Stihl 034AV strange problem

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hardhat

hardhat

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So been getting my 35 (ish) year old 034AV back up and running. It had sat for a long time and carb was gunked up. Rebuilt carb. Saw runs really fat when laying on clutch side and dies. It just loads up with fuel and dies. Though t it was an air leak. Redid crank seals and base gasket with no real improvement. Saw runs much better after carb rebuild but still exhibits positional behavior. Figured it had to be an air leak as I had to chase the tune on the carb a bit as well.

Anyhow after spending a little more time with it today, I have discovered something strange. If I turn the saw off and lay it down on the clutch side for a few minutes it floods. I have to crank on it while holding full throttle for 5 or 6 pulls to get it to clear. It then runs pig rich for a few seconds and then cleans up and runs fine until I put it on its side again. If I sit it on the ground upright and leaning toward the flywheel side (it is a bow saw), it starts and runs fine.

Have replaced fuel line, impulse line, intake boot, av mount, crank seals, base gasket. Only thing that helped was rebuilding the carb. I will say one thing, I did not mess with the fuel inlet needle valve, I just put a new diaphragm in as that part of the carb seemed ok.

Could that needle valve being off in the carb cause these symptoms? I swear when you sit it down on the clutch side for a few minutes and then start it, it almost acts like you had poured gas in the carb. Starts up super rich and then cleans up.

Just throwing this out here for ideas before I take it to the dealer because I know you can score a piston running it with an air leak. Piston and cylinder look great btw.
 
Manic84

Manic84

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Make sure that the metering lever/spring is not weak or binding somehow, that can happen on things that sit for awhile. But if it was dirty as you say, it's usually a good idea to just replace the needle outright, especially if you run into gummy residue/varnish, if you do, make sure to clean the carb thoroughly.

Check that the needle is seating properly and is free of any debris, do as Ozhoo suggested, if you have a tester that is.

Set the lever height to manufacturer specs, go ahead and post what kind of carb you have.

If you've already replaced the base gasket, crankshaft seals and the usual suspects, I'm kinda leaning on it not being a air leak, unless you think you've installed the seals wrong somehow.

Also, with it flooding out like that, it's possible it could be a fuel tank venting issue as well.
 
hardhat

hardhat

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Tillotson carb. I did not mess with metering lever. Will have to look up how to set those. Guess I have gotten lucky on carb rebuilds in past with the lever as I just set it wherever. Tank vent crossed my mind, but couldn't figure why position would affect it so immediately if that was the problem. Saw will run rich and die within seconds if you turn it with clutch side down and also runs rich if you turn it on its side to cut.
 
Mad Professor
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When you check needle and seat, if it is just debris/gunk and it cleans up you can reuse the old needle (inspect seat well). Then the metering level will not need adjusting (assuming it was OK to begin with). If you change the needle be sure to check/adjust this.

Which carb?
 
Vintage Engine Repairs
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Hey :)

Before you replaced all those parts at a guess it would have been cheaper to get a Mityvac and metering lever gauge. I’d avoid spending any more on it until you know what it is. A pressure and vacuum test in both carb and saw will tell you so much.

If the metering needle has been sitting without use for a long time, I wonder if it could have deformed in its seat by the pressure of the spring which in turn would mean the metering lever is sitting higher and thus more fuel than should be is inside the metering chamber of the carb?

This is all a guess and not coming from a place
of experience, just logic, but it’s a great place to start :)

A Mityvac has been the best investment I have made saw wise. With one I check leaks on everything from the crank case, seals, spark and decomp plugs to fuel and oil tanks, hoses, lines, carb needle seats, carbs, intake manifolds, check valves and so much more it’s a worthwhile investment :)
 
hardhat

hardhat

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mississippi
Hey :)

Before you replaced all those parts at a guess it would have been cheaper to get a Mityvac and metering lever gauge. I’d avoid spending any more on it until you know what it is. A pressure and vacuum test in both carb and saw will tell you so much.

If the metering needle has been sitting without use for a long time, I wonder if it could have deformed in its seat by the pressure of the spring which in turn would mean the metering lever is sitting higher and thus more fuel than should be is inside the metering chamber of the carb?

This is all a guess and not coming from a place
of experience, just logic, but it’s a great place to start :)

A Mityvac has been the best investment I have made saw wise. With one I check leaks on everything from the crank case, seals, spark and decomp plugs to fuel and oil tanks, hoses, lines, carb needle seats, carbs, intake manifolds, check valves and so much more it’s a worthwhile investment :)

True that. Some of the stuff i figured needed replacing just because it is a 30 + year old saw. I've got a mityvac and guess there is no reason I can't do a vacuum test. Not interested at this point in totally disassembling saw (i.e. splitting case). If there is a leak there, I'll just take it to the shop.

Hopeful that the metering needle is the problem. I will put the new one in from the carb rebuild kit and see what happens.
 
Vintage Engine Repairs
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Messages
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True that. Some of the stuff i figured needed replacing just because it is a 30 + year old saw. I've got a mityvac and guess there is no reason I can't do a vacuum test. Not interested at this point in totally disassembling saw (i.e. splitting case). If there is a leak there, I'll just take it to the shop.

Hopeful that the metering needle is the problem. I will put the new one in from the carb rebuild kit and see what happens.
hehe use it for sure :) best of luck with the outcome!
 
TheTone
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Jan 31, 2017
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North Central Arkansas
If your needle valve seat needs cleaning (assuming it's metal), here's a tip I got from one of the older (in terms of experience) guys on the forum. Take a Q-tip, cut it in half with a razor knife, moisten the stick end, and dip it in baking soda. Stick it down in the hole where the needle valve was, and twirl it with a little pressure. Do this a couple of times, then wash it out well.This will clean and smooth the valve seat.
 
SteveSr

SteveSr

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If your needle valve seat needs cleaning (assuming it's metal), here's a tip I got from one of the older (in terms of experience) guys on the forum. Take a Q-tip, cut it in half with a razor knife, moisten the stick end, and dip it in baking soda. Stick it down in the hole where the needle valve was, and twirl it with a little pressure. Do this a couple of times, then wash it out well.This will clean and smooth the valve seat.

I have used a Q-tip shaft and regular carb cleaner. Either should clean out any gum or residue.
 
SteveSr

SteveSr

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I've got a mityvac and guess there is no reason I can't do a vacuum test.

Pressure test the fuel inlet on the carb with your Mity-vac. It should hold 7-10PSI indefinitely. If it doesn't (and I suspect that it worn't) you will have found your problem. If you are using an OEM carb kit you can usually reuse the old metering lever to save having to readjust the new one. However, I always check them anyway.
 

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