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Metering rods and powerjets

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Hi, all.

I'm bored and thinking about carbs.

I've never owned a Lectron or any other metering rod motorcycle carb, but a metering rod appears to function very similarly to a needle in most oem 2 stroke carbs. (Please correct whatever misconceptions I have). As the slide opens or closes the tapered rod varies the effective cross section area of a fixed orifice, much like a needle does for a main jet. Obviously the metering rod uses turns instead of clip position to control its height relative to the throttle opening.

The adjustable powerjet is added to give the tuner the ability to make adjustments externally instead of swapping brass mainjets. While a powerjet and a mainjet are not the same, adjustments on non-electronic carbs have maximum effects in similar throttle opening ranges. Electronically controlled powerjets as found on the YZ250 are a bit different, and outside the scope of what I am talking about.

Getting to my point, why not simply add an externally adjustable powerjet to a PWK to avoid opening the carb to make changes?(on some bikes it can be a pain to swap brass) What am I missing here? Lectron guys: have you gone down this path with adding a powerjet to a stock carb, and if you did, were you able to get similar results?

Edited by clappedoutkx

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Hi, all.

I'm bored and thinking about carbs.

I've never owned a Lectron or any other metering rod motorcycle carb, but a metering rod appears to function very similarly to a needle in most oem 2 stroke carbs. (Please correct whatever misconceptions I have). As the slide opens or closes the tapered rod varies the effective cross section area of a fixed orifice, much like a needle does for a main jet. Obviously the metering rod uses turns instead of clip position to control its height relative to the throttle opening.

The adjustable powerjet is added to give the tuner the ability to make adjustments externally instead of swapping brass mainjets. While a powerjet and a mainjet are not the same, adjustments on non-electronic carbs have maximum effects in similar throttle opening ranges. Electronically controlled powerjets as found on the YZ250 are a bit different, and outside the scope of what I am talking about.

Getting to my point, why not simply add an externally adjustable powerjet to a PWK to avoid opening the carb to make changes?(on some bikes it can be a pain to swap brass) What am I missing here? Lectron guys: have you gone down this path with adding a powerjet to a stock carb, and if you did, were you able to get similar results?

 

not really,   the metering rod flat does something a round needle doesn't.  It's the way the fuel globs hit it and go around, many divided vs. all of them whole  (over simplified). That's the claim of better fuel atomization.    The lectron is also internally vented vs vented to atmosphere, why they claim better sensitivity to air density changes.

 

When I messed with lectrons years ago the quality control on the rods was horrible. You'd get 2 numbered the same that fueled different, the size and shape is so critical. A nightmare on a twin or triple carbed machine running at the edge of lean seizure already.    It's my understanding that issue has been resolved. 

 

You can a PJ to any carb,  I know Dicks Racing is still messing with them.  

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The thing with a power jet is that it only is in play in the upper rpms. I haven't messed with a lectron, but I have had a decent amount of time to screw around with a smartcarb (had one on my previous '11 300xc). Highmarker is right about the venting, although with modern machining, the benefits outweigh the negatives. The carbs both are great at what they do, but are more sensitive to air leaks and the such. I spent about a day or two setting my sc up and the fuel mileage, low end and midrange was greatly improved. I really didn't spend a bunch of time on the upper rpms, so I can't really comment on that.

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Internally vented... I wonder which side of the slide the bowl is vented to, and if check valves are needed (in the Lectron). Orangy, are you thinking that the add on powerjets are much more Rpm sensitive than a mainjet (in addition to throttle position of course)?

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The ones I messed with were dial a jets.  It's nothing new been around for some time, never catches on, then resurfaces under a new name about the time everyone forgets about them.  Some guys make em work, some guys give up.  Yes you jet the main down several sizes then add adjustable fuel back with the powerjet? which gives it tune ability.  And yes it's not exactly the same as changing main jets, so some needle tuning is often needed.  IF, the PJ fails somehow you either have it over fueling, or running several jets sizes too small.  I found the whole thing MORE sensitive to alt and temp than just a mainjet swap, but it was easier.

Haven't seen the check valve in the new lectrons, but am aware that the smart carb uses one.  So if the bike tips over it doesn't flood the motor.  I would advise if using one in the winter cold temps to run a thinner injector type oil vs a thicker race type oil. What happens is when the fuel evaporates away after sitting a few days the residual oil can "stick" the check valve.  You'll go to start the bike and won't get fuel without tapping on the carb with a rock to free it up.  To a certain extent you see the same thing with conventional float pivots and needle valves. Turn the gas on and it runs on your foot.

 

In my feable mind they shouldn't be called power jets.   A real power jet cuts fuel flow down, not add it.

Edited by highmarker

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Yeah, I know add on powerjets are nothing new, I'm just suddenly interested in them. Failure mode would be terrible for sure. If I were to run one I wouldnt use the Dial a jet or intellajet; the varieties that only add fuel, not air also seem a bit less risky. You mention having to play with the needle, too. What areas do they mess up the needle usually? Clip change, or new needle? I'm a bit surprised to hear the DAJ made your bike more sensitive to the conditions. Huge turn off for me, although at least its adjustable.

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my egts were all over the place running them, not sure if temp and alt were to blame or inconsistency in the way they pulled fuel vs. a fixed brass jet

 

don't let me discourage you from trying though, I know guys that liked them.  One guy has one on a CV carb on his dual sport.  Most people don't try them because of having to drill hole in the carb.

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In my experience, powerjets, dial-a-jets, thunderjets, insert name here, work well and are the most tunable in applications where the engine is running predominatley in the 3/4-W.O.T. position (drag, ice, Flat track, TT etc.) and are the most effective in systems that run a relativity low manifold absolute pressure at high rpms. (4t with high lift short duration, 2t with stock height exhaust port(s) and reeds, some rotarys.)

The idea is that you are mixing fuel with air at more than one point (needle jet nozzle). The ideal set up would be for the fuel and air to meet in the center of the venturi, like in a Holley or similar automotive carb, or from a fuel ring around the outside of the venturi like those cool Dyson fans that you can put your hand through the middle. So the power jet adds a second, and in some extreme, huge displacement drag motors, a third location for the fuel to enter the airstream, creating a potentially more "saturated" air fuel mix, hopefully, stoichiometric!

the cons are: very sensitive to pressure changes, both atmospheric and manifold. Requires sometimes extensive mods to carb, often not reversable. doesnt like to be "bounced" around alot (causes rich "blurps")

on small engines, usually causes lean flat spots at the 3/4 throttle opening area while the power jet is transitioning in.

Basically, if your hitting bumps and are not at WFO all the time, they arent for you.

Spend you money on new tires 👍

Scooter

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