Zama to Walbro swap

[Dead Eye]

Hi everyone,

I'm new to this forum, and well, pretty new to forums in general. Anyway, I've got a Stihl FS-55r that I bought brand new back in 2008. From damn near the first day I've had nothing but trouble with those Zama carbs that Stihl insists on using. They've been through countless revisions and supersessions and still can't get it right. My question is this: Which Walbro fits this trimmer? The Zama I have currently is a C1Q-S186B. It looks like a Walbro WT series is going to be the answer, but which one?

 

[AVB]

Just what kind of problems are you having?

I never had problems with any of the Zamas that Stihl subbing. Except for needing a new 4mm adjustment tool.

Now the those darn clones that are on Ebay (Ripbay) I had nothing but problems with them.

 

[Dead Eye]

The trimmer has always been a beast to start. But the biggest issue I see with them is their piss-poor check valve design in the purge plate. The tiniest piece of trash will clog them, and then that's it; it won't prime. I have a cheap Weed Eater hand-held leaf blower that has a Walbro on it, and I've never done squat to it except adjust the mixture and it's worked great year after year; even with old gas.

 

[AVB]

Trash shouldn't entering the carburetor via the fuel in the first place. That is why there is the fuel filter on the line and the carburetor internal filter screen. As for the primer check valves design they are basically the same on the Walbro.

Here in my shop my biggest problem with the carburetor mounted primers is with those so called techs that use a wire probe and damage the flat rubber valve by poking thru it or completely poking it out. Also the use of compressed air will damage them along with carburetor cleaners. In the 7 years I have been working on the Walbro and Zama carburetors I had only 3 primers that failed. Even those that were fully clogged with old dried fuel are usually cleanable. I have more problems with the Walbro external primers. Btw they use the same check valve design too which is a flat piece of rubber that is spring loaded.

The only thing I use to clean carburetors is soap and water in my ultrasonic unit. Of course I pre-clean the carburetor exterior with fuel mix to remove excess trash and dirt. I simply don't use carburetor cleaner in those compress gas cans nor a dip style cleaner as they will damage the plastic and rubber parts.

 

[Dead Eye]

Well, there's always some garbage in today's gasoline, no matter what you do. As for the check valve design that's underneath the primer bulb, Zama uses the two tiny holes with the little flaps, but Walbro uses that mushroom looking thing; which is brilliant yet simple and almost never clogs.
In any case, I'm done with Zama. My original question has yet to be answered: Does anyone know which WT series Walbro will fit on a Stihl FS 55R ?

 

[backhoelover]

I'll check stihl when I get home. Thinking 55 is zama carbs only

 

[Dead Eye]

I'll check stihl when I get home. Thinking 55 is zama carbs only

 

[Dead Eye]

Yeah, that's what I've been seeing in various catalogs that I've been able to download. However, I've seen a few Walbro WT carbs that have the same configuration as far as bolt pattern, linkage, pulse port, etc. The issue seems to be that the bore and venturi are smaller. This Zama I have is a 14mm bore with an 11mm venturi. I'm thinking it's not a good idea to go smaller.

 

[Lightning Performance]

I went down in size on an HT101 pole saw. Didn't know it at the time. Ran OK. Lacked top end. No big deal. It's great on fuel.

 

[Dead Eye]

So, any other suggestions? Anyone?

 

[Dead Eye]

Yeah, I feel like I shouldn't have to screw around with this thing as much as I have, especially considering the kind of money Stihl charges for their equipment. I guess if I can't find a suitable carb upgrade then I'll just reinstall oem, clean it up, and sell the POS.

 

[Lightning Performance]

I tuned a 110 trimmer 3x's. the guy got pissed and sold it. He bought a 13? model and loves it. Vacuum test it and pressure test it too. Could have a bad seal or blown cylinder base gasket.

 

[Dead Eye]

You really think the engine has an issue? I mean, don't get me wrong, I'm not ruling anything out. It's just that this trimmer doesn't have very many hours on it despite it's age. In my 30+ years of small engine experience, 8 times out of ten the problem is fuel system related.

 

[bill saf]

I have a 55R trimmer and that zama carb has a sweet spot to start ez. heres what I did to mine pull the screen out of the muffler pull the caps on carb and adjust the l after its running and comes up to temp fatten it up some. I hit the primmer on mine 2 times and start in 3-4 pulls wot. If I prime it any more it will flood. just my 0.02 worth

 

[backhoelover]

I have a 55R trimmer and that zama carb has a sweet spot to start ez. heres what I did to mine pull the screen out of the muffler pull the caps on carb and adjust the l after its running and comes up to temp fatten it up some. I hit the primmer on mine 2 times and start in 3-4 pulls wot. If I prime it any more it will flood. just my 0.02 worth

+1 all units are set lean from factory