Carburetor intake insulator and o-ring damage

G-Man · Post by **G-Man** » Mon Apr 07, 2014 12:52 am

Rob

Nice job!

G

SWARDLAW · Post by **SWARDLAW** » Mon Apr 07, 2014 11:13 am

I had the same problem two years ago with the spacer on my ca78 and was at a vintage rally and couldn't get a replacement at that time. A gentleman on a old triumph told me to cut a paper gasket to replace the o-ring. The gasket paper I bought at advance auto and used a knife to cut out the shape of the spacer. It fixed it so I could ride the rest of the weekend. That gasket is still on the bike.

Snakeoil · Post by **Snakeoil** » Mon Apr 07, 2014 11:56 am

If it pops the side out again, I will fill the groove completely with epoxy and use a paper gasket. I was going to do it this time, but wanted to see if the JB Weld fix would hold up.

Glad you hear you had success with the gasket.

By the way, if you put your location in your profile you'll get help quicker here. There seems to be an unwritten rule of no location, no response. I believe the intent is to show where you are in case others that can help will know that they are local to you. I understand that. I met a rider on the Triumphrat forum that needed help and I ended up letting him use my specialty tools to pull his clutch hub and similar stuff.

regards,
Rob

Snakeoil · Post by **Snakeoil** » Mon Apr 07, 2014 1:52 pm

Looks like it will be plan B. I finished putting the bike back together and as I was headed out to get a fresh batch of ethanol free premium, I decided to take my flashlight and see how clearly I could see those repairs so I could keep an eye on them. One of them has already let go.

So, that's it. I'm going to pull them out again and this time bead blast the grove so it has something to bite into and epoxy the whole damn thing and use a paper gasket.

I suspect it might be that I'm using US O-rings instead of metric and there is too much expansion when the carb is tightened down. The two o-ring assortments I have do not go up to 28.5mm so I'm reliant on what I can find locally.

I realize that a lot of Hondas are running out there with this design. So, that's why I think the root cause is the o-ring I'm using.

The good news about this is this could also be the root cause of some of the running problems I've had with the bike over the years. If that insulator was breaking shortly after reassembly, then that would explain why I had everything right and yet it still would not run consistently well.

regards,
Rob

regards,
Rob

Snakeoil · Post by **Snakeoil** » Mon Apr 07, 2014 5:08 pm

I check the depth of the groove in the insulator and it measures 2mm. So the proper O-ring would be a 2.5mm based on what I found on the web for metric O-rings. In inches, that would be 0.0984". I then checked standard inch O-rings and closest size is 3/32" which is 0.09375. So, if anything, the inch O-ring would have less compression and exert less force on the insulator block.

So, now I'm starting to think that the material, which I think is Bakelite, is just so old it is not able to handle the stress any longer.

I pulled my carbs off and looked at the failed insulator as well as the repairs and unfailed one under a 10X loupe. I found a crack on the ID root of the groove. That is disturbing because if a piece breaks off the ID, it will be swallowed by the engine.

Here you can see the ID of the insulator starting to break thru. This happens to be the one that did not fail the repair.

Here is the other side showing the crack at the root of the groove ID.

So, I have bead blasted both insulator blocks and filled them with standard JB Weld Steel epoxy. It has a 4-6 hour set time, which provides for a stronger end product. Tomorrow I'll trim off the excess and install them with a paper gasket and Hylomar on both sides of the gasket as a belt and suspenders approach.

I'm starting to wonder how many riders with erratic engine running issues might not have the same problem going on.

regards,
Rob

rrietman · Post by **rrietman** » Mon Apr 07, 2014 10:46 pm

Rob; I have a bag full of broken insulators as well. I have never seen one come off an old engine that was not severely warped (heat/design?) if you can get an unbroken one and flatten it, there are no worries for the little bit we run these vintage machines anymore.
Good luck
Randy

G-Man · Post by **G-Man** » Tue Apr 08, 2014 2:22 pm

Rob

I don't think the material is bakelite. More like a reinforced resin material sold as Tufnol in the UK. There are various grades using paper or cotton as the reinforcing material in some kind of phenolic resin. A kind of light engineering version of FRP.....

http://www.tufnol.com/tufnol/default.asp?id=117

G