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

[paulbaker1954]

Just because parts are new Paul don't discount them as a potential source of the problem. I presume you made sure what type of plug cap/plug for instance the Boyer system prefers to be installed with.
Your problem does sound carb related but sometimes the solution lies elsewhere and you lose loads of time and effort focusing on the wrong part just because your convinced it must be there.

Agreed but this running problem only occured when I changed the head gasket before that was running like a dream.

I did do some work helicoiling  the float bowl threads whilst the carbs were off and some fiddling with float levels etc

So - either the new head gasket or the carb fiddling has caused this. I have now got an OEM gasket, courtesy of DSS, to fit plus am going to check all the idle circuits and pilot jets for muck/debris. I think will also do a compression comparison across the 4 pots as well.

Guess its just a question of systematically working through what has changed!!

It feels like a fuelling problem as above 4K is running really well with no misfires

[K2-K6]

A couple of things to throw in for consideration.

If you removed the coils during work,  then double check earthing route is ok now.

Make sure plugs are at minimum specified gap.

The backfire may be a symptom / red herring of the Boyer as others have found similar effects with it.  They fire all plugs all of the time on later systems which I can't quite grasp.  They state it but don't elaborate so hard to see what is happening and why.  Anyway it does seem to give that effect under certain conditions of having unburnt fuel around. I'd separate that effect from your other problem initially.

It does look like an idle circuit impairment though as it cleans up when getting into main jet area.

The bit on other thread about winding the idle screws in and out to extreme should help you identify which carb if one circuit is blocked partially to at least give you a target to focus on.

If it helps to describe the effect,  a non fire (if all other parts are OK)  could be described as the mixture being unable to burn when sparked,  either from being too little fuel or too much in the air fuel ratio. What this does is not allow the flame front to daisy chain out through the mixture from the spark on the plug as it's supposed to do. It's unlikely to be excess as it would need to have something significant to deliver that from idle circuit. Probability is that one of the circuit is restricted as that's what is normally impaired.

You can clean these small fuel routes any number of times before they get to run competently,  a right royal pain if they keep doing this.  But they will get to run ok eventually.

[paulbaker1954]

Stripped carbs yesterday and blockages in the idle circuit in cabs 1 and 2. Also looked like a small restriction in pilot jet 2. Blew all through a few times with carb cleaner etc and all seem ok but guess I will only know when I get it all back together again.

No idea what causes this as they were fine before but I guess it only takes a small particle.

Anyway carbs back together and took the opportunity to helicoil all the float bowl screw threads.

[AshimotoK0]

Stripped carbs yesterday and blockages in the idle circuit in cabs 1 and 2. Also looked like a small restriction in pilot jet 2. Blew all through a few times with carb cleaner etc and all seem ok but guess I will only know when I get it all back together again.

No idea what causes this as they were fine before but I guess it only takes a small particle.

Anyway carbs back together and took the opportunity to helicoil all the float bowl screw threads.

Posting your rubbers today Paul ...so hopefully with you Monday

[paulbaker1954]

Posting your rubbers today Paul ...so hopefully with you Monday
[/quote]

Thanks a lot Ash much appreciated👍👍

[K2-K6]

Interested to know what particals were found,  would you describe them as clear/grey looking with a slight crystalline feel to them,  ie a bit gritty?

That's what I generally see on small jets and passages of things I'm cleaning to get them running correctly.

[paulbaker1954]

Interested to know what particals were found,  would you describe them as clear/grey looking with a slight crystalline feel to them,  ie a bit gritty?

That's what I generally see on small jets and passages of things I'm cleaning to get them running correctly.

Sorry didn't really notice them as I just sprayed volumes of carb cleaner through the pilot jets and the idle circuit and then tested with my "bagpipe" blowing method.

What mystifies me is how they got blocked so quickly given all the carbs were stripped and ultrasonically cleaned only last year and not many miles since. I did have a couple of the bowl threads helicoiled and I then helicoiled the rest (once I found out how much the machine shop was charging!!) so I wonder if a tiny bit of swarf or muck got in whilst I was doing this. The idle circuit holes are so small bore I guess any small particle is going to cause a problem. Funny it was on on 1 & 2 as well, 3 & 4 were perfect.

As I am fitting a new head gasket I noticed that the inlet valves on 1 & 2 were very "whitish" as with the plugs which would indicate a really weak mixture so I assume that when the idle circuits are blocked it is pulling in virtually no fuel until the main jets cut in

Anyway we will see when it all goes back together again !!

[K2-K6]

Agree with your assessment of jetting. Looks like 1 and 2 are running juuuuuuust enough fuel to satisfy demand at tickover,  but as you start to bring the throttle up then the air increase plus asking the cylinders to produce more torque makes it too lean to fire on those two,  until the main needle taper starts to deliver fuel that brings along normal air fuel ratio.

As to why it has got partially blocked from being clean initially,  I've some thoughts on that which I'll put into another thread.

It'll be interesting to see how it performs after your reassembly.

[paulbaker1954]

As to why it has got partially blocked from being clean initially,  I've some thoughts on that which I'll put into another thread.

It'll be interesting to see how it performs after your reassembly.

Look forward to hearing your thoughts on this as I seem to have endless carb problems over the years all down to idle circuit issues

[AshimotoK0]

As to why it has got partially blocked from being clean initially,  I've some thoughts on that which I'll put into another thread.

It'll be interesting to see how it performs after your reassembly.

Look forward to hearing your thoughts on this as I seem to have endless carb problems over the years all down to idle circuit issues

My mate got a 3k mile 500K1 from DK ...couldn't get it to run after extensive carb cleaning , new seals etc etc so he bought another set of carbs ... same thing .. so he was desperate to enter it in the Claasic Ramsey sprint,  so I 'loaned' him my 500K0 carbs and it ran brilliantly and I believe he won a race on it ... just need to prize my carbs back from him.. think he's taking it this year again and then it's time to get 'em back. The issues on the two 'failed' sets was corrosion of the casting where the main jets fit being eaten away. I did think of somehow sleeving it in brass ... maybe someone has done similar or has suggestions ... seems to be very common with 627B carb sets 

[Seabeowner]

seems to be very common with 627B carb sets 

Seems to be very common on bikes from USA, my UK bikes have both been fine,

[Erny]

As to why it has got partially blocked from being clean initially,  I've some thoughts on that which I'll put into another thread.

It'll be interesting to see how it performs after your reassembly.

Look forward to hearing your thoughts on this as I seem to have endless carb problems over the years all down to idle circuit issues

My mate got a 3k mile 500K1 from DK ...couldn't get it to run after extensive carb cleaning , new seals etc etc so he bought another set of carbs ... same thing .. so he was desperate to enter it in the Claasic Ramsey sprint,  so I 'loaned' him my 500K0 carbs and it ran brilliantly and I believe he won a race on it ... just need to prize my carbs back from him.. think he's taking it this year again and then it's time to get 'em back. The issues on the two 'failed' sets was corrosion of the casting where the main jets fit being eaten away. I did think of somehow sleeving it in brass ... maybe someone has done similar or has suggestions ... seems to be very common with 627B carb sets 

This is interesting information (corrosion)

Maybe can explain my issues too?
I have set 022A (US 550 K1) and suspect that my issues are caused by corrosion eat casting, despite carbs are clean after rebuilt by Gerben. He did blasting also from inside and a lot of pitting is visible on carb body inside bowl and casting of main jets too.

I'll continue in another thread

[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.