Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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Old 05-03-2010, 01:27 PM   post #1 of 8
hydrosmurf
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Default Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

This is going to be two posts in one.

A used SRM-210 trimmer was given to me in a non-running state. I removed the carb, and gave it a good cleaning with carb cleaner, but I stopped short of removing the metering lever and needle. With the information I found on this forum, I was able to locate the mixture screw (high speed needle) with the plastic cap on it. This particular carb only has one adjustment screw. I removed the cap, and I was able to turn the screw with a regular driver, but I was unable to remove the screw completely because of what looks like a brass insert. I didn't know what to do at that point; so, I decided to put it back together while I still remembered where everything went. Once I got it back together, it fired right up. Yeah!

However, it's running lean. It has been starting right up, and it will idle perfectly, but it struggles to reach full speed. Even when it does eventually get there, it surges up and down. Right now I have the high speed screw turned all the way out (turning it in makes it run worse). The top of the screw head hits the bottom of this brass insert preventing me from turning the screw out even more, or ideally, from removing the screw and blasting the opening with carb cleaner. Below is a break down image of my carb. Item "10" is the plastic plug, and item "11" is the high speed needle. The picture doesn't show the brass insert. On the ZAMA website, they have a parts breakdown of a generic RB type carb, but they call it a "main jet" and they say to remove it to clean it. They say to inspect an O-ring, but I didn't see one of those.





What do I do? Do I try to get rid of this brass ring so that I can remove the mixture screw? Has anybody been able to remove this screw to clean the carb? Should I just buy a new carb for it? I new carb is going to run me $60.00, how do I know if that is going to be worth it, ie, how do I tell if the rest of the trimmer is going to last $60.00 worth of carburetor?

Is there some other trick to go about this? I have spent a lot of time on the internet trying to find the answers, but it seems like nobody has ever been prevented from adjusting the mixture screw enough to make the trimmer run correctly.

I had a look at the store, and the new Echo trimmers have carbs that look exactly like mine (single mixture screw with a black plastic plug covering it).

Any help with this would be greatly appreciated.

So after using the trimmer for about an hour today, (it is somewhat useful) I noticed something that I haven't before. When the trimmer is in the normal position, that's when it doesn't rev up to full speed without bogging and almost stalling. When it's sitting on the ground (when I'm adjusting the high speed screw) it revs up pretty good. When I have it rotated 90 degrees from normal to edge along the sidewalk it works well too. After I realized this I turned it upside down and it also works pretty well. This I thought was strange. It has nothing to do with the fuel filter not being in the fuel because I checked for that. What else could cause this?

The reason I haven't bought the rebuild kit for this yet is that I don't know for sure that it is going to fix it. I remember reading that there is a non serviceable check valve somewhere inside the carb. Also, if I can't remove the high speed screw, how do I really get this carb completely clean? Should I just buy a new carb?

Has anybody experienced something like this and just had to replace the diaphragms to fix this?

Regards,

MP
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Old 05-04-2010, 03:30 AM   post #2 of 8
H-D
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

To me, a two stroke revs up faster (no load) when it's lean than it does when it's 'fat' (won't work & live long though). Since you don't know a good history on this engine, why not check the exhaust/muffler for carbon build up? I know that they'll run smoother/better with a fatter mixture when they have a 'cob' up their butt! The MMO treatment won't hurt a thing either.
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Old 05-04-2010, 09:13 AM   post #3 of 8
hydrosmurf
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

Thanks for the response. I did take a look at the arrest screen, and the exhaust port. The port looks fine -- maybe 0.5mm of buildup in some areas, and I didn't put the arrest screen back in. The weird thing is that it runs pretty well in different positions besides "normal operation." I don't know what would cause that.

MP
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Old 05-04-2010, 04:32 PM   post #4 of 8
H-D
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

I've had more than what I figure is my share of grief from deteriorated fuel lines on chainsaws & other small two strokes. Not the clunker filters themselves, but the actual line. Maybe the 'new' gas is going to be an issue here as well? I wouldn't know a Zama carb if it bit me, but I recall 'O' ring deterioration being a major factor in no/poor run conditions on another brand (Tecumseh?). In that instance, the 'O' ring sealed the discharge nozzle to the main body. Neoprene 'O' rings don't appreciate being immersed in 10+% ethanol (Viton is WAY better). Also, does your application pressurize the fuel tank? If so, the pressure line & tank cap enter the realm of possibility. One last try, the tiny flap valves integral to the diaphragms/gaskets stiffen without use. You might try soaking them in the MMO if you have it down again.
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Old 05-04-2010, 04:38 PM   post #5 of 8
sixbales
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

Try cleaning the fuel filter that's in the tank. Bend a small hook on a piece of wire and fish it out of the tank. Blow it out thoroughly and give 'er a go!

I've had good success in two cases by cleaning the fuel filter.
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Old 05-04-2010, 04:49 PM   post #6 of 8
hydrosmurf
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

This how much of a newb I am:

What does "MMO" stand for?

I did replace the fuel line with a clear line so that I could see the fuel running through it. It looks fine there. The vent, and vent line are still the old stuff though.

So if it runs well when it is upside down, then maybe it just needs some new gaskets and diaphragms?
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Old 05-04-2010, 05:21 PM   post #7 of 8
H-D
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

I'm sorry, MMO is Marvel Mystery Oil. Most grey beards have at least heard of it, regardless of their opinions of its merits. It used to have a distinctive sweet smell (35 years ago?) that I recall from a natural source from my childhood (can't remember now). Within the last couple of decades they changed the formulation to something that smells like 80% Dexron. If you have a little time to spare, search "Marvel inverse oilers". I'm cheap (& getting cheaper), so I try the cheapest alternatives first. As far as being new...do you realize how few grown men have absolutely NO concept of how ANY mechanical entity works, NOR any knowledge of basic maintenance??? Be PROUD you're NOT a yuppie (throw away *&^##s!!!).
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Old 05-05-2010, 09:25 AM   post #8 of 8
hydrosmurf
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Default Re: Echo SRM-210 Trimmer - ZAMA RB-K75 Carburetor

I like you am cheap. I've been learning this stuff so that I don't have to buy new stuff to replace broken stuff, or pay someone to repair my stuff. It's also why I haven't just bought a new carb yet. I don't want to spend the $60 if I don't have to. Even though I think I need one, I still might just try replacing the gaskets and diaphragms to see what happens.

I just wish someone on here knew how to clean out the high speed mixture screw/port thing on this carb.
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