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Echo PB770T Bogging Down

Conquistador3

Conquistador3

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OK, I have this PB770T which has proven to be an extremely tough nut to crack.
According to S/N it was manufactured in 2012 and has about 350 hours on it.
Symptoms are very simple: it bogs down before reaching full rpm. It never dies while running, just fails to reach full rpm. It idles perfectly and starts at second pull from cold.

What I have tried so far:
1)Carburetor rebuild
2)Low hours carburetor from a known good runner
3)New fuel filter and spark plug
4)Gutted the tank vent, then removed it altogether
5)Pressure tested
6)Visually checked the piston for scoring
7)Checked for air leaks (read on though)
8)Cleaned the passage feeding air to the diaphragm pump
9)Cleaned the exhaust side from carbon
10)Regapped the ignition coil

Absolutely nothing solved this issueor even pointed in one direction. It keeps on bogging down after about two seconds of full throttle applied but idles beatufully.

I know older Echo backpack leafblowers had a tendency for leaky seals, but that usually happened on the starter side, which seem fine on this one. I haven't checked the fan side, but that's just because I am lazy and dismantling backpack leafblowers is not my calling... still I haven't heard of a PB770T with leaky seals yet, perhaps they all get straightgassed long before that point. ;)

If anybody has any idea it would be greatly appreciated: the thought of diamntling that thing to replace the seals only to have it bog down once again is not exactly enticing...
 
Gaspowered

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I have worked on a few of those Echo backpack blowers before. Last one I did was a smaller model, I think it was a PB550T. I went through the carb, new plug, fuel filter, basic tune-up. It fired right up and bogged immediately. Pretty much all Japanese power equipment manufacturers, Echo, Shindaiwa, Tanaka, Redmax, etc. use those Walbro WYJ carburetors with the "barrel" intake on their blowers. From my experience on those carbs most of them don't have needle valves. Some may have one, and others may have those two tiny little needles, just like on that 550 I worked on. I almost didn't see those tiny little things. They are designed so that you can't tamper with them, (California carb.) You can buy the adjustment tools on eBay for cheap, and I had the one to do it, but it was too big and wouldn't fit at all. All I did was take a small roll pin and tap it onto the low speed needle and turned it about 1/4 of a turn. Ran great. I am not sure if you carb has the tiny little needles, and if it doesn't I would check your metering lever height. Since those are Cali carbs that's all you can do in the way of adjustment. There are China carburetors on eBay that have one needle, I would try one of those.
 
Conquistador3

Conquistador3

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These newer Echo's have WYK series carburetors. They used to come with the -345 and now should come with the -406.
You can adjust the single adjuster using a small size (not regular size) Single D tool, but it's an extremely tight fit. I absolutely hate them because even with the right tool it's so easy to mess up the adjuster. Walbro probably made them out of cheese.

Still neither carburetor solved my problem, and one comes from a known good runner. At this point I suspect either the fan side seal or the ignition is to blame, unless there's something else I haven't thought of.
Tomorrow I'll see if I can source some crankshaft seals for it and resign myself to dismantling the damn thing. It's the last chance I give this thing, after this I am done because it makes no more economic sense: a coil is €100 and the flywheel is €110.
 
Gaspowered

Gaspowered

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These newer Echo's have WYK series carburetors. They used to come with the -345 and now should come with the -406.
You can adjust the single adjuster using a small size (not regular size) Single D tool, but it's an extremely tight fit. I absolutely hate them because even with the right tool it's so easy to mess up the adjuster. Walbro probably made them out of cheese.

Still neither carburetor solved my problem, and one comes from a known good runner. At this point I suspect either the fan side seal or the ignition is to blame, unless there's something else I haven't thought of.
Tomorrow I'll see if I can source some crankshaft seals for it and resign myself to dismantling the damn thing. It's the last chance I give this thing, after this I am done because it makes no more economic sense: a coil is €100 and the flywheel is €110.
Yeah, those adjustment tools are crap. If it's not your carb then it must be a seal leak, like you said. Good luck on it. The good thing is though is that it's an Echo and parts are readily available. That's a really good blower and I would recommend getting it going. Also, when I said my adjustment tool was too big, it was one of the small ones, and it still wouldn't fit and stripped out the "D" shape. The Walbro tools are very hard to acquire and very expensive.
 
Manic84

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How many pulls does it take to start when warm?

I was going to suggest the spark arrestor, but you've already gone though the exhaust side.
 
Conquistador3

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How many pulls does it take to start when warm?

I was going to suggest the spark arrestor, but you've already gone though the exhaust side.
One pull. It starts instantly like it has always done.

I have a couple extra things to try over the next few days, but from what I have been able to gather that blower is living on borrowed time.

I'll keep you posted and thanks everybody.
 
LegDeLimber

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I don't see a new fuel hose mentioned. That black hose of Echos is nice and flexible but it gets soft and gummy after a while, especially if it's ever been exposed to alcohol.
You may have already swapped it , but just not listed it.

You should check the spark to see if it jumps an honest 1/4" or 6mm gap at normal cranking speed.
Jumping a spark plug gap (.025~.030"), in open air, is not true/useful test of the ignition.
you need to see a good blue spark across that 1/4" gap at normal cranking speed, not jerking the rope out wild pulls.

On changing the seals?
I think they put all of the dang screws (in the blower housing) from the frame side, rather than from the motor side. arrrrgh!
I know they did that on the smaller units.
Makes for more than double the labor just to get to the fan/impeller side seal, vs if they had built them with the screws installed from the motor side.
 
Conquistador3

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Sorry for the omission: all fuel lines are brand new Tygon.
The ignition works well on another unit and a unit from the same known good runner gives the same bogging symptoms. That's a pretty good test I'd say. :laugh:
The worst parts of getting to the seals are the need to split the fan housing to remove the vent (a lot of screw) and especially removing the starter lug and the flywheel from the other side. In fact I'd take the fan housing disassembly any day other removing those flywheels.

Now a few extra things I have learned since.
The original carburetor floods even after a full rebuild. I've had it happen before on a Honda GX carburetor and it means the carburetor is so much scrap metal.
My compression tester is most likely junk (so a new compression test is needed).
Yamabiko is going nuts here: seals are a special order and I won't even get into how much they are. More on this on the chainsaw forum.

Yamabiko advertises these blowers as 300 hour units, and I must say they are true to their word: this unit is now well over 350 hours. What they don't say is how expensive parts for them, how long it takes to have them are and how much stuff starts breaking down all together. If our Chinese friends didn't sell pattern carburetors I wouldn't be even bothering.
I think I'll just fix this blower and put it up for sale and get a Stihl. It has been dead reliable for its design lifespan but it's time for a change. ;)
 
banditt007

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I read through this quick so bear with me....Check the air intake side of your blower, could be a seriously clogged up air filter/intake tube/choke stuck ext. I didn't read if its acting like the choke is on and 4 stroking running really rich but not reaching full rpm, or if its that smooth bogginess indicating lean. Here is what I would do, pull off the air intake right before the carb, start it up and run it. Try to go full throttle. Any significant change? Then when full throttle I would dribble some gasoline mix right into the carb.....Does the engine rpm increase and start sounding like its running where it should be? That should narrow it down some. Also try dumping all the fuel out of it, and make sure you have fresh clean mix. Simple stuff first.
 
Conquistador3

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Thanks for your concern but this is not an easy case, as I explained before.
Everything easy and reasonably cheap (carburetor, fuel lines, carbon buildup etc) has already been tried, and the only thing I solved right now is the flooding and it took a new carburetor to do so.

The crankshaft seals should be on their way here (if the MIT graduate I ordered them from placed the order right) and if those fail to fix the issue the blower is going to be broken up for spare parts: as said this is a high hour unit and with no aftermarket available and spare parts so expensive it makes no economic sense to go any further.
 
LegDeLimber

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Just a tom-fool question here.
Did you have a compression number?
Seems like the smaller (pb-620) units that I've seen, with high hours and worn rings, seemed to "weep" a lot, past the crank seals.
If the fan side seal is leaking , the crankcase, back of fan housing and all around the carb be covered with oil after just a few hours of running.

Picture of a High hour pb-620 (landscaper unit)
It almost looks like the fuel tank is leaking, but it isn't.
Leaking fan/PTO side seal makes an oily mess of the unit.
Pic is a few years old, Can't recall the compression.
Probably under 130psi though.
 

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Conquistador3

Conquistador3

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The 770 is built somewhat different from the 620 (chunky oil seals from the CS620 chainsaw to say one) and mine is so covered in dirt it's difficult to tell the brand, but there's a light oil residue on the left side of the tank, which is definetely not leaking. For the record we only run 2% premix here so oil residue is minimal one case or the other.
Compression is around 135/140psi. The gauge has been dropped one time too many and is not as accurate as it used to be.
I won't take the fan off until I have the seals because I have no idea when they'll get here but I do hope the fan is easier to pull than the one on a Stihl BR600. :laugh:

I will be picking a new backpack unit over the weekend: this old Echo right now is more a case of finding out all that's wrong with it than to be put back in service.

Thanks again.
 
LegDeLimber

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For anyone reading.
Forgot to mention that the reason for asking about compression would be the lack of power to hit top rpm with a blower.
That fan puts a pretty good load on the engine and low compression can be a reason for not getting top revs out of a blower.

I'm only online occasionally, these days
( got some health matters going on. plus I seem to be forgetting a lot of what i used to know)
So please forgive me if I'm sometimes long about checking back in on threads.
 
Conquistador3

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For anyone reading.
Forgot to mention that the reason for asking about compression would be the lack of power to hit top rpm with a blower.
That fan puts a pretty good load on the engine and low compression can be a reason for not getting top revs out of a blower.

I'm only online occasionally, these days
( got some health matters going on. plus I seem to be forgetting a lot of what i used to know)
So please forgive me if I'm sometimes long about checking back in on threads.
Yes, these engines are always running under load. They wear out relatively quickly and coupled with the difficulties in pulling the fan on many models that's the reason why blowers end up being broken up and/or thrown in the trash instead of fixed: it often makes no economic sense. Just to do some back of the envelope accounting: 1 new genuine carburetor $80, 2 crankshaft seals $15, 2 piston rings $20, 1 cylinder base gasket $5. That's $120 in parts already. Throw in three hours of labor (removing and installing the fan is a lot of timel) and that's an extra $120. $240 already, for a high hour unit. Commercial users wouldn't even think about it and homeowners/farmers would probably throw it away after replacing the carburetor.

To get back to us all the best for your health issues and if I don't die of old age before the oil seals get here we'll be back at this sooner or later.
 
Conquistador3

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Finally we have a breakthrough: it's the secondary ignition coil. :crazy:

After remembering that many years ago an Alpina chainsaw drove me nuts with similar symptoms, I decided to simply heat up the ignition with my trusted heat gun set to 80°c to simulate conditions after running a few minutes under load.
With the ignition coil heated I get 315 ohm on the primary (specs are 300-350) and a big nothing on the secondary (specs are 2,500-2,900 ohm). Sadly I could not borrow a known good runner, but I am pretty sure this time I nailed it.
Off to find a spare hulk with a scored cylinder then.
 
Conquistador3

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Here is the final diagnosis.

The original carburetor floods badly even after a clean and rebuild, I suspect due to a melted or otherwise damaged check valve.
The fan side crankshaft seal leaked very lightly.
The ignition coil gave weird secondary resistance values when heated up.
Compression is a bit on the low side (a little over 135psi vs 145psi as given by Echo).

After a new carburetor/filter/lines, new seals and a used ignition coil it seems to be fixed. I still need to test if it will start from cold: the crankcase was badly flooded after the mini-rebuild so it took a while for it to start. If it's good, it will hit the local classifieds this evening or tomorrow morning. If not I am just dismantling the damn thing for parts: I have thrown too much time at it and I am not spending another penny on it.

I have to say I am pretty impressed by Echo engineering: the leafblower lasted over the advertised lifespan before starting to come apart pretty much everywhere, and if aftermarket carburetors didn't exist it would make little economic sense to fix it (a Walbro WYK-345 or -406 are about $90 plus shipping).
 
Greg 625

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Get shindaiwa string trimmer w echo engine. That 1.1 cu in or whatever. after 2 tanks they scream and shindaiwa is shaft drive thats why $50 more than echo
 
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