MS200T Zama C1Q-S126 Troubleshooting

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sven556

sven556

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So I have three carburetors that I have removed from ms200t saws that weren't running, all zama C1Q-S126. I've rebuilt two of the saws and put on brand new oem carbs, and the other usual rubber bits, and they are running great. As I get more into working on saws I want to learn more about how these carbs work; so I don't just clean them, throw a kit in them and hope for the best. I do know about the accelerator pumps and I'm going to try the "accelerator pump delete" mod, that has been posted on this forum many times, once I can determine the rest of the carb is good. Before I do that I want to check the rest of the carb, from what I understand it is mainly that the check valves are working and the needle seals. I will put in a new carb kit. Here is a photo of the carb:View attachment 20211130_172727.jpg
The main nozzle (one that goes through the body at an angle) I can test with a piece of fuel line over the hole and the high needle closed and air will go through but not be sucked back through, on all three carbs. Is that the correct way to test that valve without removing it? The hole in the center is also a check valve right? I can't get any of these to test. I did remove the welch plug on one carb and it looks like there is a hole from under the plug to that check valve that is letting air through. How can I test this valve? Thanks!
 
Woodslasher

Woodslasher

Make McCulloch Great Again!
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@lone wolf
20211130_172727-jpg.945296
 
lone wolf
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So I have three carburetors that I have removed from ms200t saws that weren't running, all zama C1Q-S126. I've rebuilt two of the saws and put on brand new oem carbs, and the other usual rubber bits, and they are running great. As I get more into working on saws I want to learn more about how these carbs work; so I don't just clean them, throw a kit in them and hope for the best. I do know about the accelerator pumps and I'm going to try the "accelerator pump delete" mod, that has been posted on this forum many times, once I can determine the rest of the carb is good. Before I do that I want to check the rest of the carb, from what I understand it is mainly that the check valves are working and the needle seals. I will put in a new carb kit. Here is a photo of the carb:View attachment 945296
The main nozzle (one that goes through the body at an angle) I can test with a piece of fuel line over the hole and the high needle closed and air will go through but not be sucked back through, on all three carbs. Is that the correct way to test that valve without removing it? The hole in the center is also a check valve right? I can't get any of these to test. I did remove the welch plug on one carb and it looks like there is a hole from under the plug to that check valve that is letting air through. How can I test this valve? Thanks!
I replace , not test the one that is in on an angle , Now that you took the Welch plug out it may be hard to get a seal.
 
alexcagle

alexcagle

Cutoff Saw Specialist
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Broken Arrow,OK
The center idle circuit orifice backflow function is not critical if there isn't a purge primer on the saw.
A leak on the idle circuit welch plug will cause a wandering idle, and may load up and die. I use lacquer thinner to prep; (to dry the area, and remove oil residue), then use the two part "liquid" type JB weld to seal the welch plug's edges. Smear it over the entire welch plug surface as well as the edges for best results.
Then, an overnight stay in a warm dry place will help it to fully cure. My old oven has standing pilots, so it stays warm enough for this task.
They sell a replacement accellerator pump plunger kit from Stihl for that saw.
I buy them to use on Stihl TS420 carbs, as they have the same plunger, but don't offer a kit in the IPL.
Those accelerator plungers get galled over time, which is ok to a certain extent, as the o-ring doesn't ride on the galled area of the bore. However, it can cause fine brass metal shavings to microscopically contaminate the plunger's o-ring, thus creating an air leak right into the metering chamber. This can cause a stumble upon acceleration.
Does that make sense?
 
sven556

sven556

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Thanks Alex. So it's ok if the center orifice/ valve flows both directions? This one doesn't have a primer bulb.

Lone wolf, you're letting me down here! Just kidding. I know it's easier to replace, that's not the point. Understanding what is wrong is the point. I replaced the carbs on the first two saws I did. Now I would like to figure out the issue with one or two of these.
 
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