Echo SRM-266 won't accelerate for 2 minutes until warm and then runs fine.

jim45

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My Echo SRM-266 string trimmer is about 2.5 years old and has developed a problem. It is easy to start and will idle indefinitely but will not accelerate (bogs down) until it has warmed up for a couple of minutes. Then it works fine for as long as I want to use it, typically 2 - 3 hours at a time. I've rebuilt the carb and the exhaust spark screen is clean but nothing I have tried eliminates the problem. Is there an ignition module problem that can cause this? It's still under warranty but the Echo repair places are backed up for weeks and I need to finish weed whacking for the year so I can't afford the delay of taking it in right now.
 

jim45

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Thanks for the reply. I tried everything in the troubleshooting section of the user's manual before rebuilding the carb. The fact that it runs great after warming up has me baffled. That means that none of the filters, screens or carb passages are blocked and the spark plug is working fine. The only thing I can think of is that the ignition module has some sort of timing retard feature built-in that retards the spark for starting and then goes to normal timing for high speed operation. I can't find any info on that possibility. I haven't checked the compression but I don't think it would start so easily if it was low or run so well after it warms up.
 

bertsmobile1

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Sounds like it has worn a little and the balance between the idle jet & high speed jet is off a bit and needs adjusting.
FWIW then tuning you are supposed to leave them idle for a FULL 5 MINUTES to ensure that the carb & engine has reached a stable operating temperature.
Personally I would not worry about it.
Your problem could also be a change in the fuel formulation at the bowser.
This is one of the reasonas why so many top shelf hand held makers supply fuel in sealed containers because the locally available fuel can vary wildly day to day.
 

jim45

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Sounds like it has worn a little and the balance between the idle jet & high speed jet is off a bit and needs adjusting.
FWIW then tuning you are supposed to leave them idle for a FULL 5 MINUTES to ensure that the carb & engine has reached a stable operating temperature.
Personally I would not worry about it.
Your problem could also be a change in the fuel formulation at the bowser.
This is one of the reasonas why so many top shelf hand held makers supply fuel in sealed containers because the locally available fuel can vary wildly day to day.
Echo seals the jet adjustments on the carb so they are very difficult to get at. I was thinking that since it accelerates well and runs well at high speed and full power after warming up that the mixture is okay. We actually have two SRM-266 trimmers and the other one is running fine using the same fuel and oil so I think that's not the problem.

I've spent a lot of time looking on the web for info on 2-stroke ignition modules to see if they do typically have an ignition retard function that retards the spark at very low speed, like when starting, to make it start easier. At 10,000+ RPM I think the spark would have to be well before TDC in order to run well but I don't think that would work at very low speeds. If they do have a retard function, and it sticks somehow in that mode until the engine warms up, that might explain my problem.
 

bertsmobile1

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I can see you are now fixated upon the coil being defective so it will be a waste of time going any deeper into the trimer.
The engine should always be allowed to fully warm up before it is used.
No hand held engine will start then accelerate to full speed until it has warmed up.

If you brought that trimer into my workshop you would get told to go home & not worry about it because it is functioning within normal operating parrameters.

As to the Hall Effect trigger chip embedded in the coil , yes there is some spark timing done on the chip.
Usually they are parallel circuits with lower resistance to reduce the lag in the spark.
If you really want to know what they look like Kawasaki & Kohler both publish the trigger wiring schematics.
It is a moot point as it is a chip is not servicable

As for the caps on the jets.
They are an EPA requirement to prevent your average fool fooling with the jetting.
You can not properly clean the carb without removing the needles .
OTOH is it comes into a Echo workshop with the plugs removed then the warranty is also removed.
 

jim45

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Thanks for trying to help. This is our 4th Echo trimmer in the last 15 years and only this one shows this problem. We do let the engines warm up before using them but there's something different about this one.
 

bertsmobile1

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It really sounds like the idle jet is blocked and it is starting and idling on the high speed jet.
Rotary valve carbs will happily do that.
Or the idle jet has backed off a little so it runs a little too rich when the main jet kicks in.
In the latter case the fine droplets of fuel do not vapourise in the crankcase till it gets hot enough to evaporate them.
Remember that only GASSES burn.
A carburettor disperses five droplets of fuel into the engine and it is the heat in the engine that converts them to a gas.
Modern fuels are heavier than older fuels and contain just enough volatiles at room temperature to provide just enough flammable gas in the cylinder for the engine to start.
From then on you are using the heat in the engine to vapourise / evaporate the tiny fuel droplets so they can burn as a compressed gas in the cylinder.
Hence the 5 minute warm up.
if you take the air filter off and have a Captain Cook at the rotary valve chances are the odd one out will be open further than the others.
 

jim45

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Thanks for the detailed explanation, that makes sense. I noticed when rebuilding the carb that the rotary metering design is a little different than previous Echos I've worked on. Instead of having the little metal roller that rolls up a ramp to open the metering valve more and more as the throttle is increased it has a plastic bump that glides up the ramp. They probably had a lot of trouble with people losing the metal roller (very tiny) when working on the carb so they replaced the metal part by moulding a plastic bump into the same spot. Now, with a lot of usage the plastic bump, or the ramp, is worn and thus the metering is off. The carb rebuild kit came with a replacement metal roller but it was not needed in this version of the carb. However, I think wear of the little bump or ramp would reduce the fuel flow at high speed thus making it run less rich. Maybe a new carb is called for.
 

bertsmobile1

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A Tiny Tach is not particularly expensive and a worthwhile addition to your tool box so you can check the max RPM under full load ( String out to full length ).
If it is running way too fast (> 10% ) then the high speed mixture is too lean and will shorten the engine life.
 
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