Accelerator Pump O-Rings - Carburetor Lookup.

[Vintage Engine Repairs]

I’m a big fan of having an accelerator pump on a carby, but the o-rings are a known weak point.

For your reference, buy them from an o-ring supplier - it’s about 20-30 cents a piece. From Stihl / Zama, you can buy one size and not the other.

Lots of people block off the accelerator pump drillings and in some machines this works well, like the 200t, on other machines, this affects metering chamber volume and will cause strange running characteristics. I have yet to repair a machine that has a worn piston or bore yet (I’ve changed about 30-50 o-rings with 100% success rate), but that does happen and is worth checking too. Having the o/rings on hand and the repair being 15 mins labour and a 30 cent o/ring can make a quick fix and a happy customer. I hope it helps.

Size one - 3x1 (metric) Which Fits:






Size two - 2.3x0.8 (metric) Which Fits:

 

[DND 9000]

It can be done, but makes not much sense. Not only the o-ring is worn, also the pump piston and it`s seat is worn too. So this o-ring fix will only help for a short time. It is better to use a new carburetor in such a case.

 

[Vintage Engine Repairs]

It can be done, but makes not much sense. Not only the o-ring is worn, also the pump piston and it`s seat is worn too. So this o-ring fix will only help for a short time. It is better to use a new carburetor in such a case.

Interesting you say that - as mentioned, I have done it to about 30-50 carbs on many different machines for customers and never come across a worn piston or bore or had them returned. I do check them. Pistons new are 3.980mm and the bore new is 4.000mm.

The carbs stop sucking fuel long before the piston or bore wears in my experience, but I have heard people mention worn pistons and bores so it must happen and this i mentioned it in the op.

Stihl sells the o-ring for the 3x1 on its own and the 2.3x0.8 comes in all the rebuild kits. There is good reason for it I guess!

 

[ZeroJunk]

I know guys who do tree work daily that are just in the habit of goosing the saw constantly between cuts. Don't know why. Habit I guess.

The only one I have any regular experience with is the MS200T. Stihl had a kit that I think is discontinued that replaced the O ring and the piston.

Simpler to replace the complete carb IMO . I don't see how you could do it in less than an hour and with just two hands. And, if the screw gets loose it will wreck the saw...

I don't have the time myself.