Stihl 038 Magnum AV/Electronic Diagnosis

[Sam R]

I guess I'm on a roll this week. Someone brought an ancient chainsaw into the shop this week - an 038 with the complaint of "doesn't run". By the way if anyone can elucidate me - when did these come out? I'm going to guess late 70s at the earliest but probably the 80s. It's damn heavy duty, feels like it was a good saw in its day.

A couple things of note:

• Good spark
• No box cover for air filter
• Extreme amount of sawdust/crud built up around air filter but no apparent penetration into venturi
• Heavy scoring on exhaust side p&c, w/ some scoring on intake (possibly from ingestion - there is visible crud on top of the cylinder)
• Rings stuck from exhaust scoring
• Carburetor: H = 3/4 out, L = 1 3/4 out
• Air filter totally saturated but nothing of note on inside of the box filter
• Muffler is rusty and has one small puncture near the bottom on f/w side, arrester in good shape

I'm definitely leaning toward a lean running condition, factory setting has H side set at 1 turn out, which indicates it may have been leaned out when it stopped performing well. It might also have an air leak - I didn't p/v test it since it's basically parts at this point. Exhaust scoring is concentrated on one thick center band right across the exhaust port. Intake scoring is much more spotty and minor.

Surprisingly the 52mm p&c are still available the 50 is out of stock. I haven't measured what it's got yet but all together w/ p&c, gaskets & carburetor + other things like filters, labor, etc it estimates to around $500. Once I can speak to the customer if he really wants it to run again I'll complete the diagnosis to suss out any other potential issues.

 

[rd35]

Yep, I agree the carb was probably set too lean. The interesting thing about a lean set carb is that, with the clearance of the opening in the high jet being smaller than it should be, it not only creates the lean condition, but it also catches and holds smaller debris in the gasoline which, then, restricts the opening even more thereby making the mix even leaner. In the field I have solved, on several occasions, a lean condition issue by simply screwing the H needle all the way in and then back out to where it was. This clears any dirt in the jet by mashing it on through the jet opening. Not, by any means, is this the best way to fix a clogged jet, but, surprisingly, it usually works.

 

[rd35]

OBTW, Hi neighbor!!!

 

[Sam R]

Hey neighbor! Come by Rural King and see me, we can talk a little shop.
That's a good tip - usually when I'm taking a carb apart to clean them - per Stihl - I use the non-flammable brake parts cleaner to spray out the various holes and checks. I think they say non-flammable probably because it doesn't have alcohol that could ruin o-rings and things like that.

I'd really like to find out some history on the saw - see what I can find about it. I think these old ones took 40:1, didn't they? I wonder if he's been using Motomix in it...

 

[rd35]

I'll look you up the next time I stop in there. My wife was in there yesterday buying chicken feed! I was shocked the day I walked in and saw that all the Echo equipment had been replaced with Stihl!!!

 

[Sam R]

Yeah buddy. I think Echo is a fine machine but I'll always be a Stihl man.