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

[canucklehead]

I have an Echo SRM2100 straight shaft weedeater. Started acting up in June/July and I replaced fuel line, fuel filter, and cleaned carb twice. I also cleaned spark arrestor (screen) & the muffler. Muffler & screen were both very clean already. Checked compression and it is 120-130.

After carb cleaning, it seemed to be better, but soon after it got worse. I thought maybe carb diaphragm was worn & local repair shop said that is like the fuel pump. Found it almost as cheap to buy a complete new carb vs a rebuild kit, so I bought a new carb. It was better but I can't get this to hit the high notes and scream like a 2-stroke should. Doesn't matter how much I play with the "H" screw, it will not rev as high as it should. I'd say it sounds like 3/4. The adjustment screw is almost all the way in to get best response (maybe 1/4-1/2 turn out). More out I turn, it stalls.

When muffler was off and I could see piston, I carefully scraped away a bit of carbon/crud build up, but it wasn't too awful. There was also something that looked like a jet by the exhaust port..it had some black crud. Tried spraying it, but not sure I did much to it.

I bought new gaskets for intake as I thought maybe it was sucking air. I have NOT installed them. Local shop said if sucking air I'd rev higher. I tried spraying WD40 around intake gasket areas while running (was told this would change performanace if there was a leak). No change.

Shop said these types of issues are usually related to hardened carbon deposits/buildup for exhaust. So where do i check that? How clean/resolve? I asked if i had to tear down head to clean that and they said no.

I googled searched and found an almost identical thread and that one eneded with guy saying it seemed to eventually fix itself. I'm stumped...

 

[Coyote machine]

What were original symptoms when it started acting up? You replaced the in tank fuel filter? And spark plug gap/condition?
What grade fuel and at what ratio are you running? How many hours on the unit?
You could have gummed up rings, or one stuck to the piston from poorly burned fuel, improper atomization, scored cylinder walls, etc.

 

[canucklehead]

new NGK plug. I have not re-checked gap but it was correct when installed. spark looks good when I ground plug to head.... but i know that can be misleading.

prior to carb replacement, I had issues where it was hard to start and would only run at low to mid RPM, so would almost power out/bog down when I tried to whack heavier weeded areas. replacement carb improved this, but still isn't revving as high as it should. It is better but not right. And adjusting high idle screw has limited affect. Usually you can almost blow up engine when you start tweaking that screw.

I run 50:1 mix using Amsoil synthetic. I called Amsoil techs and they said whatever their mix ratio oil is rated will not damage my stuff. They said mfrers rate their mix based on cheapest oil available. I run my dirtbikes and all other 2-stroke equipment on this same fuel and mix with no issues. I also used regular gas but have been using premium lately, and looking for non-ethanol blended fuel. But most of it was run on 87 regular, like all my other stuff. As far as I've heard, the ethanol is hard on carbs & gumming up, but not hard on engines.

I don't know my hours. I use it around my small acreage, maybe once per week, so not a ton of use.
If I had ring & cylinder wall issues, would i still have such good compression? (120-130). Would that affect how high it revs?

 

[Midniteoyl]

I have an Echo SRM2100 straight shaft weedeater. Started acting up in June/July and I replaced fuel line, fuel filter, and cleaned carb twice. I also cleaned spark arrestor (screen) & the muffler. Muffler & screen were both very clean already. Checked compression and it is 120-130.

After carb cleaning, it seemed to be better, but soon after it got worse. I thought maybe carb diaphragm was worn & local repair shop said that is like the fuel pump. Found it almost as cheap to buy a complete new carb vs a rebuild kit, so I bought a new carb. It was better but I can't get this to hit the high notes and scream like a 2-stroke should. Doesn't matter how much I play with the "H" screw, it will not rev as high as it should. I'd say it sounds like 3/4. The adjustment screw is almost all the way in to get best response (maybe 1/4-1/2 turn out). More out I turn, it stalls.

When muffler was off and I could see piston, I carefully scraped away a bit of carbon/crud build up, but it wasn't too awful. There was also something that looked like a jet by the exhaust port..it had some black crud. Tried spraying it, but not sure I did much to it.

I bought new gaskets for intake as I thought maybe it was sucking air. I have NOT installed them. Local shop said if sucking air I'd rev higher. I tried spraying WD40 around intake gasket areas while running (was told this would change performanace if there was a leak). No change.

Shop said these types of issues are usually related to hardened carbon deposits/buildup for exhaust. So where do i check that? How clean/resolve? I asked if i had to tear down head to clean that and they said no.

I googled searched and found an almost identical thread and that one eneded with guy saying it seemed to eventually fix itself. I'm stumped...

You dont have any attachments/mods/extra heavy line on it do you? How easy is the shaft to turn?

 

[eddie48]

Sounds like a toughie. If the problem is carbon buildup closing off the exhaust, you usually get a lot of smoke. If you are not getting smoke, then I would start looking at other things. Does the carb have a limiter on the HS adjustment screw? If so, take it off and you will be able to adjust further. The other possibility that comes to mind goes back to what Midnightoyl had to say; is something binding up in the drive line/head or clutch? They would get pretty warm to the touch if that is what is happening. If you do decide to go after carbon, you will find it in the exhaust port after removing the muffler but I don't expect that to be the case if the muffler itself is clean.

 

[Coyote machine]

Midniteoyl & Eddie48, you guys are thinking along the same lines I am, but beat me to the keyboard.

I have the same model Echo, SRM 2100SB but it has a split shaft, (boom) that allows one to add various things aside from the weedeater. Seems to me, if the OP disconnected the head unit from the shaft it would tell a lot- might be a shaft bearing seizing up or the weed eater head unit.
Something is obviously not right, and there is not much more to do with the engine but back out the H screw 'till it falls out:confused3:

 

[canucklehead]

I am using something like 0.80 string....pretty medium duty for one of these. I hear ya on the shaft binding up with crud and I'll double check that. It does get wound up and I'm always cleaning it off. I remember my brother giving that area a good scrape but I'll look better. How complicated is it to remove the head?

 

[sd455dan]

I have an Echo SRM2100 straight shaft weedeater. Started acting up in June/July and I replaced fuel line, fuel filter, and cleaned carb twice. I also cleaned spark arrestor (screen) & the muffler. Muffler & screen were both very clean already. Checked compression and it is 120-130.

After carb cleaning, it seemed to be better, but soon after it got worse. I thought maybe carb diaphragm was worn & local repair shop said that is like the fuel pump. Found it almost as cheap to buy a complete new carb vs a rebuild kit, so I bought a new carb. It was better but I can't get this to hit the high notes and scream like a 2-stroke should. Doesn't matter how much I play with the "H" screw, it will not rev as high as it should. I'd say it sounds like 3/4. The adjustment screw is almost all the way in to get best response (maybe 1/4-1/2 turn out). More out I turn, it stalls.

When muffler was off and I could see piston, I carefully scraped away a bit of carbon/crud build up, but it wasn't too awful. There was also something that looked like a jet by the exhaust port..it had some black crud. Tried spraying it, but not sure I did much to it.

I bought new gaskets for intake as I thought maybe it was sucking air. I have NOT installed them. Local shop said if sucking air I'd rev higher. I tried spraying WD40 around intake gasket areas while running (was told this would change performanace if there was a leak). No change.

Shop said these types of issues are usually related to hardened carbon deposits/buildup for exhaust. So where do i check that? How clean/resolve? I asked if i had to tear down head to clean that and they said no.

I googled searched and found an almost identical thread and that one eneded with guy saying it seemed to eventually fix itself. I'm stumped...

Have a similar unit JD240 built by Echo and have used it since bought new in the 1980s since you have already checked compression and carb and it must have spark , I would suggest removing the oil fill plug on the bottom drive unit .
Ours always eventually runs (leaks) out the oil and the friction goes way up , I started noticing the same symptoms that you described and filled the bearing unit with a mixture of mobile one extended performance oil with a small amount of STP oil treatment,.
My son needed it to do a drive way for a family friend and had used it a couple weeks earlier at the same place , when he got home he asked me what kind of tune up or rebuild I had done- and I asked him why . He said although the trimmer had worked OK the earlier time , that now it SCREAMS and totally shreds the vegatation ... IT was all related to the friction in the drive head.
MY :2cents:

 

[radioman]

I have a 4 cycle troybuilt trimmer that after 1 summer of use, it would die like you say and not get the high revs. either. I would take carb apart EVERY time I use it since I couldnt rev it. and trying to squeeze trigger would stall it. Taking carb apart, clean membranes and carb, reassemble solves it till it clogs again. The tank appears to be clean, even after emptying and using fresh gas from store/filtering before pouring. I went thru this scenario more then several times and it finally stopped and worked normal. :confused3: Maybe - just maybe you need to reclean carb? Those small engine carbs have really small jets compared to let say your bike.

 

[Gary Fowler]

I had an old Poulan string trimmer that did that. Cranked perfectly, idled good but wouldn't rev up. I cleaned carb, ran Seafoam 50% solution and nothing. Finally took it to a repair shop and they removed some baffles in the muffler. Said it was all carboned up from running at too low RPM which I was doing a lot weedeating around my fence and some rocky areas. Runs like it should after cleaning the muffler.