How does the needle jet play into performance?

[nobackhair]

Going through a set of carbs from a 78. Has a Z6 needle jet. Stock is a Z2. The Z6 origin was in 73 and 74. They look the same from pics except the oring placement. Don't know what effect it creates by leaving them in there. Only mods I've done is pods and 2 into 1 exhaust. Still has a 135 main and primary is stock. Lowered the needle to 4.

 

[5twins]

I don't think you know what you're doing, lol, or at least not how to explain it properly. First thing, Mikuni needle clip slots are counted from the top down. Stock position for the '78-'79 carb set was the middle or #3 slot. If you mean you lowered the clip to the #4 slot then you haven't lowered the needle, you raised it and made it richer. If you were counting the clip slots from the bottom up then yes, you did lower the needle one step from stock (the #3 slot) and made it leaner. But, with a richer Z-6 needle jet, things may still be too rich. Yamaha had to use the smaller Z-2 needle jet to get the 135 mains to work without causing break-up in the upper midrange, and it just barely does that. Any increase in main jet size, even one up, will cause that break-up unless the needle is leaned a step.

 

[nobackhair]

I’m going to get the Z2’s. What you said in reference to the needle jet made sense. I did intend to move the needle up. But leaving the Z6 in would be in the negative. I assumed with air pods and 2 into 1 I would have to riches something so I thought I’d start with the needle. When I got the carbs they were 3 1/2 out.

 

[nobackhair]

I meant raised the needle.

 

[nobackhair]

I realize after posting this request for help why I don't visit anymore. I'll still look for answers but......

 

[bosco659]

I realize after posting this request for help why I don't visit anymore. I'll still look for answers but......

5T answered your only question in your original post. Other than that you've only made statements about what you have done. This forum is great for getting help and information. If you need a specific answer to a question, you just need to ask.

 

[5twins]

And I'll also add that your posts aren't all that easy to understand. You don't explain things very clearly sometimes or completely. For instance, the last line in post #3 says that when you got the carbs they were 3 1/2 out. What the heck does that mean? If we don't understand what you've done or what you're asking, it's difficult to help, and most folks won't bother to try.

 

[nobackhair]

I apologize for my ignorance. And to you. The 3 1/2 out was referring to air fuel screw which specs suggest 2 1/4 to start with. When I made that and other statements like that I guess I was seeking a reaction when I should of put it to a question. At times I get to lazy to do my research and ask those who know. That's one of the advantages of this forum.
As far as my negative additive historically when I reached out I wasn't getting help unless it was you. Typically it was of some help. But I'm getting somewhat old now and haven't worked on my bikes for quite awhile and I forget things I was knowledgeable about. It was just suprising that the words you chose to start things out were a bit botheresome.