Stihl 039 running issues

[dyager]

Need some help here. Working on 039 that won’t stay running. Rebuilt the carb, replaced fuel line and filter, spark plug, and impulse line. Fired up and runs good for a minute or two then idles up and dies. Won’t restart but has good spark. Any ideas are most welcome, thank you, Dan

 

[dyager]

Well the spark is orange if that helps

 

[Wood Doctor]

Clogged air filter might do that, but looks like a bad air/fuel mixture from the carb. I'd just replace that carb and see if that fixes it.

 

[Old2stroke]

Obvious thing to check first is the tank vent, when it starts to run lean crack the tank cap to let air into the tank and see if it cures the problem. Other things that can cause fuel starvation: Any leak in the impulse from crankcase to carb, control lever that's set to low, clogged screen filter in carb input, fuel pump faulty (gasket on wrong side, cover leaking)
What was the original issue that caused you to rebuild the carb?

 

[Wood Doctor]

Obvious thing to check first is the tank vent, when it starts to run lean crack the tank cap to let air into the tank and see if it cures the problem. Other things that can cause fuel starvation: Any leak in the impulse from crankcase to carb, control lever that's set to low, clogged screen filter in carb input, fuel pump faulty (gasket on wrong side, cover leaking)
What was the original issue that caused you to rebuild the carb?

Good point, I forgot about a bad tank vent. That's a potential problem also.

 

[Ozhoo]

Did you use a chicom fuel hose? They suck goat balls and have been known to kink.

 

[dyager]

Obvious thing to check first is the tank vent, when it starts to run lean crack the tank cap to let air into the tank and see if it cures the problem. Other things that can cause fuel starvation: Any leak in the impulse from crankcase to carb, control lever that's set to low, clogged screen filter in carb input, fuel pump faulty (gasket on wrong side, cover leaking)
What was the original issue that caused you to rebuild the carb?

It would run for a couple minutes then die. I’ve noticed that the L and H screws don’t seem to change much of anything

 

[dyager]

Did you use a chicom fuel hose? They suck goat balls and have been known to kink.

It’s a Stens but I’m sure it is Chinese. I’ll surf for OEM

 

[Old2stroke]

It would run for a couple minutes then die. I’ve noticed that the L and H screws don’t seem to change much of anything

When you start a cold engine with the choke on, the fuel chamber of the carb gets filled due to intake vacuum and the closed choke, even if the fuel pump isn't working, then when it starts and the choke is opened, it will continue to run for a few minutes until the fuel chamber is empty and not being refilled by the fuel pump. Fact that it starts with the choke on means that the filter, fuel line and carb inlet valve are probably good and it's just the fuel pump section that isn't working. Check to see if you are actually getting impulse pressures by squirting a drop of oil down the impulse line and see if it moves up and down when the engine is turned over.

 

[Vintage Engine Repairs]

Main nozzle check valve or tank vent.
Run a pressure and vac test on the crank case, hoses and fuel filter too.

 

[a. palmer jr.]

Yeah, it's possible you have an air leak between the cylinder and the bottom cap of the engine or around the main crank seals. Hard to tell without testing it..

 

[Oletrapper]

Well the spark is orange if that helps

Spark should be blue. Might have a coil breaking down? jmho OT
Let us know what you find.

 

[stihltech]

AIR AND PRESSURE TEST!.
If you do not have that means to do one, spray some brake cleaner arounf the sealing surfaces and seals. If it affects the running you will get closer to the problem. If it does not, the high speed nozzle may not be sealing. We can guess all day but a full diagnosis will find the issue. And you will keep your hair.

 

[Old2stroke]

After you get it started, will it transfer off idle and run at full speed under load and then just die after a few minutes of running to idle?

 

[dyager]

After you get it started, will it transfer off idle and run at full speed under load and then just die after a few minutes of running to idle?

That’s exactly what it’s doing. I can run it wide open. After a couple minutes it bogs and dies. Won’t take any throttle at this point. I considered the coil but I have spark after it dies

 

[Old2stroke]

If it dies while running at full speed in a cut, it sounds like a serious fuel starvation, either a restriction in the fuel supply to the carb, faulty tank vent not letting air into the tank or a failure of the fuel pump to deliver fuel to the carb or an internal problem with the carb. Not the nozzle check valve, if it sticks open, it will only affect the idle. Have to read all the previous posts relating to fuel starvation and methodically go through all the possible causes. Your original post made it seem that this was just a problem at idle.

 

[grizz55chev]

Have you pulled the muffler yet to get a look at the piston!?

 

[a. palmer jr.]

It’s a Stens but I’m sure it is Chinese. I’ll surf for OEM

Make sure the fuel line isn't kinked where it bends going into the carburetor..

 

[a. palmer jr.]

Did you use a chicom fuel hose? They suck goat balls and have been known to kink.

Also the impulse hose. If it leaks the carb won't work right..

 

[dyager]

Have you pulled the muffler yet to get a look at the piston!?

Yup. Looks pretty good