That 3rd needle
 

This is a question for the experience engine tuners... I have a reasonably good understanding on how to tune the HSN and the LSN but have not played with the spraybar or MID needle... What affects does adjusting this have on performance? And how do you know when to make adjustments?

Oh....that thing???......
 

Personally, I would leave it set at factory and not touch it.
They do this to make it easier to machine the precise bore of the fuel chamber. You can adjust it to set your fuel/air ratio for when your engine is at idle.
I have seen a lot of real good engine guys come with this messed up. We always go back to factory and she works fine. For any adjustment I have ever seen, I have not found an offroad person yet that can tell the difference blindly.
Some of the elite onroad 1/8th guys can but they are freaks on the mid band and its usage. In offroad we tune a little different because we are off the gas so much.
Don't worry about it. I do use it to break down the carb and clean it though.
Good luck!
TEX
:cool:

Agreed. Stick with the factory setting. I have seen some super tuners manage to get some improvement from it but it takes even them all day of messing with it.

what if you are usnure of what the factory settings are? I have a samurai 521 team infinity modded engine here and i think the MSN has been changed and would like to return it to stock though the manual does not mention a stock position...

how does one fine a good position for this needle?

The mid needle changes when you transfer from the low speed needle to the high speed needle in relation to to carb travel. This is more useful in on road where you may want a lean bottom end for crisp response off a corner, and run the high speed needle slightly rich to cool the motor off on top end. You absolutely could use the mid needle for the same purpose in offroad to get more bottom/mid range power, I just have never seen the need to.

Just adjusting the mid needle alone is generally going to screw you up. If you crank it in, you are doing 2 things - leaning the bottom end out, and taking longer to transfer to the main needle, which will compound a lean condition. Turning it out will cause the opposite effect - richer low end, and quicker transfer to the main needle.

You may need to adjust the low end needle when you touch the mid range needle. Now you can see why everyone says leave it and forget it. You can mess up your tune in a hurry.

I have personally only adjusted the mid needle in on road applications. The only engines I had that needed the adjustment were modded ones.

I would recommend messing with the mid range AFTER the engine is tuned to the temp you desire. If you have some kind of flatspot in the power band, or the engine is not clearing out quickly enough for track conditions I would consider mid range adjustments.

if you fancy it give it a go, the simple rule is whatever you do with the mid you do the opposite with the LSN, so if you turned the mid in 1 turn you take the LSN out 1 turn to keep the mix the same, i had read that the v-spec benefitted from a turn in on the mid as it had a rich mid from stock you have nothing to lose from trying this just remember to turn the LSN as well or you will be to lean/rich depending which way you go, just for reference the OS .12 CVR has no LSN if you look carefuuly what they have as a LSN is actually the MID needle and this is how they make the carb !

Is your engine tuned properly now and running the temp you want? If it is there is probably not much need to mess with it.

I have had modded motors that ran well but had a momentary dead spot in the powerband. RPM would stop rising at about where a non modded engine would top out, then the RPM would shoot again. It sounded almost like a car with a 2 speed. The carb could not clear out the low end fuel fast enough to keep up with the rising RPM.

You would want to use the mid needle to dial this out, and transfer to the main needle faster. to do this you would richen the mid needle, and possibly lean the bottom end needle. Go slow with the mid needle. A small adjustment can go a long way.

Thanks for the replies guys... I might try a little bit either way and see what happens


Does this work the same on the Speed? Anyone else heard of this?

Good answers on this...Here we go......
 

It can work the same. Keep in mind things like clearing out and running right all depend on clutch, pipe and header as well as initial settings. I would definitly run at the recommended setting and get everything right. Once you can duplicate what you like, then move on to the more advanced setting of the mid adjustment.
These guys are correct in the fact that it will do two things. Watch your low needle mix setting if you move the mid.
Usually the mid is flush with the carb body from the factory. Yours? I have never seen this engine before.
Good luck and let us know how it goes.
TEX
:sweat: