Help with Old Stihl 028

[dodge man]

One reason myself and someone else said take a look at the piston is you can get bad scoring. This was a MS250 I rebuilt. I’m still not sure what happened to it, probably straight gas but maybe an air leak. It’s not a great picture but it’s looking in the exhaust port and you can see how the piston and rings are scored in the lower left of the picture.

 

[4Liberty]

Sounds like it’s leaking air somewhere. How’s the rubber hose that the carb mounts to? Are the clamps tight? If it’s leaking there it will do exactly what you described, as well as the cylinder base gasket or seals. A loose clamp or the rubber boot are much easier to fix. At any rate none of it is really difficult. If you get around to doing seals be extra careful with the flywheel nut. They must be exact torque and it’s inch pounds. Too loose sheared keys too tight and you’ll twist off the end of the crank. Ask me how I know . They are really easy to work on don’t be scared. If you do the base gasket I haven’t put one back in yet. I used gasket eliminator you gain compression.

 

[xyz123]

I have a Guy at ACE Hardware, all he does is maintain Stilh engines
for all the Lawn Service Companies ....he can look at one and tell you what is wrong and what it will co$t to Fix/ and when you get it back it Runs better than it ever did !

Your lucky and rare these days. Here ace stihl had a locals saw for almost a year.

Couldnt figure it out throwing parts at it and racking him up a big bill on a saw not worth 50-75 IMHO. Putting new carb, new flywheel, new coil etc etc.

I told him get your saw and let me check it. He did. I could tell what it was in seconds. Low psi and pulled muffler scored. Duh on them and shame on them.

Stihl even has a checklist they are suppose to follow.

 

[Tbone07]

1. Almost no point in troubleshooting anything else until you get a proper leak-down test done. Genuine Stihl or Chinesium carb, doesn't matter if you have a leak.
2. There are leak down tester kits out there for sale, or you can build your own through McMaster Carr like I did. Takes awhile to get proper fittings, but it's worth it. I use a bulb like you see on a blood pressure cuff. You cannot just blast air in there, could blow out the seals.
3. Chinesium carb definitely isn't preferable, but you should at least get it to run enough for you to know it's capable. Then again, it's a crap shoot with those cheap carbs
4. Compressions testers can be inaccurate, but they rarely read high. Yours probably ok, look through exhaust port check for scoring and general condition
5. $20 says the last owner threw an Amazon carb on and fooled with it awhile, then gave up because it was old and who cares?
6. Don't throw it away if you give up on it. Someone will take it for parts if nothing else. Like me

 

[4Liberty]

One reason myself and someone else said take a look at the piston is you can get bad scoring. This was a MS250 I rebuilt. I’m still not sure what happened to it, probably straight gas but maybe an air leak. It’s not a great picture but it’s looking in the exhaust port and you can see how the piston and rings are scored in the lower left of the picture.
View attachment 4721416

Still using the compression release?

 

[Snobdds]

1. Almost no point in troubleshooting anything else until you get a proper leak-down test done. Genuine Stihl or Chinesium carb, doesn't matter if you have a leak.
2. There are leak down tester kits out there for sale, or you can build your own through McMaster Carr like I did. Takes awhile to get proper fittings, but it's worth it. I use a bulb like you see on a blood pressure cuff. You cannot just blast air in there, could blow out the seals.
3. Chinesium carb definitely isn't preferable, but you should at least get it to run enough for you to know it's capable. Then again, it's a crap shoot with those cheap carbs
4. Compressions testers can be inaccurate, but they rarely read high. Yours probably ok, look through exhaust port check for scoring and general condition
5. $20 says the last owner threw an Amazon carb on and fooled with it awhile, then gave up because it was old and who cares?
6. Don't throw it away if you give up on it. Someone will take it for parts if nothing else. Like me

I think you mean a pressure/vacuum test. Two stroke motors need zero air leaks anywhere. If you don't have a pressure vacuum tester, use a can a brake cleaner. While the engine is runing, spray around the flywheel and clutch, if the motor dies...you have an air leak. If those pass, spray around the intake behind the carb, same thing, if it dies, then you have an air leak.

However, investing in a pressure/vacuum tester saves a lot of time and frustration. You can test fuel lines, impulse lines, and carbs with the tool.

Your #6 is very important...I would rather have a good used part than a new chinesium part.

 

[dodge man]

Still using the compression release?

That saw doesn’t have a compression release.

 

[danielk]

Still using the compression release?

My saw, a different stihl, has a compression release. Is there a problem with using these?

 

[WinterDeere]

My saw, a different stihl, has a compression release. Is there a problem with using these?

I have decomp valves on some of my saws, and it always seems to me that a saw that's been sitting on the shelf any period of time takes many more pulls of the cord to start, if the decomp valve is depressed. It's hard to set up a double-blind test on this, as I'm sure the number of pulls of the cord is going to vary on any saw that's been sitting awhile, even if you kept all controllable variables the same. But it seems to me I usually achieve a cold start in 3 pulls or less without decomp, versus a half dozen or more with decomp pressed.

I suspect this is because the decomp valve might reduce the amount of vacuum pulling fresh fuel up thru the carburetor, and so it might not affect fuel-injected saws nearly as badly.

Because none of my saws that have decomp valves are that difficult to pull start, I usually just don't bother pushing the decomp button.

 

[bgr]

Been a while since I have worked on my saw, but isn't there a crankcase vacuum hose to the carb to supply the pressure pulses to operate the fuel pump on the bottom of the carb. I remember not getting fuel because I had not found a bad hose.
I also remember a lot of new chinese carbs which did not work and now look for OEM carbs.
The emission control carbs on the new saws don't rebuild well, but the old carbs rebuild OK with a good kit.