026 Surging, What Do You Think? Crank Seals? Carb Needs Cleaned? Or ?

[bulletpruf]

I have a pretty nice 026 Pro that I went through a year or so ago. IIRC, it got new fuel lines, carb kit, new rings, etc. I did not change the crank seals.

I've used it quite a few times and it's been running great.

However, today I pulled it off the shelf to take down and buck a medium sized tree and it started surging. It does it loaded or unloaded.

I took the top cover off, threw a new BMPR7A in it (had a Champion), drained the fuel and put in fresh pre-mix, and cleaned out the air filter (it wasn't dirty at all). Cut some more with it and same deal.

I'm thinking it's not getting enough fuel. Doesn't seem like it would be a carb tuning issue at all, since I don't think it would surge if the tune was off. I'm inclined to remove the carb and see if there's any debris in it. I guess I could check the fuel filter at the same time.

I'm thinking I should go ahead and change the crank seals, too. Saw is a 1999 model so they could be 23 years old.

Thoughts?

Thanks

 

[Jedthro]

Tank vent?

 

[bulletpruf]

Tank vent?

Didn't think of that! That would be an easy fix. I'll check.

Thanks!

 

[Wood Doctor]

Carburetor strainer screen (small part) might be clogged, but I'm not exactly sure what you mean by "surging". However, if you think it's not getting enough fuel and you replaced the pickup body (fuel filter), that would do it.


Part #14. I've run into this clog-up several times. Crank seal work is the last thing I would do to fix this issue.

 

[bulletpruf]

Nope, not the tank vent. Pulled it off and it looked good. Cleaned, reinstalled, and then ran the saw without the fuel cap on. Same issue.

 

[bulletpruf]

Carburetor strainer screen (small part) might be clogged, but I'm not exactly sure what you mean by "surging". However, if you think it's not getting enough fuel and you replaced the pickup body (fuel filter), that would do it.

View attachment 985771
Part #14. I've run into this clog-up several times. Crank seal work is the last thing I would do to fix this issue.

That's kind of what I was thinking. More likely to be a carb issue than a crank seal issue.

By surging, if I go to wide open throttle, loaded or unloaded, the saw will go to 13,000 or so rpm and then back down to about 2,000 rpm, even though I have the throttle wide open. Then it will jump back up and back down.

 

[Gamma Woods]

How's it run without the air filter installed? Sometimes the choke spring doesn't work properly.

Also, is it an OEM or AM fuel line? I've had AM that seemed to be fine without the filter, and idles fine with the filter on until I give it throttle. The linkage kinked the line and would lean out until I took the filter off and poked the kink out. Doesn't quite match your symptoms, but something to keep in mind.

Behold, the single greatest mod you can ever do to a Stihl. Although I expect this cheap Chinese rubber to disintegrate fairly quickly.

 

[bulletpruf]

How's it run without the air filter installed? Sometimes the choke spring doesn't work properly.

Also, is it an OEM or AM fuel line? I've had AM that seemed to be fine without the filter, and idles fine with the filter on until I give it throttle. The linkage kinked the line and would lean out until I took the filter off and poked the kink out. Doesn't quite match your symptoms, but something to keep in mind.

Behold, the single greatest mod you can ever do to a Stihl. Although I expect this cheap Chinese rubber to disintegrate fairly quickly.

I'm running OEM fuel line. I'll take a look to see if it might be kinking.

Thanks

 

[Gamma Woods]

Well, see how it runs without the air filter, or with a different filter if you've got one. Inspect the filter to see if the choke is springing properly. The symptoms don't really match the line kinking but just figured I'd mention it. Don't think this is an impulse line malfunction.

I agree with the consensus that the carb should be taken apart and cleaned, trace the jets/circuits with spray cleaner to make sure they are all open. Might need to be kitted.

Issue with ignition strength/timing maybe.

How's the compression looking/condition of the piston?

Does it seem to run really hot?

 

[Aknutter]

Carb upgrade to a wt-194 walbro. If replacing or want a better tune.

 

[bulletpruf]

Well, see how it runs without the air filter, or with a different filter if you've got one. Inspect the filter to see if the choke is springing properly. The symptoms don't really match the line kinking but just figured I'd mention it. Don't think this is an impulse line malfunction.

I agree with the consensus that the carb should be taken apart and cleaned, trace the jets/circuits with spray cleaner to make sure they are all open. Might need to be kitted.

Issue with ignition strength/timing maybe.

How's the compression looking/condition of the piston?

Does it seem to run really hot?

I'll pull the muffler and eyeball the piston, but it only has a few tanks through it on a new Meteor piston. Note - low compression isn't going to cause this issue, but a roached piston is a clue that it's running lean. Having said that, I do know how to tune a saw, and if it was running lean, it wouldn't be difficult for me to figure it out.

Does not seem to run hot.

Carb had a kit a year or two ago.

Does not act like an ignition issue.

Thanks

 

[bulletpruf]

Carb upgrade to a wt-194 walbro. If replacing or want a better tune.

Already has the good Walbro carb.

thanks

 

[Gamma Woods]

I meant that low compression can indicate a damaged piston, which can be associated with excess heat. Sometimes issues don't present themselves until a component reaches a certain temperature.

I don't know if the 026 Pro has automatic ignition advance, but bouncing between the "advance" and retard can make a saw surge/hunt. I've only ever seen that at idle, and I'm not even certain that's something that could happen at WoT.

Don't kit the carb if it doesn't need it, but makes sense to inspect and clean.

I would take work that was done a year ago with more than a grain of salt, but not much more. Don't take it as gospel truth that something isn't a problem just because you worked on it in the past. If you can't hunt down the source of the problem elsewhere, then there's no reason not to double check. Of course you can push those avenues of troubleshooting down to a lower priority, they are less likely to be the problem, but when you get stumped you've gotta revert to the basics (hell, even retorquing bolts and checking the butterfly condition and throttle linkage movement). Not trying to doubt your work, but lots of **** can happen (particularly with fuel these days) in a year or two or three.

There's still the ever-looming possibility of an air leak, at crank seals or several other places, so if you're taking the carb off anyways it doesn't take long to pressure test.

Way out in left field is a mechanical issue, something binding or catching and applying load. Long shot, but a bit of twine wrapped in the clutch can do funny things. Highly doubt this is the case, but if the problem doesn't lie anywhere else....

Do some inspection and testing, don't think of it as your baby that you've already worked over, but work on it like a barn find. Record a video so the Googlers can see if their problem matches yours.

 

[av8or3]

Sounds like you should pres/vac test it to rule out the air leak. Should do that first on an 026. I’ve built a bunch of em’ and that is always the first thing I do.

 

[bulletpruf]

Piston looks perfect. Compression is 167 psi. No issues there.

Fuel line and impulse aren't kinked.

Will try to pull carb later today for disassembly and cleanup.

 

[Wood Doctor]

One last shot: it might be an electrical ignition problem, either a defective module, a connection, or the flywheel is mistimed. It may not be fuel related at all. I'm praying that my 026 PRO never suffers from this mishap.

 

[KASH]

Open the high and low needles a 1/2 turn.
Kash

 

[stihltech]

You will never know if you repaired it without a vacuum and pressure test. Don't have the tools? Get some spray brake cleaner. Start the saw. At idle.spray behind the flywheel,around the clutch,between the cylinder and fuel tank and around any gaskets. Any change indicates a leak.

 

[bulletpruf]

You will never know if you repaired it without a vacuum and pressure test. Don't have the tools? Get some spray brake cleaner. Start the saw. At idle.spray behind the flywheel,around the clutch,between the cylinder and fuel tank and around any gaskets. Any change indicates a leak.

I have to check to see if I have my Mightyvac here. Half of my tools are back home in Texas. If not, I'll use the brake cleaner method.

 

[Mad Professor]

Seals come in the gasket set, good idea to install them on a rebuild. If I recall from others here, 026 is usually flywheel side that goes first.