum if it matters.
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Let me check. I will get back with you. I am pretty sure the low speed helps to feed the high speed on that saw. So there maybe a need for some low speed adjustment.
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I did some looking around. The low speed does help to feed the high speed. 028 are the same way. So that means if you mess with one screw you are going to have to adjust the other. I am thinking that your low speed needs the adjustment now. The basic setting should be 1 turn out from a lightly seated postion on both the L and H screws. I think you are going to want to back the low speed screw out ( richen ) I may have it backwards it has been a while since a messed with a carb like that. I think if you take the low speed in and out you will see a big difference in how it runs.
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Thanks. I started it at 1 1/4 turns out on the low and 7/8 out on the high. I messed with both, but I didn't mess with the low much. I will check it out hopefully this evening. If that don't work where should I check next? Would a bad intake boot cause my problem? I wouldn't think so - seems to me it would run lean if it was bad. I can't think of anything else that could be my problem since I have replaced so much already. Someone actually threw this saw away. There was a lot wrong with it when I got it. It is the largest Stihl I have ever had and I wanted to see how it would perform in comparison to my Husqvarna 288XP (which is by far my favorite saw that I have ever owned). I thought it would be cool to have a big saw from each of the big two.
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Make sure the fork in the metering needle isn't bent if it's a captivated arm. If you have a pop of gage you can check the sealing ability of the needle
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If the boot was torn or leaking the saw would be way lean and screaming. I think it is in the carb adjustments. Start there and then go back through the carb. I have a feeling your low speed is the problem.
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Thanks, I'll check it. I got a new plug for it today. I'll put it in and adjust the carb while it is running. If I can't adjust it out I will pull the carb and check it out again.
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@Al Smith I know he is into these. So just in case he has info too.
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Well, I put in the new plug and put the settings on the carb at 1 and 1 and it still did the same thing. I played with the screws and nothing helped. A guy on another board said the choke flap could be the problem. I removed the filter and that was the #%$@-&$ problem! Apparently the aftermarket filter I bought is a pos...
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Glad you got to the bottom of it.
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That is right I forgot about that. The choke is in the air filter and is held opened with a spring inside the filter. I have seen the spring pop off before and then the choke flap flops around.
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Another problem that seems to crop up on the 038 series is the annular buffer shock mount which is on the left hand side aft of the engine .
These can become worn out allowing the intake boot to become stretched which will tear them on the under side .It's nearly impossible to tell if the boot is damaged unless it's removed and inspected .Obviously with a slight tear it won't leak air all the time and will cause a lean out at high speeds .Won't happen all the time though .I've changed around 4 or 5 of these things along with the buffers .
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New trouble. It seems this is not my only problem. I still can't get it to run right. It runs best with the high side turned all the way in. It runs Super rich. Muffler is wet inside from fuel. I pulled the carb apart and everything looks decent. Carb holds vacuum. What is the problem?
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New trouble. It seems this is not my only problem. I still can't get it to run right. It runs best with the high side turned all the way in. It runs Super rich. Muffler is wet inside from fuel. I pulled the carb apart and everything looks decent. Carb holds vacuum. What is the problem?
Is this with the air filter removed ?
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I put the original filter back on with a heavily tensioned spring. It still doesn't work like it should with it on or off.
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Is the saw real rich with the air filter off and the high speed needle seated ?
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Yes. I pulled the plug and it was wet.
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I pulled the carb and the arm for the needle was slightly up, so I removed it and bent it until it sat flat like it was supposed to. It is still rich. I will check again tonight to see if I got the diaphragm and gasket backwards. That is the only other thing I can think of. This is the only carb I can remember working on that had a plastic fuel pump center.
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Another problem that seems to crop up on the 038 series is the annular buffer shock mount which is on the left hand side aft of the engine .
These can become worn out allowing the intake boot to become stretched which will tear them on the under side .It's nearly impossible to tell if the boot is damaged unless it's removed and inspected .Obviously with a slight tear it won't leak air all the time and will cause a lean out at high speeds .Won't happen all the time though .I've changed around 4 or 5 of these things along with the buffers .
Thanks Al, but I don't seem to be running lean. I am over rich if anything.
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Does it rev higher than the last video with the air filter off or is it still cutting out at similar RPM's in similar fashion ?
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Pretty much the same until I completely close the H setting. Then it sounds about like it should. It does seem to be pulsing a bit though.
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Sorry, but just being clear .......... this is with NO air filter - correct ?
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Yes. It still has a pulsing sound with or without filter.
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I suggest going over that carb again ............ swapp carbs if possible
IIRC, you did rebuild the carb ? Did you see any dirt or corrosion anywhere in there ?
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I did rebuild the carb. It was not as bad as some I have built before that gave no trouble. There was some trash in it when I pulled it back apart. I blew it all out with canned compressed air (keyboard duster). The saw was thrown away, so there is no telling what it has been through. I think I will go ahead and buy another carb for it and see how it goes.
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i have had a few carbs look good, but couldnt tune ............ corrosion in the passages that couldnt be cleaned.
Is it possible that you inadvertantly swapped high and low adjusting screws ?
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It is possible.
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Is there any difference in the carburetors on a 038, 038AV, Super, and Magnum? I am looking at some online that only list for 038, not Magnum. I don't want to get the wrong carb. Lots of the ones I see have an extra port on top, so o am steering clear of those. I figure I will get another Tilliston or a Bing.
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I am not going to pretend to know, someone else here would be better qualified to answer that one.
I can check on my 038 Mag and see what carb its got, then you could be sure. Mine is all origional
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Based on the IPL's I have the 038's either run a Bing 48A101 or a 48A125 or a Zama C3-S148 or C3-S149. Those are all listed weather a 038, 038S,038M. i would check to make sure you have the right inlet needle. hopefully you kept the old one to compare. Had a husky 394 do the same thing you are talking about would not gain rpm with the H needle all the way in. found out that the inlet needle in the kit was not the one that I needed. But needed one out of a different kit. Look real close at the taper where the needle comes in contact with the seat. Also is your metering lever flush with the chamber floor. You can try to drop the lever below the floor and lean it out that way.
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Unless it's been changed the Mag uses a Bing carb.
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I don't know the history on the saw. It has a Tilliston carb. It has a plastic bottom on it. I took the carb apart again and cleaned it again and adjusted the needle arm again and now it runs like a dream! I want to get a 20" or longer bar to put on it. I am not buying a new chain for that short bar that is on it. I will put it in some wood as soon as this wet weather ends long bar or not! Thanks for all of the help! I have learned a lot working on this saw. If it was a lesser saw I would have just parted it out!
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Glad you are up and running. Happy cutting.
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Thanks!
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Glad you are up and running. Happy cutting.
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