Help Request on Stihl 028 AV Super Wood Boss - Bogging

[cookies]

If you order a new aftermarket carb off sawzilla they made me a offer recently when completing my purchase to add their solo tachometer to the order for under 30 bucks. I own a solo tac and it has worked great for setting carbs up on saws, mowers, generators, 4 wheelers, blowers etc
I have experienced very few problems with their parts over the years when oem is nla, and they have a few rapid shipping options. When dealing with carbs on saws I replace the fuel pickup hose, impulse hose and fuel filter at the same time, the hoses loose their grip/stretch, their rigidity/strength and if disturbed can cause further gremlins and a tune up never hurts.

 

[cbrTodd]

Looks like I've got a couple paths going for a carb at this point. I ordered a Stens aftermarket carb since I have had good luck with their mower parts over the years. Maybe better quality than the standard Amazon? I also ordered a new Walbro check valve and aftermarket repair kit for the OEM carb (including the Welch plug). Assuming the plug and check valve fit, maybe I can fix the original carb. It will be a while before any of it arrives though.

If neither of them fixes it, I likely will stop putting time and money into this saw and put it aside as a tinkering project for later rather than a 'main line' saw as I had been hoping for it to go back to being. It's one of the few things I have to remember my aunt and uncle, who both passed over a decade ago now, so it's not getting trashed. I just need something I can trust to run when I need it. I'm not sure what a replacement saw would even be though - Stihl dropping parts support and only selling stuff through their dealer network makes me mad. But I don't know if there's really a better option...

 

[Okie]

The 028's are normally worth the extra effort. I have some I use in the woodlot and one is at least 40 years old and has only needed a carb kit once. (and very reliable as a go to saw)
One thing that they don't like is long term storage without being exercised and stored in a area that get temperature gets hot.
Your looks like a low hour clean saw.

You need to do a careful check of the fuel tank after long term storage as you mentioned the saw has been subjected. (BEFORE INSTALLING ANOTHER CARB) I've found sticky molasses type film inside chainsaw gas tanks and also a very fine mold usually black or grey color and both will get past the in-tank filter and clog/restrict the inlet screen in the carb and do it fast and make the saw starve for fuel at high rpms but still idle and start ok.
The carb inlet screen has to be REMOVED for proper inspection and cleaned. It will sometimes appear to be clean when viewing still in the carb, but restricted due to being fine screen and bright color.

 

[stihltech]

Did you ever try the tag wire trick I told about? Saves pulling the welch plugs many times.

 

[cbrTodd]

Ok folks after a few days waiting for parts, I have some good, bad, and slightly confusing news.

I pulled the welch plug out of the original Stihl carburetor. Everything under it was spotless clean. That’s something that I don't plan on doing again. I had already cleaned out all the passages leading to it from the top side except for the one that leads to the L mixture screw, and that one was already verified open by flowing carb cleaner through it. My torch nozzle cleaner tool is like a “tag wire” on steroids, and having multiple sizes in the set means I can generally be right at the passage size without either reaming it larger or leaving crud in it. Probably the best $0.50 I’ve ever spent at a yard sale… The fuel tank was spotless clean and gum free and the screen was completely clean as well.

I checked the high speed fuel check valve with tubing and it behaved as I expected. So I put a new rebuild kit in the carb (welch plug, needle assembly and pivot / spring, fuel pump sheet and gasket, diaphragm and gasket) and pressure tested the needle valve. It only bled down a little bit and it did that fairly slowly, so I deemed it good enough to try. I pulled off the recoil cover and loosened up and re-set the coil gap (still using the original coil) using the same piece of folded paper that I had used previously. I don’t think it ended up any different than it was, but I did it. From there I put the rest of the stuff back on, added fuel, and tried to start it. It started but wouldn’t rev above idle at all. It was different sounding than before, like it wasn’t getting air flow. So I took the muffler screen off and that made no change. Then I put that back on and took the choke assembly completely out of the air filter, and it ran like it was supposed to. I’d done that at least twice before, but without this particular carb kit, so I’m thinking maybe I had both internal carb gasket issues and a choke issue, and I’d never managed to have both corrected at the same time before. Regardless, at that point I was able to tune the low speed screw so that it accelerates instantly to high speed, and then tune the high speed so that it just barely wants to 4-stroke at free rev max speed. It no longer had the intermittent miss at unloaded high speed, either. I went and sawed with it for a while like that while I had it running, and it was fine. It would restart hot with 1 pull. It was back to being a valuable contributor to the ‘homestead’.

After I was done working it, I dug back in my saved parts pile and found the original 1985 air filter that I had saved that has the flocking worn out in many places. I took the choke lever out of it and put it and its spring in the aftermarket filter that I was using without any choke plate in it, and went to make a couple test cuts with it that way. That would start and run, but it was definitely down on power. So I think it’s still likely blocking air flow more than it should be when the choke isn’t on. The spring has plenty of tension but I am wondering if something in the internal filter shape isn't right. I’ve ordered a New Stihl filter and will install it when I get it. But if I have to install the aftermarket filter again without the choke plate in the meantime to get more stuff cut up, I’ll likely do it.

So the bad part is I’m not sure exactly what the original issue(s) were. I suspect some combination of the carb rubber parts and the choke lever, but regardless I have a path to the saw being useful again.

Has anyone ever tried to adapt one of the newer round air filters onto an 028 AV Super, even if it means having to run a separate choke lever and leave off the current air filter cover? If the replacement OEM filter doesn’t provide the necessary flow without removing the choke plate every time, I may pursue something like that. I really hope that’s not needed.

Thanks for everyone’s help in getting the saw back running!

 

[Okie]

Good to hear you are onto something good.
and thanks for the update comeback

028's are normally worth the extra effort to repair.

Just a tip about 028's and air filters when in use.
When a 028 starts running little strange at the woodlot clean the air filter INSTEAD of grabbing a screwdriver.

When one of my 028's with the OEM air filter starts running like the carb needs tweaked I just clean the air filter using 25lbs of compressed air from the air compressor INSTEAD of grabbing a screwdriver and knob dicking the carb.
If I've used one of them in the woodlot for several hours I clean the air filter before storing the saw.
Summary: My 028's do not like for the air filter to get even slightly restricted.

About your 50 cents torch tip cleaners. Get a set or two of motorcycle carb jet cleaning tips. The look about like torch tips cleaners except they do not have the raspy edges and They are smaller size than normal tip cleaners. I recently got into a Honda carb and some of the emulsion tube holes were smaller than a tag wire and the motor cycle itty bitty tips worked good and fixed the carb. If you piddle around repairing carbs you need these.
Here is two sets for one money on fleece bay.
Item 132386258417

 

[SteveSr]

AM air filters are mostly trash as you just found out. How many hours did this cost you?

What are your current "L" and "H" carb screw settings from lightly seated?

The OEM carb kit for your WT-16B is a Walbro K10-WAT or D10-WAT and should still be widely available.

When you installed the carb kit did you adjust the metering lever height per the instructions in the manual? New levers MUST always be adjusted. I usually just reuse the old ones as they don't tend to wear but I ALWAYS check them just in case Bubba was in there before me!

 

[Chevboy0167]

3D printer tip cleaners available in various sizes, metric that is. Work very well as carb passage cleaners. Also paint gun tip needles out there also.

https://www.amazon.com/Cleaning-Nee...B0C6P8RLJQ&psc=1&ref_=pd_bap_d_grid_rp_0_61_i

https://www.amazon.com/3D-Printer-M...c=1&ref_=pd_bap_d_csi_pd_ys_c_rfy_rp_crs_25_t

 

[cbrTodd]

Thanks for the heads up about the carb jet cleaning tools (and 3d printer nozzle cleaning tools). It wouldn’t hurt to have that laying around, even if I’ve not needed it so far.

On the 028 in general, I agree it’s worth putting the time in to get it right. It’s a great saw when it’s running as intended. Regarding keeping the air filter clean… what kind of individual would mess with the carburetor tuning rather than check for and blow off a dirty air filter? Not me and not anyone I would allow to use my tools. In my opinion, if a normally happy machine suddenly needs a carb adjustment to run, something is wrong and needs to be addressed. Before this year, I hadn’t touched the screws on that carb since I cleaned it and put in the replacement diaphragms in 2018.

I didn’t buy a gauge for the needle lever height in the carb, and the manual didn’t have a numerical spec (that I could find anyway) to set it with calipers. So I left it as-is and it seems to be working. It was right at the height of the adjacent metal in the carb body, which is where the original was. It may not be perfect, but it’s close enough to work, so it’s staying like it is unless it misbehaves. The literature I found said that the OEM kit for the WT-16 carb is K2-WT. That’s good to know that the number is different now. I had no luck finding K2-WT kits that didn’t appear to be old enough that they were likely bad from age anyway.

About the issues with the choke on the new filter, for sure I spent some time figuring that out. But I installed that filter in late 2018 and used the saw a couple times a year through 2023 before I had any issues with it this year. I hadn’t expected the choke flap to be something that would suddenly start causing issues. I’d have a hard time calling that one ‘junk out of the box’ since it did work fine for 5+ years of occasional use. I’m hoping the Stihl one fixes all those issues, but even if it doesn’t, I now know what symptoms it produces. My local Stihl dealer has yet to be able to source a single part I've asked about on this saw, so I'm not seeing much better of an option than new old stock parts or aftermarket parts at this point. As far as the needle settings, I didn't measure them to have an exact reference point, but maybe 1 turn out on the Low and 1 1/8 on the High? Both were slightly in / lean from the listed 1 1/4 baseline.

For me, the bottom line is that I’ve learned several important steps towards troubleshooting 2 stroke engines and diaphragm carbs as a result of this incident. I know how to narrow down issues much better than I did a few weeks ago. If I find myself narrowed down to a carb issue in the future, I know what the circuit paths are now and how the high speed check valve works, so I’m much better prepared, whether or not I end up having to go with an aftermarket carburetor. And I know some checks to do on an aftermarket carb to make sure it isn’t grossly wrong before even installing it if I get forced down that path. In looking at the older carbs I had laying around, I did find that the first Amazon carb I bought in 2018 to steal the diaphragm out of (I had never run it, I used its rubber parts for the OEM Walbro carb) actually had a faulty high speed check valve in it out of the box. So my success rate on the amazon carbs is now known to be less than 100%, too.

Again, I greatly appreciate all the help provided. I probably won’t be on this forum much going forward though as I’m just a homeowner who does tree work when nature dictates it.

 

[VinceGU05]

I would definitely be interested in carb manuals if you have them! I'm sure that would be helpful.

I think I see what you're talking about but there's no chamfer on the top of the cutting edge. Just some dark colored gunk on top and bad lighting. It was dull though, but 5 strokes with the 3/16 file at 25 degrees on each tooth and it was back where it should be (I had to look at the chain package I keep in the case).

On the clutch, yes it had some discoloration but it came off very quickly with sandpaper. I reassembled it using the Stihl carburetor and it still ran like junk and bogged, but it made a few more chips before doing so.

So I put the 'good' rubber parts back in the Amazon carb body and tried to start / tune it and that was noticeably better than the Stihl carb. It still doesn't want to idle any more and it's got no power once it gets to full speed, but it will get there easier without load. You could even cut some with it if you were patient enough to plug along at about 1/3 the intended operating speed. I'm not that patient.

At this point I'm willing to go get a true Stihl / Walbro OEM replacement and give that a shot. So since folks are saying that what's listed in the manual may or may not be right, can you tell if it's the 1118 120 0601 from the pictures in the last post? If not, how do I find out what it is? Can the dealer tell from the saw's serial number?