My Echo SRM-2100 line-trimmer has given very good service in the ten+ years I’ve owned it, from fully mowing my half-acre yard when I lived in the cabin on 123rd St, to the limited lawn I have now. Commercial-grade (straight-shaft) Echos have a very good reputation for durability, and a low exhaust note which is less annoying.
But lately it’s been hard to start, and simply would not idle; I have to hold the trigger all the time. These symptoms are usually related to fuel delivery, maybe a clogged idle circuit. Well it’s been faithful for a long time, so maybe it’s time for it some love.
First thing I did was installed a ‘tune-up kit’ from Home Depot, which includes a sparkplug, and air and fuel filters. But what to gap the plug at? You always need to gap new plugs because the same plug might be used in different engines, so they’re never set at the factory. Fortunately, Echo has very good documentation, which gives the gap as .026″. (first Operator’s Manual pp 25)
Alas, with these new parts installed, the symptom did not change. The next likely suspect is the carburetor. Fortunately 2-cycle engine carbs are very simple, at least compared with 4-cycle engine carbs. So I sits me red arse down and takes it apart.
This is the breather, with the cover and filter removed. The carb is under it, and all is held to the engine block by those two gold screws. You’ll notice the choke, the black doo-dad which pivots over the intake venturi to restrict air going in. This makes the air/fuel mixture rich for easier starting when the engine is cold.
On the side of the carb you can see the throttle and throttle cable. When you pull the trigger it retracts this cable, which pulls the springed pivot, which opens the internal butterfly valve to let more air in the engine. Faster air sucks more fuel into the venturi, and a higher volume of air and fuel means the engine can’t help but increase its speed. To free the carb you have to remove the cable from the pivot; just twist the pivot and the cable slips right out.
(Click to enlarge)
It’s important to note which pipes go where. Taking pictures is always a good idea. In this case the black pipe at the bottom of the picture comes out of the fuel tank to a white one-way valve, which lets air into the tank as fuel is used. The clear-yellow line is vapor-recovery, which scavenges gas fumes from the tank and lets them be burned in combustion, rather than being released into the atmosphere. The black line in the middle is the actual fuel line; it runs into the tank to the fuel filter.
And sproinnng, here is the carb taken apart.
Starting at the left you’ll see the priming bulb, which is used to draw fuel from the tank into the carb, to aid starting. Then there’s the fuel pump head, then its gasket, and the black reed sheet. (click to enlarge) The carb body is in the center, with the diaphragm side up. You’ll notice the black Lo, and Hi needle valves at its top. Then comes the diaphragm offset gasket and the fuel pump diaphragm itself. Finally the pump cap.
Since no one else knows how this works I’ll tell you its secrets: Air pressure from the movement of the piston causes the fuel pump diaphragm to move in and out, in the space provided by the diaphragm offset gasket. As it moves out it draws fuel from the tank, and as it moves in it pushes that fuel through orifices to the other side of the carb where the reed valves capture it as one-way valves. The diaphragm then withdraws and the reed valves close and the fuel is sucked into the venturi. How much fuel is provided, is regulated by internal needle valves, two of which are adjustable, and the third responds to pressure. (engine speed)
Here the internal dynamic needle valve is disassembled.
Needless to say you must be very careful with these tiny parts.
And below is the reed valve sheet over the area of the carb body where it fits. Notice the two flaps which flap over holes… those are the one-way valves. (Click to enlarge)
When I first started this, I thought I could get away with a simple cleaning. I took everything apart and soaked the metal parts in carb cleaner (auto parts store) for a couple hours. Then I pulled a wire out of my wire brush and probed all the jets, trying to clean out the varnishes, crud, and dirt. Then I vigorously swished the carb in cleaner, blew it out with air, and put everything back together. Worked just as ‘good’ as it had before… :/
I had no idea that it was possible to get a carb kit for
a) A machine this small and specialized; and
b) A machine this old;
… but sure enough a search on eBay turned up just the thing, sold by user randysenginerepair (937.927.5429). Ordered it for about $10 and installed the kit, which included all gaskets and the diaphragm, and the internal needle valve parts. It does not include the gasket from the carb body to the engine though, so save that one. It also does not include the primer bulb, and mine was cracked, so I ordered that on eBay.
I reassembled everything with the new parts, and took apart the muffler to clean the spark arrestor screen as per the first Owner’s Manual, pp 26. But, there was no spark arrestor screen, so somebody had already taken care of that ‘useless’ thing for me, lol. Just don’t run it in dry grass…
Now it is time for adjustment. Mine is a ‘non-emissions’ model, which has its own procedure in the first Operator’s Manual, pp 28. Went through that, then set it up according to the Fine Tuning Section. I don’t have a tachometer and I think that’s a silly requirement, so I tuned the Hi to make the machine run best at full throttle. When I was done it ran like a bat outta Hell, from idle to high throttle. But that’s not all that should be done to fix up this machine.
Next, my cowling was loose; it’d lost two of the three screws and I’d better fix that. The pic to the left is what the head looks like when you remove the line spool. Notice the nylon hex-head inside the splindle? Get a socket about that size, ~3/4″, grab the outer housing, and turn that hex head like you’re screwing it in. Yes, screwing it in, screws it out, because line trimmers rotate clockwise, and when you put a left-hand thread here it will tighten the head as it spins, rather than loosen it. The nut is righty-loosey. I removed the head, and lo, there was the bezel, missing the screws. So I found two to match from my supplies, put LocTite Blue on all three, and put them in.
Side Note: With LocTite Blue, a screw can be removed down the line, if need be. there are very few cases where you’d use LocTite Red, as it turns solid, rather than gummy. Also, never remove the air from a tube of LocTite, as it sets up in the absence of oxygen.
Right, now it’s time to lube. There’s a transmission at the end of the straight shaft, which should be lubed, and there’s a flexible driveshaft inside the pole which should be lubed, eh, at least every ten years or so. I always keep a container of synthetic high-temp grease, for all occasions. (auto parts store) The transmission has a bolt on its side — remove that and get the grease in. Here you have two choices:
a) Buy a package of ten zerc fittings for $9 at the auto parts store, nine of which you’ll never use; or
b) Buy a grease needle, similar to a basketball fill needle, except for grease.
This grease needle can be used for many purposes, including injecting new grease into sealed bearings, tie-rod ends, ball-joints, etc, greatly extending their life. Just don’t use it to inject grease into your butt-cheeks… as it seems some are inclined to do. :(
Now let’s grease up that flexi-driveshaft. First you have to get off the tranny head. Remove the two clamp bolts, and the centering-screw. The tranny just slides off then, exposing the naked driveshaft! Grab aholt of it, and yank it out by the roots. It’s basically a tightly-coiled spring with the tensile strength to withstand the work a line-trimmer has to do. Slather it with grease. Don’t be careful or stingey.
Then slide it back in the pole. Rest assured, it will self-center when it comes to the clutch assembly at the engine-head; just turn it a bit when it hits the back, until it seats in the socket. Put the tranny back on, and you’re set to go.