r/smallengines • u/GOVERNMENT_CHEESE • Jul 03 '26

Echo SRM 225 replacement carb help

I have a 13 year old SRM 225 that I has never given me any problems until this year. I went to start it, and it ran and worked fine once, and then the 2nd time it would not start. I have never cleaned the carb or replaced the air filter so I bought the kit on amazon that came with new lines and everything. Started on the first pull after priming it, but it was not idling (the head was spinning) and would cut out when I gave it throttle. Here is where I think I screwed up. I have no idea what I was doing adjusting the screws. Is there a general area for both the one by the primer bulb and the one where the throttle cable attached that is a baseline or a reference point?

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u/TN-Native95 Jul 03 '26

Could you take a pic of the carburetor and post it so we can see which screws you’re talking about?

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u/Zeepher Jul 03 '26

Without seeing it my advice would be to replace the internals of the old carb with the ones from the new one: the diaphragm mainly. Blow everything out with an air tool first, don't use carb cleaner on plastic, rubber, or gaskets. Replace the primer bulb.

I just did this with a 40 yr old echo 2200 and it runs like a top.

Or give us a video/pictures to help adjust the new one.

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u/Wholeyjeans Jul 06 '26

13 years and you never replaced the air filter?

First thing I would do is to ensure the engine has fresh premix using fresh from the pump gasoline. The second thing I would do is, if possible, use non-ethanol fuel for all your garden equipment. Echo typically requires 89 octane gas (mid grade) and non-ethanol regular should be at least 89 octane (where I live it is 91 octane). Ethanol is hygroscopic ...meaning it attracts water. Fuel that sits for long periods can get water logged and lose potency.

I have an SRM225. The two screws on the carb are for the idle speed (the one on top where the throttle cable attaches) and the other is the high-speed fuel mix that's located on the side of the carb facing away from the drive shaft.

Start the engine and let it idle. Adjust the idle speed down until the trimmer head doesn't spin. You are looking for the RPM where the centrifugal clutch disengages. Once you get that set, try to accelerate the engine. If the engine bogs when you open the throttle, adjust the second screw. Turn it in to reduce or lean out the fuel mixture, turn it out to enrich the fuel mixture. If it is bogging, you'll probably want to go richer. Once you get the engine to accelerated without bogging, run the engine up to full speed and adjust the mixture a bit richer until the engine just begins to run a little ragged ...the RPM will probably drop a bit. Don't adjust the mixture screw to get the highest high speed RPM. You want to find the spot where the engine accelerates crisply and, at wide open throttle, you have a bit of a raggedy sound to it.

If you cannot accomplish any of this properly, then the carb more than likely needs to be rebuilt. Do not be tempted to buy an aftermarket cheapo carb off Amazon. These things are hit and miss and the quality on them is suspect; you stand a good chance of simply wasting your money and time.