# Replace Zama rotary carb with Walbro?



## FergusonTO35 (Jul 25, 2013)

Hey guys. I have an Echo SRM-225 weedeater with a Zama RB-K93 rotary carb. I think the high speed mixture needs to be a tad richer, today I'm going to remove the plug over the jet and see if turning the jet out a little helps. Some report it does, some report it does not. Anyway, I was wondering if any of the Walbro WYL carbs are a direct replacement. I see that Shindaiwa uses them on some of their machhines. You can get them on Ebay and other places pretty cheap and the WYL's look identical at least in design and construction. Anyone have experience with these? Can the WYL's be adjusted at all? Thanks!


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## FergusonTO35 (Jul 25, 2013)

Well looks like I won't have to replace the carb. I removed the jet from the carb, cleaned it, and reinstalled. I then ran the weedeater and found that this jet functions the same as the high speed needle in the older carbs. A bit of tuning and its now running great.


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## LegDeLimber (Jul 26, 2013)

hmm, went to zamacarb.com and the page came up without a visible image displayed.
hit the pdf option to get "foxit reader" to open the pdf file, was the typically un-helpful 
"image not necessarily representative of actual part" sort of disclaimer (grumble).
couldn't see anything resembling an adjustment screw
and no mention or visualization of moving the needle in the center of the barrel.

If the needle has no threaded manor of adjusting, but isn't permanently
affixed 
i.e. molded into the barrel plastic or using some other method of confinement
For those lean conditions:
we may still have the option of "shimming" it upward
with some tedious method of disassembling, fiddlement then a trial run..
repeat process till satisfied....


If we've got a rich condition, obviously it's a bit harder to lower the needle
in a precise or repeatable fashion.
so often then you're into trying plug nozzles (epoxies, etc) and reopen
to smaller diameter with the same try it, tear it down again, assemble & try it again loop.


back in the days of dirt biking (you could purchase various carb parts then) people would even end up taking a larger (which would cause leaner mix)
and spinning it in a drill to facilitate very lightly sanding a butterfly kiss 
worth of metal off to re-contour the needle profile.

the way those old sliding barrel type carbs flowed meant the needle 
overlapped and affected a very wide range of the throttle range
( somewhere around 20% open, up to full throttle)
and we needed a lot of fine tuning for motorcycle operation of course
so thus the chasing of the shape and flow characteristics of the needle
and the emulsion tube diameter and shape, etc....

I think we'll find the rotary barrel carbs will respond in a similar fashion
as the old Mikunis and Honda's ubiquitous keihins

look at the way a starting lever raises the barrel 
(but not opening the effective venturi size )
to get the needle lifted for a slightly richer mixture for cold cranking. 
just gonna be a pain to work around the engineering/manufacturing efforts 
that are in place to prevent us from it.

If the barrel types are set up correctly, 
It's just seat of pants anecdote here, 
but I think they give better response and running
than our well known and loved shaft & plate type carbs.

just wish they weren't being morphed into a modern analog (correct term?)
of a Tecumseh fixed jet/body orifice, 
no choke gotta use the damn punch-bubbles carb 
of the later Craftsman products before Tecuseh went under.

Hopefully I've stirred some helpful contemplation of the little buggers
with my missives here.


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## FergusonTO35 (Jul 26, 2013)

Fortunately my machine has no problems at all with starting, idle, and initial acceleration. The problem I was having is that it sounds and acts lean. When you squeeze the trigger it will rev to the stratosphere but has no torque, bogs in heavy grass. I know these machines are lean from the factory and I'm sure the wear on the diaphragms over the years has increased it. Also, I have used 36:1 mix for years with perfect success. Echo presumes you are going to use 50:1. Alot of folks say that more oil causes the engine to run leaner. I don't quite agree with that but I do believe it is always best to tune the machine to whatever mix you are using.

am referring to the jet/needle (seen it referred to both ways) that is on the same side of the body as the primer bulb with a plastic plug seated over it. It can be seen in the carb parts diagram for the SRM-225. I think what it does is control how much fuel is delivered to the jet inside the throttle barrel under high speed, it does not have its own orifice into the airstream as the butterfly types do. This jet looks like a mini version of a screw in jet for a float carb. I tuned it so that the engine has light 4 cycling at free speed which goes away when cutting grass. Works alot better now and is very enjoyable to use.


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## LegDeLimber (Jul 26, 2013)

good to hear that you got it smoothed out.

Wondering if we all need to start posting pics of these carbs when we're working on them
as it seems like I'm running into more dead ends with the newer carbs 
when needing pics or info (makes a fellow suspicious of why that is)

kinda odd when something like a carb on a four year old machine 
pulls up a "discontinued" and the page/diagram is no longer available...


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## FergusonTO35 (Jul 30, 2013)

Where are you finding a 4 year old carb discontinued? With Echo, at least, the parts and diagrams are everywhere. I learned how to fix mine from YouTube videos.


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## LegDeLimber (Jul 30, 2013)

My memory is going fuzzy on me (nother story of it's own)
but seemed like it was Poulan "box store" model.
I've gotten so that if a neighbor asks me to look at something
I'll tell them let me look it up for parts availability before I'll even touch it.

granted some stuff uses a common kit or a carb can be swapped 
if you change throttle shafts etc.
But sorta pointless to track down a suitable carb and do all the changover
when you know they'll just let it sit with e-gas in it as soon as you hnad it back
and corrode the new carb.
Tell them were to get the non e-gas but soon as they find out 
it's hihger price they go to the e pump.

Have you noticed the ryobi/homelite carbs are being superseded
over to those ruxing (rue-thing ?) carbs.
and No ones got a kit for the ruxings, just selling the entire carb only.

If you find a vendor listing for the original walbro or zama for the trimmer
they're often wanting crazy money for it (especially walbros)


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## FergusonTO35 (Jul 31, 2013)

Most late model Poulan and Weed Eater machines use the same interchangeable Zama and Walbro carbs. There are a small, one needle series used on the Featherlites and a larger two needle series used on the larger ones. I find they are readily available from alot of different places, such as Ereplacementparts.com and Parts Tree. As to Ryobi and Homelite using Ruixing it makes sense they would do that as they are chicom throwaway anyhow.


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## LegDeLimber (Aug 2, 2013)

Yeah, kind of a pisser that you can't get a ring or piston
for the late model 26cc stuff.
Just the "short block" only in the ipl and it's as much as tossing the P.O.S.
and getting another one.

I like the old 30cc stuff though.
My old Homie pse-3000 stick edger that I grabbed new for $36 
and converted to a trimmer has run well. 

Last year I grabbed a WT-628 for it, expecting an 11mm venturi
(per Walbros site no less) and actually it's about 8mm
Price was too cheap to justify returning.

...so I "wallered' out the venturi a bit and while the plates were out,
I soldered over that stupid hole in the choke plate
and then crimped and soldered the primer pipe shut.
no more punch-bubble plague!! 

The old Homie's a single piece tube vs the two piece multi-tool ones 
and is smoother in the hands than any other cable driven ones
that I've messed with.
I'd put it about on par with the lower end solid shaft drives
that I handled back when I still worked in a shop.
I pull the cable and give it a good wipe down & relube at least once a year.
But then I've noticed a fresh greasing seems to make any of them feel a bit better.

Loaned it to my neighbor once** and took me ten min of standing there
telling the guy it's not for sale when he was done.

**getting a few favors in for when my knee work happens in a few more weeks.


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