# Questions about Stihl Zama Carbs



## quid_non (Nov 13, 2007)

Been wrenching around with my old FS 130 (see recent thread) and an old FS 90. The FS 90 continues to be very hard to start and sometimes wont start at all. I checked/reset the valve clearances (both had a bit excessive lash). That may have helped some but still hard to start. Good spark (bright blue) with tester and plug in. Decided to check carb - replaced with another carb I had around the shop. I noticed that both carbs are Zama C1Q bodies but have different IDs. One was C1Q-S173, one was C1Q-S110 and others I have from past rebuilds/replacement were C1Q-S98 and C1Q-173 another is a C1Q with no other ID. They all look identical. I likely mixed up my carbs for FS-130 and FS-90 over the years. Went to the Zama site to learn a bit more and got even more confused - evidently the ID number refers to the venturi size for this series? Stihl part numbers are 4180-120-0601 thru 4180-120-0610. 

Can the FS 130 and FS 90 use the same carb even though the FS130 is a larger in terms of displacement? Where is the venturi located on these things?

What else would be good to check for the poor starting of the FS90 - exhaust screen is clean, new mix, new plug.


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## paulr44 (Oct 14, 2008)

Okay, you've stepped into the twilight zone. Stihl bamboozles me as to why they have like 3, 4, 5 or more carbs. per unit. 2-strokes went through port timing changes, that's understandable. And other times it was for EPA limiter cap complaince. Else, twilight zone.

Hard staring on a 4-mix motor after stale fuel, water in fuel, fouled plug, plugged ex. screen, fuel soaked a/filter (leaky tank vent or carb). Those are the basics. Valve lash usually (unless insufficient which we've been seeing on some new HT131's up until late) won't affect starting other than giving you a hard time pulling it over. After the basics, bad carb., or on rare occasions bad coil. A bad coil often won't advance timing, after hard-starting engine will lug on throttle up, sound like it's laboring. Rare, but happens. A sheared flywheel key will also give similar symptom.

And of course, if the primer bulb won't return the fuel filter or carb. screen is most likely plugged save for other carb. restriction.

Spark should ALWAYS be tested with a proper test device, having a gap of about 0.150", as a spark plug outside the cyl. doesn't provide the necessary load on the coil. Search my previous posts, I've stated this many times.

Now, I want to point out Stihl used to give you a 0.1mm feeler gauge and a rocker cover gsk. with new units years ago, as you CANNOT re-use the gsk. Any CC leaks will prevent the fuel pump from working right. Won't affect starting if you primed it, but will affect running. We've also seen the fuel pump impulse hose (that fat hose under the carb.) harden and leak as well. Just so you're aware of things...

Years ago, I did the research. FS 110 and below use the ...0611 carb., FS 130/131 use the ...0610. This keeps my stock simpler. Forget all the C1Q #'s, go with what I'm telling you, it'll be fine. That is not to say they might need tweaking once installed, and you need a special screwdriver that technically we can't sell you due to EPA laws (and yet you can find them on Amazon/Ebay, go figure).

I'm at a loss, "where is the venturi?" Are you having a bad day? It's that big FN hole in the center.

AND for those of your reading this working on anything made withing the last 3 yrs. such as an FS91, FS 111 the carbs. I list aren't appropriate.


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## paulr44 (Oct 14, 2008)

And BTW something else I've mentioned in previous posts, Stihl bought Zama years ago, and many of their carbs. aren't listed as they're proprietary. Also, they're usually cheap...most under $60, many under $35. Not all, but many...


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## quid_non (Nov 13, 2007)

Thanks - the distinction on the carbs helps. That said, I thought I knew what / where a venturi was...I certainly appreciate how it works. What confused me was doing a little digging on the Zama site:
Zama - Welcome to the ZAMA Group
for example - - Scroll down to C1Q - S131 and hit the hyper link
there it lists the rebuild kit# (RB-165) and the venturi size (13.5 mm). Now if I go t measure the venturi on the carb (either inlet or outlet side) with a caliper - I get significantly larger (~15mm even at the narrowing inside), Not much of a difference but wanted to make sure I was in the right area. So with that said, indeed the two carbs I mixed up (FS 90 vs. FS130) differ in venturi size with the 130 venturi larger. That makes sense since it has a larger displacement and needs more fuel?
I am now a TOTAL believer on your comment re: install a new valve cover gasket after adjusting the valves - I spent way too much time trying to figure out why the unit was NOT getting fuel past the carb - turned out to be a slightly leaky valve cover gasket... as soon as I replaced it the problem went away.

btw... add the FS131 to your list of non-appropriate carbs? Stihl makes a big deal about these units using a pleated air filter vs. the older foam insert.

Thanks again for your insight and time - points well taken. I'm off to the "Outer Limits" now!


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## paulr44 (Oct 14, 2008)

1. The venturi is the smallest point in the throat of the carb., not the opening at either end. Look up Bernoulli effect.
2. The pleated air filter belongs to the new series of units, which I was referring to as being made in the like 3 years. The newer 4180 series engines have several visible distinctions over the old type, such as a concealed spark plug/boot, with a separate access panel in the engine cover. The fuel tanks are 30% larger as well. The recoils are different too.
Also, many of the newer units in general have the push-in and twist choke which also bumps the throttle open a bit.
I haven't worked out the new unit carb. applications, haven't had to change enough to be pain to look them up.
3. You are correct about the FS131, I had HT131 in my head. The FS131 is the new type, while the HT131 was discontinued (replaced by the HT133, also discontinued), then brought back with the new type engine but maintains the same model number. Old HT131 and FS130 uses the 0610 carb. Funny how the lower P/N services the larger engine.
BTW if you work on Stihl 2 strokes like the FS/HL94 units, those carbs. went through a change too - easy distinction, old type has primer bulb on top, new type in front.


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