026 - no power in cut

[NovaMan]

So I was sawing some wood today, and all of a sudden, SHAZAM! No power in the cut. Saw acted like it was running out of gas, but still had almost half a tank. It was pretty hot, so I let it cool off a bit and tried again. Same problem - free revved fine, but no power about 0.5 seconds after the chain hit the wood. Took the muffler cover off, and saw no scratches on the piston or in the cylinder. Spark plug was a nice chocolaty brown color. Fuel filter seemed to be clear, gas was clean, had oil in it, and wasn't at all watery. Fuel line and impulse hose both looked OK and seemed supple when probed with a screwdriver - they aren't all cracked and dried out looking. Air filter was a little dusty, but shaking it, knocking it, and brushing it off didn't help. When I got home, I took it apart a little more extensively, cleaned it up (even though it wasn't really very dirty), and put it back together. I tried it in a log, and it gave up immediately. Now it doesn't even really want to free rev, so now it acts exactly like it does when the fuel tank is running dry. What did I miss?

 

[Patrick62]

Lack of fuel

Two things:

Check impulse line again, maybe cracked somewhere not visible.

Carb may have lost it's fuel pump, or somehow the needle/seat jammed up.

Either way the engine is running way lean. Don't want to burn it up...

-Pat

 

[mountainlake]

Intake boot maybe, take the carb apart and clean. Steve

 

[sugarbush]

check the screen in the muffler.

 

[Fish]

Check the fuel line where it dangles in the tank, it might be becoming
too supple, and go through the carb.

 

[Erick]

Change the fuel filter in the tank and check/clean the inlet screen in the carb. Like Fish said if the line in the tank gets to soft (like gum) it could collapse.

May need a new diaphram/carb kit in the carb. No reason not to replace both the fuel line and impulse hose while you've got it down... good cheap insurance for the years to come.

 

[Lakeside53]

All the above, and worst case a flywheel side crank seal.


I can't really see a sudden failure of the diaphragms though...

 

[Taxmantoo]

Maybe throw in a new plug, just because it's cheap and easy.

Another thing that's cheap and easy is to blame that guy in WA who worked on it last.

 

[slabmaster]

Change the fuel filter in the tank and check/clean the inlet screen in the carb. Like Fish said if the line in the tank gets to soft (like gum) it could collapse.

May need a new diaphram/carb kit in the carb. No reason not to replace both the fuel line and impulse hose while you've got it down... good cheap insurance for the years to come.

What would cause the fuel line to get (like gum)? Could it be the ethonal in the gas? Usually rubber gets harder when it ages.Not softer.

 

[Fish]

Don't know why, just have seen a bunch of bad/soft fuel hoses on 024/026
saws

 

[Erick]

What would cause the fuel line to get (like gum)? Could it be the ethonal in the gas? Usually rubber gets harder when it ages.Not softer.

Not exactly sure what the process is, but I suspect it is the alcohol in the fuel breaking down the natural rubbers. All I know is I have pulled lines from many things including saws where the fuel hose was completely deteriorated and felt like bubble gum, it will actually rub off on your fingers and leave a sticky black residue. I can only describe it as being like the residue left when you pull a piece of tape off of something that has been in the hot sun.

 

[NovaMan]

Well, I guess the only thing I can say for sure is that the screen in the muffler is clean.
I'll take the saw apart on Monday and better evaluate the hoses and lines then.

 

[slabmaster]

Well, I guess the only thing I can say for sure is that the screen in the muffler is clean.
I'll take the saw apart on Monday and better evaluate the hoses and lines then.

I think the screen in the carb would cause it if it was full of wood dust.

 

[slabmaster]

Not exactly sure what the process is, but I suspect it is the alcohol in the fuel breaking down the natural rubbers. All I know is I have pulled lines from many things including saws where the fuel hose was completely deteriorated and felt like bubble gum, it will actually rub off on your fingers and leave a sticky black residue. I can only describe it as being like the residue left when you pull a piece of tape off of something that has been in the hot sun.

I've seen the same thing on an 066 fuel filter.The black rubber that holds the weight on was like black gum when i changed it.It was stuck to the tank bottom and came off on my hand when i touched it.I won't run ethonal laced gas in my saws anymore.I talked to a JD dealer friend of mine and he said this new ethonal gas is breaking down plastic parts in lawnmower engines also.

 

[NovaMan]

Yeah, ethanol is for drinking, not for burning.

Well, I took my saw apart today. I sucked on the impulse hose and the fuel line, and they both held vacuum, so I conclude they are crack-free. They're not gummy, so I'd say they're 100% good. As far as the intake boot/elbow, I looked it all over and stretched it and played with it, and I can't find any cracks in it. The fuel filter is clean visually, but it doesn't suck as freely as I would imagine it should, so maybe I ought to replace that.
Should I put a rebuild kit in the carb while it's easy to do so?

 

[Lakeside53]

You need to do a pressure / vac test...

 

[NovaMan]

On what?

 

[Lakeside53]

The entire crankcase... from boot to muffler.

 

[NovaMan]

Ah, OK. I'm kinda tired right now, but I'll pull some vac on it tomorrow and see what happens. Thanks Andy.

 

[RED-85-Z51]

All the above, and worst case a flywheel side crank seal.


I can't really see a sudden failure of the diaphragms though...

Ive seen em where they were at the end...hell, PAST the end of their life, and more than crispy. But the saw, trimmer, blower, whatever, ran fine. Suddenly it would just lose power and die..either flooding, or too lean.

My guess was that that the diaphragm would stick in either the UP or DOWN position momentarily and cause the Metring level to either flood the carb/engine or run out of gas.

The fact it free revs fine makes me think the Carb isnt the problem. Im thinking possible timing slip myself. That would be Sudden, and cost tons of power, but under no load it would appear to work fine.