Topic: Mikuni Needle Jet

[rtbmrgl]

I have a question about simple jetting. I hope this makes sense.

Mikuni jet needle O-0 is one step richer than N-8. My question is what do think the jet needle clip position would be to equal the same richness using the different needle jets.

Example-- would clip in the 2nd (O-0) position be the same as 4th (N-8). Jet needle has 5 positions.

[simon#42]

it will never be the same as the n8  the o0 is richer everywhere , that is the whole point of using a richer needle
you could try and raise the clip a notch but that would make it to weak  . if you want it the same as an n8 use a n8

[rtbmrgl]

thanks simon,
I thought about the next size leaner needle, but there seems like a lot of different tapers so I thought a leaner jet would be the best way to go.
 

[simon#42]

what problem are you trying to solve ? 

[rtbmrgl]

Situation is it runs rich with clip on 2nd position (from top) after installing Boysen Reeds, which they said is normal and leaning mixture maybe required. So was thinking going one size leaner needle jet to get the clip closer to the middle, so to have leeway riding in higher elevations. I live at sea level.
The plug didnt foul, but at times after starting cold sometimes it will foul. Once engine hot, no fouling.

[simon#42]

in that case one size  smaller on the needle jet may well be the best option , i would not change the needle clip position .
what bike is this for ?

[scottly]

it will never be the same as the n8  the o0 is richer everywhere ,

The needle clip position and needle jet are mostly effective in the low to 3/4 throttle range, not everywhere. When I was dyno-tuning the "ditch pump", I found the the proper main jet required the needle clip to be in the top, leanest position to prevent a blubbering rich condition just off idle. One of these days I might switch to a leaner needle jet so I can have some adjustment range with the clip, but it's not a major issue.

[simon#42]

if it was rich just of idle i would change the throttle cut away ... unless it was your ditch pump scottly , then i would just throw the lot in a skip and be done with it .


only joking !

[rtbmrgl]

in that case one size  smaller on the needle jet may well be the best option , i would not change the needle clip position .
what bike is this for ?

Some trail riding, desert, mostly street.

[simon#42]

sorry mark i meant what type of bike is it and what is the problem you are trying to rectify

[rtbmrgl]

sorry mark i meant what type of bike is it and what is the problem you are trying to rectify

Oh no problem Simon, I guess I left out an important piece of the puzzle. Its a 1974 Yamaha DT250.
I talked to a old Yamaha guy and he said to go back to the stock reeds, there are no or negative benefits with Boysen reeds on this bike.

Your input was much appreciated, thanks.