Yet another MS200T issue.

[paddy1000111]

Just for a laugh (and whilst waiting for my new carb) I adjusted it to one turn on the high and the low. You can hear the bog. It's almost like the H jet isn't opening up until a certian RPM and then popping open (sticky check valves?) once it's open it's fine and accelerates as long as its not dropping below a certain RPM. The bog is much, much more pronounced with a chain on, when it's cold or with the chain "resting" on some wood.

 

[Vintage Engine Repairs]

Did you correctly set the metering lever height in the carb after fitting a new spring, lever and needle? Did you also check that the idle passages in the carb were clear and that you can confirm visually that you could pass carb cleaner through into the Venturi through all passages?

Same with H jet did you see fluid pass through and that the check valve in the main jet was clear and that you can unseat and seat it and hear it gently pop repeatedly?

If the screws are that far out, and the saw holds pressure and vac, then the issue is the fuel not getting to the Venturi, so backtrack from there. Did you remove the welch plugs and clean inside them before putting new ones back in? Did you tap them down too far during re-seating or did you accidentally block the passage up when removing the plug?
Also, don’t get confused thinking that 1 turn out is where the screws should be. It’s a starting point to proceed with tuning from.

 

[paddy1000111]

I did not set the meter height, I can create flow through all the passages with carb cleaner but I didn't check the check valves. I wish I did now but I'm just at the point of buying a new carb. After tuning it the other day I counted the screw turns and they were about 1 turn out on both so it wasn't that. It must have been before I was thinking about with the ridiculous carb settings.
I didn't remove the welch plugs in the end, it's something I have never bothered to do as the OEM carb kits don't come with replacements. My current plan is to wait until the new carb is here and try it. If it fixes it then I will dissect the old carb (I think the H jet check valve is knackered) and see if I can fix whatever is wrong with it as a learning thing and then keep it as a spare. If the new carb doesn't fix it then I will resell the one I have bought and then replace the cylinder/piston as lonewolf said.
I appreciate the 1&1 is the starting point for a fresh tune, hence the stihl workshop manual and tach in hand

 

[SteveSr]

I did not set the meter height, I can create flow through all the passages with carb cleaner but I didn't check the check valves. I wish I did now but I'm just at the point of buying a new carb. After tuning it the other day I counted the screw turns and they were about 1 turn out on both so it wasn't that. It must have been before I was thinking about with the ridiculous carb settings.
I didn't remove the welch plugs in the end, it's something I have never bothered to do as the OEM carb kits don't come with replacements. My current plan is to wait until the new carb is here and try it. If it fixes it then I will dissect the old carb (I think the H jet check valve is knackered) and see if I can fix whatever is wrong with it as a learning thing and then keep it as a spare. If the new carb doesn't fix it then I will resell the one I have bought and then replace the cylinder/piston as lonewolf said.
I appreciate the 1&1 is the starting point for a fresh tune, hence the stihl workshop manual and tach in hand

Looking at your video it could very well be a sticky/ing main nozzle check valve which is basically non-repairable unless you can get a replacement main nozzle assembly and make a puller to get the original one out. Sometimes it bogs sometimes it doesn't based on if the check valve gets stuck or not.

If the valve sticks closed it will idle all day but won't rev up. If it sticks open it won't idle due to the effective air leak that it creates. I think that either the Walbro or Zama service manuals show how to test a main nozzle check valve.

 

[paddy1000111]

Looking at your video it could very well be a sticky/ing main nozzle check valve which is basically non-repairable unless you can get a replacement main nozzle assembly and make a puller to get the original one out. Sometimes it bogs sometimes it doesn't based on if the check valve gets stuck or not.

If the valve sticks closed it will idle all day but won't rev up. If it sticks open it won't idle due to the effective air leak that it creates. I think that either the Walbro or Zama service manuals show how to test a main nozzle check valve.

Sounds like the issue, it's obviously getting stuck closed. It will idle/start/stop all day long but it messes about coming off idle!

 

[KarlD]

Isn’t a standard intake (rough surface with a lump) supposed to enable a better fuel/air mix? If you’ve removed the lump and smoothed out the rough, maybe the fuel isn’t mixing with the air sufficiently? I’m quite possibly wrong though

 

[paddy1000111]

Isn’t a standard intake (rough surface with a lump) supposed to enable a better fuel/air mix? If you’ve removed the lump and smoothed out the rough, maybe the fuel isn’t mixing with the air sufficiently? I’m quite possibly wrong though

I would usually agree but the lump creates a large vortex that creates a lot of turbulence into the intake reducing airflow. The internals in the carb, the surface on the intake boot (it has a knurled finish if you've looked?) and the joint between the boot and the cyl head will create more than enough to mix the fuel properly. All I've enabled is a larger amount of air to be sucked in during the small amount of time the port is open. I've gone off what other guys have done though...

 

[KarlD]

I would usually agree but the lump creates a large vortex that creates a lot of turbulence into the intake reducing airflow. The internals in the carb, the surface on the intake boot (it has a knurled finish if you've looked?) and the joint between the boot and the cyl head will create more than enough to mix the fuel properly. All I've enabled is a larger amount of air to be sucked in during the small amount of time the port is open. I've gone off what other guys have done though...

Ok cool, that all makes sense. Good luck sorting it...currently rebuilding one of my old 200t’s and am dreading choosing which carb to use and getting it running

 

[paddy1000111]

Ok cool, that all makes sense. Good luck sorting it...currently rebuilding one of my old 200t’s and am dreading choosing which carb to use and getting it running

I've just ordered a c1q-126a, I'll tell you how I get on. I think the choice is pretty much accelerator pump or no accelerator pump? I thought I want one and I'll look after it, if it leaks ill stick a pump rebuild kit in it. Depends on what sort of cutter you are, if you open the throttle cut, then close I would say the accelerator pump, if you're a guy who revs the engine 3 times before each cut then get one without it? But I'm sure someone will chime in with more knowledge than me!

Good luck with the rebuild. Have a look at your exhaust before you put it on by the way. I found mine was massively out of flat on the sealing face and the little knob (red circle) that rests against the cylinder was holding it off the mating face. I ended up machining the face on mine then grinding the knob so it had the correct setting for the gasket!

 

[KarlD]

I've just ordered a c1q-126a, I'll tell you how I get on. I think the choice is pretty much accelerator pump or no accelerator pump? I thought I want one and I'll look after it, if it leaks ill stick a pump rebuild kit in it. Depends on what sort of cutter you are, if you open the throttle cut, then close I would say the accelerator pump, if you're a guy who revs the engine 3 times before each cut then get one without it? But I'm sure someone will chime in with more knowledge than me!

Good luck with the rebuild. Have a look at your exhaust before you put it on by the way. I found mine was massively out of flat on the sealing face and the little knob (red circle) that rests against the cylinder was holding it off the mating face. I ended up machining the face on mine then grinding the knob so it had the correct setting for the gasket!

Ok, thanks for the heads up on the exhaust, I’ll have a look when I get that far.
This thread summarises where I am with the carb choice
https://www.arboristsite.com/community/threads/ms200-carbs.342812/I ended up getting three rebuilt by a local small engine mechanic but haven’t ruled out just buying a new one. Did you get yours through Stihl dealership?

 

[paddy1000111]

Ok, thanks for the heads up on the exhaust, I’ll have a look when I get that far.
This thread summarises where I am with the carb choice
https://www.arboristsite.com/community/threads/ms200-carbs.342812/I ended up getting three rebuilt by a local small engine mechanic but haven’t ruled out just buying a new one. Did you get yours through Stihl dealership?

If you're in the UK, I got mine from L&s engineers but I have a trade account. Rebuilding a carb yourself is very easy and there's loads of guids online if you want one. The rebuild kits are about £8 for an oem one from zama (not stihl). Give it a go, for £8 you could have a decent carb!

 

[SteveSr]

Ok, thanks for the heads up on the exhaust, I’ll have a look when I get that far.
This thread summarises where I am with the carb choice
https://www.arboristsite.com/community/threads/ms200-carbs.342812/I ended up getting three rebuilt by a local small engine mechanic but haven’t ruled out just buying a new one. Did you get yours through Stihl dealership?

Any carbs that are rebuilt must be tested in an otherwise well running saw. There are significant defects like the accelerator pump and main nozzle which are either difficult or impossible to fix. This is why dealers don't even try to rebuild carbs. They just replace them.

 

[angelo c]

Guys. Its the carb. I've probably replaced 40 of them where wolfie may have done 200. He says "carb"....its CARB. Sorry

 

[lone wolf]

Guys. Its the carb. I've probably replaced 40 of them where wolfie may have done 200. He says "carb"....its CARB. Sorry

He also ground on the intake port.

 

[lone wolf]

Any carbs that are rebuilt must be tested in an otherwise well running saw. There are significant defects like the accelerator pump and main nozzle which are either difficult or impossible to fix. This is why dealers don't even try to rebuild carbs. They just replace them.

I have 50 - 65 percent success rate with unmolested carbs.

 

[angelo c]

I have 50 - 65 percent success rate with unmolested carbs.

Not me...I collect bad carbs....someday there will be a value to the antique 200t carbs....I'm gonna retire on all I collect ...

 

[lone wolf]

Not me...I collect bad carbs....someday there will be a value to the antique 200t carbs....I'm gonna retire on all I collect ...

Good luck buddy.

 

[SteveSr]

I have 50 - 65 percent success rate with unmolested carbs.

Well... You (and I) are not the average OP!

 

[lone wolf]

Well... You (and I) are not the average OP!

Just sayin that was unmolested ones once people touch them forget about it !

 

[paddy1000111]

I've been doing a bit of research for the sake of learning. I didn't realise the check valves in these are a thin piece of plastic? I had a look at the carb cleaner that I'm using and it contains MEK and a load of other things with a specific warning not to use on paint. Probably melted the valves...