Most of the Echo machines I work on have the Zama RB series carburetors, I find myself looking at an absurd rate of failure with these carbs. The zama RB-188
(needle included) kit, which works for most carbs in the RB series, comes out to about $10
(USD) each. While the GND-106
(gaskets and diaphragms only) works for some in the series and comes out to $8 each, some carbs respond to a simple rebuild, others do not.
People bring me these aftermarket carbs to put on their machines and they honestly have a 50/50 shot of working. People see the price of a OEM carb, get sticker shock, then see a aftermarket carburetor priced about the same as a kit, but don't want to bother getting a kit trying to rebuild it and still have it not work, so they get the carb.
That's fine, but these aftermarket carbs I've found either show-up DOA or have a limited life and then fail like the OEM carb would: Bogging, can't run off choke, excessive flooding or leaking fuel, sometimes you get a good one, it all works out and everyone's happy, other times... not so much.
While you can adjust both the OEM and aftermarket carburetors to try and make them run better, which can sometimes solve the problem, you have to constantly go back and forth on the needles as they're real touchy to adjustments, so little 1/8 turns is the way to go.
But if an RB series carb is on the way out, it becomes governed by what I like call "The Rule Of Four" where you can ONLY adjust the needles four times before you push it over the edge and you can't adjust it anymore and it fails completely. So you have to get good, like... OCD good at adjusting it.
Now as I said earlier, some respond to a rebuild and others do not, and it took me
AGES to figure out the reason why these type of carbs fail so.
After ruling out an air leak of any kind and all other possible things under the sun, numerous RB carbs (killing a few) and descending into madness, in the end... I did not come out empty handed.
It all lies down to the main nozzle check valve, which thanks to design is just under the main jet, and is UN-serviceable. Because of the use of cheaper materials in the manufacturing process, this check valve is quite weak and prone to failure and thanks to ethanol laced gasoline, it's a death sentence for it. I've noticed for those that use the engineered premixed fuels, it does last a little longer but it's just a matter of time.
The classic symptom I've found is an overfilled purge bulb, I'll see it swollen with excess fuel and know that even if it runs now, it probably won't down the road. The check valve either gets gummed up or fails outright, sometimes a good soak in WD-40 overnight or cooking it in a ultrasonic cleaner for awhile might free it, but if it does you got lucky... and the clock starts again.
Because the valve has failed it'll leak fuel, flooding the engine royally, spilling out the muffler even while running, you'd think it's the needle or spring but no. As the engine runs and everything cycles though the carb and bulb, it'll suck in air unregulated pumping excess fuel to the metering chamber and will over-power the needle & spring or bypass it completely - flooding the engine, or if the valve is failing/gummed and not working properly, it'll bog, become unresponsive to rebuilds or adjustment, all because it's failed and there's nothing to regulate the fuel/air flow in the carburetor.
Here is a schematic of the Zama RB series to maybe help visualize what I've rambled about
The conclusion I've come up with is: you're either damned if you do and damned if you don't.
I try to get as much as I can out these carbs, because in the back of my mind, is the thought that every aftermarket carb I send out might come back later and some have.
(maybe it's just luck?) And no one wants to pay
(I don't blame them) for an OEM one
, just to have the same problem later. It's just not practical
(economically) or even feasible in my location.
(echo dealer service here is... difficult)
