028 troubleshooting...tearing hair out.....

[chestand]

I just joined this group yesterday and it seems to be populated with genuine good guys that want to help each other. Good. The lack of attitude is refreshing to say the least.
I inherited a non-running 028 WB and recently decided to resurrect it. It's an older model with the gas tank as part of the metal handle. As it stands now, I can get it to act as if it wants to start when choking it, and to try to start and make maybe a dozen revolutions before dying when the control is moved to the run position. Compression is good. So far I have:
Installed a rebuild kit in the carb (Tillotson HU40A) including new diaphragm, gasket, fuel pump diaphragm and gasket. Removed both low and high adjustment needles and sprayed carb cleaner through the passages as well as every passage in the carb. Both adjustments are one turn open.
Removed and inspected the rubber intake manifold and the impulse tube. Both look perfect.
Replaced the fuel line and filter.
Removed and inspected the muffler and exhaust port. Both clean. There is no screen in the muffler BTW. No noticable scoring in the piston/cylinder.
Replaced the plug. Gapped to .020.

My questions are these:
How likely is it that the crank seals are leaking badly on this saw? Can crank seals leak badly enough to lead to a no-start situation such as this? How difficult is it to replace them?

Even though there is spark present, could the points/condensor be bad?

I was so frustrated last weekend that the whole shooting match almost ended up in the dumpster. Luckily, I cooled down.

Any help that you all could send my way would be so appreciated.
Thanks All.

 

[Marco]

Usually with a bad seal they will race and not idle, carb has to be opened up abit though. If you have acess to an air compressor that has a regulator that can be turned down to a couple pounds you can block off the exhaust and carb by making some blocking plates out off a chunk of innertube. Go to an auto parts store and get yourself a widget that goes in a plug hole that is used with air to hold valves shut on a car engine. Put this in your plug hole and WITH A POUND OR TWO of air pressure pressurize the whole mess with your plates installed and start squirting soapy water at the thing around the seals and gasketed areas. If you have bubbles there's your problem.
I worked on an 028 that would run, but not right once. It ended up being the wrist pin hole on the piston was wowed out and you couldn't find the problem til you pulled the cylinder.
hope this helped

 

[Kneejerk Bombas]

This will sound really amateur, but when a two stroke gives me grief like this, I use a squirt bottle to add fuel as I try to start it. If you can get it running on this fuel, you know it's a fuel delivery problem.

 

[Al Smith]

Check the setting of the fuel shut off lever on the carb.This is critical.If it is set too low,it won't let in enough fuel,and will do as you descibed.Too high,and it will flood.An 028 is a peppy little saw,hang in there,you'll get it. Generally speaking,bad seals will become more evident as the saw warms up,not usually at start up.Tillotson has an excellent web site that desribes about all proceedures and trouble shooting for their carbs .

 

[Molecule]

you can check if the seals are sucking in, by spraying carb cleaner or starter fluid at either end of the crank (at the flywheel or behind the clutch) when the saw in idlying. If they are leaking inward (my own *speculation* on this being that inward leaking seals result in a lean-seizure condition at WOT due to inability of the fuel pump to generate adequate fuel flow, (it operates off both negative and positive crank pressures) so fuel-pump starvation occurs, e.g. not starvation by straight volumetric diultion of the air-fuel mixture from an adequately jetted carb) the saw will spurt up in revs, or maybe decline. If it changes rpm when you squirt at it, the seals are probably shot.

 

[Fish]

It is important, when going through a carb, to remove the metering lever and needle,
and remove the screen on the fuel pump side, and visually verify that this passage
is completely clear. The older Stihls, when they get some age, the foam insert in the
fuel filters break down, and the particles go into the carb.
With that being said, and checked out, then I would say that the points are likely
culprits.

 

[chestand]

Thanks each of you for your suggestions.
I have downloaded and printed the manual from the Tillotson website about the HU40A. It was a valuable reference when working over the carb.
If I do need to check the points, how does one go about pulling the flywheel? I see a nut holding it on and I also see some larger threads cut into the flywheel itself. Can I assume these larger threads are for a puller?
Also, does anyone have a source for dating a Stihl saw via serial #? The 028's is E6589684. A dealer i visited last weekend said that Stihl's s.n.'s are crytic to say the least.
I'm not giving up on this. I'm drawing strength from your colletive brain trust.
Lastly, what could I expect $wise if I were to take this problem child to a good Stihl shop for a diagnosis?

Again, thanks.

 

[Fish]

It is hard to say, but you may have to invest some bucks, as the saw techs
need to pay bills too. If you wish to keep the cost down, and you are handy, just keep on posting here, these guys have little else here to do, as they are
all on disability from losing limbs and appendages to chainsaw/alcohol accidents, the Canadian ones I am unsure of, as they have everything paid
for, even paying for our military deserters.
But I digress...........................................
Also the Canadians have weak, pissy beer.

 

[galde]

I would check ignition timing next. There are timing marks on the flywheel and crankcase. The breaker point gap should be 0.35 to 0.40 mm on the 028AV and 028WB. The air gap between flywheel and coil legs should be 0.20 to 0.30 mm. You can have a good spark, but if timing is off it will not run right.

 

[njforestfire]

hey fish - there you go instagating again!!

 

[Chris J.]

Dang, Fish!

You nailed it--how long did you live in Canada, eh?

 

[Ax-man]

How about the passages under the Welsh plug?? Could that cause it not to start?? I'm working on a 020 AVP with a Tilly, that is giving me fits like this 028. I know the problem is in the carb because it will fire with a squirt of fuel down the throat of the carb.

The inlet screen on this one was plugged, easy fix right new diaphrams still no go. Carb did pressure test, no leaks but nada on the H & L circuits. Popped the Welsh plug let the carb body soak, reinstalled new plug only now I have an air leak and still nothing on the H&L.

So question is if the passages under the Welsh plug are blocked how or can you get them unplugged and is there any way to seal a Welsh plug or I'm SOL and try again with a new kit or is the carb just junk.

This is not the first 020 carb I have had a go round with this. What I don't understand is it is just a hunk of metal with holes, how can It just fail and not work. I have had other carbs worse than these, they clean up beautifully and run very good when new kits are put in them.

Larry

 

[fishhuntcutwood]

I just joined this group yesterday and it seems to be populated with genuine good guys that want to help each other. Good. The lack of attitude is refreshing to say the least.

And you've been reading this forum? You should have been on the Off The Topic forum last week!

But I digress this is indeed a great site with great guys, and there's really nothing to add to what's been said above. I say, keep at it, and you'll get it. Saws are remarkably simple machines, and when you get them figured out and dialed in, they become even more fun. Keep us posted on your progress, and welcome to AS!!

Take care all,
Jeff

 

[stihltech]

skip

When you try to accelerate, does it sound like it is missing? Points, put in an aftermarket module.
Open up those carb screws another 1/2 turn. May be too rich, but you can then adjust the carb.

 

[sedanman]

Nail polish will seal welch plugs.

 

[sawracr]

Stop throwing parts at the saw, and start with a compression test. A saw will run with a bad air leek, not correctly but it will run. Remember the three componants compression, spark,and fuel, you mingh also check the impulse line. Jon

 

[Ax-man]

Thanks Paul

I needed to hear it from someone else, they say the same thing in the " Chain Saw Service Manuel "

Can the fingernail polish be put on thick or just a light coating??

Larry

 

[asharrow]

Guys here helped me get my 020 AVP going. It would start and run for a minute or so, then no spark. I put an aftermarket ignition module in and that cured it.

I did have to replumb the pulse line before it would run at all.

My experience as a user has been that I have never found a running problem to be because of a caruretor problem. Always getting air somewhere or an ignition problem.

Jim in Maine

 

[Fish]

Pulling welch plugs can be tricky, so while I have the carb in hand, I clear the holes
in the throat of the carb with a pice of wire. I must stress however the importance
of removing the needle and also removing the screen on the other side and visually
verifying that the passage is clear

 

[stihltech]

fish

Guys, listen to Fish when he is being straight with you. It will save you a lot of aggravation.