# Echo hedge trimmer engine problem



## Dimark1009 (Nov 2, 2006)

Hey guys, got yet another 2 stroke question for you... 

A customer brought me in an Echo hedge trimmer model HC-180. 

you guessed it, it wont run. 

The fuel is fresh, got spark checked all the obvious. It has a Zama RB4 rotary carb. on it. 

at first it seemd like a fuel delivery problem, it would try to start on a little fuel mix shot directly into the carb.So I immediately thought carb problem. took it all apart cleaned it, wasnt dirty at all. 

I checked the spark arrestor, not clogged. It still only pops if you squirt fuel into the carb throat, but it takes a lot of pulling just to get it to do that. 

I did a compression check, got 120 # both times. It is getting fuel to the plug now. 

the only thing I didnt do was check for air leaks, but I thought on a 2 stroke an air leak would make it run wide open , not prevent it from starting.

what am I missing? I can get Ryobi, weedeater, Craftsman and all the bottom of the barrel stuff to work, but I dont seem to have any luck on Echo stuff.

cant figure why... 

Thanks,

Mark


----------



## 30yearTech (Sep 14, 2006)

No, an air leak in the crankcase can prevent a 2 cycle from starting. It depends on the size of the leak as to what affect it will have on an engine, but generally will not make the engine run wide open. A large leak (such as a crankshaft seal that has come out) will prevent the engine from drawing any fuel into the cylinder.


----------



## mopar4u (Jul 14, 2006)

do a leak down test


----------



## Dimark1009 (Nov 2, 2006)

Yes, my next step was a leakdown test, Thanks Mopar. I just have to figure out how to get the "plastic" apart to get the muffler off. 

30yeartech (or anyone for that matter) Has anyone else had bad/marginal results working on Zama's rotary carburetors?

I have cleaned/rebuild many a carb Walbro/Bing etc...

I just seems every time I work on something with a rotary carb it becomes a problem. all the internals seem the same as a normal diaphragm carb. but never got 1 to work quite right. 

I dont think thats my problem on this machine but jusy in the past. 

is there anything special about those rotary carbs?


----------



## dawgpile (Apr 28, 2008)

Is the purge(primer bulb) system working OK? In other words, are you able to press the purge bulb and get fuel fully through the system? Also, is it possible the carb was disassembled and re-assembled improperly or with a part missing? The rotary carb has a few extra small parts along with the classic issue of getting the pump and metering diaphragms and their respective gaskets in the right order. Might be worth a double check if you rule out an air leak. Here is a parts diagram link in case you don't have it. Keep us posted and good luck!

http://www.m-and-d.com/zama_carburetor.html


----------



## Dimark1009 (Nov 2, 2006)

*Leakdown test next...*

Thanks Dawg,

I took the carb apart to check for restrictions , 99.9 % sure its back together right.

when I push the purger bulb I can see the fuel moving thru the lines. Just to make sure I'm correct on something, if you look in the tank and see the return line from the carb. you should see fuel coming out of the return hose and pouring back into the tank when you press the bulb? the bulb is full of fuel. 

how do you guys normally blank off the carb and exhaust to do a leakdown test? 

just slide something between the motor and carb/muffler and retighten? 

put the pressure into the spark plug hole? 

put the piston at TDC or BDC?


----------



## 30yearTech (Sep 14, 2006)

Dimark1009 said:


> Yes, my next step was a leakdown test, Thanks Mopar. I just have to figure out how to get the "plastic" apart to get the muffler off.
> 
> 30yeartech (or anyone for that matter) Has anyone else had bad/marginal results working on Zama's rotary carburetors?
> 
> ...


Yes, rotary valve carburetors can have issues that extend beyond the diaphragms and internal components of the carburetor. The rotary valve itself is subject to wear, there is a ramp that on the valve that lifts the valve as it rotates. There can be wear in the ramp that prevents the valve from lifting as it should and can cause a lean run condition. There can also be wear on the valve itself as well as the needle and nozzle. 

This is also true for Walbro rotary valve carburetors.


----------



## Dimark1009 (Nov 2, 2006)

so, if thats the problem is it easier to just replace te whole carb? 

how do you go about diagnosing if this rotary part or ramp is the culprit?


----------



## 30yearTech (Sep 14, 2006)

Yes, it's easier in most cases to replace the carburetor assembly. The rotary valve is available separately, but by the time you replace the valve and install a kit, you are pretty close to the price of the carburetor...

If the valve is bad the unit will usually start, but it will just not run well, bog down with no power.


----------

