Time To Play... Diagnose This! - Internal Carb Failure

[trains]

2 common sizes, but actual dimensions are beyond me at the moment (its dinner time and I should be at the table hehe), Tom should have them handy tho.

 

[Vintage Engine Repairs]

I had a carb I put to the side a while ago I suspected had an issue with the accelerator pump... decided to pull it apart yesterday. The primer would suck air & it was impossible to tune. First indication the O-ring wasn’t sealing was the fact the little piston would fall into/out of the hole with no resistance. To confirm it was leaking I removed the spring & placed the piston in the hole upside down (so the O-ring sat where it should to seal). I then spraywd soapy water into the hole & pumped the primer. The soapy water was sucked past the seal & into the primer bulb so it clearly wasn't working. On closer inspection the O-ring was cracking & hard as a rock.
I rummaged through a few other carbs & found another C1Q carb that appeared to be identical with the exception of the accelerator pump piston being smaller. Got me wondering if there are common sizes for these (& therefore common O-ring sizes to keep on hand). Original carb was 5mm piston, 5.5mm bore. Second carb was 4mm piston, 4.5mm bore.
Curious to know what size O-rings you've come across Tom

Sure, I’ll copy and paste my reply to Steve’s similar posts on OP3 forum:

“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

The above are the only 3 I have come across.

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

Once I understood 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.

 

[J D]

Thanks for that... I take it those sizes are internal diameter?

 

[Vintage Engine Repairs]

Thanks for that... I take it those sizes are internal diameter?

That’s it mate, o-rings are measured internally and then cross section.

 

[SteveSr]

I just ordered both of the 1mm CS rings from here:
https://www.theoringstore.com/store/index.php?main_page=index&cPath=368_65

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

I also got a chance to test run the saw with the new carb. Ran about 3 tanks through it. It didn't cut bad for a cheap saw.

When the o-rings come in I'll reassemble the original carb and try it to see if the o-ring was the root cause of the issues.