CR Carbs

[Jiggles]

(Psssst, wouldn't this be great in a general tech sub forum!?!?!?!)

So I was talking to a mechanic today who was telling me that with CR carbs, which I guess the slide is mechanically operated instead of vacuum operated, that he was able to get a ninjette with a stock airbox + snorkel up to 34hp and pod filters up to 38hp. The specific ones he was talking about were 31mm as opposed to the ninjettes stock 28mm.

Now I'm quite a carb n00b so forgive me if I'm naive in saying, wouldn't you HAVE TO open up the airbox and increase the airflow in order to get more power? Specifically 9 more hp, a 36% increase???? I mean, no doubt cr carbs are better and easier to tune with a better and more consistant AFR curve but **** man, that just seems insane. If it's true though, I'm down for raping some 300s

@Racer x I believe has 32mm carbs and I believe he's also done quite a bit of engine work. Last I heard he was pumping out 34hp with larger pistons.

So whats the deal with CR carbs? Are they really that much better or are they just a little bit better. And how do CR carbs stack up to fuel injection? I'd imagine the precision of EFI would be even better right?

[choneofakind]

Carbs rock for dumping lots of fuel at top end, EFI is nice and smooth and happy. That's all I know. I still need to tune my map before I go into fair comparisons between the two.

From what I've read, CR carbs also aren't as happy on street duty as CV carbs.

I know Eric will have more to say on that since you tagged him, so I'll let him talk since he knows oodles more about them than I do.

[Racer x]

I have never gotten 38 hp . But I use a conservative dyno. I did get 34.

The CR specials are a dream come true. Yes if you whack open the throttle at low RPM they will gasp and you have to let off and smoothly open the throttle . But if you know how to ride. You don't whack the throttle anyhow.

Tuning is super easy. There are a full range of air jets needles main and pilot jets available.

I am not bashing FI it has its place. But there carbs work so well I am hard pressed to change.
I only use the carbs with open stacks. But feel they could be tuned with an air box and beat any other fuel system. The only down side is the choke. The do have a choke but it is mounted on the carb. So that you can't reach it with most fairings. Starting is the only real issue. FI will start all the time if it is tuned properly. Getting a race motor running with a big carb on a winter morning is a test of skill.

[Motofool]

Originally Posted by Jiggles

........Now I'm quite a carb n00b so forgive me if I'm naive in saying, wouldn't you HAVE TO open up the airbox and increase the airflow in order to get more power?........

You wouldn't have to, but reducing resistance and friction by increasing traverse sections always increases volume of air moving between two pressures.

The dilemma with the Venturi portion is that increasing the section reduces the suction effect and the fine control at low flow conditions.

Our carburetors are a compromise for fuel economy and proper control during a huge range of riding conditions.

Special purpose carburetors are only good for that specific purpose and perform marginally for the rest.

No Venturi for EFI, means that engine breathing can be improved.

Copied from http://faq.ninja250.org/wiki/How_a_c...eat_Compromise

"VARIABLE VENTURI - Getting Sucked In
A venturi is a tube with a convex taper, (one end wider than the other). As air enters the wider end it's squeezed into the narrower section of the tube, lowering the air's pressure. The area of lowest pressure is just past the narrowest point and is called the depression. This has always seemed counterintuitive, but Bernoulli's Principle outlines the fluid dynamics involved in this effect. This lowered pressure, or comparative vacuum, is separate from the engine vacuum. A variable venturi varies the venturi diameter at the depression by raising or lowering an obstruction. This obstruction is called a slide. On a CV the slide is called a piston or diaphragm valve.

CV or SLIDE CARB - The Great Compromise
Both the CV and conventional slide carbs are classified as variable venturi carbs. The slide on a conventional carb is directly connected to the throttle cable. Twist the throttle grip and the slide is raised in the venturi. On a CV carb the throttle cable is connected to a butterfly valve that varies the volume through the venturi. It's not the throttle, it's the pressure difference from the venturi to the outside atmosphere that moves the slide.
So which type is better? That depends on what you want to do. The manufacturers will tell you the CV is the next best thing to electronic fuel injection. It does feed a precise amount of mixture to smooth out throttle response, reduce pollution, and stretch your fuel budget and gas tank range.
This is great for tarmac cruising and feeling warm and fuzzy about doing your part to reduce global warming while pocketing some spare change. It sure makes it easier for the manufacturers to get the EPA approval stamp on the bike.
But what if you feel that no matter how much you hop up your little beast, you're never going to match the belching of that cager in the gas guzzling V-12 ? What if you don't mind spending more for gas, and when you go off-road you want a burst of power to blip over obstacles or steer through a wash without fanning your clutch while waiting for the vacuum to build in the venturi? If you can discipline yourself to control the throttle so that you don't bog your engine, then you want a conventional slide carb.

40 MM - Size Matters
With the same engine and carb design, a 38mm diameter venturi will more accurately meter the mixture on the low end, while a 41mm diameter will do a better job of supplying mixture at higher engine speeds. It's another factor to consider if you replace your carb."

Link to original page on YouTube.

[Jiggles]

Originally Posted by Racer x

I have never gotten 38 hp . But I use a conservative dyno. I did get 34.

The CR specials are a dream come true. Yes if you whack open the throttle at low RPM they will gasp and you have to let off and smoothly open the throttle . But if you know how to ride. You don't whack the throttle anyhow.

Tuning is super easy. There are a full range of air jets needles main and pilot jets available.

I am not bashing FI it has its place. But there carbs work so well I am hard pressed to change.
I only use the carbs with open stacks. But feel they could be tuned with an air box and beat any other fuel system. The only down side is the choke. The do have a choke but it is mounted on the carb. So that you can't reach it with most fairings. Starting is the only real issue. FI will start all the time if it is tuned properly. Getting a race motor running with a big carb on a winter morning is a test of skill.

You've done some engine work as well right?

Well damn now I have a tough decision, slide carbs or EFI. -_-

And thank you motofool as always for the never ending information

[choneofakind]

Slide carbs are cheaper in the long run, and easier to tune.

[Jiggles]

Originally Posted by choneofakind

Slide carbs are cheaper in the long run, and easier to tune.

Easier to tune than EFI?

[Motofool]

Originally Posted by choneofakind

Slide carbs are cheaper in the long run.......

They can also develop some wear between the moving parts, rattling and air intrusion or by-pass,............but that takes many, many miles.

Could you, Chris, explain us more about the application of EFI to the Ninjette?

[Racer x]

Both EFI and carbs are easy to tune. If you know what to do.

[Jiggles]

The ecotrons kit can be tuned with a smart phone via bluetooth. That is just too damn cool. I'll have to talk to Matt and see if he can make his kit compatible with a larger TB (Ninja 300's should fit) and if I can get it to work with my current wideband O2.

I'm very tempted to get slide carbs now but ultimately I will want EFI on the bike and I just can't justify buying both

Perhaps I can talk some sucker into getting them....

[Racer x]

If you are going to mostly ride on the street than go with EFI.

[Jiggles]

Street and trackdays for a good while. If I want to get into racing I'll probably buy another 250 specifically for it.

However, I do want to make my 250 as fast as I possibly can (no nitrous though ). Long term goals will be boring the engine along with some other engine mods. It makes me wonder what will be better for more midrange and top end power, slide carbs or EFI. Which is why @chode needs to go get a dyno done

[ninja250r81]

Carbs / EFI

Winter Drivability: Poor / Excellent

Summer Drivebility: Excellent / Excellent

Skill Level Required: Average / Advanced

Initial Cost: $200+ / $1000 (typical)

Long-term cost: High / Manageable

Performance: Good / Better

Turbo-compatible: Poor / Excellent

Supercharger-compatible: Depends / Excellent

N2O-compatible: Good / Good

Emissions Friendly: Poor / Excellent

"Wow" Factor: Fair / Excellent

Reliability: Good / Excellent

Fuel Distribution: Fair / Excellent (Port and Direct)

Intake Configurations: Limited / Unlimited (Port and Direct)

Pros: 6 / 12

Cons: 8 / 2

sorry forgot altitude correction: poor / excellent

[Jiggles]

You lost me at winter drivability poor

[n4mwd]

Originally Posted by Jiggles

The ecotrons kit can be tuned with a smart phone via bluetooth. That is just too damn cool. I'll have to talk to Matt and see if he can make his kit compatible with a larger TB (Ninja 300's should fit) and if I can get it to work with my current wideband O2.

Since when?
The ECU doesn't have bluetooth and there isn't an app for it in the app store.
Its a nice thought though.

There is a selection for bluetooth in the ProCal setup, but ProCal is a generic program that Matt modified for Ecotrons. Its just a vestigial selection.

[Jiggles]

You can buya bluetooth attachment for the ECU and I believe the app is currently on the android store but not yet iphone

[alex.s]

haha apple sucks

edit: oh wait i sell apple software... just kidding

[n4mwd]

You can buy an adapter:




But there doesn't seem to be an android app for it. Not if its called ProCal anyway.

[Jiggles]

Not sure what its called but he sent an email a while ago saying you can log data with the phone and that soon you'd be able to tune from the phone

[Mountain Dew]

From my experience, CR carbs are the **** (they're the end-game carb upgrade for us sohc4 guys) but they're not great for the street.

[Jiggles]

Not great for the street why? Cuz of the annoying choke placement?

[alex.s]

here's what i've learned about street bikes... oem knows a lot more than you do.

[Mountain Dew]

My bad, I was misinformed. The older CR carbs were pretty much race carbs. The new ones are fine, but upgrading carbs seems like a waste unless you're doing engine work (porting) or some serious intake mods.

[Jiggles]

Guess its not a waste then

[alex.s]

Do a ramair jiggles

[Racer x]

The carbs defenetly have a place on a cafe racer or naked bike.

[ryan.chin]

Carbs are for noobs.

[Jiggles]

Originally Posted by ryan.chin

Carbs are for noobs.

600s are for noobs

[ryan.chin]

Originally Posted by Jiggles

600s are for noobs

Jiggles is for noobs

[Jiggles]

Noobs love to jiggle

[ryan.chin]

Everyone hates Jiggles.

[choneofakind]

Originally Posted by Jiggles

Easier to tune than EFI?

Maybe not easier, just faster. It's taken some learning on my part to get to where I am. I like how the bike's turned out so far, but it's been a fun little tinkering project. If you're looking to just bolt stuff on and go for it, you'll have to consider how much time you want to put into it. I'm not quite far enough to do a dyno yet. It will happen next summer though. I want to get the timing figured out. I think right now the timing is suitable for the newgen, but not as aggressive as the pregen. I want to get the timing to mimic the timing of my '99 that it had from the factory, then I'll re-do the learning time, and get it dyno'd in rich mode to see where I'm really at AFR-wise. Right now, it pulls well, but seems to have a little less oomph above 12k.

Originally Posted by Motofool

Could you, Chris, explain us more about the application of EFI to the Ninjette?

On my bike, I didn't write the code. That part was all done by the lovely gents at ecotrons.

I mean it's the same parts that any fuel injection system has. I just find that isolating one variable on a carburetor is much easier because I can take it apart, play with it, change one thing, and physically see what change is made. Maybe it's just my mindset, idk. Once you learn a little about what you're reading with the data you can collect on the efi, it's easy.

I only said that the carbs are cheaper because they're so darn easy to tune, again, because it's easier for me to visualize and think about. ymmv. However, my experience with my dabble into the FI world has been very good. I'm happy with my results so far

[Motofool]

Thanks, Chris

[Mountain Dew]

Originally Posted by Racer x

The carbs defenetly have a place on a cafe racer or naked bike.

I'd rather have Mikuni RS34s instead of Keihin CRs. MUCH more streetable with an accelerator pump and fast idle circuit.

[Racer x]

Me too

[subxero]

CR carb on my MX bike works great, immediate throttle response. As long as bike is jetted correctly there is never an issue. Rode it Saturday in snow conditions with out a hiccup. Would like to do this mod to my bike as well but i already have a lot on my plate and can't afford to dump to much cash into the bike right now... or at least more than i already have.

Could definitely see getting access to the choke on a street bike being a PITA, plus you could not make adjustments on the fly, would have to stop and pull over to adjust unless you could devise some cable design which might not be terribly hard.

[Racer x]

I suspect the 34 are to far apart for the 250 ninja. I don't know for sure but it looks like the adjustments and return spring is between the carbs.