Saw loses power during LONG cuts

[Soundchasm]

Howdy All,
It's been a few months since I could spend any time here. An oak dropped a large branch (30") onto my property. I was happily working the big rounds with my little Husky 435, 16" bar. New chain, new bar. I got buck-fever and poured close to the last of the 50:1 gas from the one gallon container instead of mixing more. I sensed I wasn't being too smart, and then the saw began to bog down halfway through the big rounds. Of course I saw dirt in the bottom of the gas can.

I cleaned out the gas can, cleaned out the fuel tank, got a replacement fuel filter, fresh fuel, but it still loses power in the thick of it. I'm getting chips (not dust) and the chain is sharp.

Can I try a carb adjustment, or will the carb need to be replaced, or could there be worse in store? It runs fine for short cuts, but I can no longer just bury the thing, and if it is bogging down, it'll die when I let off the throttle.

"IF" you own the carb tool, the saw is superb. With the factory settings it was virtually impossible to start. Once corrected, the thing has become a tiny little monster. I don't mind putting effort into this.

Thanks,


Greg

 

[DougA]

I would think there is dirt in the carb if there was dirt in the gas can. The carb has very tiny holes and very thin rubber flaps to control the gas correctly. It takes very little to go out of whack. If you are comfortable, take apart the carb and clean it. If not, have someone do it for you or buy one on eBay.

Other cause will be a plugged air filter, which is my usual cause of problems but the dirty in the gas points to dirt in the carb.

 

[Soundchasm]

Thanks Doug. I just replaced the spark plug to sort of postpone dealing with the carb, but now it won't achieve full acceleration. I tried diddling the carbs to 1.5-2 turns which I think is the universal standard, but no effect. It just chugs along with an open throttle and dies when the trigger is released.

I guess I have nothing to lose if I fiddle with a carburetor at this point! When I was a kid, I remember some automotive book that said carbuertor was a French word that meant "Leave Alone".

I'll check the air filter to rule that out.

 

[DougA]

Clogged air filter will result in not being able to get high revs or running rough on high.
Minor Carb problems can be partaking solved with carb adjustments but it's strictly a stop gap.

On a Stihl, there are only two tough parts to cleaning a carb. One is wiggling it to get it out. It feels like it's stuck but it just pulls out as you disconnect the gas lines and throttle stick as it's coming out.
The other more serious problem is carefully putting everything out on the table in order as you take the carb apart so that you remember how it goes back together. Never done a Husky so no idea but someone will help you on that.

 

[Soundchasm]

Doug, I just checked the air filter per your suggestion. At first it didn't look clogged but that's because I wasn't understanding it. The light bulb went off as I began to clean it. It's a permanent filter and I think the mesh was clogged with super-fine powder. The mesh is pretty clean now, but it's too late for me to try and fire it up now. I also have a can of carb cleaner and I'll give it a shot or two of that tomorrow and see what happens.

Here are a few other pics. The one is down the cylinder hole. Not sure what that's supposed to look like, but it seems pretty carboned up.

Thanks for the reminder!

 

[jrems]

If the carb checks out ok, Pull the muffler and look at the piston through the exhaust port for scoring( deep gouges). It's possible since it was so heavily loaded in the cut it overheated and trashed the piston and you now have low compression. The flywheel could have also spun and you could have no power due to the incorrect ignition timing.

 

[Soundchasm]

Thanks Jrems. If the clean air filter and shot of carb cleaner don't work, then that's my next step. It's every bit as hard to pull-start the thing in it's current condition, so maybe that means there's still correct compression?

So far everything has come off this saw fairly easy, so I may as well check the cylinder when it comes on deck.

 

[hman]

Look at the screen in the muffler they can get plugged and cause no power and die at idle.

 

[Jon1270]

The carb on on the top of the piston is no problem. The old plug looks fine.

If the fuel line and filter are intact then dirt shouldn't have gotten into the carb.

Is the chain getting oil? Sometimes if the oiler fails or the oil hole in the bar plugs up then the bar can heat up and increase resistance on long cuts.

Unfortunately the fact that it has compression doesn't mean much. Until the rings start sticking in the groove they can still seal against the cylinder bore fairly well, so compression can feel fine on a scored top end... for a little while.

 

[BenTN]

As suddenly as this happened. Sounds like fuel starvation to me, clogged filter in tank, kinked/cracked line or trash in carb.

Jon stated a good point about bar oil. Check/clean the oil ports on the bar and check for good flow.

 

[Pug]

Check the compression. Should be 100 plus pounds. If it got hot and scorched the rings it can effect power, starting etc.

 

[Soundchasm]

Thanks to each here. Today's saga is that the air filter is clean, but that had no effect. The saw starts, but chugs along at full-throttle and would love to run full-out but can't. Took the air filter out and tried a few shots of carb cleaner, but no relief.

For added info, when I topped off the gas tank today, the bar oil did NOT need filling!! Also, when I was pull starting for about the 20th time, a little plastic tooth shot out, so that piece will need to be replaced as well. I already know that one is a bit of a PITA.

So, I'll order a carb replacement online, check the oiler, take off the muffler and check the cylinder, but if the new carb doesn't fix it, this particular saw may become a throwaway.

I think the new ones at Lowes are $269, and I have used the crap out of this little saw (6/11). If the repairs aren't more than the cost of a new saw, I could still see turning this into a second saw, and maybe it could handle an 18" bar.

 

[jrems]

Before you order a replacement carb, pull the muffler and check the piston. Post a picture back here of it.

 

[jatoxico]

So, I'll order a carb replacement online, check the oiler, take off the muffler and check the cylinder, but if the new carb doesn't fix it, this particular saw may become a throwaway.

Have you tried gently seating the carb adjustment screws then returning them to their position? Sometimes that can clean any build up.

 

[DougA]

If the oiler was full, that means the oil line is plugged and you could be running the chain/bar too hot. It's likely caused problems with the piston as others have said. If check the piston and try running the saw with no chain at all and see what happens. If you are really lucky, you'll just need to replace the chain & bar and unplug the oil line.

 

[Soundchasm]

Before you order a replacement carb, pull the muffler and check the piston. Post a picture back here of it.

I can't get the muffler off with any tool I own. I think it's an allen screw, but I can't get anything to bite. Of course, I can't really see in there.

Why does the music from Benny Hill play every time I try something mechanical?

 

[Soundchasm]

Have you tried gently seating the carb adjustment screws then returning them to their position? Sometimes that can clean any build up.

I have open and shut both the high and low several times, but there was no change... Drat.

 

[jrems]

It might be a torx bolt. Does it have a star shape instead of a hex like an Allen ?

 

[Soundchasm]

I can't imagine getting tech support from Husqvarna (or anybody else, for that matter) on a weekend, so this is great.
Here's the best shot of the cylinder wall. I don't see anything that looks like a vertical scratch. All of the markings remind me of the finish level when I use 000 steel wool on polyurethane.

I just needed to find the right allen wrench!!

 

[Jon1270]

What's the piston look like? That shot only shows us the cylinder wall on the intake side, but most damage typically occurs on the exhaust side.

 

[jrems]

Yeah, get a picture of the side of the piston. You can just make out the top of the piston and it does look very clean. You would usually see gouges there as it would be the hottest spot on the piston. Get a better pic of the side of the piston though the hole so we can rule it out. You may be lucky it might just be a carb issue. If it is get a cheap $20 Chinese one off eBay if they make them for your saw. Also check the impulse line to the carb.( it's the one that connects the base of the cylinder to the bottom( usually) of the carb. It what's moves the diaphragm in the carb. If there is a crack or leak it in the rubber line it might not be able to pump enough fuel at full throttle.

 

[Jon1270]

For added info, when I topped off the gas tank today, the bar oil did NOT need filling!!

BTW, I'd fix this first and see how it works before you go tearing half the saw apart.

 

[Soundchasm]

What's the piston look like?

Man, tough crowd!!

OK, I I have pic of the top, middle, and bottom of the piston. BTW, it's necessary to defeat the camera autofocus. For this camera, the only way is to let it focus on the outside, and then move the camera forward about 1.5". With my naked eyes, er, bifocals, I don't see anything remarkable or obvious. I do see a color change from top to bottom (blue-ish to not blue-ish).

I'll put the muffler back on and look for the oiler clog. Thank you guys.

 

[Jon1270]

Welp, the motor itself is fine.

 

[jrems]

Piston looks beautiful. No problem there. It could be a slipped flywheel like I mentioned earlier. But I would check out the carb and impulse line next.