Echo SRM 2100 running erratically

[Mr Mower Man]

I have an Echo SRM-2100 in the shop, and it's running strangely. The fuel tank was empty, except for a little "syrup" at the bottom, so I poured out what little I could and put fresh fuel in it. At first, I thought it was just a mis-adjusted carburetor. The low speed screw was out way too much, and the high speed screw was in too far. So I started over with both of them about 1-3/4 turns out, and I got it adjusted to where it was idling smoothly, responding well to the throttle, and running smooth at the high end. I thought it was OK, but a few minutes later I picked it up again and started it, and it idled fast, then slow, then fast, then slow, then fast, and then died. I started it again and ran it for a couple seconds at high speed, but when I released the throttle it died again. I tried playing with the carburetor adjusting screws again, but it wouldn't improve.

So then I dragged out the training materials I got from my 2-stroke engine class at the GIE+ EXPO last fall and started doing some testing. I haven't gotten to do this stuff often enough to get good at it. I spend most of my time on v-twins these days. So the first thing I do is check the compression. I got 120 lbs., which I'm assuming is good enough (I wish it were just a little higher). The next thing I do is test the fuel inlet. I pressured up the fuel line and it held 10 PSI. Good. So then I blocked off the intake and exhaust ports and gave the crankcase a pressure test. It held 7 PSI for a minute. Good. Then I pulled 14 PSI on the crankcase to see if that would hold for a minute. It wouldn't hold 14 PSI, but it did hold once it got down to 12. Did I just find my problem? Leaking crank seals? I know technically it failed the test, but I would've thought that bad crank seals wouldn't hold 12 PSI vacuum. It's awfully close, and I'm afraid to tell the customer definitively that he has leaking crank seals.

What do you think?

[bgsengine]

your symptoms would be consistent with crankcase seals leaking , might also want to pull a cover and see if flywheel has any radial play (up and down) indicating failing crank bearings.

as I read your description of how it ran I was leaning towards suggesting to check for air leaks (I assume you did the full fuel system test including vacuum test as well, and verified fuel tank vent) Also check your spark plug (correct for the unit?, gap?) but other than that it does sound like crankcase leak (might also want to check for cracked insulator if it was not part of the crankcase P/V test you did)

Other than that I'd say seals would be likely - try repeating the P/V test again but this time with access to flywheel and see if you can wiggle it around or move it in and out and see if your pressure or vacuum readings drop.. Given the gunk in fuel tank I'd also wonder if the carb has been checked for stiffened diaphragms (which will also affect fuel delivery and adjustments) and checked the inlet filter screen. Given the type of gunk you describe in fuel tank, unit sat for a long time - Could also be possible that intake or carburetor gaskets dried out and split or cracked (tiny impulse leak?) from the heat/cool cycle.. double check fuel filter (I assume it is new also) if you find anything in the carb's filter screen

[thomd51]

I don't think the seals are your problem ............the metering diaphragm is the culprit . it's probably stiff and needs to be replaced ,also replace the inlet needle , being careful to adjust the inlet needle lever........probably a zama c1u..k16.........don't use carb cleaner....use 2cycle fuel ..and don't blow out passages with full force compressed air just a little pressure . there's a check valve in the idle passage that's easy to damage ...........SRM means " shoulder rotary mower " .

[KE4AVB]

Actually all three are right. Except it is not 14-15 PSI vacuum it should inches of mercury reading as is measurement for vacuum.

Yes it can be seals not just crank seals but gaskets too especially the cylinder to crankcase. May even to just loose screws. But first a good carburetor breakdown, cleaning, replacement bad diaphragms, adjustment, and reassembly. Yes the metering diaphragm get stiff and causes problems but don't forget the pump diaphragm as the check valve tabs can deform and not seal good. This is something I do any unit that has sitting a long time but it is just a habit I got into which saves me a lot time on diagnosing a problem. During the vacuum test you should rotate the crankshaft which will be a better test of the crank seals and bearings as side in the bearing can show up during this test especially if the seals are borderline good.

As for cleaning I only use soap, water, and an ultrasonic cleaner then light blow dry. And not residual soap the only bench priming is need to remove the soap and water. Yes are small check valves that can be damage from high air and carburetor cleaner. When cleaning I always remove the mixture screws to allow better cleaning access. The UC is something I have now been using for 5 yrs now and I there not a can of the dip or spray carburetor cleaner in my shop. I still had new can of dip cleaner in 2014 which I gave away. I don't have a can starter fluid.

Now finding what is really causing the problem as these seal system with fuel mix and air going nearly everywhere all you can is start with the most likely culprit and follow a set test sequence looking for problem as you go. As I said I first eliminate the carburetor and go from there. Everything in a two cycle is interdependent on all the components being right and yes there are some that can make you to want to take sledge hammer to them. Thanks goodness it don't happen that often though.