A few answers..maybe...
I have been too busy to do much browsing and posting and finally sit down to get caught up, and see the MS 200 carby is still driving everyone nuts. So maybe I can shed a little light on some of the topics that have come up in this thread.
First a little history-
As I have mentioned before all STIHL saws use series numbers. The first 020 was the 1114 series, with a mag housing and was built in both top handle and rear handle configurations. The best info I have is that the 1114 came out in 1971 and production was stopped in 1994. I have one of each of these versions in the collection and they are neat little saws. Then the 1129 series came out in 1994 as a direct replacement for the 1114. It was around 2000 that STIHL started switching all the saws from the 0XX model designation to the MS whatever so the naming would be consistent through all the product lines and so the numbers could just go up as replacement models came out. So someday you will probably see a MS 201, and so forth. I wonder what will happen when the MS 209 needs replaced? But I digress…
Next lets talk about the carb function. Just go over to Magnus site and read this picture post I did on the ZAMA for my 036.
http://www.chainsawcollectors.se/phpbb3/viewtopic.php?f=124&t=7810
I don’t think I posted it here but I might have. Anyway that discussion on theory and testing is pretty much accurate for the carbs on your saws. Just about any saw that uses a butterfly carb and no purge primer. Now there are variations, such as a part load jet and accelerator pump, but the theory is the same. I will try to find some time to do a picture thread on the 200 carb, like I promised Al about a year or two ago when he sent me that carb that he thought was cracked. But in the meantime to answer some questions you folks have asked, the high speed nozzle has a flat disc check valve in it, about ¼” in diameter that may be a black rubber material or clear Mylar. It is a pressure sensitive disc and it’s only function is to prevent an internal air leak into the metering chamber at idle. It is not there to keep fuel from leaking out. It only seals closed when the engine is at low RPM and venturi pressure on the choke side of the throttle butterfly is higher than on the engine side. So if it is stuck shut the engine may idle OK but will die when you give it throttle, and if it leaks the engine will run OK at WOT because the check valve is always open when the engine is revved up. If it is leaking it will cause erratic idle, such as dying when you let off the gas one time and idling fast the next time, or it may tune out fairly well in the morning but not idle right later in the day. A crankcase air leak may act the same as well. A bad accelerator pump o-ring can behave similarly but may also cause a stumble when you give it throttle. The o-ring and check valve can be tested and that is what I will do a pic post on. I have a better way to do it than the 036 carb thread shows. I think I mention this about cleaning in the other thread but only use a non-flammable spray for cleaning and rinsing, not choke spray and never a rubber tipped air gun against an opening.
Older carbs used a light green glue to seal the welch plugs and high speed nozzle in place so they would not leak and fuel additives may dissolve that glue and turn it into a slime that will plug up passageways and make the check valve leak. We seem to blame everything on ethanol in the fuel but I am not so sure that is the only additive that is the culprit. There is other stuff used today that may be interacting with the ethanol and together could have something to do with it. ZAMA now uses a red epoxy that appears to be impervious to whatever is going on in the fuel and I will find out for sure which S number ZAMA carb for sure has it. I am fairly certain it is the S 126 but I will have to open one up and see.
I looked on the parts list and the MS 200 T has used ZAMA carbs, S 32 is the one Al mentioned with the triangular Welch plug, then a S 61, S 96 on the rear handle only, S 61, S 127 on the rear handle and S 126 is the latest for the T model. When you look back at the 1129 020 it started out with a S 16, also with the triangle Welch plug, then a Walbro WT 326, then back to a S 32 that carried over to the MS 200T. I will see if the Walbro is still available and if so try it on my saw just for kicks. May be a while as I have to be at the GIE-EXPO next week in Louisville.
About filters, the correct STIHL filter, which you can pop the cap on and pull out the sintered plastic body, will not pass vapor bubbles into the fuel line. That is why STIHL switched to that type from the old foam in screen container or the felt type.
The white stuff on the screen on the fuel pump side is showing up more and more on many different applications. Not sure what it is either but I heard that Briggs & Stratton was seeing the same thing on float bowl carbs and had it analyzed to find it was dissolved aluminum! Yikes!
STIHL is going to market the fuel in a quart can that will have like a 2 year shelf life and won’t gum up but it will be too pricey for anyone other than homeowners. Someone else has some out now and I have heard it does seem to work well but $6 a quart is a lot, although cheaper than a carb replacement every spring.
So anyway maybe this gives ya’ll a little to read up on and I will add some more as I can.
Eddie
Or maybe a Early Christmas Squirrel!
