Needle Jet/Jet Needle Replacement ?

[Jeff in W.C.]

Quick question. 15k miles since my last carb rebuild. At 15k, would you replace the jet needles and needle jets? I searched but couldn't find a recommended time frame. While the jet needles have some discoloration, I could not feel a ridge with my fingernail.

[SteveD]

Personally I’d leave it for now. Good question re frequency, my guess is 30-40Kkm or when mileage starts to reduce.

Do you have a common ride you do where you can gauge fuel use? If you’re fussy enough to do that run as and do comparison of fuel use, you’ll “know” when they’re getting worn as mileage reduces.

I changed mine years back and haven’t thought about it again.

[barryh]

Generally it's the needle jet that wears more than the needle. I'm on 22,000 miles on the same jet. I think 30,000 is considered time to change.

Needle jets are hard to measure for wear. There is only 0.02mm or 0.8 thou difference between the next size up of jet so that's probably the amount of wear that should trigger a change.

One thing I've done for many years now is dose the fuel with TCW3 2 stroke oil in a ratio of 1:640 which amongst other effects may provide a little lubrication and reduce carb wear.

[melville]

Yes, probably going to do that soon on Ernst. Over 30K miles on needle jet and needle and MPG is stuck on 40. Although part of that might be the very bulky Aerostich jacket. The springtime weather is improving and I wore the much slimmer Alpinestars jacket today. Although today's miles were with pillion, but she's a wee skinny thing.