Carb Jets - WhenTo Replace?

[BPT]

I know that there are certain parts that will change and wear over time, like the needle and its corresponding jet, for example. And the float needle as well. What about the others, are they good nearly indefinitely as long as they're kept clean?  Or are there any particular problems that show up and indicate they might need replacing?
I need to rebuild the carbs currently on my bike, which has been sitting for a while.  I also have a spare set that I acquired and have never run and was considering doing these as well.  I was starting to make a list of pieces and parts to buy and that made me wonder about this.
What do you all replace "just because" and what do you deem unnecessary to mess with unless you have a specific reason? And since the one set hasn't been run so therefore "condition unknown", would that make a difference to you?
Budget is a consideration and as many of you probably know, some of these tiny carb parts aren't exactly cheap.

Thanks

[Barry]

. What about the others, are they good nearly indefinitely as long as they're kept clean? 

I would say there is no need to replace jets that are not subject to mechanical wear in operation.   I'm fairly confident that my mains and pilot jets are the originals.

If new jets were being considered, a concern I would have is how much you could trust new jets to be accurately sized.   We tend to assume that a new replacement jet will be the same size as the old one but I've seen data that showed some quite wild inaccuracies in the way new jets were machined.    Have a read of this, it's not about our carbs or our bikes but it will open your mind to the idea that new carb jets may not be very accurate.

http://www.saltmine.org.uk/martin/jet_sizing.html

[Bob_Roller]

Other than the jets you mentioned that are subject to wear for the most part they won't require replacement, unless damaged .
I've had to replace 3 idle jets that got clogged and I could not get them open .
Since I went to a pleated paper element fuel filter, no issues since .
The only jets I have ordered, were from a Bing carb business here in the US .


http://bingcarburetor.com/index.html

[BPT]

Thanks guys, that's what I needed to know.  I was thinking the same but wanted to be sure I wasn't missing anything. As far as where to get them, in the past I would've looked at Motobins but with price hikes and shipping costs I don't think they're as good for us in the US as they used to be.  The other options off the top of my head would be Bing, as Bob suggested, Euromotoelectrics and Max, although Max can be expensive. Any other suggestions are welcome.  I know that there are some other brands of things like diaphragms and even no name brands of the gasket/o-ring rebuild kits, but I haven't heard anything about the jets. Are there crappy repros of these as well (so therefore one needs to only order from a reputable place)?

Barry - I haven't read your article yet.  When it comes to buying new ones, are you saying there could be a problem even when buying legit Bing jets? 

[Barry]

Barry - I haven't read your article yet.  When it comes to buying new ones, are you saying there could be a problem even when buying legit Bing jets?

I really don't know but when you have read the article I think it makes the point that production of carb jets might not be the exact science we think it is and that introduces  the possibility of new jets being worse than old ones.  That's persuasive enough for me to leave well alone as far as jets that are undamaged and not worn.

[Justin B.]

I thought that I had read somewhere that the main jets in the Bings were subject to some wear due to the "needle" vibrating in the jet hole and introducing wear.  Seems I also read that needle and jet should be changed as a pair but as old as I'm getting I'm not staking my life on it!

[BPT]

Barry - I read that article, very interesting. It seems strange that they would change something like this where tiny amounts can make a big difference without accounting for it somehow.  It was late when I read it and I was tired but I think the guy was talking about Mikunis.  Was there something there to indicate that our Bing jets would be the same?

Justin - if the first one you're talking about is the float needle, I was wondering the same thing. I know that if you have issues with the jet surface that you can use valve lap compound to smooth it out. I was wondering if that was acceptable if replacing the float needle as well, to clean up the jet surface or just replace it completely.

[georgesgiralt]

I thought that I had read somewhere that the main jets in the Bings were subject to some wear due to the "needle" vibrating in the jet hole and introducing wear.  Seems I also read that needle and jet should be changed as a pair but as old as I'm getting I'm not staking my life on it!

Hello Justin,
I've not checked but I doubt the needle be so long it could reach the main jet which is at the other end of the jets holder. But price is not that will refrain from renewing it. And given the actual price of fuel, saving on fuel will pay for it soon.
As per the manufacture of jets, carb builders in their wisdom used brass for them because it is very easy to maintain a very high accuracy in the shop. It is difficule to machin, though, you need proper tools and lubricant but frankly, high precision is "easy" to achieve if you decide so. So I bet the carb maker which is the culprit in that article has tried to save money by farming external production in a sloppy factory unable to achieve proper work.
I renew the needle and needle jet every time I service my carbs and it shows with improved fuel mileage and ease of tuning. And it is not costly nor difficult.
Just my 2¢

[Barry]

Barry - I read that article, very interesting. It seems strange that they would change something like this where tiny amounts can make a big difference without accounting for it somehow.  It was late when I read it and I was tired but I think the guy was talking about Mikunis.  Was there something there to indicate that our Bing jets would be the same?

Yes he was talking about Mikuni's but I believe what he measured could well be indicative of all carb jets.  Producing jets is a high precision   business. As an example a 1000th of an inch error in machining a main jet would typically make it the next size jet up or down and produce a 10% change in the mixture strength. I'm just sceptical that new jets are always identical to the originals in every way.

Justin will have meant the needle jet and a similar degree of precision applies.  A one size change in needle jet is only 0.0008"  So you can imagine that it doesn't take much wear for a needle jet to be worn to the next size bigger which would produce a 10% change in mixture strength.

[Justin B.]

Kinda makes you wonder if they jut don't "drill" a buncha jets then flow them to see how they should be marked!  I know hard-core hot-rodders will do that to make sure jets are matched in their multi bbl carbs.

[Barry]

Kinda makes you wonder if they jut don't "drill" a buncha jets then flow them to see how they should be marked!  I know hard-core hot-rodders will do that to make sure jets are matched in their multi bbl carbs.

I think they do, using compressed air for convenience. That would work once a comparative benchmark had been established.   

[georgesgiralt]

Frankly, with brass very high precision is easy if you decide to go this way. But I think they cut corners to save a huge amount of money (like the tire maker saying "if it's black and round, sure it is a tire")...