2-stroke won't rev. Thinking carbon/exhaust port?

canucklehead · Sep 18, 2013

as far as I can see, when I pull the muffler off there is a large open rectangular hole from cylinder to exhaust. I did clean muffler with brake cleaner and compressed air, but it seemed to have zero restriction. And of course, the little spark arrestor screen (which was also clean). There is something in the exhaust port area that looks like a carb jet... not sure of it's function, or if that might be plugged up. i don't want to ruin that area.

sd455dan, where is oil plug/access? Do you think that's more to do with JD than Echo models? I think it's worth having a better look down below to see if there is a restriction.

sd455dan · Sep 18, 2013

canucklehead said:
as far as I can see, when I pull the muffler off there is a large open rectangular hole from cylinder to exhaust. I did clean muffler with brake cleaner and compressed air, but it seemed to have zero restriction. And of course, the little spark arrestor screen (which was also clean). There is something in the exhaust port area that looks like a carb jet... not sure of it's function, or if that might be plugged up. i don't want to ruin that area.

sd455dan, where is oil plug/access? Do you think that's more to do with JD than Echo models? I think it's worth having a better look down below to see if there is a restriction.

canucklehead the JD 240 is a 2 stroke straight shaft trimmer built by ECHO, but manufactured in the 1980s It looks like the new Echos that i looked at last time i visited home depot
The oil check hole is down at the bottom of the straight shaft- it threads in at 90 degrees to the trimmer shaft (believe it takes a 1/2 inch wrench)
it is an oil lube hole for the bearing that supports the actual cutting head.
when the oil runs or drys out the friction goes way up and the engine uses most of its power trying to overcome the resistance to rotation in the gooey bearing. The oil hole should be full to the threads, IIRC the manual said to use 90wt gear oil- but it revs and cuts better with some synthetic engine oil, at least for me... good luck

canucklehead · Sep 19, 2013

I was able to spin the string holder pretty easy, but it doesn't keep free-spinning round & round. Probably about the same tension as a properly set up wheel bearing.

I removed the entire head. I found the bolt/hole you are talking about. 1/2" sounds correct cuz i used a 13mm wrench. There is also a phillips head screw on the top. I think the phillips is a grease hole for the square driveshaft.

Anyways, I removed the oil bolt. Funny you said gear oil cuz I had some synthetic 75-90 gear oil and that's what I dumped in 9before reading this). Not as much as you indicated. It was difficult to get it to force air out and go in. There was grey grease in there already, so I gave it a pump of grease when I was done.

I cleaned off some minor grass wrapped around head....not much.After all this, it runs exactly the same. I'd say it reaches about 1/2 rev. From 1/2 to full throttle there is no change. The "H" screw is maybe 1/4-1/2 turn out. Any more than that and it runs worse.

Frustrating. I have always liked Echo products, probably more than my Stihl stuff. This one is making me reconsider.

Funny tho.... my 14-16" old McCullough chainsaw still runs great and starts easier than any 2-stroke I own. And gets no respect from others.

Midniteoyl · Sep 19, 2013

Cant remember.. did you change the fuel line? Could be swelled maybe?

Coyote machine · Sep 19, 2013

Throw some Seafoam in the fuel tank and run it till it stops smoking. Follow directions as to dosage.
And check to make sure spark plug boot is making good solid metal contact with plug's end, and that the wire is connected to the screw in the boot. If you take it to your local shop they can use a RPM tool to see where it tops out, and properly adjust the carb screws.

canucklehead · Sep 19, 2013

I thought I changed the fuel line as I did fuel filter. I also thought I blew air through the line and it seemed good. I see it is black line and I usually get green line from my local store so I'll try again.

would leaking intake gaskets cause these issues?

eddie48 · Sep 19, 2013

Intake gaskets probably won't be the culprits. Air leaks tend to make the engine run lean and at higher rpms, at least until it blows up. Is the string head shield still on the machine or has it been removed? If it has been removed, how long are you letting the string get? Long string will, all by itself, slow down the engine. With reference to the discussion about the head being poorly lubricated; as I recall, this machine has a clutch between the engine and the shaft. That should allow the string head to be turned pretty freely. If it is as tight as a wheel bearing, that may be too tight. Unclamp the head from the shaft and pull it off. Then see how easily the head turns. That may give some insight.

sox3 · Sep 21, 2013

Could be a crankcase leak or crankshaft seals. We would disassemble and use blocking plates on intake and exhaust
then put in water tank. One of the blocking plates had a nipple to pressurize the crankcase. I have seen your problem on chainsaws more than trimmers.

sd455dan · Sep 22, 2013

eddie48 said:
Intake gaskets probably won't be the culprits. Air leaks tend to make the engine run lean and at higher rpms, at least until it blows up. Is the string head shield still on the machine or has it been removed? If it has been removed, how long are you letting the string get? Long string will, all by itself, slow down the engine. With reference to the discussion about the head being poorly lubricated; as I recall, this machine has a clutch between the engine and the shaft. That should allow the string head to be turned pretty freely. If it is as tight as a wheel bearing, that may be too tight. Unclamp the head from the shaft and pull it off. Then see how easily the head turns. That may give some insight.

Just as Eddie says- I just rechecked mine and it does spin freely, also remembered that before I re- lubed the bearing and gears it was as the OP said a normal wheel bearing set up, - is to much friction - wheel bearings are assembled with pre load (timken tapered roller)
the grease the OP added is far to heavy, I would try and remove the power head from the shaft - start the engine and if it will rev you have your answer, If it won't then i would keep looking for an answer... good luck Canucklehead