‘Spare’…. hmmmm… o ring

Windmill John

Windmill John

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Jun 4, 2022
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Location
East Sussex, England
Just rebuilt carb and….. argghhh!!! Where’s this bugger from!?

I removed again the accelerator pump, not that one. I removed again the two air cut off diaphragms, not the seal from either of those.

Any ideas? Cheers.
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IMG_0336.jpeg
 
Actually.. I do recall an o ring sitting in situ when I removed the accelerator pump weeks ago, but I cannot see a position for it now and I cannot see it in the exploded diagram in Clymer!
whilst I’d rather resolve this before sticking them back on the bike, I may try without….. and wait for a:
Fuel leak!
Air leak,
Nothing to happen… perfect 😊
 
Feel for your situation. Just went through the opposite on my cb160. CMSNL diagrams depict an air screw o-ring that was on neither of the existing air screws nor in the 'complete' rebuild kit from Common. Having said this... it's running great now and looks like it doesn't require one? Fun with vintage bikes! Best of luck.
 
Ahaa… checked David Silver and it probably is the mixture screw.
Clymer picture wrong. When I removed the mixture screws, I only recall the tiny metal washers.
See… I’ve answered my own question; possibly. 😉
 
Just saw your post. Yes mine didn’t have one in either mixture screw. I’ll pull them out and see how I feel. If Clymer was correct, then the spring and screwing them in would tear the o rings. So I guess it’ll be o ring, metal washer then spring.
 
Well, don’t tell me off, but having separated this type of linkage before and then had a leak at the crossover, I didn’t actually separate the carbs, so not that.
I did though, fully flush the crossovers.
 
if it ain’t broke, no sense in fixing it!

Is it possibly part of the old “boot” on the accelerator pump that tore off?
 
Not part of the boot. There’s definitely an indent all the way round the o ring where it’s been pressed against something.
No worries, when the novelty of searching wears off, I’ll refit the carbs and test.
Appreciate the input though.
 
Do you have this O ring in the accelerator pump bowl, since you have a leak in the drain pipe on this bowl? This picture is missing the O ring too, yet there is a round one that needs to be in there. It will leak like a #$%## if you don't have one in place. :(

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The O ring was there.
When I compared the ‘spare’ o ring size with the mixture screws, I decided to fit new o rings there, even though it’s not clear it has them.
They‘ll have a tiny effect on mixture, but I can tweak when running.
Thanks for all input, carbs can go back on the bike the next time I’m in the shed.
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IMG_0339.jpeg
 
Wrong order. From carb body out:

O-ring
Washer
Spring
Screw

Ring seals to limit air from entering around the mixture circuit.
 
I was just testing you…. 😉 The way I have it, wouldn’t that also stop fuel or air entering via the threads?
Also, if o ring goes in first, that would be a pain to remove. Maybe the spare o ring was blown out from there…
 
Windmill John said:
I was just testing you…. 😉 The way I have it, wouldn’t that also stop fuel or air entering via the threads?
Also, if o ring goes in first, that would be a pain to remove. Maybe the spare o ring was blown out from there…
Click to expand...
The O-ring seats against the carb body, the washer squishes the O-ring to seal on the screw. The way you have it the threads will just cut into the O-ring ruining it.
 
Windmill John said:
Also, if o ring goes in first, that would be a pain to remove. Maybe the spare o ring was blown out from there…
Click to expand...
Yes, it is. I straighten out a paperclip, bend tip 90 degrees then cut it off about 0.5mm long and file 'squashed' end where wire cutters crushed it.
Probably made thousands over the years, quick and simple, gave to students
It's very common to find two or three O-rings in carb body, enough that fuel screw doesn't actually work.
Judging by how 'flat' it is, good possibility it was stuck in carb body?
 
Well… thank you all firstly.
You’re right, didn’t doubt it for a minute.
I removed the mixture screws and had fun getting the o rings out as per Jim’s comment. Had to use a thin screwdriver to hold down the washer to allow me to remove the o ring.
As per crazypj’s post, yes there was an o ring still in there and when I got it out, the ‘spare‘ o ring was obviously his brother.
The paper clip method worked.
I noticed when fitting, the o rings played about. So what worked for me was to install the spring, then washer, then o ring on a narrow screwdriver, tip the carb up and place the screwdriver in the bore. I then removed the screwdriver, job done.
Just to confirm, I held the open bore of the carb outlet to the sun and could see light through the passageway.
Once again, thank you for all input.
 
I just put spring, washer then O-ring onto fuel screw, O-ring should be tight enough and spring just short enough to hold everything together for assembly.
Don't remember ever having an issue doing that.
Suzuki were the only manufacturer that listed the O-ring separately, probably still have a part number somewhere safe.
Do you mean you put spring in carb body first?
 
No, in EzPete’s order.

O-ring
Washer
Spring
Screw

I‘ve fiddled with a load of Bing carbs and the o rings in those fit in a recess in the needle much easier.
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IMG_2026-06-14-210146.png
 
Yeah, fitting the O-ring over threads or head of screw is a bit difficult, has to be done 'dry' or you lose a lot of o-rings. :LOL:
Haven't done many Bing (BMW) carbs since TWS dropped them when they wanted exclusive 'boutique' dealership early 80's.
We were selling Suzuki's about 20:1 so dropped BMW and picked up Yamaha.
Had to ask, didn't understand use of tiny screwdriver.
I meant to ask, how did you get screws out with the limiter cap still fitted?
 
It looks like a PO had ‘tuned’… okay, nibbled off the two stops on the carbs; so they could fiddle with the mixture I guess.
Re fitting, I used a thin screwdriver to drop all the bits into the recess, then looked in to ensure correct alignment before I screwed in the mixture screw.
One of the things I loved about Airheads, you could work on the carbs just by walking past the bike 😁
 
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