Stihl 038 Woes

[djg james]

Last time I was out cutting firewood, my saw started to act up. Started fine, strong at the start of the cut but would loos power about 1/3 the way through the log. Had to constantly pump the throttle to get through the cut. Removing saw from the log, revving the engine and then resuming the saw cuts awhile and then bogs down again.

To me, it sounded like it was either starving for fuel or air. I cleaned the air filter and the fuel filter. I did NOT check the fuel line (possibly collapsing). I'll check it tomorrow.

In another thread, someone who was having troubles with their saw, was told to check a loose spark plug boot. I did check mine and it was loose. But snugging it up didn't help any.

Someone in another forum suggested I adjust the carb to ensure one of the adjusting screws hadn't vibrated out of position. I'll check that tomorrow.

So, I guess if the fuel line is OK, the next step would be to remove, disassemble and clean the carb? Being sure to check for cracks in the rubber parts.

Anything else I could do to diagnose the problem?

 

[cookies]

remove carb, clean and inspect it, check fuel hose and impulse...it sounds like your impulse hose came off.

 

[ballisticdoughnut]

Remove muffler and inspect piston. If it’s scored you have bigger problems.

 

[djg james]

remove carb, clean and inspect it, check fuel hose and impulse...it sounds like your impulse hose came off.

I'm a visual person and am chainsaw parts/repair illiterate. I had to look that up. I'll check that tomorrow.

 

[L34]

038!!
choke flap not pulling shut due to weak spring?

 

[L34]

Remove air cleaner and try it.

 

[Jasonrkba]

I had a stihl do that one time and it turned out to be a dying ignition coil. If its starved for fuel and you are pushing through a load you could ruin the piston and possibly cylinder. Those air filters do have trouble but most often give problems starting.

 

[stihltech]

Fuel tank vent. No air in, no fuel out. Try opening the fuel cap and see if it improves.

 

[Hermio]

Last time I was out cutting firewood, my saw started to act up. Started fine, strong at the start of the cut but would loos power about 1/3 the way through the log. Had to constantly pump the throttle to get through the cut. Removing saw from the log, revving the engine and then resuming the saw cuts awhile and then bogs down again.

To me, it sounded like it was either starving for fuel or air. I cleaned the air filter and the fuel filter. I did NOT check the fuel line (possibly collapsing). I'll check it tomorrow.

In another thread, someone who was having troubles with their saw, was told to check a loose spark plug boot. I did check mine and it was loose. But snugging it up didn't help any.

Someone in another forum suggested I adjust the carb to ensure one of the adjusting screws hadn't vibrated out of position. I'll check that tomorrow.

So, I guess if the fuel line is OK, the next step would be to remove, disassemble and clean the carb? Being sure to check for cracks in the rubber parts.

Anything else I could do to diagnose the problem?

I had this happen with a 441C. Turns out the cylinder walls were scored after I changed the sapark plug and got sawdust inside. It lost compression when it heated up.

 

[djg james]

I had this happen with a 441C. Turns out the cylinder walls were scored after I changed the sapark plug and got sawdust inside. It lost compression when it heated up.

Oh $hit! I'm not up to that level of repair yet. Hope it's something more simple in my case.

 

[djg james]

Fuel tank vent. No air in, no fuel out. Try opening the fuel cap and see if it improves.

Yes,I thought about that last night. I'm going to remove the vent and try it today. Clean it, of course, before reinstalling.

 

[gerrywoodsy482]

Ignition coil problems can be sneaky. If the fuel-related checks don't reveal much, it might be worth looking into the ignition coil as well. Pistons and cylinders don't take well to prolonged starvation, so timely diagnostics could save you from bigger troubles.

 

[djg james]

Ignition coil problems can be sneaky. If the fuel-related checks don't reveal much, it might be worth looking into the ignition coil as well. Pistons and cylinders don't take well to prolonged starvation, so timely diagnostics could save you from bigger troubles.

In the other thread I cited, someone mentioned an inline spark tester. Would this be useful to check the coil? As I said, I'm still learning.

 

[leaf]

Absolutely agreed as to "stop using and start fixing" (whether you do the fixing or someone else does. Most of the possibilities (not getting fuel to carb) are pretty simple fixes that will instead cost at least a new piston / ring if not fixed.... (Ignition coil, not so much, but it "sounds" more like a fuel issue....)

 

[djg james]

I had a stihl do that one time and it turned out to be a dying ignition coil. If its starved for fuel and you are pushing through a load you could ruin the piston and possibly cylinder. Those air filters do have trouble but most often give problems starting.

I only finished two cuts with it acting this way. Then I put it away.

How do I check the coil?

 

[djg james]

Absolutely agreed as to "stop using and start fixing" (whether you do the fixing or someone else does. Most of the possibilities (not getting fuel to carb) are pretty simple fixes that will instead cost at least a new piston / ring if not fixed.... (Ignition coil, not so much, but it "sounds" more like a fuel issue....)

I have stopped using it. Only finished two cuts with it acting this way. This afternoon, I'll check out everyone's suggestions.

 

[leaf]

Eyeball method... pull spark plug, ground outer part of plug, pull cord/handle -- look for continuous "hot," crisp, blue flashes in plug gap (imagine whether or not plug would spark as well under compression in cylinder). "Soft" spark / yellowish / "uncertain" / irregular/ saggy -- can lead you to doubt coil. Good coil and connections make for a kind of snap,snap,snap that indicates coil working.

Highest tech method ... get an oscilloscope and a better quality inductive secondary side lead "probe." Look at scope traces for regularity and voltage.

Semi-tech method that can help -- Measure electrical resistance values on primary and secondary side, compare with specifications from "workshop manual" / other sources...

 

[Gord404]

one thing I do right off the bat is check the color of your spark plug- if absolutly white then then usually means you have problems like air leak or fuel starvation- a coil can work when cold and when it gets hot it acts up

 

[Mad Professor]

Yes,I thought about that last night. I'm going to remove the vent and try it today. Clean it, of course, before reinstalling.

fuel vent is just gasline with 2 screws. get real gasline proper size, PUSH the screws in not screw them, or it won't vent right

 

[Mad Professor]

Sounds like fuel delvivery. Check fuel line and filter. Screen inside carb on intake side, junk beneath carb impulse cover, impulse hose, and carb diaphraghms.