Eivind E

Where I race temperatures vary from morning to afternoon. Humidity varies as well.
What is a perfect race tune at 10AM for the qualifying run equates two flameouts at 5PM for the finals.

So you will have me believe that when I *NEED*, well not only me but also everyone else on the track, to adjust the carburation in order to succeed, we are doing something wrong?
Well if doing what is right means that we will flame out twice and have no chance of winning, then I'd rather be doing it wrong.

You have to take into account that not everyone lives in the same place.
If you have humidity ranging from 40-80% and temperatures ranging from 70F to 95F the same day, you are not going to be able to run the same tune the same day, and certainly not on different days!!
There's no such thing as a universal truth for everything carburation related.

Maximo

iTrader: (11)

I am going to say that people often times mess with their needle settings when they shouldn't be... Yes some minor tweaking if there is a massive weather change, but for the most part we go gallons here without barely touching the needles..............unfortunately the guys who usually have tuning issues are the ones who can't stop messing with the needles... and trust me, I am extremely proficient at tuning these engines ....

nitroexpress

I have to agree with Eivind E.

A while back, the temp dipped 40 degrees and the humidity went up 25 - 30 points. Those that didn't tune for the main ran out of gas. Those that went richer because they only considered the temperature, ran out of gas. The smart ones had no trouble.

Maximo

iTrader: (11)

during the race season we see temperatures between 15-30 c...humidity from 30-90 % ... Usually once I have a engine base lined we do not have to touch the mixture screws much..... When the 02 density changes I alter the idle gap size.....on a cold day they tend to need a smaller gap...on a hot day they need a larger gap....on a dry day they need a smaller gap, and on a humid day they need a larger gap.......... 30C and 90% humidity we will run upwards of a .7 mm gap and on a really cold dry day of 0 degrees we will run as small as a 0.3 mm gap and even smaller on some engines........ The needles themselves are somewhat self regulating in that the density of the incoming air will regulate how much fuel it picks up from the spray bar(venturi) into the incoming air stream,,,...A dense air charge automatically picks up more fuel then a less dense air charge does.....which does regulate the air/fuel ratio in itself.....Of course this relationship operates on a curve and the closer the needles are to an ideal baseline the more range they will have in tolerance to weather changes and the effects of the weather changes on the engines tune and running characteristics.........again this is all relative to the baseline tune that is on the engine..If the engine is off its ideal setting it may be more dramatically affected by a weather change then a engine that is closer or at its ideal baseline...........And I know I am not the only one who rarely touches the engines needles...I talk to many guys all over the world who also share similar experiences and beliefs....Once you have these engines dialed in you should rarely ever have to touch the mixture needles......Of course I am saying rarely...... And If your engine requires tuning multiple times on every single race day I am going to say there is something not right going on...and without being there it is difficult for me to say exactly what it is.......

Eivind E

I'm in the south of Spain, you're in the north up in Canada, I think it's fair to say the climate is completely different and you may not have experienced what we have here.

nitroexpress

A bit of clarification on your theory. Since you are only changing the idle, are you saying that idle speed will change as the temp/pressure changes (with no adjustment to the idle gap)? And by keeping the idle speed constant (by adjusting the idle gap), the mixture will stay optimal?

Maximo

iTrader: (11)

idle speed is most definitely affected by changes in temperature and pressure without any adjustment to the idle gap itself...the more 02 rich the atmosphere the higher the idle RPM....which often times fools guys into thinking the LSN is lean... and conversely will fool guys into thinking the LSN is too rich... the engine will go from sounding racy and pingy at idle, all the way to loading up and stalling simply by the available O2 in the atmosphere changing...this often fools guys into messing with the LSN ...And I have seen this hundreds of times, guys trying to adjust the mixture screw when all that was out was the idle gap size for the conditions......

And no to the mixture staying the same, the idle gap has no effect on the mixture.....Tho the idle gap size can affect the idle air/fuel mixture, but only at idle....often times guys mistake the idle mixture behavior for the actual LSN mixture.... In other words a engine may behave rich at idle, but really be too lean on the LSN adjustment ( especially so in long LSN carbs ) ...all it needs to behave this way is a too small idle gap........... And conversely a engine may appear to be lean and racy at idle, but really be too rich on the LSN... all it needs for that to happen is the idle gap to be too large for the conditions......... This phenomenon is what often times throws guys off finding the correct tune to begin with....As often times having the wrong sized idle gap will exhibit behaviors that can throw even the most experienced tuners for a loop....The shorter the LSN the less you will see this effect, as with a ultra short LSN the needle really only controls the idle mixture..on a a long needle Nova the needle needs to regulate the fuel delivery curve over the entire throttle pull as the primary function, adjusting the idlle mixture is its secondary function...this is why having the right sized idle gap is soo critical to these engines operating correctly...as if the idle gap is wrong it will force you to adjust the LSN to compensate to adjust idle mixture, which can affect the entire fuel delivery curve over the entire throttle pull......... This is where I see many people go wrong when tuning a nitro engine.... they try to use the LSN to adjust what the idle gap should be adjusting.........Once you understand how these carbs work in detail, it becomes quite easy to tune them........Anyways if anyone has any serious questions feel free to pm or call me.....

22Racer

iTrader: (67)

I do agree with most of what you said Neal but (the idle gap has no effect on the mixture....) The needle is tapered, moving the idle gap does move the needle in or out of the spraybar some.

Rex

Maximo

iTrader: (11)

it affects it at idle,, but doesn't really change the taper position in relation to throttle position...it only really moves the start point....I could have been clearer in what I wrote ....