Ray Heffner

I think the problem is the carb or ignition from your brief description.  The carbs are factory set to meet EPA guidelines but that has nothing to do with operating properly.  The OPE manufacturers have had a rough time making machines you like and want to buy again after the EPA shoved their rules down their throats.  If you can still find them on E-bay and if your carb can be adjusted, try buying the carb adjusting screwdrivers that fit your carb.  There are 4 or 5 different shapes.  For a while, the EPA made it impossible for you to buy these tools.  But they weren't buying you a new trimmer either. 

It sounds more like an adjustment problem of the carb.  A bad diaphragm or needle set would not cause that problem especially since a new carb was substituted.  If you had screwed up and left old gas sit in the carb over winter, it might have gummed up the carb.  But since it's been having problems for a while, I doubt that was your problem.  Before you invest any money in adjusting tools, check the compression and the cylinder condition.  If they are a problem then don't waste much money on a repair. 

From experience I have noted that if you bring a running unit in and they tell you it's a carb problem, they either don't have the tools to adjust the carb or it has a possible timing problem.  I have another entry in here telling of a 128LD trimmer that ran bad because of how the spark plug wire was routed in the case.  That simple of a problem, no simple solution though.  A new carb wouldn't have fixed that problem and a new coil didn't fix it either.  But if you ran the unit with the cover off, it ran great.  Put the cover on and it ran like crap.  With problems like that the MFG wants to try simple fixes like the carb and coil and hope that you eventually give up and go away. poor customer service.  I can't blame the seller because he makes very little commission and warranty repair costs are so small he can't even pay the technician for the labor without losing money.  They will provide the part and some silly sum like $20 to the seller to do warranty repairs that last an hour or more to troubleshoot let alone the paperwork and repair actions.  If the repair technician is making minimum wage, he might break even.  In some cases, it's cheaper to lose you as a customer than to invest lots of money to fix your unit and make you happy.  Carb adjusting tools are forever.  The will fit in tool box until you need them.  Almost every carb made has an adjusting screw, but unless you have those tool, you won't be able to even play around.  The EPA has great intentions but reality doesn't seem to fit into their lives.  My neighbors vintage auto looks like a mosquito spraying truck in Miami.  He calls his 25 year old roto-tiller Smoky for a reason.  And the country bumpkins burn their leaves and trash every fall.  But your tiny 30 cc engine might cause some glacier to melt by depleting the ozone. 

Try the free test first, remove the front cover and see if it runs better when the spark plug wire is moved.  If that fails, consider the carb adjusting tools.  A lot of MFG's make great larger engines but the smaller ones have problems because the tolerances are so small. 

The type of 2 cycle oil you use is important too.  Most stores sell you those little bottles for easy premixing.  It works but I prefer the oil for snow mobiles better.  These usually come in 1 quart bottles and you can refill those smaller bottles for a whole season (or two) of use from that one bottle.  Use it in your chainsaw, leaf blowers and other stuff like post hole diggers too. 

The use of the engine is the issue here.  Most 2 cycle engines are designed to run at WOT wide open throttle so they can use a different blend of oil.  A 2 cycle snow mobile is designed for varying throttle positions.  The smaller engines have a hard time of burning the oil additives causing the ash problems they say they prevent.  I think they are referring to the spark arrester screen getting clogged by unburned oil and causing the engine to bog down.  Remove the screen, hold it in a pair of hemostats and hold the screen in front of a propane torch until it glows red, burning off the oil deposits.  Wire brush, reinstall.  Back to my last post, I would rather clean the screen and replace the plug every year or two than replace the entire weed trimmer or chain saw.  I have a Stihl concrete saw that suggests a higher oil ratio mix for the first 3 fuel tanks then going back to the leaner mix.  The saw is almost $400, I'll stick to the higher oil blend.  The E85 fuel is getting some bad hits for causing engine problems.  I mentioned the fuel line problem before and can see premature cylinder wear in 2 cycle engines.  They don't have the oil lubrication like a 4 cycle so any thing they do to cheapen the stuff can't be good for your gear.  It's well known that E85 isn't as good as the normal unleaded gas in your big car, I doubt it helps that poor little engine at all.  It sounds stupid but look at the cylinder head, the outside of the head.  Remember what that head looked like brand new?  A head that got too hot has a darker color, a blue black look.  Reminds me of the exhaust pipes on a motorcycle. 

I read a lot about people replacing the heads of their small 2 cycles.  Before going that way, check the compression.  Most manufacturers don't tell you the "correct' compression because there are many variables, including the local temperature.  They will tell you to check it after warming up the engine.  Generally values of 125 and 150 are good.  Let's be real, you don't have a problem after the engine is started.  You have a problem getting the engine started to begin with.  The compressions values I listed in my previous post are for a cold engine, when you first try starting it.  The values I gave are good indicators of it's future life expectancy.  The engine will probably start at those values, it may be hard to start but it should still start.  No shop is going to put rings in a $200 mower and certainly not a $100 trimmer. The labor costs are prohibitive.  A compression tester is pretty cheap and accuracy is not critical since the readings are relative anyway.  If your want to check it for accuracy, put it on your air compressor with a good digital tire gauge to verify the values.  The compression tester you buy aren't laboratory quality so their accuracy is fair at best. 

Having a low compression on your mower and wonder what might help.  Take off the head.  Look at the cylinder for scoring or odd light reflections.  Over time, the movement of the piston will cause uneven wear on the cylinder and in a small way, makes it oval shaped, mostly pronounced at the bottom of the piston bore.  These are usually perpendicular to the engine shaft.  A few thousandths means a loose seal in the rings.  If you have the time and want to re ring the piston, take it apart and determine if you can use a new set of original sized rings or if you need oversized.  Does the top of the cylinder have a lip and you can't push the piston out the top of the cylinder.  You need a ring reamer to remove that lip.  More importantly, that mean the cylinder is worn and you will need over sized piston and rings.  If there is no lip, try installing a regular sized ring set and check the end gap before installing them on the piston.  I've seen old rings so badly worn the end gap was almost a quarter inch.  A new set should be about 5 or 7 thousandths.  Low compression rings are in the 20's or more.  Check the end gap at the top, middle and bottom on the cylinder.  You might have to do a light honing to round things out.  As you know, bad rings can cause high oil consumption and also cause more oil to fill the valve tappet area of the engine and (depending on the engine design) feeds back into the carb, clogging the oil filter or out the breather tube leaving a puddle of oil on the floor. 

I guess I should mention the disclaimers.  No matter what you do, you are still fixing an old engine and they usually have one or more problems.  No matter what you do, you will still have an old engine.  Your hopes are to extract more life from your toy at minimal cost, because you certainly aren't going to get like new performance from an old engine.  Many times I would have liked to slap our customers that bring in a dead 10 year old machine and expect their $75 repair should give them like new performance.  Many places charge $50 an hour or more so that bill includes labor and a few parts. Prayers are free, miracles cost more.  If you take your toy to some repair shop and he advises you that it is wasted money, listen to him.  I know you can find some shop that will take your money and attempt repairs, but it's still an old machine.  If he advises against the repair, and you have some DIY skills, ask if he has a similar machine in his scrap pile he'll sell for the parts he thinks you need.  Many customers donate their old stuff to them for parts.  Some of the junk we got, it wasn't even cost effective to put needle valves in the carbs because the 1 hour labor cost alone exceeded 50% of the equipment cost.  Go to YouTube, watch a few videos, buy the parts and play around.  What's the worse you can do?  Lose a part or completely kill an engine that was at death's door anyway?  Sure beats spending $75 on a $100 dollar engine.  Shops don't want to lose money attempting to repair low priced stuff.  It seriously dips into their small profits. 

An odd place to look for problems on the smaller 2 cycle stuff, seals and gaskets.  Ok, many cheap engines don't use seals and gaskets are rare too.  Many weed trimmers have plastic covers screwed directly to the engine and they become loose overtime.  The compression will be good but hard starting.  That's because that bad seal / gasket is not creating the vacuum in the crankcase to suck in the fuel mix.  Loose engine covers, carb plumbing with small holes, even loose cylinders cause those problems.  I once repaired a chainsaw that wouldn't start and made a clicking sound when you pulled the rope.  The cylinder head was loose.  The movement of the piston was pushing the cylinder up and down, making that clicking sound.  Many of the screws used on those cheap trimmers and saws are self tapping.  Add an external star washer if possible or thread locker. 

I've got a few years fixing engines small and big.  From Poulons to Gravelys.  I'm sure I don't know it all and like getting advice from people.  My trophy wall includes everything form cheapo trimmers to front end loaders, small back hoes and a Ditch Witch or two.  A healthy mix of commercial and residential stuff. 

I've had a ham radio license since the early 80's, KD8CCV.

Ray

I have serviced countless brands of OPE over the years and just discovered a problem with a few 128LD trimmers that make it almost impossible to run right.  We removed the covers at the shop and discovered the engine ran FINE when the spark plug wire was removed from it's normal routing by the bolt hole.  When you placed the spark plug wire back into it's proper place, the engine would bog down and die.  This was attempted with a new ignition module with the same results.  There  are only two wires in the area, the spark plug wire and the grounding wire for the ignition module.  Flexing the wire did not affect performance but when the wire was placed back into it's proper place around the bolt hole, the engine quickly died.  No sharp edges or burrs were found.  Both the new and old ignition module had the same results.  If the shop were darker, I would check for leaking electricity like with wet car spark plug wires.  Other new spark plugs were swapped in the test with the same result.  In both cases, the spark plug wires were very clean, one was brand new.  Any ideas would be appreciated.  Dielectric grease?