A little project

[Crow99]

My 30  year old Mac trimmer.  It was not running well so I put it away maybe 20 years ago. With my new found interest in working on such things I dragged it out of the pile and decided to clean it up and see if I could get it going.
After I got most of the dust and cobwebs off, I did pressure and vac tests.  Initially it slowly leaked down from 7 psi and wouldn't hold much vac at all. I could actually hear the front seal leaking..... and I could see it sucking two stroke oil past the seal.  Apparently this was why it had been running poorly.  Fortunately i had stopped using it before it caused damage. The compression feels good when pulling the starter.   Anyway I made a seal puller out of a small screwdriver and carefully replaced the seal.  I noticed that the spring in the old seal was broken; don't know if it happened when it was removed or not.  With the new seal in place it holds 7 psi pressure and maybe 13 in Hg vac (not quite 15 in).  I put a Zama RB10 kit in the carb and have new fuel line and filter on order.
The piston and ring look ok. I noticed a good bit of carbon buildup... I carefully removed it in the exhaust port but did not pull the p & c,figuring to leave well enough alone for now.
Now my question for you old saw guys.. The 1984 owners manual says to only use leaded regular gas.... of course today we have no choice but to use unleaded.. my plan is to use S.E.F. or Tru- Fuel at  40:1 with Husqvarna oil. Not to start an oil or fuel thread, but do any of you know if I might expect any issues in this regard?


  

  

 

[JohnG28]

You should be fine running tru-fuel at 40:1. Don't put more oil in it though, that stuff is pre mixed already. Or you can just mix 2 stroke oil with pump gas and you would be fine as well. Hope you get it running again.

[Crow99]

Thanks, JohnG28.  That's about what I plan. I have a couple of cans of the 40:1 premix and more unmixed stuff. I plan to keep ethanol far, far away . I just found the printed fuel instructions a bit odd and was wondering if someone knew what issue (s) they might have been addressing 30 years ago.... and if anyone knew of any issues with today's fuels and the older 2 stroke engines.. I haven't read or heard of any myself but thought I'd see if anyone has.
Btw I see this machine is almost as old as you are..

[celliott]

The old homelites, macs and others called for 16:1 or 25:1 using 30wt motor oil, and they run just fine on modern gas and oil mixed at 32:1 or 50:1
It should be just fine if you have the high speed jet tuned properly for the fuel you're using.

[Crow99]

Ok another question is what do you guys think about leaving the carbon crust on the piston and in the combustion chamber and just allowing it to "run out" I.e. clean itself while running...  As opposed to taking the p & c off and cleaning them beforehand?  Afaik no base gaskets are available and I'd have to make a new one.  Gaskets and case joints seem nice and tight and I'm not interested in disturbing them if I don't have to.

[Ianab]

if someone knew what issue (s) they might have been addressing 30 years ago....

Low quality 2 stroke oil mostly. The oils weren't very good, but if you poured some extra in the mix, engines ran OK.

Ian

[JohnG28]

I believe the lead in fuel was to prevent detonation or "knock", do I assume they suggested to use leaded gas for this reason with high compression 2 stroke engines. And the higher ratio of oil in the gas was because of lower grade oils at the time. Don't worry about taking the thing apart over some carbon deposits, it should run OK and burn off some. Yeah, I have some older ones myself. 3-4 of my saws were born before me!  :D

[Crow99]

Yeah, years ago I remember using some nasty brown 2 stroke oil in it.... Amalie I think. I might still have a bottle of it in the shed. I never throw stuff away. Well I did the last time we moved which was 37 years ago.
The only thing I have that was made before I was born would be a few guns.  Back then I think they were still trying to figure out how to attach steam engines to saw chains.  But one thing that strikes me about this humble trimmer is the quality of construction... minimum plastic, two part cases (no clamshell stuff either) bearings and seals on each end of the crank, etc.  When the line and filter get here I will hopefully fire it up. It also has all kinds of spark. I guess I'm beginning to see what people see in a lot of the old machines.

[sharkey]

Nice job on cleaning the carbon out of that exhaust.

That power head looks like it was made by Echo.  The off switch makes me think it is a SRM-200BE.  You may be able to get additional seals from your local Echo dealer.  Go over to parts tree and take a look at the drawings and see if Im right.  Echo made some of the Mac power heads and all of the Mantis and Technic Tool engines.

That new Shindaiwa/Echo Red Armor oil will clean that piston up if you want to go that route.

[Al_Smith]

I may have that models' parts list in  my stash of goodys .If so it would be a simple matter of just cross referencing those seals .

With the exception of Stihl products most seals can be cross referenced .

BTW you don't need leaded gas .Fact Mac recommended in some of the early kart engines to use "white gas ",lantern fuel which contained no tetra ethyl lead what so ever .

[Crow99]

Sharkey...  yeah, I started by trying to scrape the carbon out with a popsicle stick like the manual said.. I plugged the port with some paper towel.  But flakes were going all over. I vacuumed it up as much as I could and thought, "this is bs.  "  so I saturated a q-tip with some 2 stroke oil and that seemed to loosen it nicely and I was able to get it all out that way. Seemed like a pretty good little trick.
Al... I was able to come up with an IPL on the net that had a part number for the seals.. it was 216500 iirc. I ordered them from my usual parts source in Maryland. They back ordered them for a couple of weeks but did send them. I got two but only replaced the front one for now since it was the one leaking.  With that one replaced it does hold pressure and vac.  The machine has never had ethanol gas in it because I stopped using it may be 20 years ago, so I figured I'd wait and see how the other one does.  It is the easier of the two to get to anyway.  My fuel line and filter should be in today so I should get to fire it up soon..
Interesting theory about it maybe being an Echo. It does seem well built anyway. I've come to appreciate such things more over the years..

[JohnG28]

Yeah, the oldies are sure built a lot more rugged than most products are today. Sounds like it's going well so far.

[Crow99]

Well, my little machine is up and running as of yesterday.  It seems to run all right on the 40:1 mix although generally the needle settings seem to want to be a bit leaner than the factory suggested 1 turn out.  As I remember from years ago it seemed to want to run a bit "fat" anyway so I'm thinking maybe the carb isn't / wasn't all it's cracked up to be even with the rebuild kit on it.

There was one more little pitfall to overcome before it ran though.  The first time I tried to crank it up, it managed to flood so badly there was fuel spurting out of the spark plug hole when I attempted to clear the flood..  as in a stream of it.  Never saw an engine flood this badly.  After scratching my head and disassembling the carb a couple of times to check things, I discovered that there must have been some gunk or corrosion on the inlet needle seat that was preventing the inlet needle from seating solidly, and was allowing fuel to essentially "free- pump."  After trying a "redneck pop-off test" (hooking a fuel line to the inlet and blowing gently through it) which it failed big time, I decided to gently re-face the brass needle seat with a #22 drill... a couple of gentle twirls by hand with the drill bit and the seat looked much cleaner and more even.  I could feel crispy crunchy "stuff" as I began to twist the drill too.  It seemed to hold pressure with the needle, lever and spring in place after that.
I managed to get it running and dialed in some basic adjustments.  So it's running again after 20 years, and I feel that this was a decent learning experience for me on a not too difficult project.  I certainly  know the insides of a Zama carb better than I did if nothing else.... The 40:1 fuel ratio looks about right, although I plan to try some 32:1 through it later on as a concession to its age perhaps.
For my next project, I'm going to take a Husqvarna 395, decrease the squish to .018, raise the exhaust port and grind in some finger ports, and install a 36" bar with a full skip chain.. I need to limb a few small trees in my back yard..  OK, folks, I'm KIDDING there!!!!  ;D ;D ;D 8)

[sharkey]

Hey Crow,
Glad its running.  I had a real problem getting a Walbro HDA inlet needle to seal.  I ended up using silver polish, a makeshift drift, a q-tip, a heavy spring and a winderosa needle.  The brass seats dont seem to be used too often anymore, apparently they were too soft.  Later seats are either stainless or aluminum.  Dont forget to grease the shaft bearings, the clutch bearing and the gear head. 

I will be watching for those 395pics!   

[Crow99]

Sharkey,
Don't hold your breath waiting for the 395 pics.. (I would love to have a 395, or a 390, or an old 288 or...or..) That sort of thing is a bit far down the road for me.  But never say never..

I realize this little project is a bit mundane by most standards, but it was an interesting learning experience for me.  And I've got a working trimmer for my troubles.  I've been a tool and machinery geek for my whole life, been doing gunsmithing and some machine work part time for 40 or so years, but am just now getting more serious about small engines.  A lot of the stuff transfers over, but there's always something new to learn.  When I was starting out an old guy in the shop said he learned something new every day and that's what kept it interesting for him.  I'm trying to take that advice...