Author Topic: Stihl 039 dies when hot (Read 21085 times)

Bilge Rat · « **on:** February 19, 2014, 07:12:04 PM »

Hi,
my 039 stalls/dies after a few minutes of work. Sounds like it is out of gas.

Has good non ethanol gas, gas line new 2yrs. ago. Carb rebuilt 2 yrs. ago also.

After it dies and will not restart it does have spark, checked with an inline tester.

The compression seems good, it wears me out trying to start it. I have not put a compression gauge on it yet.

I have pulled the carb and cover off the motor to check the rubber intake boot, it looks good no holes.
The top of the piston, rings and cylinder walls are clean, no carbon or scuffs. This was from looking in sparkplug hole and intake.

Where does the second hose to the carb come from? Is the small hose from the fuel tank with the plug in it have a vent hole in it ?

I am chasing a fuel problem and need some information on how the fuel system works.
Thanks.

thecfarm · « **Reply #1 on:** February 19, 2014, 07:13:47 PM »

Will it start in about a ½ hour of just sitting? I suppose you changed the fuel filter?

Bilge Rat · « **Reply #2 on:** February 19, 2014, 07:32:26 PM »

Filter is clear.

It will start after about 30 minutes.

JohnG28 · « **Reply #3 on:** February 19, 2014, 07:59:19 PM »

Try opening up the fuel tank when it shuts down, could be vapor lock. If you hear a hissing sound and can restart the saw after that then it is a tank vent issue. Could also be a bad coil that has less pop once hot.

Bilge Rat · « **Reply #4 on:** February 19, 2014, 10:05:42 PM »

Vapor lock,
as in the tank vent clogged?
The tank vent is the tube with the threaded plug in it, does it have a hole in the plug?

The pulse tube is original, i was thinking it could have a leak near the motor that may expand.

Does the pulse tube supply an impulse that drives a diaphragm acting as a fuel pump?

I am going to start at the tank,filter, pulse tube, vent, go thru the system.

On a boat, a clogged vent will shut the motor down too. Opening the cap is the test for them.

Outboards are easier compared to the cramped space in a chainsaw.

Thanks

JohnG28 · « **Reply #5 on:** February 19, 2014, 10:35:55 PM »

Yes, as in clogged tank vent. It is actually the plug in the vent line that lets the tank vent some without fuel loss. I'm not familiar with the exact one on an 039 but the check I referenced earlier would check for that issue. The impulse line does make the carb function as you said and is another good place to check out.

Andyshine77 · « **Reply #6 on:** February 20, 2014, 02:04:00 AM »

Over time the line will shrink around the grub screws preventing the tank from venting properly. This is very common on saws with this set up.

joe_indi · « **Reply #7 on:** February 20, 2014, 09:21:20 AM »

1. Blocked fuel filter. (Yes you have checked it. Check it once more)
2. Blocked strainer in the carb.
3. Make sure the H and L screw are not turned in to their stops.
4. Its a 039.Old enough to have a stiffened metering diaphragm.Replace it.

luvmexfood · « **Reply #8 on:** February 20, 2014, 09:27:44 AM »

Just to make sure I am thinking right the pulse tube is the tube on the right of the carb that goes to the saw body?

Bilge Rat · « **Reply #9 on:** February 21, 2014, 12:08:47 AM »

Work got in the way of the chainsaw issue today.
I did get to check the fuel vent.
The vent does not vent! Lung pressure on the fuel fine into tank and nothing out the vent.

With a vacuum gauge the vent will keep the tank at 14hg. That can't work. Most lift pump type fuel delivery systems on boats and cars have a problem with anything over 6hg of vacuum.
I will get a new vent tube and while i am in there a pulse tube and carb kit.

JohnG28 · « **Reply #10 on:** February 21, 2014, 12:51:55 AM »

If you're going to take things apart, might as well do a carb kit, new fuel lines (and vent line!) and new impulse line. Get it all done at once and take apart once and all is well for some time.

And lmf, yes, that would be the impulse line. Runs from the crank case to the carb and provides a pulse to operate the carb.

Oliver1655 · « **Reply #11 on:** February 22, 2014, 07:10:41 AM »

Please note the "screw" in the vent tube is NOT screwed in. You push it in. If you screw it in the threads cut into the tubing & create a seal which loses the venting intended.

Al_Smith · « **Reply #12 on:** February 22, 2014, 08:33:19 AM »

I'll tell you a quick way to find out and simple .Pull the vent tube off and shove a piece of small fuel line on .If it dies out that isn't the problem .

It could be something like a seal heating up and all the sudden causes huge air leak .When it cools down the seal shrinks .I've got a little Poulan that does the same thing I just haven't fixed yet .

Bilge Rat · « **Reply #13 on:** February 22, 2014, 04:01:13 PM »

I was wondering about why they used a threaded plug in a hose for a vent. If you turn it in the plug would cut into the tube and form a seal.
Pushing it in makes sense.

I have some fuel hose hanging off the vent now, about to reassemble the saw and try it. Great minds think, maybe not alike but as long as we are thinking .

The carb kit, impulse hose and vent are not in stock anywhere in town so a quick test is all i can do today. I guess tomorrow is a get on the tractor and plow some dirt day.

Waiting on parts is a drag.

Thanks for the tips on saws

Bilge Rat · « **Reply #14 on:** March 01, 2014, 06:31:17 PM »

Update.

I put a new impulse line, carb kit and vent tube on.
5 pulls and it's running. Adjusted carb and cut some 4 to 6" limbs into cookies with no issues.

The vent tube was hard and the carb parts were less than perfect but no holes or hard. Carb was clean inside.
The needle valve was a little out of adjustment and the point of the needle at the sealing area looked like it was not fully contacting the seat.

I could not run the saw hard, no big wood at home but it worked well.

The only thing wrong now is i want another saw to play with!!!

Thanks to everyone for the help and information on here.

ShaunUK · « **Reply #15 on:** March 02, 2014, 04:36:31 PM »

Had the same problem with my husky 50. Would run for 5-10 mins then just die. When cooled off would start again untill hot. Prob was the coil, replaced it and all fine now.

KiwiKen · « **Reply #16 on:** March 04, 2014, 05:24:54 AM »

Interesting Shaun. I'm no expert but I've read a thread on Arbourist where an experienced person said that this type of problem is often due to a failing ignition coil. Worth remembering.

Just bought an 039 (online) and hoping it won't have similar problems.

Grandedog · « **Reply #17 on:** March 04, 2014, 05:45:30 PM »

Howdy,
The thing that will clue you in on the ignition issue is if the saw stops like the ignition switch was turned off in full stride.
Regards
Gregg

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Author Topic: Stihl 039 dies when hot (Read 21085 times)

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