Yet another MS200T issue.

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paddy1000111

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Hi everyone,

I've just got done rebuilding an MS200T and I am having a bit of an issue. I have followed the stihl manual for the rebuild using all genuine parts. Starting with the crankcase it was re-assembled with hylomar non-setting gasket and a new oem paper gasket along with the head and has all been pressure/vac tested (pass). I don't have a compression tester but when starting if I hit a compression stroke it nearly dislocates my wrist so it can't be too far off. The carb was stripped, ultrasonically cleaned and then re-assembled before pressure/vac testing (pass) using all genuine rebuild parts including the "pop-off" valve. It's had a new fuel tank and lines (no kinks and pressure/vac tested to check the breather is working) And before anyone asks, yes, I've connected the pulse line (can you tell I've been googling the issue) :angry:

The only "mod" I made to the saw was to open the exhaust itself up a little (I don't have a mesh filter) and I polished the ports on the head but made no adjustments to the port timing. I also made the intake port round and got rid of the lump inside. I followed the guidance of as many posts and videos as I could so I doubt that's the issue but I may be wrong...

In the way of tuning I followed the stihl manual to begin with- set idle to 3700, tune to the sweet spot then reduce the idle to 2800 on the L screw before setting the H screw to 14000rpm and it was sluggish. I then did the chainsawr and steves small engine saloon method by tuning the sweet spot at 2800 and then adjusting the H. It was better but its still sluggish to accelerate. I also don't seem to be able to retain 4-stroking at 14,000 rpm either and it sounds lean so I end up tuning to 13400 as 14000 sounds very smooth

The main issue I am having is when starting, it starts fine, usually within 3 pulls and then idles but if I even touch the throttle then it bogs and if I snatch the throttle it bogs and dies. If I allow it to warm up and get to operating temperature it's back to how I tuned it. I am at a bit of a loss, I've even tried to open/close the L and H screw when it's cold to see if it makes it run better but there's no change so it can't be tuning related. My only thought is it maybe a dodgy plug? I've had an engine do the reverse of this where it would bog and die when hot and that turned out to be a faulty plug, I've got a new one on the way to try.

Another interesting issue is it seems to run best when the L screw is all the way out (to the point it has no adjustment anymore) and then the idle set to 2800?!

As you can tell I am at a complete loss with it, hopefully someone here can guide me!

The closest I have got so far can be seen here although again, after tuning it wouldn't run cold:
 
Thanks for the help,

My current carb is a c1q-s61a. It doesn't have an accelerator pump so it's not that.

Here's what I have done with the intake:


I've not touched anything inside the cylinder wall at all. Just opened it up a little at the front and polished the roughness out. Apart from that it's untouched....

If it is the carb, I have the choice between a s126a with the pump or an s32 with no pump. What's the better one?
 
Thanks for the help,

My current carb is a c1q-s61a. It doesn't have an accelerator pump so it's not that.

Here's what I have done with the intake:


I've not touched anything inside the cylinder wall at all. Just opened it up a little at the front and polished the roughness out. Apart from that it's untouched....

If it is the carb, I have the choice between a s126a with the pump or an s32 with no pump. What's the better one?
Nothing wrong with a rough intake smooth exhaust rough intake! Start with the carb.
 
Thanks for the help,

My current carb is a c1q-s61a. It doesn't have an accelerator pump so it's not that.

Here's what I have done with the intake:


I've not touched anything inside the cylinder wall at all. Just opened it up a little at the front and polished the roughness out. Apart from that it's untouched....

If it is the carb, I have the choice between a s126a with the pump or an s32 with no pump. What's the better one?
No matter which one if they are good.
 
No matter which one if they are good.

You don't think I messed anything up with the porting then? Just leaves the carb I suppose :(

I'll have to order a new carb so was just wondering which one to go for. I guess the one without the accelerator pump is better?

I'm borrowing a compression tester next week anyway. Thinking I may check compression, redo the crankcase pressure/vac tests and change the spark plug for a spare before I sink £80 on a new carb but you're probably (definitely) right. Just seems odd that it changes when the engines cold or maybe the carb is drying out and that's why its not running when it's cold. I'm just getting annoyed with the 200 :dumb2:
 
You don't think I messed anything up with the porting then? Just leaves the carb I suppose :(

I'll have to order a new carb so was just wondering which one to go for. I guess the one without the accelerator pump is better?

I'm borrowing a compression tester next week anyway. Thinking I may check compression, redo the crankcase pressure/vac tests and change the spark plug for a spare before I sink £80 on a new carb but you're probably (definitely) right. Just seems odd that it changes when the engines cold or maybe the carb is drying out and that's why its not running when it's cold. I'm just getting annoyed with the 200 :dumb2:
Well I dont rule out what you did to the intake but a known good running carb on there will start to point to the intake if all else is accurate. Your vac and pressure tests passed and you used all OEM parts if i read right? Whare are the H and L settings on the carb now 1 out ea?
 
Well I dont rule out what you did to the intake but a known good running carb on there will start to point to the intake if all else is accurate. Your vac and pressure tests passed and you used all OEM parts if i read right? Whare are the H and L settings on the carb now 1 out ea?
The H and L settings are nuts. The L is about 2 out and the H is on 2-3 turns out. I can't imagine how doing the intake would make much of a change. I didn't take much off. Vac and pressure tests were perfect and yes, all the parts were oem!
 
The H and L settings are nuts. The L is about 2 out and the H is on 2-3 turns out. I can't imagine how doing the intake would make much of a change. I didn't take much off. Vac and pressure tests were perfect and yes, all the parts were oem!
put them at one out each if it dont run its the carb or your experimental handiwork. Let me know what happens at 1 ea.
 
Okay sure, I started at 1ea but it ran like crap. I'll video tuning it from 1 ea and post it up if I can
 
Ran like crap as in lean, I'll post up a video tomorrow to show you. It's odd though because it's running rich when it starts and when the carb is removed its dripping with oil. I'm wondering if the carb is letting fuel push through and run into the crankcase when it's not running. It smokes quite a bit when started
 
Ran like crap as in lean, I'll post up a video tomorrow to show you. It's odd though because it's running rich when it starts and when the carb is removed its dripping with oil. I'm wondering if the carb is letting fuel push through and run into the crankcase when it's not running. It smokes quite a bit when started
Simple bad carb or your intake messing around . Try another carb or new OEM .
 
I'd be astonished if it's the intake. I just took the advice of others who have done the same. Its not touched the intake port on the cylinder wall so apart from slightly better airflow nothing has changed :confused:

If I order a new carb am I better ordering one with or without the accelerator pump?
 
I'd be astonished if it's the intake. I just took the advice of others who have done the same. Its not touched the intake port on the cylinder wall so apart from slightly better airflow nothing has changed :confused:

If I order a new carb am I better ordering one with or without the accelerator pump?

The Zama S126 with is the latest version and is fine they all work fine till they crap out dont worry. How much they rob you for one over there?
 
£94 with the VAT over here and that's with a trade discount or I would be looking at £115 ish.... Hence why I am looking at all options. In a way I wish it was my port fiddling as a new stihl piston and cylinder head is £67. When I did the porting I followed a load of other threads, watched a guy on youtube to see how he got on afterwards and then started another thread to ask around before I went ahead. A lot of people have been there and done it before me and theirs definitely don't run like mine. This saw was a dead one off ebay. Turned out when I got it that the piston and cylinder didn't have a mark on them and I was hoping a nut and bolt rebuild would get it running again but sadly no. I found lots of issues from a faulty oiler, snapped clutch springs, all the AV mounts broken and stuff that I was hoping it would be a simple fix!

 

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