Air Screw O-Rings crushed on installation

[mpidsadny]

Hi Everyone,
Just to fill everyone in, I am rebuilding a 1979 GS850 that has sat in a barn for the past 24 years. It has Mikuni VM26SS carbs.
I’ve encountered a problem during carb reassembly where the o-ring on the air adjustment screw is getting crushed and split during installation.
I am using o-rings from an ebay carb rebuild kit fitted onto the original brass hardware.
Has anyone else encountered this issue? I don’t want to keep purchasing o-rings are having them break on installation as I am in Canada and there aren’t many good parts resources that ship quickly here. Does anyone have any useful tips?
Thanks!

[phydeauxmutt]

I use a drop or three of oil on any o-ring when I install it.

No problems yet, as long as the o-ring is the proper size to start with.

[mpidsadny]

I use a drop or three of oil on any o-ring when I install it.

No problems yet, as long as the o-ring is the proper size to start with.

I have that a try on the remaining two air screws I installed. One of them went in fine and the other split . Thanks for your input, it’s always appreciated. Perhaps I’ll try a different type of oil. I’ll try measuring them and comparing to the specs listed only to see if they’re even the right fit!

[Agemax]

Sounds like a dodgy ebay carb kit. O rings probably slightly larger than they should be. If they split with a small amount of lubricant applied then i am certain they are the wrong size.

(Also assuming the holes and threads are clean and free from corrosion and burrs!)

[mpidsadny]

Sounds like a dodgy ebay carb kit. O rings probably slightly larger than they should be. If they split with a small amount of lubricant applied then i am certain they are the wrong size.

(Also assuming the holes and threads are clean and free from corrosion and burrs!)

I’ve cleaned up the hole the best I can, but may go back in there with a tiny razor blade. Do you have any suggestions for o-ring kits? I know cycle o-rings is no more and don’t know where to go.

[Nessism]

You need O-rings sized 2.8mm (ID) x 1.6mm (thickness)

Use silicone grease on the O-rings during install into the carb bodies.

[93Bandit]

Sounds like the wrong size O ring.

Check post # 8 in this thread, inwhich I posted a link to an ebay kit that has all the o rings you'll need. I posted 2 links in that post, one for CV the other for VM carbs. Be sure you order the VM kit. I have used the VM kit without any issues. https://www.thegsresources.com/_foru...o-ring-sources

[mpidsadny]

Sounds like the wrong size O ring.

Check post # 8 in this thread, inwhich I posted a link to an ebay kit that has all the o rings you'll need. I posted 2 links in that post, one for CV the other for VM carbs. Be sure you order the VM kit. I have used the VM kit without any issues. https://www.thegsresources.com/_foru...o-ring-sources

I purchased a set from the seller zed1015 linked in that thread as retro-motorcycles has my kit out of stock. The seller I bought from sounds legit and advertises them to be made out of viton. Thanks for your post!

[sacruickshank]

one more check on size. If you have the original washer for the pilot screw, the oring is usually the exact same size as the washer. Also, most fit snuggly over the main body of the pilot screw. if the oring is larger than the washer or fits loosly on the screw, chances are its too big and will get squished or ripped on assembly.

[Agemax]

We need to be clear on what screws you are referring to here. Is it the AIR screws on the side of the carbs, or the fuel pilot screws on the underside of the carbs?
IF it is the fuel pilot screws you are referring to then they must have a washer on them, between the spring and the O ring, otherwise the small spring will damage the O ring.
The air screws on the side have no washer, just a spring.

[Nessism]

We need to be clear on what screws you are referring to here. Is it the AIR screws on the side of the carbs, or the fuel pilot screws on the underside of the carbs?
IF it is the fuel pilot screws you are referring to then they must have a washer on them, between the spring and the O ring, otherwise the small spring will damage the O ring.
The air screws on the side have no washer, just a spring.

There is no washer on either pilot screw for the VM carbs. It's the BS CV carbs that have the small washer with the pilot screw.

[Agemax]

There is no washer on either pilot screw for the VM carbs. It's the BS CV carbs that have the small washer with the pilot screw.

You are right, i stand corrected