'93 026 questions

[mdavisfps]

Hi all,
My neighbor has a '93 026 which loses power and then shuts off at WOT -- especially after the engine has warmed up. Air filter and exhaust screen are both clear. Don't know about the fuel filter, though. It sounds to me that it's running very lean at top speed prior to cutting off. I put a tach on it and it showed a max of 15,000 at WOT. The original specs call for 12,500. Our local Stihl dealer says that 15,000 is correct for this saw.

First question: Would the engineers who designed this engine endorse 15,000 as a safe max rpm, or is this "correct" only because that's what the EPA folks (and, therefore, USA Stihl dealers) want to see? I just remember hearing that exceeding the maximum recommended rpm could result in damage to the engine. No?

Second question: I've read in a number of posts in this forum that whatever max rpm you have the saw set to, you still want to run just a little bit leaner than when it 4-cycles. Any leaner, higher rpm maybe, but less power. Did I understand this correctly?

Third question: This saw has a hole labeled "H", but no screw head visible -- just a soft, almost fiber-like blockage halfway back the hole. Did this saw come with a high speed limiter and is that what I'm seeing? (My '91 025 has an adjustable "H" screw).

Fourth question: If the saw is indeed running too lean at WOT can this be corrected by adjusting the "L" screw to a richer setting?

Thanks for any information/suggestions.
Mark

 

[Ozhoo]

First statement: That saw has an air leak and should be thoroughly diagnosed before being run again

 

[mdavisfps]

First statement: That saw has an air leak and should be thoroughly diagnosed before being run again

Thanks, Ozhoo, for the quick response. What makes it so obvious that it has an air leak?

 

[blsnelling]

Factory RPM on the 026 is 14,000 IIRC. No, 15,000 is not OK. I wouldn't be surprised if it has a scored piston.

 

[fearofpavement]

Do two things.
1. dump the contents of the fuel tank out into a clear glass container and see what you find.
2. pull off the muffler and inspect the piston for scoring.

Probably either the piston is scored or the fuel filter is plugging up from debris causing the shutdown. Fix it before running it more.

 

[blsnelling]

Could also be a bad crank seal. The flywheel side PTO is a rather common point of failure on these. Any saw that age should be gone over entirely.

 

[mdavisfps]

Factory RPM on the 026 is 14,000 IIRC. No, 15,000 is not OK. I wouldn't be surprised if it has a scored piston.

Brad,
Clarification, please. "Factory RPM was 14,000" -- even though the manual at the time stated 12,500?
When the 026 was in production, might it have gone through some changes during the years, including "Factory RPM"?

What do you mean "No, 15,000 is not OK"? ... but the dealer SAYS that 15,000 is correct. I guess that was what I was concerned about; that the dealer might be saying that only because EPA is making him say that. (Or is just my paranoia showing?)
Thanks,
Mark

 

[blsnelling]

No way is 15K OK on a stock 026. As far as factory RPMs, I've never heard of them calling for 12,500. I understood them to be 14,000. Do you have the manual? I would like to see that for my own education if so. Thanks.

 

[GrassGuerilla]

Brad,
Clarification, please. "Factory RPM was 14,000" -- even though the manual at the time stated 12,500?
When the 026 was in production, might it have gone through some changes during the years, including "Factory RPM"?

What do you mean "No, 15,000 is not OK"? ... but the dealer SAYS that 15,000 is correct. I guess that was what I was concerned about; that the dealer might be saying that only because EPA is making him say that. (Or is just my paranoia showing?)
Thanks,
Mark

If the dealer is telling you 15,000 rpm is ok for an 026 I'd stop getting info from him. He's wrong.

Pull the muffler and inspect the P&C. Maybe post a couple pics. You've received great advice already in this thread. Stop running it as is. The cylinder is likely still salvageable, piston is probably shot. Now to both prove that and find the cause before going further. The guys here will help you through it if you let them.

 

[mdavisfps]

Thank you all for your suggestions -- and warnings! The saw's in the dealer's shop right now. It'll be interesting to hear what they have to say. Anyone want to bet it involves recommending buying a new MS260?

Regarding recommended max rpm: Brad, my apologies regarding the manual. The manual for the 026 does not specify max rpm. Mine for the 025 does specify 12,500 (I just looked at it). I had seen another posting on this site where someone had stated that their manual for the 026 had stated 12,500, plus some similar "reports" online that it was 12,500. One search for 026, however, had a photo of some document with a Stihl logo indicating 13,000, supposedly for this saw.

The manual for the 026 does show a label and hole for "H", but the hole is blank, while the "L" hole shows a screw head. Don't know what that indicates, but from the above postings, the "H" adjustment (if there is one) is probably not the answer, anyway. Can only hope that it's just a clogged fuel filter; otherwise, the dealer may get their wish.

At the risk of emphasizing my ignorance even further, would still like to know whether setting the "L" screw to richer results in more fuel in the mix at WOT???

Thanks again,
Mark

 

[blsnelling]

Adjusting the L needle does have an affect on WOT. That's why the H should have a final adjustment after the L is dialed in. WOT is a combination of both L and H fuel, even though the L does not have near as significant of an affect on the WOT tuning.

 

[mdavisfps]

Adjusting the L needle does have an affect on WOT. That's why the H should have a final adjustment after the L is dialed in. WOT is a combination of both L and H fuel, even though the L does not have near as significant of an affect on the WOT tuning.

Thanks, Brad. Regarding 14,000 rpm, I just found a 1999 specs sheet from Stihl for the 024 and 026 listing 14,000 as the max rpm for those two saws. Whether or not a '93 spec sheet for the 026 would have been different than the spec sheet for the '99 026, I don't know.
Mark

 

[mdavisfps]

Just an additional observation: the '99 spec sheet clearly shows an exposed "H" adjustment screw for the 1999 026, just like the "L" screw, with the basic "out one turn" recommended initial setting.

 

[blsnelling]

Some 026/260s have adjustable carbs, others do not. I would expect a 026 to have a fully adjustable carb though.

 

[mdavisfps]

Some 026/260s have adjustable carbs, others do not. I would expect a 026 to have a fully adjustable carb though.

Me, too. But based on the '93 manual, as well as actually looking at the saw, the earlier models either weren't adjustable for the "H" setting or were hidden behind something, while the spec sheet for the later '99 026 clearly shows an exposed adjustment screw.

Thanks, Brad. Gotta sign off for tonight.
Mark