You choose (but you had better have reasons)

[PowerPlant Patrick]

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.

The great strength of a two-stroke is its simplicity and that includes carburetor.  I tune all bikes and until EFI is closed loop, it has just added hassle.... it takes me thirty minutes to install a CRF sub-frame.  It takes me 30 seconds to install my CR subframe.

[JohnN]

Welcome to the forum PowerPlant Patrick.

For those interested there is an article about one of Patrick's bikes on the main site, check it out!

http://twostrokemotocross.com/2009/09/2010-honda-cr250-elsinore/

[Out of Order]

Closed loop, hell they have open loop too. Not sure about the new EFI MX bikes though. I know in cars you usually have closed loop at idle and at lower rpm for emissions purposes to keep the engine at stoichiometric Air Fuel Ratio. Then at higher rpm and Wide open throttle the ecu goes into open loop, which the ecu doesn't go by the O2 sensor. Instead it goes by pre-programmed maps in the ecu.  

DI and EFI engines are purely to make the Nazi EPA happy. Will it make more power, most likely not. Will it pollute less, well yea. You can still tune a DI or EFI engine if you have the right equipment, I have done to cars before and all the tables in the software do look intimidating at first, but I got use to it after a while. But I would rather play with the good old carby.

[JohnN]

While the EPA has been working on cleaning up emissions for machines used for recreational riding (it seems that a very high percentage of motocross bikes never see a race track!) these standards do not apply for cosed course racing. At least they don't at this point.

Personally if the same or similar performance gains can be achieved with a multi-circuit carburetor, I don't see a need for DFI or EFI on a motocross bike.

The only reason I even considered it was because it would help with emissions and allow new two-strokes to be developed that could be ridden off-road that would meet or exceed EPA standards. As I've mentioned before if there were not significant performance gains, the added complexity would be just another marketing "technological improvement".

[Out of Order]

3 circuit carb? I'm thinking the Mikuni powerjet carb that came out in 1976. The first metering system was the Idle circuit, then the second was the main circuit. With the introduction of the powerjet carb we now have a third metering system, the powerjet circuit. This circuit is used when full throttle is approached, the air moving past the tip of the powerjet delivery tube creates a depression great enough to allow atmospheric pressure to push fuel through the power metering jet and up the delivery tube into the air stream. Therefore, the powerjet has the effect of enriching the mixture past five eighth throttle providingair pressure is high enough to create a vacuum of sufficient intensity to discharge fuel.

Then in 1996 Keihin came out with there powerjet carb. This carb featured an electronically controlled solenoid valve to shut off fuel flow to the powerjet in the upper RPM range. This served to lean the mixture about 10% which allowed the engine to over-rev 500-800 rpm, and in some cases there was a peak power increase.

I could go on and on and on, but it would take a week to write about it. So that pretty much sums up the powerjet carb.     

[ford832]

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.

Hey!Take that back!
Although there is some truth in it but it depends on the age of the mechanic.Us older types were around in the carb days and still around in the EFI days.I'd take EFI over a carb anyday.A carburetor simply can't adjust the way fi can.I believe Husaberg has the only closed loop bike system presently so that's a bonus but even so,it's a very simplistic,crude set up.You rarely change a map in a car due to the fact the computer varies it automatically according to conditions.Bike systems generally don't or to a very limited extent because they have a largely fixed set of parameters to go by and need to be this way because of the very limited number of inputs.Of course,to add everything a car has would add a fair amount of weight.A car works so well because it can react to very small variations in inputs.You need to remember a modern day system just doesn't alter the air fuel ratio.It also varies timing,idle speed etc and adjusts to air temp,pressure,itake airflow speed,engine temp,load,gear among other things.Add to that the fact the new oxygen sensors are now called air/fuel ratio sensors due to the fact that they no longer use .46v as a rich/lean threshold but adjust to the exact reading.Carburetors are to fuel injection what a stick is to an AK47.BUT,with my truck,if something goes wrong I take it in to work and use the gear to fix it.If my bike was fi, in some cases you'd be forced to resort to a trip to the dealer.Therefore,if it was up to me,I'd keep fi in vehicles and stay with the carb on the bike.It's simple to tune,has less parts,complication and weight,and when properly set up,works well enough.

[AFG]

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.

Juliend if memory serves me most oil injection systems were given the heave-ho because they couldn't meet demands of racing. Most of the designs I remember used throttle position to determine how much oil to spray into the mixture. The problem of oil starvation would occur at closed throttle, high rpm load conditions. CanAms in the late seventies used oil injection, many of the bikes around here were seizing up during long fast races. It was determined the cause was people were chopping the throttle when brakeing comeing into corners. No throttle no oil. The solution was to wire the pumps wide open.You couldn't just cap it off and pre-mix as this would starve the main bearings of oil, something in the design of the rotary valve Rotax motor during that period. I think by 1980 Rotax made changes to the motors that allowed premix without the main bearings starving for oil. At least that's what I remember.

[offroader]

Hi guys new here.Just came out of lurker mode.Gonna have to say and i could be totally wrong lectron or psi big air carb.

[JohnN]

Hey Off-roader - Welcome to the forum....

Mad and others... this is the one reason that I had any interest at all in direct injection. Anything further for racing would have to be because of performance and level of complexity.

Global Giving Video Competition -- 4th place winner!

[Out of Order]

I like the animation art, pretty cool. To me DI isn't that complex, as long as they keep the catalytic converter, EGR valves, and other emission controlled things off of the bike. But, then I have experience in automotive so that's why I'm not scared of it. Although every one has to admit that someday (be it tomorrow or next year) two stroke bike technology will have to advance to survive. It's all about survival of the fittest.

Also, two stroke road bikes have been gone for over 20 years, so I think this is the technology that will possibly bring them back if some manufacturer backs it. All I'm saying is that I'm waiting, and if it doesn't happen, well I might have to build my own!!

With closed circuit bikes there are no emissions per the EPA. For now lets hope it stays that way.