TOPIC:

The pictures say all that is needed!
I ordered a set of six for myself and they'll be going in right after I set-up a customers carbs.
Old Idle jet - Mikuni and probably originals



New Mikuni

The difference is huge Bob!
I am wondering, in the last photo the darker specks are discoloration or just some dust?

I’ve been following this post with some interest for sometime now and have been wondering if the problem I’m having with the misfiring between 1500 and 2500 rpm could be attributed to the pilot jets. I don’t have a microscope to check the condition of the jets but I remembered something from my apprenticeship as a plumber/heating engineer. Decincification. Could this be what’s causing the loss of material/pitting to the jets. Brass contains zinc and under certain conditions the zinc can migrate from the brass leaving the surface pitted or even porous.

Found this on the web which could possibly explain why the jets have been left in this condition after prolonged contact with petroleum.

file.scirp.org/pdf/JMMCE_2014043011513328.pdf

Regards

Martin.

I am wondering, in the last photo the darker specks are discoloration or just some dust?

An omission on my part. Appears to be discoloration (perhaps some oxidization) which is highlighted by the smooth shiny finish.

The old jets are probably in their present condition due to old age, exposure to various chemicals/additives, dezincification, electrolysis and inherent flow-erosion.
Regardless - New jets were not an option........ they were mandatory !

I just read the article Martin suggested and can't agree more with what you are saying scotch. Added vacuum, high velocity flow, whatever detaches itself from the jets hitting more areas for more erosion, and that's the result. I had no idea by the way, and it was great to read, that brass preforms worst in petroleum! I was also thinking what would make a better material choice and titanium came to mind, but yes, that would be probably more expensive. I think the makers didn't even consider it and if they did, it would make more sense from the production and maintenance perspective to make them from brass and simply replace with new when needed.

You're absolutely right Stan, the cost of manufacture has to be balanced against the jets' service life, so if it takes 10 + years to errode to an extent that degrades performance, and the whole set only costs a couple of hundred dollars, then that's a perfectly acceptable mid-life service cost I think.