The difference in length is not a problem but if I were you I would NOT change needles unless
yours is definitely worn or bent.
The ZH needle is OK but the KN is probably better.
Are your throttle shafts good and tight in the body? That is usually the biggest problem
other than float valves that don't close (and flood).
In general I have done better getting the parts I need rather than kits.
Joe Curto is fairly close to you and can probably get parts to you the next day.
If you do try to separate the needle from the socket be VERY careful of the needle.
I usually clamp it in a vise between a couple blocks of soft wood.
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George Downs, Bartlesville, Heart of the USA!