What is this carb part and does it matter that it's cracked?

[Sirhc]

Hi Guys,

While rebuilding my carbs, I've noticed a fine hairline crack running about ½ to 2/3rds of the way down the brass tube that goes up into the float assembly (indicated with a red arrow on the attached pic).

It's definitely a crack and not a scratch or mark and both carbs are the same – I've tried a search and found nothing.

What is this carb part and does it matter that it's cracked?

Thanks,

Chris


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[yamahonkawazuki]

Anyway we can get a macro of said crack/s? tbh im thinking it IS critical, ( if anything is cracked or loose or broken inside a carb, usually it wont work @ 100% . but cannot tell w/o being able to see it.

[prmas]

That may be an "emulsion tube", which is a mixture modifier for the progression between fuel supply systems (pilot/main). As both are the same it may not be a crack. It may have been made that way. I have never had my carbies apart so I am not sure what is in there but car carbs have various styles of emulsion tubes with graded holes or slots. I am sure that someone here will have an exact answer as many OP have had theirs apart. In the worst case it would only result in a slight change to the mixture at light throttle openings. If it is running OK and not gulping fuel I would leave it alone. 

[Sirhc]

Ha Ha yeah Yama - I was being kind of tongue in cheek when I said that! Definitely think it's likely to matter 

That said I've been reading up on mikuni carbs and it looks like it might be part of the enrichment (choke) circuit so I'm hoping that it's only an issue when the choke is on? I really don't want to have to buy new carbs

I did take a pic, but it didn't show up on the image – I will try again with a better camera.

prmas - they are the same in as much as both are cracked but one crack seems longer than the other (I should have been clearer there!) so I'm fairly certain that it shouldn't be there. And yeah, I'm definitely an "if it aint broke don't fix it kind of guy" but it does run poorly. It bogs really badly off the line, and gets worse as it warms up - seems to be quite rich in that region. I've currently got the pilot screws set at 2.5 turns out (which improved it) and I'm thinking of trying 2 turns out to see if it helps further. That seems to be counter intuitive to what everyone else here says (i.e. 3-3.5 turns out etc) particularly with the pod filters.

This thing looks like a tiny little (fixed) jet – its a brass tube with a plug in the end that has a tiny hole in it. The tiny hole makes me think that any fuel flowing through it is likely for low revs rather than WOT and that maybe the cracks are letting too much through – hence the need to lean the mix with the pilot screws?

Thanks guys,

Chris

[The Buddha]

That is the float retaining pin plus it has a tiny orifice to send gas to the gluc-gluc-lab

I dunno if a crack gonna be too bad ... is it horizontal or vertical ... horizontal it may break off, and then your floats have no way of fitting on it ... vertical, may not be of any consequence it may be OK.

Cool.
Buddha.

[yamahonkawazuki]

That is the float retaining pin plus it has a tiny orifice to send gas to the gluc-gluc-lab

I dunno if a crack gonna be too bad ... is it horizontal or vertical ... horizontal it may break off, and then your floats have no way of fitting on it ... vertical, may not be of any consequence it may be OK.

Cool.
Buddha.

always the option of a smear of jb-weld if need be. but I don't care for a bandaid on a problem. it would work, BUT how long idk?

[prmas]

If it is brass you can just gently solder the crack shut without any problem. It sounds like it is too rich on the progression from idle to main circuits. Have you had the exhaust gas analysed? An experienced mechanic can diagnose many carby/mechanical problems just from the digital readout. Even with a fully functional Catalytic Converter it is not too difficult. As the revs slowly increase from idle the CO2 should rise slightly and any CO and HC should decrease slightly. If the opposite happens it is too rich on progression. On a standard setup under no load (hot engine and exhaust) you should have virtually no CO (<1%) or HC (<200ppm), CO2 of around 14-15% and O2 of no more than 0.5%.

[Sirhc]

Hi Buddha - Luckily the crack is the vertical, so It shouldn't break off. My only concern is if its making things run rich? Thanks toy you I now know its flowing fuel, but err...  whats a gluc-gluc-lab 


Yama - I'd considered that (or even sleeving it with heat shrink or something like that), but yeah like you I like to know it's fixed "properly" - pramas's idea sounds more "propper" so I'll probably go with that.

prmas - I've not had the exhaust gas analysed - I'd be really interested in seeing the results of that, and maybe doing a dyno run (just for the hell of it!) but the bike cost me £300 so I can't really justify spending mechanic money on it  I'll have to keep an ear out for a "friend of a friend" who has access to one! 
So I think I'll take your suggestion of soldering it up and see what happens?

Thanks,

Guys

[hornet6]

Hi. My carbs are giving me the same type of problem....chugging at low revs,then picking up a bit further in the rev range. And its running very rich. A local mechanic told me that maybe one of the diaphrams could have pin holes in it...which would explain it running rich and being heavy on fuel. I intend to take the bike off the road next weekend and have a good look at the carbs to see what the problem is.     

[prmas]

Well Sirhc, my 4 GAS Analyser is at your disposal. The only problem is 20 odd hours in an aeroplane for one of us. You and your bike or me and the analyser. 

Try the soldering. I have done it in the past with broken emulsion tubes and it usually works as long as you don't fill up the tube with solder. Just lay it gently on the outside. 

[Sirhc]

Hi Guys,

Finally got around to sorting this - pulled the carbs off, dismantled them totally and soaked them overnight in Lemon Juice.

Built them back up making sure all the o-rings and gaskets were good and then soldered the cracked brass.

Seems to have sorted the low speed bog!

Yeah, ok I broke the first rule of fault finding by changing two things at once, so I cant say for certain weather it was fixing the crack or the carb clean, but it seems to have addressed the problem.

I suspect it was actually the carb clean (the crack was REALLY fine - less than I remembered but definitely there!)

Chris