Chainsaws....

Dumb question - would you expect a saw to pop on starting fluid, and is it normal to have significant blow back through carb when cranking?

Got a Husky 394 that's pissing me off. Had the saw for several years, bought used with unknown history. Always been a pain to start, but seems to run decently under load though it didn't like to idle for long. Doesn't get used much as I use smaller saws for most stuff and it's always a bear to start. Tried to use it today and couldn't get it to start at all. Magento gap, plug and grounding is good, and looks like a healthy spark.

I tried spraying some starting fluid down the carb throat figuring that would at least give me something and still no sign of life. I also noticed it was blowing back out of the carb quite a lot - almost seemed to be more air blowing out than being sucked into engine, through I'm sure that's illusion. Had the compression release in if that make any difference.

I've done quite a lot with 4 stroke engines, but have never really done anything but run them with 2 strokes, so not sure what is normal and where to go looking next. Wouldn't be surprised if it's just plain worn out, but I'd also hate to tear it apart and find it's a carb problem or something.
 
sdmuleman said:
Dumb question - would you expect a saw to pop on starting fluid, and is it normal to have significant blow back through carb when cranking?

Got a Husky 394 that's pissing me off. Had the saw for several years, bought used with unknown history. Always been a pain to start, but seems to run decently under load though it didn't like to idle for long. Doesn't get used much as I use smaller saws for most stuff and it's always a bear to start. Tried to use it today and couldn't get it to start at all. Magento gap, plug and grounding is good, and looks like a healthy spark.

I tried spraying some starting fluid down the carb throat figuring that would at least give me something and still no sign of life. I also noticed it was blowing back out of the carb quite a lot - almost seemed to be more air blowing out than being sucked into engine, through I'm sure that's illusion. Had the compression release in if that make any difference.

I've done quite a lot with 4 stroke engines, but have never really done anything but run them with 2 strokes, so not sure what is normal and where to go looking next. Wouldn't be surprised if it's just plain worn out, but I'd also hate to tear it apart and find it's a carb problem or something.
Click to expand...

Check the reeds.
 
I’ve had to replace 3 husky 372 coils on my saws, they used to be a known, out of warranty issue. Can’t speak to the 385 or 394.
Check spark and compression
 
Spent some more time on my thinning job yesterday. Ran my 044 and the 362 for limbing. I love that 44. hauled home another load of locust and a big hedge tree. I only work 2 days this week so I hope to get it finished up after Christmas. I need to buck up and split some of the wood I have hauled home too.
 
TrikeKid said:
394s don't have reeds.

Does it have spark? Might be as simple as a sheared flywheel key or bad coil. It should pop with supplemental fuel in the intake. I generally use a squirt bottle of premix.
Click to expand...

How?

It has to have some sort of backflow preventer to keep the pressure in the crank case and not just blow it back out of the carb.

Since he said he has air blowing out of the carb, the reeds or reed valve is a highly likely place to start.
 
Chevy_man said:
How?

It has to have some sort of backflow preventer to keep the pressure in the crank case and not just blow it back out of the carb.

Since he said he has air blowing out of the carb, the reeds or reed valve is a highly likely place to start.
Click to expand...
I've never seen a saw with reeds
 
they're still in snowblowers and boat motors and snowmobiles
think it's just a "larger motor" thing where in the little tiny motors they can get away without and it results in both a weight and cost savings (and less parts to break off and destroy everything else)

BUCKLAND said:
Yup, but when those reeds opened up, hold on cause here comes the power band.
Click to expand...
uhhh I don't think that they work like that
they just keep the crankcase suck from blowing back out the carb
so they're opening and closing the entire time the motor's running
 
Reeds are better because they pass air with a pressure difference and don't rely on port timing or rpm. The thing is more power = more heat, and nobody wants to lug around the extra weight or deal with the complexity with liquid cooling on power equipment. You'll run up against air cooling problems way before maxing out the piston port.
 
TrikeKid said:
The vast majority of saws are simple piston port engines. I have some really old saws with reeds but that went away in the early 70s for most.
Click to expand...

I can't remember the last time I had a saw apart. I assumed that since every one of the dozens of 2T engines I've worked on has them, that there has to be something. Even my 70cc ice auger has cute little reed flaps behind the carb.

But, if the piston is the seal I'd guess he's got a piston or a port issue to have air blowing back out of the carb.

I did assume he checked that there wasn't a nest in the exhaust... :laughing:
 
TrikeKid said:
You gotta go way back to find a reed saw. Newest one I have with reeds is mid 60's. They turn about half the RPM of a modern saw maxed out
Click to expand...

Think that's more age, port timing, and ignition system limitations.

100 and 125 dirt bikes are spinning 10,000+ rpm with reeds. Although the modern carbon fiber ones last a lot longer than the old fiberglass.
 
BUCKLAND said:
Yup, but when those reeds opened up, hold on cause here comes the power band.
Click to expand...

486 nailed it. They're always flapping with every pressure pulse.

You thinking of the power valve on a bigger engine? They open the exhaust port with RPM, so they can optimize exhaust pulsing across the whole range. More torque and more hp. They're all setup on a governor, but some snap open and some are smooth and progressive enough to never notice.

Would be fairly useless on a saw where they're only designed to be run wide open at full rpm.
 
[486] said:
they're still in snowblowers and boat motors and snowmobiles
think it's just a "larger motor" thing where in the little tiny motors they can get away without and it results in both a weight and cost savings (and less parts to break off and destroy everything else)


uhhh I don't think that they work like that
they just keep the crankcase suck from blowing back out the carb
so they're opening and closing the entire time the motor's running
Click to expand...
It was a joke to the 2 stroke power band of a dirt bike.

Not a good joke

My bad
 
Chevy_man said:
You thinking of the power valve on a bigger engine? They open the exhaust port with RPM, so they can optimize exhaust pulsing across the whole range. More torque and more hp. They're all setup on a governor, but some snap open and some are smooth and progressive enough to never notice.

Would be fairly useless on a saw where they're only designed to be run wide open at full rpm.
Click to expand...
Ya, I was just kidding about that.

Been running power valves sleds since my first snow check 2001 ZR 800 LE with APV.
 
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