David Jenkins
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| posted on 17/7/21 at 01:10 PM |
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Today's annoyance
Finally got time to put the bike carbs back on my car. All went together neatly, turned on the ignition - and a fine spray of petrol came out of one
of the carbs' internal connectors. 
I knew what it was as soon as I saw it - the 2 outer pairs of carbs have a connecting piece with o-rings on the ends. If the carbs haven't been
used for a long time the o-rings dry out (maybe helped by ethanol) and need to be replaced. This first happened when I originally fitted the carbs
ages ago, and now they've been lying idle for a year or so. Easy enough to separate the carbs and change the o-rings, if you can find the right
type.
I did a bit of research and found HNBR o-rings - Hydrogenated Nitrile Butyl Rubber - which, apparently are resistant to most fluids found in cars, and
are commonly used in the motor industry. Although only one failed, I'm going to replace all four. Had great fun finding an eBay supplier with
imperial sizes (my Japanese carbs contain a weird mixture of metric and imperial sizes!) but eventually I found just one listing. Hope they're
good...
With any luck I'll get this car back on the road just as the current hot, dry weather finishes... 
[Edited on 17/7/21 by David Jenkins]
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theconrodkid
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| posted on 17/7/21 at 01:56 PM |
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i feel your pain, i wanted some similar rings, found them in Scotland, gave them a bell...send us a cheque, when it clears we will sent the O rings ,
managed to get them from the good old US of A in the end
who cares who wins
pass the pork pies
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Mr Whippy
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| posted on 17/7/21 at 03:35 PM |
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Hope this time you have ordered spares...
Too hot today for open top cars anyway. Even in the tin top the kids were burning themselves on the seats and seat belts. Too hot to do very much
really, we had a picnic in the park hiding under a tree but the garage is sickeningly hot, I'll have to wait till evening to go in there.
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David Jenkins
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| posted on 17/7/21 at 03:42 PM |
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Supplier only had 4 available. They'll do until I can order a few more.
I know what you mean about the heat - I did most of my car work at 8am - 11am. This afternoon the sun's moved round to the front of the garage
so there's no way I'll be working in there! I had a couple of M6 nuts sitting on a black metal sheet in the full sunshine, and I nearly
burnt my fingers picking them up.
Telly's boring tonight (most nights!) so I might spend a while out there once the sun's gone down.
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40inches
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| posted on 17/7/21 at 04:15 PM |
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quote:
Originally posted by Mr Whippy
Hope this time you have ordered spares...
Too hot today for open top cars anyway. Even in the tin top the kids were burning themselves on the seats and seat belts. Too hot to do very much
really, we had a picnic in the park hiding under a tree but the garage is sickeningly hot, I'll have to wait till evening to go in there.
Took the hardtop off the MK yesterday, put on back on today 
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Dingz
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| posted on 18/7/21 at 10:11 PM |
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HNBR won’t last too long, you need Flourocarbon, trade name Viton for modern fuels. Sorry if I was still working I could have sorted some for you.
Imperial sizes are still very widely used in the o ring world.
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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Mr Whippy
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| posted on 19/7/21 at 06:27 AM |
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quote:
Originally posted by Dingz
HNBR won’t last too long, you need Flourocarbon, trade name Viton for modern fuels. Sorry if I was still working I could have sorted some for you.
Imperial sizes are still very widely used in the o ring world.
Flourocarbon... is that not the stuff that if burned turns into so horrific an acid that if it gets onto your skin they have to chop limbs off??
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snapper
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| posted on 19/7/21 at 06:35 AM |
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Same issue with my carbs which I fully rebuilt with new Viton O rings.
The where the plastic T piece fits in the carb body is a sharp edge which tore one of the O rings and broke the plastic T piece O ring slot, which
meant I had to separate the carbs again.
This time on refitting the T pieces the other one shattered when I did up the fuel pipe clip.
I could find brass replacements of the right size and plastic secondhand ones were 48Euros, a helpful guy on a Gacebook forum sent me a pair.
What a faff.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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David Jenkins
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| posted on 19/7/21 at 01:54 PM |
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quote:
Originally posted by Dingz
HNBR won’t last too long, you need Flourocarbon, trade name Viton for modern fuels. Sorry if I was still working I could have sorted some for you.
Imperial sizes are still very widely used in the o ring world.
You've opened up a can of worms for me! I decided to do a deeper bit of research, and realised that o-ring materials is a very complicated
subject - but it does seem like Viton is the stuff I need. The research seems to suggest that Viton is a bit better than HNBR when dealing with
petrol/ethanol, but both can be susceptible to long-term damage. In my case, the original o-rings (which I'm sure were Viton) were OK until
they dried out, so maybe they suffered some damage but, being swollen in use, didn't allow a leak.
To be absolutely sure, I've ordered a set of Viton rings, although it was a struggle to find 5/16" i.d. x 1/16" section rings. I
found some that are fractionally thicker section (not by much) so I hope those will work OK.
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David Jenkins
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| posted on 19/7/21 at 02:00 PM |
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quote:
Originally posted by snapper
Same issue with my carbs which I fully rebuilt with new Viton O rings.
The where the plastic T piece fits in the carb body is a sharp edge which tore one of the O rings and broke the plastic T piece O ring slot, which
meant I had to separate the carbs again.
This time on refitting the T pieces the other one shattered when I did up the fuel pipe clip.
I could find brass replacements of the right size and plastic secondhand ones were 48Euros, a helpful guy on a Gacebook forum sent me a pair.
What a faff.
Originally my carbs had plastic T-pieces, but when I respaced them I had to make new ones out of brass as the originals were too short. My lathe + a
background in model engineering comes in useful sometimes!
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Dingz
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| posted on 19/7/21 at 04:15 PM |
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Glad you found some, the story is that when viton is burnt and mixed with water it can form Hydroflouric acid which is very nasty stuff indeed but
here is a section from a government issued statement.
As with many urban or industry myths, there may be a tiny element of truth that makes the story more believable. In this case it goes back to 1981 at
the National Nuclear Corporation in Risley (UK). An experiment was been carried out to see what happens when a Viton O ring was heated to about 400
Celsius in sealed test rig. When the worker dismantled the apparatus a clear liquid was ejected under pressure very close to his fingers. This led to
discomfort and an untreated deep-seated burn developed over a period of days – eventually leading to amputation of part of his finger. The incident
was investigated by HSE and, on repeating the experiment it was shown that hydrofluoric acid (HF) was produced (from hydrogen fluoride gas in presence
of water). It can cause corrosive burns due to free hydrogen ions, and chemical burns from tissue penetration by fluoride ions. However, it is readily
treated by the use of calcium gluoconate gel.
Most cars will have fluoroelastomer lined fuel hoses and any seals in the system will be too so don't get too worried Mr Whippy, I dread to
think of what chemicals are released when an EV catches fire!
The next materials up from flouoroelastomers are Perflouoroelastomers which I guess will be needed for the new fuels they are developing, the problem
is a few years ago they were about 50x more expensive!
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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rusty nuts
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| posted on 19/7/21 at 06:13 PM |
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All seals in Norwich are very helpful if you need any seals in the future David
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David Jenkins
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| posted on 19/7/21 at 06:25 PM |
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quote:
Originally posted by Dingz
As with many urban or industry myths, there may be a tiny element of truth that makes the story more believable. In this case it goes back to 1981 at
the National Nuclear Corporation in Risley (UK). An experiment was been carried out to see what happens when a Viton O ring was heated to about 400
Celsius in sealed test rig. When the worker dismantled the apparatus a clear liquid was ejected under pressure very close to his fingers. This led to
discomfort and an untreated deep-seated burn developed over a period of days – eventually leading to amputation of part of his finger. The incident
was investigated by HSE and, on repeating the experiment it was shown that hydrofluoric acid (HF) was produced (from hydrogen fluoride gas in presence
of water). It can cause corrosive burns due to free hydrogen ions, and chemical burns from tissue penetration by fluoride ions. However, it is readily
treated by the use of calcium gluoconate gel.
One of my more elderly friends used to be a research chemist for most of his working life. Hydrofluoric acid was one of the few substances that he
hated working with. Really nasty stuff.
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David Jenkins
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| posted on 20/7/21 at 01:32 PM |
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LATE UPDATE: Four new Viton o-rings fitted, and now there are no signs of leaks - I love it when a diagnosis is correct!
However, I had forgotten what a total PITA it is to reassemble a set of 4 separated Mikuni carbs - at times I needed 3 or 4 coordinated miniature
hands to hold all of the pieces in place before they would slide together. Unfortunately all I had was my standard-sized pair of mitts.
Especially tricky when the last time I had them apart was about 5 years ago, and I had to remember how all the pieces fitted. Didn't have any
bits left over though, which is good...
[Edited on 20/7/21 by David Jenkins]
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Deckman001
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| posted on 20/7/21 at 05:18 PM |
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Well done David, hopefully you can get ya car back out on the road and restart enjoying driving it 
Jason
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David Jenkins
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| posted on 20/7/21 at 05:24 PM |
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quote:
Originally posted by Deckman001
Well done David, hopefully you can get ya car back out on the road and restart enjoying driving it
I will do, once I've reset the carb balancing (I had to wind the adjustment screws back so that I could reconnect all of the linkages).
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David Jenkins
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| posted on 21/7/21 at 01:51 PM |
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and... it's now running well.
Been out for a quick drive and had no problems <touches wood> 
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Deckman001
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| posted on 21/7/21 at 05:13 PM |
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Well done David, sounds good, I just need to find a bit of time to retest mine too now
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