Accelerator Pump O-Rings (Carburetor Model Look-Up)

[Vintage Engine Repairs]

@Vintage Engine Repairs Just curious where you got your o-ring dimensions from? Did you measure samples or find actual documentation for the sizes?

I think that your m2.3x0.8 might actually be 3/32" x 1/32" imperial (.094" x .031").

I am getting ready to order some wher the shipping is likely equal to or greater than the cost of the parts and want to be sure I get the right sizes.

There is no documentation on these sizes, no.
I discovered it through comparing part numbers to dimensions. So far they have all been metric - expected as they’re a German company.

Example: 195503010 is a 3x1 metric o/ring

You take the last 4 digits

195503010 = 3.0 x 1.0
195503510 = 3.5 x 1.0
195702308 = 2.3 x 0.8
OILER]ISPOILER]

This is a common numerical ordering system making P/O very efficient to fill out.

Once I figured out that was the likely means to decipher the size, I measured the bore, piston groove and checked o-ring clearance charts and confirmed it on a bunch of different carbs with accelerator pumps.

 

[Wonkydonkey]

I also took a 250 carb (C1Q S91A) & a 200t carb (C1Q 61 )apart the other day.

It was a strange looking at the small differences. I'm guessing less fuel being pumped due to the bigger sized pump in the 250 ? Although I could be wrong
Anyway the 200 carb pump an oring pics

 

[Wonkydonkey]

And the 250 carb pump , same oring just a longer piston .
I didn’t measure the springs, , they seemed to be slightly different in lengths , I guess I should have measured the Recess in the pump.
I could always pull them apart and get those sizes as I’ve yet to get the orings.

 

[Wonkydonkey]

I just realised I didn’t post the 200carb pump length . it’s got a different top shape, would This give it more movement ? By the throttle butterfly cam.

I will Investigate more when I get the orings.

 

[SteveSr]

...However just like a lot of things you have to research it .Just remember "google " is your friend .

I have been looking at several manufacturers. One of them, Marco Rubber, says that regular nitrile/buna-n is NOT recommended for fuel applications! Huh? Well apparently there are several varieties of Buna-n. One is hydrogenated which is rated for fuel use. I doubt that Ebay / Amazon can tell you which compound you are buying.

I am also considering FKM or similar compound which is flourocarbon (think teflon) based.

 

[SteveSr]

There is no documentation on these sizes, no.
I discovered it through comparing part numbers to dimensions. So far they have all been metric - expected as they’re a German company.

Those are Zama part numbers not Stihl. I didn't think that Zama was a German company.

Example: 195503010 is a 3x1 metric o/ring

You take the last 4 digits

195503010 = 3.0 x 1.0
195503510 = 3.5 x 1.0
195702308 = 2.3 x 0.8

Great detective work! Unfortunately the 2.3 x 0.8 is smaller than standard sizes. The smallest that I have found is the 3.0 x 1.0. I think that I have some of the smallest size directly from Stihl. Unfortunately they don't fit the carb that I am currently working on.

 

[Vintage Engine Repairs]

Those are Zama part numbers not Stihl. I didn't think that Zama was a German company.


Great detective work! Unfortunately the 2.3 x 0.8 is smaller than standard sizes. The smallest that I have found is the 3.0 x 1.0. I think that I have some of the smallest size directly from Stihl. Unfortunately they don't fit the carb that I am currently working on.

Yes you’re quite right mate, my apologies, but either way, yes they’re all metric that I’ve found. Try Amazon, thats where I get mine. From memory I paid $10 Australian for 20? They’re good too!

 

[SteveSr]

Yes you’re quite right mate, my apologies, but either way, yes they’re all metric that I’ve found. Try Amazon, thats where I get mine. From memory I paid $10 Australian for 20? They’re good too!

Just for grins you might want to take a sample from each lot and soak them in petrol for a month or so and see if they change size or stiffness.

 

[el33t]

Those are Zama part numbers not Stihl. I didn't think that Zama was a German company.

The ZAMA companies are owned 100% by Stihl. But it doesn't matter about o-ring sizes etc., because even if they weren't, the whole world generally uses the metric system anyway. Even the U.S. auto industry switched to it back in the 1970s and 1980s. If even some dimensions are derived from the imperial units, they are expressed in millimeters (for example) on technical drawings and in published international standards.
Besides, the length of an inch was standardized in the 1950s defined in relation to the meter.

 

[Vintage Engine Repairs]

Just for grins you might want to take a sample from each lot and soak them in petrol for a month or so and see if they change size or stiffness.

Yeah I could do that. The supplier I use is the same one that sells them in the states so it may be handy. Though I have used a number of them with no returns so far so I guess that says it all

 

[KennyWinCT]

Yeah I could do that. The supplier I use is the same one that sells them in the states so it may be handy. Though I have used a number of them with no returns so far so I guess that says it all

Good thread Tom!

 

[Vintage Engine Repairs]

Good thread Tom!

Thanks Kenny

 

[EFSM]

There is no documentation on these sizes, no.
I discovered it through comparing part numbers to dimensions. So far they have all been metric - expected as they’re a German company.

Example: 195503010 is a 3x1 metric o/ring

You take the last 4 digits

195503010 = 3.0 x 1.0
195503510 = 3.5 x 1.0
195702308 = 2.3 x 0.8
OILER]ISPOILER]

This is a common numerical ordering system making P/O very efficient to fill out.

Once I figured out that was the likely means to decipher the size, I measured the bore, piston groove and checked o-ring clearance charts and confirmed it on a bunch of different carbs with accelerator pumps.

I guess those sizes are ID and thickness of the o-rings? That makes a lot of sense that those are the dimensions.

 

[SteveSr]

@Vintage Engine Repairs Would you mind sharing your o-ring source? Either through Amazon or direct.

 

[Wonkydonkey]

I thought I,d add this here, as I’ve fixed the oem carbs piston pump with the help of this thread. cheers Tom,

Post in thread 'The Badly fixed 200t needs fixin some moar'

Nov 14, 2024

An update on the saw, as it’s taken a back seat. I’ve still got to order the off spring and make the grounding wire. Also a new clutch drum needle bearing (ting ting ting)
However. After some looksee around here and there. I found the info from @Vintage Engine Repairs posts here and on AS and ordered the oring [1 oring]
I should have ordered a few more but I’ve now done this…

When I find the carb piston pump oring link I will add it here.
Edit:
Thread 'Accelerator Pump O-Rings (Carburetor Model Look-Up)'...

• Wonkydonkey

• 

 

[Wonkydonkey]

I have been looking at several manufacturers. One of them, Marco Rubber, says that regular nitrile/buna-n is NOT recommended for fuel applications! Huh? Well apparently there are several varieties of Buna-n. One is hydrogenated which is rated for fuel use. I doubt that Ebay / Amazon can tell you which compound you are buying.

I am also considering FKM or similar compound which is flourocarbon (think teflon) based.

I got a “Viton” oring fkm iirc. As I know these are better suited for fuels/oils , I will see how it lasts.
I know buying here in the uk from a uk seller isn’t cheap due to postage etc. but I’ve got some more coming from China

 

[SteveSr]

I just ordered both of the 1mm CS rings from here:

FKM Metric O-Rings (Fluorocarbon) 75 Durometer Black Chemical Resistant Oring

Metric O-Rings FKM Fluorocarbon Duro 75 - We make placing your o-ring order and getting o-rings easy!

www.theoringstore.com

I also ordered in V75 (Viton compound). These are 75 durometer which is fairly close to the normal 70 for Buna-N.