Diaphragms

MiEchO1999

MiEchO1999

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Jul 24, 2026
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Echo GT2400 early model. Parts manual shows metering gasket first then diaphragm then cover. Google says diaphragm then gasket. Who is right. Using its engine grounded spark plug shows a small blue spark. How wide should it look like ? Wide or thin ?
 
Every cube carb I have ever worked on always had it gasket, metering diaphragm, and then cover. And the fuel pump diaphragm, gasket, and then cover on the other side. ignore spark width, and color because it can vary with atmospheric conditions, and even spark plug. It sparks that is all that matters.
 
Yes even the amount of salt (sodium) in the air can change the color orange like color similar sodium vapor lamps. Also every person color perception is slightly different.

Now the metering lever height setting is important as if set can either over rich or over lean fuel mixture.
 
Sorry but backing up a bit. Family member used several mixed gas tank fulls of very extra rich Seafoam. More is better ! Lots of dripping sticky oil out the exhaust. In cleaning muffler, combustion chamber, different sprays were used thru carb too. It wouldn’t start with new gas mix. Plug never gets wet but when grounded has a spark. Even raw mix dribbled in it won’t fire. New pump and metering parts put in and gas doesn’t flow thru carb. All orfices seem clear. With a hose and mouth pressure to line for metering with the needle Up how ez should it be able to blow thru. Compression seems 100psi. Cleaners may have washed rings clean but extra gas mix was put in to help. Still can’t flood it and doesn’t fire. Was still running before repairs.
 
First is the prime bulb passing fuel? If not then the primer base is likely faulty.

Compression seem like 100 psi and being 100 psi is two different things. And 100 psi is the bare minimum for a two cycle to ignite the fuel mix but it will still burn up the fuel on the wasted spark cycle. Anything below that is very very iffy if the engine will even hit. These Echo 2 cycles are usual around 130+ psi.

In my 17 yrs of working on the 2 cycles I only seen one that would start and run at 90 psi and that wasn't very good.
 
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I suspect that the various cleaners put through the carb has swelled the rubber disc inside of the check valves and now they are basically stuck shut. Maybe new carb time since getting them to unstick is hit and miss, and if you do get them unstuck the may stick open which will prevent priming.
 
Thanks to all for the helpful info. I still wonder about blowing by mouth thru the fuel inlet with the needle lifted to flow thru if it goes thru easily or not ? Are the check valves hidden to look at ? Yes several u tube vids agree that the gasket is first then the diaphragm next like you said.
 
There are at least five check valves.

Two fuel pump. They on the fuel pump diaphragm.

Main nozzle. Internal
Two primer. Semi internal

If main nozzle check is stuck open you will not be able to primer as there is no vacuum to operate the metering diaphragm.

Stuck primer check valves will let the primer to suck fuel mixture in and thru the cube.

When it comes to bad check valves it is time for a new carburetor.
 
Update time. Yes it can still run ! I found another carb that looks a little rough but it will start and run again. Maybe with a little tender adjusting it can all workout. Tks for all of the suggestions.
 
By the way, if you lift the needle, it closes the valve. Lower the float to open the valve.
 
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