Head to carb rubbers 16211-323-000 - aftermarket source?

[AshimotoK0]

I think carbs that just gum up with petrol residue are fine but once water gets in there you get a nasty white corrosion that usually takes some kind of media blasting to remove and inevitably afterwards it looks a bit 'moth eaten'. not so bad with float bowls but the tube formed in the main casting which the jets push into is quite delicate and can pit and erode quite badly to the point where the '0' ring no longer seals. I have heard of people saying they put some sort of sealing compound at the joint but not so sure anything is that petrol resistant. To me a decent fix would be to try and bore out the 'tube" and press in a brass sleeve. Will have to have a go sometime.

[K2-K6]

I was going to put on another thread only to separate out the subject,  but it's gathering more relevant information in here so sensible to continue.

I've been getting to the same conclusion not just for these carbs but many others that routinely block small jets that it's corrosion causing it.

It looks like ethanol could be significant in this process as it can promote properties that will advance corrosion and has been more widespread for longer period in USA fuel supply. 

Question,  do these carbs have a "handed" casting for carbs one and two compared to three and four? If so do they alter the position of idle jets in relation to centre line of bike?

If they do,  would storing the bike on side stand give the left two carb's idle jets (nearest side stand) more or less fuel level?

The zinc in casting used for carburettors effectively oxidises (darken,  tarnishing)  which offers protection from further decomposition,  a little like anodized aluminium,  and so resists plain all out corrosion generally. 

Corrosion is more effectively carried out with electrolytic assistance. One of the characteristics of ethanol inclusion is absorption of water and conversion of some parts of the resulting mix to acetic acid, half the properties of electrolysis!  The other being some voltage persistence. 
These carbs are generally not earthed,  you can try metering continuity from carbs to engine with zero connection. So if you build any inherent static? In the assembly,  is this significant enough to get small scale electrolysis going?

You also need anode and cathode to do this.  Brass and zinc appear at different points on galvanic scale making them fulfill those roles.  The residual gunge I've cleaned out of carbs looks like zinc oxide,  which ties in with the comments in previous posts that zinc is being scavenged from the casting but not going at far as to plate the brass.

The small idle jets could just be offering the best site with voltage available to propagate that action. 

Acknowledging that the above potential adds two plus two and comes up with thirteen  the elements of this plating action all seem to be present.

Could something like putting an earth strap to carb bank effectively prevent that?  Can fuel stabilisation additives prevent degradation to acid formation in ethanol mix fuels?

[Erny]

Interesting thoughts, especially part linked to electrolysis!

Nothing prevents to try it, to route one cable from carbs to bike ground point near to colis for example or main grouding point near to clutch lever. But to evaluate effect will take some time

I do believe that fuel stabilization additives helps to prevent fuel degradation, many people told me since they use them they do not observe these issues anymore. I mean additional additives they put into fuel.

[K2-K6]

Agree about timing Erny,  if it has any affect with an earth strap it could be proven in original poster's situation of compromised idle jets within a year perhaps.  Also as to why just two carb's on left side seem to by affected and not the other two.

https://www.equipmentworld.com/e-10-alive-the-corrosive-damage-ethanol-gasoline-does-to-your-fuel-pump/

Above Link gives some insight in relation to acid propagation.

Perhaps a shift to plastic, stainless or titanium jets would offer something in changing the conditions within the carburettor that are worth evaluation.

[paulbaker1954]

Question,  do these carbs have a "handed" casting for carbs one and two compared to three and four? If so do they alter the position of idle jets in relation to centre line of bike?

If they do,  would storing the bike on side stand give the left two carb's idle jets (nearest side stand) more or less fuel level?

Let me weigh in again

1) No there are not handed in respect to the idle circuits.  If you study the carbs they have brass "blanking" balls to close off the idle circuit not being used if you get what I mean.  If you look at the picture I have stolen from ERny's post. This means idle screw ends up on 1 &2 carbs on LHS of body and for 3 & 4 carbs on RHS so you can get at them to adjust





 

2) My bike is aleays parked on Main Stand and still has these idle circuit issues so I dont thin leaving on side stand is the culpit

[K2-K6]

Yes I saw, after my post, the Erny pictures of the float chambers to get the orientation.

My post is as much speculative theory,  but based on other experience of electrolysis,  than statement. Hopefully it can bring up questions and possibly answers to help here.

Many of the examples I've seen have this effect from fuel that's been filtered via those sintered metal inline filters,  so the chance of debris entering is really small.

In your case Paul we can discount the tilted storage view, but for your example only. And just relating to your specific fault on carbs one / two.

Any bikes stored on their sidestand have the potential to keep the adjustment screws on left two carb's in different condition to the two right side one's,  so it may be a longer term factor.

But to add a little more for consideration,  if those two carb's had been exposed to corrosion prior to your ownership then once cleaned and used,  it's possible that the surface within the idle circuit is much more pre-disposed to the same happening again.
With that,  what does ultrasonic cleaning do to the surface?  You often hear the statement "they've been ultrasonic cleaned but they still get blocked idle circuit" in other words,  if they've previously been corroded does the removal of (possibly) zinc from the internal idle passageway now have a vulnerable surface?

It would be interesting to get a voltage reading with the following,  positive on battery +terminal and negative on carb body,  if anyone has the facility to measure.  With ignition switched off.