Help with Old Stihl 028

[UOFan]

Hi all,

I picked up an 028 for $10 at a scrapyard back in April, and been messing with it off and on since…still can’t get it to run. Been taking up space on my workbench and I figured I might get some help here.

Bottom line, something is messed up with the air/fuel delivery. I have spark, compression, and I can get it to run with ether for about 2 seconds so I think the magneto is fine. If I can get it to run it basically red lines itself, max RPM.

I have a new Chineseium carb, replacing the (also looked new) chineseium carb it had on at the scrapyard. I haven’t messed with the idle screws on this new one yet.

I have a few questions with pictures:

First, I replaced this cracked line, looks like a fuel tank vent but it doesn’t lead anywhere. Is this correct looking? Also, not sure what the broken ground wire is supposed to be/do. I have good spark.

Next, when I have choke on, the butterfly is slightly open, more so than when choke is OFF. Seems it should be the other way around, cutting down air when choke is on. Is this supposed to be this way?

Choke off:

Finally, when I flip the saw to off, this black wire makes contact with a metal bar. Is this essentially shorting the spark to ground, shutting it off? Just wondering for my own knowledge:

Here’s how the saw has looked the past 8 months…I appreciate any help! It’s a pretty cool saw, made in West Germany.

 

[dieselscout80]

One thing to consider is possibly that the base gasket/seal between the cylinder and the case may be leaking.

 

[UOFan]

One thing to consider is possibly that the base gasket/seal between the cylinder and the case may be leaking.

Any way to do that without a dedicated leak down tester? I’ve got a compression tester and vacuum tester.

 

[dieselscout80]

Any way to do that without a dedicated leak down tester? I’ve got a compression tester and vacuum tester.

I’m not sure I’m not a knowledgeable 2 cycle guy.

 

[WinterDeere]

paging @xyz123

 

[RandyT]

Let me give some assistance in the pictures. The replaced line is the tank vent. Second the 028 carb doesn't have a choke. That is the throttle plate in the carb when in the start position is held partially open. The choke on the 028 is in the air filter. So when the on/off/choke lever is put in the choke position is moves the flap in the air filter to the choke position and also pushed the throttle linkage to partially hold the throttle open for starting.

And on a saw that old there could be a very good chance that either the cylinder to crankcase seal is leaking or the crankshaft seals themselves have failed.

 

[UOFan]

Let me give some assistance in the pictures. The replaced line is the tank vent. Second the 028 carb doesn't have a choke. That is the throttle plate in the carb when in the start position is held partially open. The choke on the 028 is in the air filter. So when the on/off/choke lever is put in the choke position is moves the flap in the air filter to the choke position and also pushed the throttle linkage to partially hold the throttle open for starting.

And on a saw that old there could be a very good chance that either the cylinder to crankcase seal is leaking or the crankshaft seals themselves have failed.

Thanks for the detailed response. Could a clogged tank vent cause issue with starting? I can’t seem to suck fuel through the line when I try.

I’ll recheck compression today and post the numbers. I seem to remember I had good compression back in April when I bought it. Not really sure how to test the seals, could I just plug all the holes, push 10 PSI of compressed air into the spark plug hole, spray with soapy water and check for bubbles?

 

[xyz123]

I've owned them and they have a cult like following. But I compared my 028 super I had to a 026 and 026 was for me over 028. So always just sold them off.

Without a proper vac pressure testing. If you can keep it running long enough you can take starter fluid spray and spray around seals, base gaskets etc. If you hit a spot where air leak it will shut off saw immediately.

Another for just seals is turn on side while running then turn to other side. If really bad seal it will shut off one way or another or just drop really bad idle or raise up.

Your china carb can be hit and miss too. 50/50 shot it is works on them sometimes.

All just WAG's over the net without having saw on bench. GL

 

[dodge man]

I have a friend with a similar saw and yes the choke is in the filter setup. Take a look and you’ll see how it works. It’s not that tough to break it down further and replace the seals. I’d also be curious what the piston and rings look like on the exhaust port side.

 

[RandyT]

Not really sure how to test the seals, could I just plug all the holes, push 10 PSI of compressed air into the spark plug hole, spray with soapy water and check for bubbles?

7 psi is the standard for pressurizing the crankcase to leak check the seals. Too much pressure can push out the crankshaft seals.