You choose (but you had better have reasons)

[Recovered]

OK, I'm frazzled by the number of folks that are screaming for direct injection. Almost anything I have seen is WAAAAAY more complicated than I think it needs to be, or is even worthwhile. Soooooooooo, I want to know what you think about this question. You may not have seen one, but there are three circuit carbs out there (I own one). It is my opinion (and you know what you have paid for my opinions) that a 3 circuit carb offers almost everything DI will, without the complication. Of course, IMHO, many of us don't have a clue how to correctly tune a 2T. Is that why everyone wants it?

So, the question is: would you rather have a 3 circuit carb or DI and why? Please don't post complicated pictures and videos...we have all seen those. Write out what you think.

M.S.

[JohnN]

While I'm not as technologically knowledgeable as some on this board, I'll add my opinions to your question.

As far as the direct injection goes, it would have to be proven to be worthwhile in my opinion and for all the reasons that you have so eloquently stated. Cost, weight, complexity and performance.

Although I do understand why so many folks are clamoring for DI, it promises to be "kinder" to the environment, the "hype" surrounding DI says we can expect performance gains and so many are looking for that next technological advancement to bring the two-stroke head and shoulders above the four-stroke.

To answer your other question, I would bet that very few garage mechanics truly understand how to properly tune and jet a carburetor properly on their dirt bike. This is not said with malice, just an observation. The easy way to answer this question is do you change your jetting for different tracks? Weather? Altitude? Time of year?  If not, you are probably one of those that does not know how to properly tune your dirt bike. I know that I am one of them!

Hey Mad Scientist - do you want to share some of your tuning tips? And what of this magical carburetor you speak of?? Inquiring minds want to know!!

[eprovenzano]

I started to adjust the jetting on my carb this past year.  The benefits are huge and all it costs is a little cash and some time.  I wish I'd started to adjust the jetting years ago.

[Out of Order]

For street use or to make the cry baby EPA happy(or piss them off) I would say Direct Injection. But for competition use I would use either carbs or EFI. Why? Because they both meter fuel, which makes power and makes people happy.  Some say carbs are easier to work on, then others say they would like to pull there laptop out and start tuning. In the end I would say what ever makes the people happy. So you decide!!

Maybe the Boyesen engine with old school mechanical injection would be cool.  

[Recovered]

Leaving DI aside...there is a nasty little thing about using a laptop to tune an engine. If you can't do it mechanically with jets, you still won't be able to do it with a computer. In fact, there is more crap to adjust with EFI. Consequently, with the laptop, instead of replacing brass and making adjustments to screws, you are "twisting" electrical screws. And if you don't understand tuning for carbs, you won't understand tuning with a laptop.

No one biting on the 3 circuit carb?? I assume every one knows all most all carbs are 2 circuit. # circuit carbs have the potential to produce maximum power with near EFI emissions! Think about that for a while.

[JETZcorp]

Being someone who knows more about carbohydrates than carburetors, I don't even know what a 3-circuit carb is, or how it compares to a 2 circuit.  I didn't even know that carbs HAD circuits.

[Out of Order]

Hey JETZcorp read this,
http://en.wikipedia.org/wiki/Carburetor

The basics are:
Off-idle circuit
Main open throttle circuit
Power valve (not the one in you exhaust)
Accelerator pump
Choke
Other elements (power jet)

When I worked on racecars we used Holly carbs which are also 3 circuit carbs. How do I know because I used to talk to the people who tuned them. I learned a lot about motors and carbs back then.

[losec]

 I just dont get the difference between DI and 3 circuit carb so I better keep my mouth shut

[Recovered]

Hey JETZcorp read this,
http://en.wikipedia.org/wiki/Carburetor

The basics are:
Off-idle circuit
Main open throttle circuit
Power valve (not the one in you exhaust)
Accelerator pump
Choke
Other elements (power jet)

When I worked on racecars we used Holly carbs which are also 3 circuit carbs. How do I know because I used to talk to the people who tuned them. I learned a lot about motors and carbs back then.

These "circuits" are more closely related to Holley carbs. Funny thing is...power valve is technically a misnomer. They are actually "economizer" valves that use intake manifold vacuum to trim the fuel curve into shape while at low load engine situations.

[MMS]

Surely one of the main benefits of DI is to remove the losses involved with crankcase scavenging which still exist despite either reeds or discs. So while I will fully agree that there is little evidence to support the use of EFI in many conventional engines despite it's increasing prevalence, my understanding is that direct injection is more an engine design principle than a use of EFI "per se".

[JohnN]

Surely one of the main benefits of DI is to remove the losses involved with crankcase scavenging which still exist despite either reeds or discs. So while I will fully agree that there is little evidence to support the use of EFI in many conventional engines despite it's increasing prevalence, my understanding is that direct injection is more an engine design principle than a use of EFI "per se".

That was my understanding as well. Unfortunately there is very little concrete information about any DI motocross machines. As I've said in the past only after "seeing" the benefits of DI would I even consider it. If it's not an "actual" improvement, why bother....

As for the 3 circuit Carburetor.... I'm all ears... please do tell.

[ferrahount]

By far I fell more comfortable with the "simplicity" of needles and jets on a carburetor than anything else (and no, I'm not new or ignorant about computers or software cause I'm a software engineer). If a carburetor (this 3 circuit wonder which I never heard about) performs almost like DI for performance (which I'm most interested) and emissions I'll go for the carburetor, cause I wouldn't add complexity to such a great design (2 stroke engine) if this complexity doesn't add huge benefits in both performance and emissions.

[Recovered]

By far I fell more comfortable with the "simplicity" of needles and jets on a carburetor than anything else (and no, I'm not new or ignorant about computers or software cause I'm a software engineer). If a carburetor (this 3 circuit wonder which I never heard about) performs almost like DI for performance (which I'm most interested) and emissions I'll go for the carburetor, cause I wouldn't add complexity to such a great design (2 stroke engine) if this complexity doesn't add huge benefits in both performance and emissions.

And here is the point...the 3 circuit carb I am talking about (and own) has NO JETS, can be tuned in  less than 30 minutes and tuned up in less than 2 minutes. You never take the carb off the bike. With more circuits you can trim the fuel curve up to get EFI performance and emissions w/o all the other crap you get with EFI IMHO. That's why I need to write a book..............................................................................

[juliend]

Sounds to me like the 3 circuit carb is a no brainer. I'd like to be able to play around with one. I too do not see the real benefit of DI on a bike, other than marketing hype. There is no real performance increase that I can see, however there is some added complexity and additional points of (electronic) failure.


What I WOULD like to see is a return to oil injection. The idea of mixing gas at one ratio for all riding conditions/speeds seems silly to me. Can anyone give a valid reason for not moving back to oil injection that does not involve manufacturers cost? The variable pump seems to me to be the perfect solution for metering just the right amount of oil when taking engine RPM and throttle position into account.

[Recovered]

Sounds to me like the 3 circuit carb is a no brainer. I'd like to be able to play around with one. I too do not see the real benefit of DI on a bike, other than marketing hype. There is no real performance increase that I can see, however there is some added complexity and additional points of (electronic) failure.


What I WOULD like to see is a return to oil injection. The idea of mixing gas at one ratio for all riding conditions/speeds seems silly to me. Can anyone give a valid reason for not moving back to oil injection that does not involve manufacturers cost? The variable pump seems to me to be the perfect solution for metering just the right amount of oil when taking engine RPM and throttle position into account.

I'll take a shot at your question but I will NOT give you the answer...yet. I hate oil injection. Like anything else, it needs to be adjustable to compensate for different BRANDS of oil (I'm working on an article where these topics are discussed with help from one of the oil manufacturer tech guys). It will then need to be "tuned up" like anything else. If it's not adjustable than you are screwed if you are not using the oil for which it was calibrated, and i can assure you, I never use the recommended oil of ANY motorcycle manufacturer.

Secondly...premix systems, even with ony 2 "circuits" (I'm taking heat from some who are dinging me for calling all carbs 2 circuit) the system self adjusts for the exact conditions which you are considering

Think about it and let me know.......................................................................