FS85X just does not want to tune in properly

[TerraForte]

I also inspected it quite thoroughly before installing it.

There were obvious differences between the knock-off and genuine Stihl carb, for sure. Such as the part line made from the casting mold. The metal quality looks subpar to the original. It was not de-burred as well, but still more than satisfactory.
The mating surface, although not cosmetically perfect, seals fine, which is all that matters.
The 'velocity stack' of the inlet opening was smooth enough for my taste.

It's a dang good replica that would be indistinguishable from the original in the eyes of 95% of the population. It's also indistinguishable in performance as far as I can tell. And I got a pretty dang good feel for this stuff after 9 years of tinkering on cars, small engine equipment, engineering school, etc. I can hear a sputtering idle, struggling to make power, bogging, popping, bearing noises, etc where other people, even after repeatedly trying to point it out, can't hear anything. Not trying to brag, it's just something that comes with years of running engines. I suppose similar to how I'm musically retarded. People say "can't you just determine the notes of a song by ear?" and I just can't. Not if my life depended on it.

In addition, the adjustment screws are MUCH better. Simple flathead type screws vs the stupid Stihl screws that break immediately. I understand that may be EPA influenced, but still frustrating as far as it concerns my user-experience.

It's quite impressive actually. You can literally slap it on and go. A 5 minute swap out. This is not typically the case in other areas, such as replica car parts. Those usually have fitment issues, need to be 'tweaked', don't fit at all, etc. I've run into that so many times.
I don't think very highly of "genuine Stihl" carburetors (more accurately, Zama, I suppose) at this point anyway. Every single Stihl tool I've owned (all used, I admit) has hard carb issues, as well as about 75% of them for sale on craigslist.
It's a concerning issue when the knock-off carburetor market is so strong due to the demand...


One thing I am concerned about though is the seemingly universal-ity of these carbs.
I purchased the carb for this trimmer, a FS85 RX. It's got the 25cc motor. Okay fine. That carb is tuned for a 25cc motor. And Stihl puts their 25cc motor in multiple different tools. Fine.
But these carbs for sale say they fit like 40 different tools. Which is a bit...curious, in my opinion.
There is undoubtedly very specific tuning differences that Stihl made between various tools. Such as a lightweight string trimmer that's supposed to scream, vs. a pole saw that needs power down low, maybe.

I also bought a carb for my FC95 edger, which is a heavy-duty commercial tool with decent power. The listing said it also fit FS45 trimmers, which is a silly, low-end curved shaft homeowner trimmer.
So...eh

 

[bertsmobile1]

A carburetor is a simple device.
It's 2019.
I trust them to use CAD software to design a part in 2019 that meets 1985 specs.

I understand there are other variables such as quality control, machinery being out of spec, etc, but I'm not going to stress over it.

I can go find a Stihl dealer, ask them for a price, have them give me the highest price they have on the screen, then say "well...Stihl says the MSRP is 1/2 that. Can ya do any better?"
"We can take 10% off, and it will be here in 2 days. We don't stock that one anymore"

I'd rather just order from Amazon, in my home, have it delivered within 48 hours, and have it work 90% as good for 25% of the price.
This is a problem created by Stihl since they insist on the dealer network. Their parts being so far out of reach has caused the knock-off market to run rampant.

Echo and etc is available on Partstree.com, so I buy their genuine parts. No issue.
Stihl is a headache, so I avoid buying their tools in the first place, and have to resort to knock-offs because I don't have time or interest in dicking around with a "Dealer" for a $7 air filter...

It is a simple priceing thing.
I charge out $ 60/hr.
hand helds have a flat $ 45 fee for a service or $ 60 for a repair ( + parts )
I can spend 20 hours trying to clean a blocked carb or $ 20 on a new one.
Thus it is a no brainer, fit a KNOW GOOD QUALITY aftermarket carb, toss the bad one in the some day box.
Every now & then I have a carb day and might clean & rebuild 10 to 30 carbs, wrap them up & pop them on the shelf for latter.
The trick is getting a good one.
There is no such thing as process scrap in China.
Every thing that comes off the end of the line gets sold, working or not.
The beast ones end up in the warehouses of after market parts wholesalers & flogged to people like me, unaffiliated repair workshops.
What is left over ends up being sold annonomously on the web where if it does not work, tough luck.
A 12 year old can build a "web shop" that looks like it is a sound company where in reality it is nothing more than a computer in some ones garage and that person is nothing more than a trader.They buy what is cheap when it is available & sell it at the highest price they can get for it, They have less than no idea of what they are selling , it is just stuff to them.
We used to rent out empty pallet space at the last warehouse that I ran on a week by week basis.
Very good for us as we could run on 100% fill rate so the cost per item despatch was as low as we could get it.
The goods would arrive , oft in a container full of all sorts of things like condoms, fake medications , maternity bras, truck part, mower parts , plants , vases , your name it.
They sent us the picking slip & despatch details & we did our bit.
Nothing odd to see the same part from the same pallet being invoiced out at different prices with different suppliers names on the invoice .
All of it sold via the web and lot via Amazon Aust or via late night TV promotion.
When the products stopped moving or we got down to the last layer or two the instructions were usually to toss the remainder in the garbage skip so they could put another full pallet in its place of faster moving goods.
Now some of this stuff was good, some had packaging that would make it illegal to sell in a real retail shop but at least 1/4 was defective trash.

In defence of Stihl & all the other original equipment companies, it costs more to store, pick & despatch most products than it does to make them, particularly if it is a carburettor for a 20 year old trimer.
A pallet space in my warehouse was about $ 5 / week and the pallet was another $ 2 /week.
Unless it was picked daily then it went progressively higher than the lower 2 rows so that means a fork pick which adds another $ 6.25 then it has to be packed, invoiced despatched to the dealer then finally billed & sold to you.
Unless people have worked in warehousing & logistics very few have any idea about just how much this adds to the price of a product.
The ignorant are usually the loudest proclaimers of just how much they are being ripped off when in reality the part is being sold to them at a massive loss.
Conspiracly & profiteering is a lot easier to sell to joe public than the cold facts.
We once worked out that a bottle of wine from a single box sitting on a pallet for an entire year would cost $ 67 by the time it got to the retailer in warehousing & logistics alone.

One of the reason why Chinese copy engines are so cheap is there are none of these costs added to them.
They go direct from the factory to the end user, which is efficient , just so long as you never have to supply parts for them.
I can get identical engines from Loncin, Zenshing, Ducar & Liffan and by identical I mean every part will interchange between them.
The Loncin is now 20% more expensive than the Ducar for no reason other than they now have a distribution network which adds substantially to their fixed costs.
The Ducar have a local agent who only stocks complete engines, if you want parts then "Honda parts will fit"
Zenshing & Liffan are the cheapest, I order them through a local agent & they arrive in the shipping container that they left the factory in.
The driver tosses mine off the back then goes to the next customer so their net distribution costs is one truck & driver for how ever long it takes him to empty the container.
If I am not here for the 2 day delivery window so miss delivery there is a $ 100 redelivery fee.
Again if you want parts the "Honda parts will fit".
They all do this because they know that adding a local distribution network will nearly double the wholesale cost of the engine, and price is their only selling point.

 

[TerraForte]

Never got an email notification for this one, so I just saw it now.

You may be right. Sounds pretty convincing. I don't have the experience with warehousing and logistics that you do, so I can't comment on that.

All I can say is 2 things regarding my experience with my Stihl tool(s) so far,

1. I stopped in a local mower repair shop that is a Stihl dealer. I asked for a simple maintenance kit for my FS85x. Air filter, fuel filter, spark plug. $20. Oooookay...I'll pay it and won't even argue. I looked at the fuel filter and it was brand-less! I was considering ordering the same maint kit for my 5 other Stihl tools but decided dropping $100 on a couple of air filters and spark plugs is pretty ridiculous. Then I ask about a clutch spring for my FC96. "That'll be about $10". I didn't say anything, but I had already ordered it from a different dealer for $4.16....I was also looking at the other stuff in stock, of course not a single item has a price tag on it, so I have to ask for every little thing from a $500 trimmer to a $4 bottle of oil. I looked at a FS91R "Oh! We have overstock on those, we'll give you a discount! We'll drop the price from $359 to $329 and do $319 if you buy more than 1!" When I went to the other dealer (3 miles away) to pick up the clutch spring, they had FS91Rs hanging (with price tags) for $329 each :laughing:
2. The carb has been working great so far. I've checked the spark plug a couple of times. I also bought a new carb for my Echo PAS-266 unit. Made in 2015 and great so far. The throttle cable was very loose, and the threads for the adjustment nut were stripped. Also occasionally stalls at idle after 30-45 seconds, and hesitates just a hair at WOT from idle. I looked into the price of new I/M gaskets and the 'rotor' piece that has the throttle cable adjustment nut threads. Rotor ~$25, and gaskets $7. Plus shipping. I just bought a whole new carb kit for $13 and it's been working great.

Last night I just picked up a lot of 5 Stihl BR600s that were "for parts or repair" from one of these big lawn companies. I just assumed the guy was the type to trash anything that was 'old' and just buy new every 3-4 years. I assumed they had gummed up carbs or maybe needed a valve adjustment or spark arrester screen cleaned.
Well I got home and pulled on one just for fun. It pulled like the spark plug was removed. Just about zero resistance on the pull cord. Odd...Is the fan moving when I pull it? Yes...
Then I checked the other 4 and they all have significantly decreased resistance when pulling.
Oh no...
Not sure if a push rod broke leaving a valve wide open or what

 

[bertsmobile1]

I have about a dozen of them here , all from one customer.
After about 3 or so years the bores are cactus.
All of them are ovaled.
The new replacement BR 700 or 750, can't remember runs 300 rpm slower.
OTOH he is still using the BR400's
What you have to remember is back pack blowers get used a lot of hours.
No one bothers to strap on on to blow a few clippings off a driveway.
This particular customer has a lot of large car parks that get blown down every day.

And yes some dealers are cheaper than others.
Down here one Stihl dealer is a stand alone outfit in an industrial estate & pays $ 2500.week rent
I get mine form a dealer who is multi brands and in on a block his family has owned for 3 generations, he gives me parts for cost +10%.
Some dealers just do not want to bother selling parts to the public because it costs them money to make the small sales.
These are usually run by accountants .
Raising & printing an invoice costs around $ 2.00 and then there is the time that the sales assistant takes to take your order, find the parts bag then print the invoice & give them all to you.
This all costs money and then there is the lost profits on your parts inventory.
I have an inventory which is about 3 times my annual turnover because as an independent it can take many weeks to get some parts ( Stihl are worse ).
Right now I am buying my Briggs parts from the USA & paying shipping to,Australia because it is taking Briggs Aust on average a month and Jacks or Parts Direct will have them here in 10 to 14 days.
So this cost me a lot of profits that I could have eaten and will not make me a brass razoo extra profit ( except the stuff I get direct from China ) and may dealers are in the same boot, only I am not paying a monetary rent, or wages.
Now if I was to factor the true price of ordering in the stock, freight, sorting them storing them then invoicing the customer I doubt I would actually be making a profit on anything that was less than $ 20 ( $ 5.00 of profit ).
So some one with an MBA will decide that all parts would have a minimum price of $ 20 each because they do not understand the value of traffic coming through the shop and can not understand what a loss leader is.

 

[TerraForte]

Interesting input, especially on the BR600 cylinders going bad.

I've been a busy guy lately. Bought that lot of 5 BR600s and managed to get all of them running. Only 1 required any replacement parts.
Out of the 5, 3 of them were 10-14 years old, and the other 2 were from 2012 and 2015.

The 2015 was the newest and nicest looking one, so that's the one I tried first. It had no resistance when pulling, so I looked deeper. Tore the whole machine down and found the cam gear (plastic) had exploded. Took out a cam follower with it. Yikes.

I priced out the parts for that one from my less-than-competent local dealer... $56 for cam gear, 2 push rods, 2 followers, and cork valve cover gasket. Ugh, fine. I'll just write it down as an "investment in my education". A learning experience, right?

While waiting for the parts to come in, I looked at the other blowers. I developed a system of going through them. First was to check valve clearances, of which they were all significantly out of spec. This step alone got one of the blowers running tip-top.
Second order was to check for spark. One had a clipped off wire lead, and the other had a coil that gave no spark. Used a jumper wire on the cut-off coil, and that blower fired up. So the coil was good, but cosmetically bad.
I swapped around a coil and got the 3rd one fired up.

After the valves and spark checked out, I was stumped for a minute or two. Cranked it several times, feeding it ether. Won't fire. Hmmm...
A-ha! Spark arrestor screen is completely clogged!
Removed the mesh and it fired right up.

Then got the replacement cam gear parts in and installed those. What a mess. The plastic bits get chewed up into various granularity and can turn into paste with the help of the fuel mix. I spent a considerable amount of time properly cleaning out the crankcase.
Installed parts, set valve timing, and away she purred.

I actually went back and got the "bad" coil to work after brushing off the contacts. So, didn't even have to fiddle with a crap ebay knock-off ignition coil!

Although they all ran, and were complete, they weren't all perfect. As you would expect from 12 year old blower that's been used commercially. Ripped straps, gouged plastics, dirty, missing a few screws here and there, wrong fasteners jammed into threads, etc.
But, they all ran, and the 'bones' were solid. They all idled perfectly, and wound up through the RPM range as they should. No knocking, no tapping, no smoking, etc. All of them would have made perfectly fine back-up machines, or even a main unit for a fly-by-night operation.

Super simple little machines, and quite robust aside from the cam timing system. But I guess the defence with that one is that it's reliable when valve adjustments are done properly. Not sure, I haven't put 100s or 1000s of hours on a Stihl 4-MIX machine.
All I know is, going forward, I would definitely jump on another "for parts or repair" BR600 if it was complete and not run over with a truck (which they all seem to look like...).

I think you are right about the BR700 - although I'm not sure it's intentional that it runs at 300rpm less. I don't even know that it does, but it's possible.

When I got these BR600s, I didn't actually know all that much about them. My dad gave me a BR550 a few years back that I used for about 1 season until it ran poorly. I just used it to blow grass clippings off of the 15ft of sidewalk kinda stuff. I took it apart, didn't really know what I was doing, and it sat in my garage.
So I learned a lot with these BR600s, specifically what the heck the difference between the BR500, 550s, 600s, and 700s is.
Funny enough it's all the same 65cc motor.
The BR500 is the "quiet one". Same price as BR600. They actually de-tune the motor and use a different blower vane to create lower air speeds, I believe. Then they put a damper (expansion tube) on the output pipe.
The BR550 is just a marketing ploy. It's about 97% identical to the BR600 - same carb, same power output, etc. Except they use a different fan that creates more air speed, but less air volume. Even though the 550 parts cost more, the blower was sold for ~$30 less.
The 600 is the benchmark comparison.
And the 700 is the newest one. Another marketing ploy where Stihl adds on $50 to again lower the air speed to raise the air volume. So they just use a slightly different blower vane on the exact same machine.

 

[bertsmobile1]

Well done.
Learning is always worthwhile regardless of the price.
You will also find that the engine speeds increase as you go up the scale.
Depending upon what you are shifting volume & speed interchange .
High speed low volume is best for simple blowing clippings off drives
High volume low speed for moving mulch around.

Now consider the time it took you to make the repairs divide it by 2 or 3 to allow for lack of experience then multiply it by the $ 50 labour fee the service centre charges.
Then factor in the cost of a crew member sitting on their butts doing nothing because the blower dosen't blow, remember the shop will if you are lucky give you 3 months warranty on the repair.
Then there is the attitude of the crew members.
The company wants them to do a top quality job yet keeps on getting this worn out blower fixed which is always breaking down & making things difficult for them.
So it is not worthwhile for most crews to spend money on repairs for small items.

All the better for you.
I supply my commercial customers with a loaner for all small tools that I repair.
In many cases it is an old worn out one they gave to me for spares that I managed to get working again.
The rule of thumb is less that 1/3 the replacement price then fix it otherwise trash it, it is just not worth their while.
The BR's come in twice a year for service & I charge $ 120 to do it.
If I factored the time I spent cleaning them before I start to work on them, I would be doing them at a loss.
That price is for a full service which includes setting those !#!#!#!# valve lashes and fitting a new rocker cover gasket.
Also a new fuel filter unit complete with tank grommet and new Tygon fuel lines.

This ends up costing the company more than run them till they break & replace but the crews work unsupervised and travel a long way from the depot so a break down costs a lot more than the repair costs.
Ideally they would carry a back up for everything but there is only so much space in a truck & trailer.

 

[TerraForte]

somewhat of an update in my quasi-"Stihl blower refurb side-hustle"

I picked up another lot of 5 blowers. This time 2 Echo PB-770s, 2 PB-755s, and 1 Stihl. I thought it was a BR600, but it turned out to be a BR700.
90% identical machine, but some interesting differences. The main thing that Stihl has done (throughout the BR range from the BR500 all the way to the BR700) is trade air speed for air volume. All the machines use the same motor (although the BR500 is choked and yields roughly 60% power compared to the rest), and same fundamentals. Stihl just tweaks the blower vane to shift on the speed vs. volume curve.
The BR700 boasts the most air volume.
Upon further inspection and disassembly, the fan housing is slightly different, and has flat-ish sides rather than a fully round shape. The blower vane also specifically says "for BR700 only" on it.
As can be easily seen via stock photos, the tube assembly is also modified with its large orange spin-nut that allows the tube length to be changed tool-less-ly, as well as the position of the throttle handle.

Other than that, the blower was 99% identical.


Anyway, I picked it up as a non-runner and assumed the worst - shattered timing gear - despite the BR700s being newer machines overall. This one had a D.O.M. of 10/2016 so I was slightly optimistic.
Popped off the valve cover and the valves did not move. Yep, as expected. So I ordered the cam gear, push rods, cam followers, valve cover gasket, and some new red [overpriced] red gasket sealant for good measure.
I did the dirty work of cleaning out the cylinder assembly of the bits of rubble and debris from the cam wheel...or so I thought.

What was interesting is that, upon removing the timing cover, the cam wheel looked perfectly intact. So I spun the flywheel side and the cam wheel did not move. I quickly found out this was because only the very bottom portion of the cam wheel was broken and it was concealed by the housing.
I go to clean out the bottom end, and the crank just pops out unexpectedly. Odd, I thought, as I could have sworn the BR600 I last worked on had some bearing caps that held it in tightly, as I did try somewhat firmly to remove it.

Well, that's cool. Now I have better access to clean everything out.
After about 40 minutes of cleaning everything out, I notice something overwhelmingly obvious staring me right in the face.

I had one of those *blink blink* moments. "Is that...supposed to be like that? No way"
Then I quickly assess that, no, it most definitely is not supposed to be like that.

So my understanding of the method of failure of this machine instantly changed. I had thought an overdue valve adjustment created a large valve lash scenario, which caused the push rod to sharply impact the cam wheel upon a sudden throttle blip, stressing it and eventually causing it to shatter. This now seems not to be the case... It very much seems that something causes the piston skirt to stress, then fatigue and fracture. Then it seems like a bit of debris gets lodged in the cam wheel teeth, and that's what causes it to shatter.
I cannot, for the life of me, figure out what causes the skirt to come apart like that though.

I had already purchased the cam timing parts, so I decided to go ahead an order a new piston/rings/wrist pin kit for $30 from a vendor I found on Amazon.
The cylinder didn't look pristine by any means, but did look similar to "good used" jugs for sale on ebay so :confused3:

Installed piston, re-assembled, and it worked. Started up immediately, and blew air. With my mild experience with the BR600s, it seemed to not wind up as much, but that could also be what you mentioned in terms of them capping the RPMs on the 700s. It didn't seem as loud, but, again, unsure if that is due to a loss of power from a shot cylinder, or simply a re-design. It seemed to blow as much as other backpack blowers, but that's not a very scientific assessment.
One odd thing is that it did a bit of a 'hang' when letting off the throttle. It would be at full throttle, then [release throttle] and it would settle at ~15% throttle for 1-2 seconds, then fall down to idle speed.
Tinkered with the H/L jets and couldn't iron that one out, so I thought maybe it was a bit of the compression charge leaking through the rings and artificially feeding it fuel, but my understanding of 2-strokes is pretty shallow in that respect.

 

[TerraForte]

Also, I had another question for you:


What's the deal with compression testing a 2-stroke?
I can't seem to get a reading that makes sense.

I tried to test a potentially ruined cylinder on a Dolmar trimmer.
I used a compression tester and it only rang up to 25psi. I couldn't believe it. I thought it wasn't threaded in enough for the O-ring to seal or some other issue. So I tested it on a very new Stihl FC96 in nearly mint condition. It barely said ~26-27 psi. Then I bought a new compression tester and the results came out the same. I pulled the starter several times, throttle open/closed, choke on/off, and all combinations. Not sure if I'm doing something wrong or if the tools aren't compatible. I tried to check very closely for air leaks but couldn't find anything.

 

[bertsmobile1]

Because of the very low volume of the combustion chamber it is hard to get good secondary pressure readings.
Unlike a 4 stroke, you need to have both primary & secondary compression.
If the crankcase seals are shot then you can not get primary pressure in which case your secondary will be low.

I never bother with secondary compression testing.
I do primary testing then leak down testing for the rings.

Apart from that most car testers expect to be seeing 200 cc or more per stroke so when you only have 25 cc they struggle so you might need to give the 50 to 100 pulls till the pressiure gauge stops moving.
This is the reason why I swapped to leak down, so much easier to do.
There are compression testers specifically designed for low volume engines but the price is a touch more than I can justify.

Back to your broken piston.
the piston pins on these are a tight fit as they run on a needle roller little end.
being a needle roller it takes 5/8 of SFA to jamb the rollers
That rod looks a little cooked to me what does the underside of the piston look like ?
If there is burned oil in there then it has been overheating probably due to a loose carb.
When you looked at these did you not notice that they all use different carbs ?
The pump & metering diaphragm are the same but the main jet & needle are different.

If unsure go to the Walbro parts pages and check the parts numbers.
If they are different then the part is different,
When it come to Cube carbs the differences can be the size of fairy wings which is why the diaphragms & gaskets are all cut slightly different shapes because you will need a metrology lab to measure the actual differences.

 

[TerraForte]

Got another stumper

Got carried away and got a Poulan chainsaw in a package deal. A "Woodsmaster 2250, 2.2CID"
Older model, seems slightly more solid than newer Poulan stuff

36cc motor, Walbro carb originally.
Got it as a jumble of parts, but everything present. Put it back together and it surprisingly fired right up.
At that point, it would rev, but would not idle. I could start it at full throttle and seemed to run indefinitely but would die upon coming down.
One of the vibration-damper springs was also broken.

Not something anyone wants to buy in this condition, but also not worth scrapping since the saw looked cosmetically nearly brand new.
So I figured I'd buy a spring kit and a clone-carb for $20 total.

Springs were quite nice actually.

Saw idled perfectly! But then died under load.
I must have spent an hour trying to tune that stupid thing but I couldn't get it right. I would turn them both all the way in, then CCW the Low ~1/2 turn until it idled perfectly, then CCW the H extremely slowly. I couldn't seem to get results that made any sense when enriching the H. I'm prepared for the "junk clone carb is junk" reply.

It will either idle perfectly and die under load, or only start under full throttle, run perfectly, then die when coming to idle.

I would get the low speed circuit tuned in perfectly, then go for the high. I would adjust the high a bit, and then it wouldn't idle! And wouldn't re-start until re-tuning the low. Then it wouldn't rev!
It was this never ending loop of either low or high speed working, but never both.

What gives?


When does the low speed circuit taper off? How much overlap between H/L circuits on these small carbs? I'm familiar with the multiple curves on a CV carb on a motorcycle, for example, always 2 or 3 jets in contribution, but I'm sure these small carbs aren't as 'smooth'.