another jetting question

[dannygraves]

well, either way I think the main needs to be changed and the floats need to be checked, so let wait and see what the outcome is

[M.F.D.B.]

So whats the deal, have you worked on the bike yet??

[cr5004life]

played with the floats with a little an it worked bike ran sweet at the dunes clocked at 60 mph in fourth gear over the face of sand mtn no nitrous it was sweet

[100hp honda]

played with the floats with a little an it worked bike ran sweet at the dunes clocked at 60 mph in fourth gear over the face of sand mtn no nitrous it was sweet

you have the best year tranny for the big dunes, have you tried messing with the rear sprocket and run the hill in 5th?

[M.F.D.B.]

played with the floats with a little an it worked bike ran sweet at the dunes clocked at 60 mph in fourth gear over the face of sand mtn no nitrous it was sweet

[100hp honda]

Load decreases vacuum, try again...

this doesnt make sense. figure a v8 with 4barel carb. the more the load, the more you have to push the pedal, the more vaccum opens the 4 barels. right or wrong?

[Ported&Polished]

Think of this. If you have a vacume operated item attached to your intake manifold, at speed, under throttle or load, the item will slow or stop working. I know because I had a vacume operated windsheild wiper setup on my old Bronco. The wipers barely worked when I floored the rig.

[M.F.D.B.]

Load decreases vacuum, try again...

this doesnt make sense. figure a v8 with 4barel carb. the more the load, the more you have to push the pedal, the more vaccum opens the 4 barels. right or wrong?

Nope, think about it this way. Say the car is a manual trans (no slip) you are cruising down the street at the speed limit, the motor is bogging, and you punch the throttle, the rpms are going to stay relatively the same (you are pumping the same vloume of air) but now the opening the motor is sucking through is much larger, LESS vaccuum.

Even simpler, if you suck a volume of air through a big straw with your finger covering 3/4 of the opening, your cheeks are going to "suck in" right?? Now uncover the end of the straw, what happends to your cheeks?? Follow??

[AlisoBob]

[dannygraves]

but that isn't load... that is throttle position, if the slide snaps open, there is no vacume until it starts to pull, which is also how the secondaries on a 4bbl work... also how the powerjet on my mikuni works, no fuel comes out when you first open it, but as the load is sustained and the throttle position the same, a vacuum will be created, and this is when on a 4bbl the secondaries open, on my mikunis powerjet starts flowing.

[AlisoBob]

You guys have this all jacked up...

[M.F.D.B.]

but that isn't load... that is throttle position, if the slide snaps open, there is no vacume until it starts to pull, which is also how the secondaries on a 4bbl work... also how the powerjet on my mikuni works, no fuel comes out when you first open it, but as the load is sustained and the throttle position the same, a vacuum will be created, and this is when on a 4bbl the secondaries open, on my mikunis powerjet starts flowing.

Correct, but the two are very closely related. And a vacuum secondary 4 barrel or CV carb work on the same theory. If load is low the motor is producing good vacuum and that vacuum is used to open the secondarys (or slide on the CV carb). When load is encountered, and vacuum decreases, the secondarys start to close, this INCREASE the velocity of air through the carb, combating the lean condition created by the low vacuum. Think of them as vacuum "averagers". They try to keep the vacuum signal to the carb good quality to keep the mixture proper. Think of vacuum as a measure of "efficiency, through ineffieciency"...HAHA Dont believe me, read it on the net!!
http://en.wikipedia.org/wiki/Manifold_vacuum

[cr5004life]

im gunna play around with gearing a lil more next time i go out, but the bike ran flawless thats all im worried about, i think i can get a few more mph with a lil gearing, but next time i go ill be shooting the spray too thanks for the help

[M.F.D.B.]

You guys have this all jacked up...

Topic??

[iggys-amsoil]

You guys have this all jacked up...

Just jet the thing and ride.

Or was that, "Don't Clyde it ride it"

[Blusmbl]

Just throwin' this out there, because load hasn't really been adequately described in this thread.

Load isn't always manifold vacuum/throttle position, it's not a direct correlation.

Load is volumetric efficiency. Namely, theoretical cylinder air charge divided by actual cylinder air charge. A very well tuned N/A motor will see load values of around 1.1 or so, while something like a factory supercharged engine will have load values of 2.0+. Load is also highest at the engine's torque peak. And, since it's unit measurement is air charge, load will increase at lower temperature/higher BP for a given throttle position and rpm, and decrease in warmer temps/lower BP.

-Nick

[M.F.D.B.]

uuhhhh...

[Blusmbl]

My bad, the cliff's notes version of that is: the only way to know how hard the engine is working (load) is to compare how much air the engine ingested in one 2 or 4 stroke cycle, to how much air the cylinder actually contains (500cc).

On a carbureted vehicle like almost every dirt bike, knowing what load is is irrelevant. I just wanted to give everyone a real definition. For fuel injection it's much more critical, though. In basic aftermarket calibration software they give you a volumetric efficiency table (throttle positon and rpm), on oem type stuff (which is what I work on), the air flowing through the engine is modeled via some very complex strategy code. I'd love to see how Suzuki is doing it on the new RM-Z.

[M.F.D.B.]

My bad, the cliff's notes version of that is: the only way to know how hard the engine is working (load) is to compare how much air the engine ingested in one 2 or 4 stroke cycle, to how much air the cylinder actually contains (500cc).

VE (volumetric efficiency) is ONE way to calculate load. In reality the CPU on a EFI motor uses the colaboration of many sensors.

On a carbureted vehicle like almost every dirt bike, knowing what load is is irrelevant.

Actually its very important. If the carburator is unable to react to changing load (vacuum) the mixture would be all over the place.

I just wanted to give everyone a real definition.

You gave a definiton of VE and how it relates to load. Load is a very simple definition. Its simply how "hard" the motor is working.

In basic aftermarket calibration software they give you a volumetric efficiency table (throttle positon and rpm), on oem type stuff (which is what I work on), the air flowing through the engine is modeled via some very complex strategy code.

Thats true of a Speed Density system. In a Mass Airflow system there is no VE table since VE is MEASURED by the MAF. In a speed density system the MAP (manifold absolute pressure) sensor tells the ECM what the manifold pressure (vaccum in an N/A application, or vacuum and boost in forced induction) is in Kpa (Kilopascals) the ECM uses this pressure and the VE table to determine Injector Pulse width (there is many other "error corrections" such as Baro, IAT (intake air temp) etc. MAF is superior to MAP in that changes can be made that effect the VE of the engine and the ECM can still "tune" the motor. If you make a change that affects VE (like a cam swap) on a MAP system it will run like shit.

I'd love to see how Suzuki is doing it on the new RM-Z.

Most bikes run a type of "N Alpha" Speed Density system. Which is basically an open loop (no O2 sensor) MAP setup. A MAP sensor determines load based on vacuum and TPS (throttle position sensor) really the only "error corrections" to the VE table are Baro (barometric pressure) and IAT (intake air temperature).

[glen howell]

Say John are you getting this, They said christ rose from the grave in 3 days,Thats why we get a day off at easter time.

[M.F.D.B.]

Santa Clause builds race motors?? SWEET!!

[glen howell]

Sorry about that I posted on the wrong thread.Glen (TEAMGSS) NAHA#42

[Blusmbl]

You gave a definiton of VE and how it relates to load. Load is a very simple definition. Its simply how "hard" the motor is working.)

Yes it is, and how do you quantify that? I'll tell you, by measuring VE. Load isn't just vacuum OR throttle position, that's what I was getting at in the first place.

I'm a calibration engineer at Roush, we do OEM work for Ford and GM, among others. I've worked on everything from 6L diesel pickups to 2010+ model year vehicles, and regardless of manufacturer, engine type, or hardware, there's a pcm parameter entitled "load", and it's just how I've described it: VE. It's the only useful way to define it. Otherwise it's better to reference something else when trying to describe a carb tuning problem... like throttle position.

Sidetracking this even further, in the absence of a map sensor on a mass air efi system, we've gone back to modeling manifold pressure. It wasn't needed until the advent of electronic throttles, now all of the OEM's are going to torque-based systems and to have any hope of it working effectively you need to know the pressure differential across the throttle plate. You know, the same thing a carburetor can do automatically with no electronic inputs.

[dannygraves]

My bad, the cliff's notes version of that is: the only way to know how hard the engine is working (load) is to compare how much air the engine ingested in one 2 or 4 stroke cycle, to how much air the cylinder actually contains (500cc).

VE (volumetric efficiency) is ONE way to calculate load. In reality the CPU on a EFI motor uses the colaboration of many sensors.

On a carbureted vehicle like almost every dirt bike, knowing what load is is irrelevant.

Actually its very important. If the carburator is unable to react to changing load (vacuum) the mixture would be all over the place.

I just wanted to give everyone a real definition.

You gave a definiton of VE and how it relates to load. Load is a very simple definition. Its simply how "hard" the motor is working.

In basic aftermarket calibration software they give you a volumetric efficiency table (throttle positon and rpm), on oem type stuff (which is what I work on), the air flowing through the engine is modeled via some very complex strategy code.

Thats true of a Speed Density system. In a Mass Airflow system there is no VE table since VE is MEASURED by the MAF. In a speed density system the MAP (manifold absolute pressure) sensor tells the ECM what the manifold pressure (vaccum in an N/A application, or vacuum and boost in forced induction) is in Kpa (Kilopascals) the ECM uses this pressure and the VE table to determine Injector Pulse width (there is many other "error corrections" such as Baro, IAT (intake air temp) etc. MAF is superior to MAP in that changes can be made that effect the VE of the engine and the ECM can still "tune" the motor. If you make a change that affects VE (like a cam swap) on a MAP system it will run like shit.

I'd love to see how Suzuki is doing it on the new RM-Z.

Most bikes run a type of "N Alpha" Speed Density system. Which is basically an open loop (no O2 sensor) MAP setup. A MAP sensor determines load based on vacuum and TPS (throttle position sensor) really the only "error corrections" to the VE table are Baro (barometric pressure) and IAT (intake air temperature).

I have to disagree with you on the MAF being superior... the only real advantage it has is in an aplication where you are doing major changes to a motor running an existing stock computer. Which is still not the right way to do it, aftermarket standalone systems almost always use a map and air temp since they are more acurate measurments. Granted on a MAP system, you have to estimate and input your VE without having it figured for you, there are a lot of things a MAF can't account for. If you add forced induction, it will run like crap since it won't know how to calculate for compressed air and the added fuel needed to safely run that boost.
But if you had an ls1 camaro and wanted to drop a cam in it with some aftermarket heads, then MAF is the way to go. But those mods are for kids anyway

[M.F.D.B.]

I have to disagree with you on the MAF being superior... the only real advantage it has is in an aplication where you are doing major changes to a motor running an existing stock computer.

Not!! The advantage is many things, but the most significant is the fact you can make many changes to the motor and the ECM can still tune it without having to rewrite your VE tables EVERY TIME you change ANYTHING.

aftermarket standalone systems almost always use a map and air temp since they are more acurate measurments.

WRONG!! They use a MAP sensor because its WAY CHEAPER then a MAF and is somewhat "universal". Not only is a MAF sensor much more expensive by itself, it is also application specific. (do to "calibration") Theres simply no "one size fits all" when it comes to MAF. Every MAF system still has a Baro and Temp sensor, most modern MAF EFI's also have a MAP sensor.

Granted on a MAP system, you have to estimate and input your VE without having it figured for you,

You also have to adjust the VE table EVERYTIME you make ANY change that affects VE. That alone can be quite time consuming!!

there are a lot of things a MAF can't account for. If you add forced induction, it will run like crap since it won't know how to calculate for compressed air and the added fuel needed to safely run that boost.

Not true, a MAF MEASURES the amount AND PRESSURE of the air entering the motor. Its the PROGRAMMING of the ECM recieving the signal that must be "boost friendly" so it knows what to do with the info.

But if you had an ls1 camaro and wanted to drop a cam in it with some aftermarket heads, then MAF is the way to go. But those mods are for kids anyway

The ONLY draw back to a MAF over a MAP is that the sensor provides an air restriction. SO for ULTIMATE power a PROPERLY TUNED MAP system will always make more PEAK POWER then a MAF. This is one of the reason MOST aftermarket EFI systems run MAP, but the MOST SIGNIFICANT is still the COST factor.