Almost dead 200T carburettor

[MattG]

So when I first got mad on saws I got a broken 200T. I ended up changing out a heap of stuff just for the fun of it, seals, pipes, piston, rings etc. When I got it running, it seemed pretty strong, but it had a problem, with starting from cold, where straight after firing on full-throttle it would fuel starve. I'd already done a full carb service (diaphragms, needle etc.) so I took @Lone Wolf s advice, and did a "quick accelerator pump" block, i.e. I forced out the plug shown by the pencil here

and filled the space with JB weld.

I don't think it made much difference. That was nearly 3 years ago. I've since put on an old non-acc-pump carb on that saw, and it goes like greased lightning.

Anyway, the other day, I decided to dig the old carb out and have another go with it. I did the acc pump block "again", but I used the method outlined by this guy:

https://www.arboristsite.com/community/threads/200t-carburetor-accel-pump-block-off.238372/

basically, you take the acc pump piston out, toss away the spring and 0-ring, and jb weld it back, sealing all the edges of the piston in the bore to stop any leaks.

In addition to that I cleaned the carb (again!) stripped anything off it and soaked it in gas for 2 days.

After reassembly with this "supposedly mended" carb, I was able to choke the saw, but again (!!!) the saw would lean-fuel-starve on fast idle.

The saw was almost impossible to get it to pick up at all off idle. I tried with everything on the L screw from 3/4 to 3 whole turns out.

Eventually I got the saw idling (very fast) by turning the LA right in. However, it was almost impossible to dial in full revs, it just lean bogs horrendously. I could once nurse it to full throttle, but even then it has NO GUTS between that and 3k.

The carb seems good only for spares. Seeing as I have basically filled the acc pump circuit up with JB weld, I'm wondering what else could be wrong......

My gut feeling is that one of L speed holes is completely blocked and I can't clear it. What else can I try (before binning it)? What about pushing out the welch plug that is in the metering chamber?



i.e. the part marked 2 in the above picture. Should I remove that? Does that give better access to cleaning all the fuel channels??

Sorry about the big essay! Just wanted to get the whole problem down and explain what I've done already. Note IS A CARB PROBLEM - the saw runs like a banshee with a good carb

 

[Mkinslow]

You probably should have removed the Welch plug the first time around. It’s more then likely gummed up behind it. I always take them out while cleaning and replace them

 

[tree monkey]

should have just replaced the acc pump in the first place, they are available.

 

[MattG]

should have just replaced the acc pump in the first place, they are available.

Hmm... I hear you Scott, but all the posts I've read in the past reckon the piston galls up the carb body, so you're better off blocking them up. I quite them with the non-acc-pump carb TBH.

 

[MattG]

You probably should have removed the Welch plug the first time around. It’s more then likely gummed up behind it. I always take them out while cleaning and replace them

A ha! So how do you do that exactly? And then re-seal etc.?

What is the purpose of the plug anyways? It seems to me that it must only be there so that people can remove it, in order to clean out these passageways.

 

[Scotty Overkill]

A ha! So how do you do that exactly? And then re-seal etc.?

What is the purpose of the plug anyways? It seems to me that it must only be there so that people can remove it, in order to clean out these passageways.

The welch plug self-seals when you hit it with a larger punch, never use sealant on a Welch plug.

We went through this same list of problems with an old 020AV I had and @blacksmith's 200T.

Replaced the whole carb on both of them (with Chinese carbs) and STILL they don't run right. I got tired of spending money on that 20av, I sold it to him. I'd rather buy another Echo CS355T instead

 

[MattG]

Replaced the whole carb on both of them (with Chinese carbs)

Ha ha. I bought a china carb once. I hated it. It started fine, and ran WOT fine. But in between those places it sucked!

How did you remove the plug then Scotty. I read these posts and they mentioned drilling which on a carb sounded downright scary:

#2
#3

 

[MattG]

Found a nice graphic about welch plug

it does make it pretty clear to me, that it's removal is pretty much essential to completely clean a carb.

Well at least it does in my naive mind..

 

[Chainsaw Jim]

You don't need to drill a hole all the way through the Welch plug to remove it. A sharp pick will finish punching through and lift it out. I've hit the cavity a few times with a bit when it popped through unexpectedly, but it never caused enough damage to ruin it.
It's easy to punch the new plug inward too far, causing it to shrink again and fall out. Don't go beyond flat, and don't be afraid to leave a slight hump.
Most carbs are finished at the factory with an epoxy around the seam of the plug, and ethanol fuel ALWAYS breaks the bond and let's chunks break free to make their way into the metering passage. Some of the more "extreme wear" type clear coat nail polish brands hold up well to ethanol free fuel. I apply it to the entire seam and immediately wipe it all away with a q tip so only what seeps into the seam remains to seal. This way there won't be any excess material to break loose.
Fuel flows through that passage and nothing can make it in there that is larger than the holes, so built up debris isn't very common with regular or light use equipment if stored properly.

 

[Scotty Overkill]

Ha ha. I bought a china carb once. I hated it. It started fine, and ran WOT fine. But in between those places it sucked!

How did you remove the plug then Scotty. I read these posts and they mentioned drilling which on a carb sounded downright scary:

#2
#3

I use a really small drill bit (like 1/16-1/8"), drill a small hole in the Welch plug, and use a 90° pick to pry the plug out. That usually does the trick.

 

[Cracker Boy]

I never had luck rebuilding these i bought a new carb problem solved

 

[Scotty Overkill]

I never had luck rebuilding these i bought a new carb problem solved

Sometimes that's your only option. I have an older MS290 that just flat-out ran like chit, rebuilt the carb twice and still ran like chit.

Bought a chinese carburetor for it, fixed it.

I think a wicker of metal or something got into one of the venturis or something, I even cooked it in the hydrosonic cleaner twice and it still didn't clear out.

 

[Cracker Boy]

Thats what happened on my 020t ultrasonic and rebuld said f it bought new oem and cured problem

 

[Backtroller]

I bought one of Dave’s good Chinese carbs and it runs fantastic. @Lone Wolf suggested this and I’m happy I took his advice.

 

[MattG]

Thanks for all your answers people, you've answered my question several times over.

Since I've got nothing to lose with it I'll probably try to get the plug out and clean and replace etc. some day when I next get bored.

Totally agree that often you've got to call it quits with these things, and spend out on a replacement!

 

[Cracker Boy]

I went with zama on mine and both high and low verses the single high speex jet adjust on the walbro wich are pain in the nutz

 

[Wonkydonkey]

I had a trimmer with a cr@p carb, took it apart and found the w-plug all loose.
At the time I was a bit new to these carbs (still am really) I went to the local stihl shop, for one of these w-plugs.

They informed me £60 for a carb kit. My sphincter loosened then snapped tightly closed for the rest of the time I was there. Which was not that much longer.
That was when I looked into the manafactures pdfs, and then read the nail varnish and also using a punch to flatten it/spread it.
Well the w-plug was oval so I found a punch that fitted into the end nicely, with a slight tap it sat tight.
Edit: I never used nail varnish,
Which now brings me onto my other carbs (Chinese mostly cr@p).
Just the other day I got a carb for the 200t, so while doing a sans gasket, I swapped out the carb, but then relised the carbs H&L screws were farther apart, doh.. Me thinks what the heck, carryon... Anyhow I fitted it and all was well till I turned the saw 90* to the side while running, it stalled out, like a crank seal on the flywheel had gone.
But I'd just done a p&v test..wtf.. So after trying to tune it for an hr, I put the old carb back on and it ran like it should.
I know what others have said about Chinese carbs and I have read a few other threads about them.

 

[MattG]

Well the w-plug was oval so I found a punch that fitted into the end nicely, with a slight tap it sat tight.

Do you tap around the edge of plug Sean? Or just in the middle of it?

Are they soft or hard? No f**kin' jokes here please people!!!!

I can see I'm gonna need to buy several of these things. I'm bound to break the first one or three

 

[Al Smith]

Some time ago a guy from Australia sent me a malfunctioning 200T carb .It appeared to me to be a casting flaw in the fuel chamber which I coated with red loctite .In conversation Adam Clark also came to that conclusion .It fixed the problem for maybe 6 months .
In further conversation Edie Anderson (Stihl number 1 ) asked me to ship the carb to Stihl USA which I did .They tested it in their carb lab and concluded it was leaking deep inside the carb under the plug but didn't further disassemble it .This was before they had accelerator pumps .
I think the problem with the Zama c1Q came about the time they shipped carb production from Japan to China .Evidently they have figured it out because I haven't heard so much about it for some time .

 

[Al Smith]

About two years after that Edie found a carb in his desk which he shipped to me just prior from him retiring from Stihl .He had forgotten about it .That was the latest model C1Q factory tuned .I never touched the screws and it's on my super bee ,modified 200t and that saw never ran so good .So they must have fixed the problem .