Anypone know what this is??

[dquarton]

This Keihin PWK AS 39mm carb came with a bike I picked up and it has some sort of brass adjustment knob on it that connects to a large hex shaped piece on the bottom of the float bowl. Anyone know what it is?

http://i42.tinypic.com/4ghxxk.jpg
http://i43.tinypic.com/70gsnr.jpg
http://i42.tinypic.com/kd33b9.jpg

[K-Dub]

Could it be a power jet of some sort? I know they have tried different things over the years to get more fuel at wot only for long wot runs. My idea would be that only at wot the carb would form enough vacuum to suck extra fuel through it. Could be out in left field but thats my first thought.

[deathman53]

I know what that is. Its a jetting system called "dial-a-jet". it allows yo to change the jetting from richer to leaner by using the top screw. When you put that in, you put a 3-4 smaller main jet in the carb. Its a thing that some say works great, others say it made their carb useless.

[dquarton]

Originally posted by deathman53
I know what that is. Its a jetting system called "dial-a-jet". it allows yo to change the jetting from richer to leaner by using the top screw. When you put that in, you put a 3-4 smaller main jet in the carb. Its a thing that some say works great, others say it made their carb useless.

OK, that sounds familiar and I think i remember the guy talking about that.....thank you!

[wilkin250r]

Originally posted by K-Dub
Could it be a power jet of some sort? I know they have tried different things over the years to get more fuel at wot only for long wot runs. My idea would be that only at wot the carb would form enough vacuum to suck extra fuel through it.
Close, but a powerjet is actually powered, it turns on and off with electrical power. And oddly enough, it works the opposite, it shuts OFF at high rpms. 2-stroke carbs aren't perfect, if you pull 20% more air through the carb, you'll end up pulling 22% more fuel (not exactly, but you get the idea). At really high RPMS and high airflow, you end up pulling significantly more fuel than you need.

If you jet for high RPMs, you'll be lean in the midrange. If you jet for the midrange, you'll be rich at high RPMs. The powerjet fixes this by adding more fuel in the midrange, and shuts off at the higher rpms when the carb is pulling more fuel on it's own.

Because it's not powered, I don't think it's a powerjet, unless that fuel line had some sort of shutoff somewhere up the line. Most likely, it's a dial-a-jet.

[dabeechman]

No, it's actually called a power jet.

Works off of the amount of air that comes across the carburetor. The more air that passes by the siphon tube, the more fuel it pulls.

This is mainly used for drag racing, although it can be used by anybody. Main purpose is to compensate for climate/elevation changes. You'll see these on just about any alcohol carburetor, as that is where they are most effective.

Although, whoever installed it did a terrible job. That siphon tube needs to be centered in the throat of the carburetor.

[atv fan 28]

The power jets should be set up like my 48 Lectron. This carb will be feed alky through a fuel pump that runs off vaccum from the motor.

http://i39.tinypic.com/1h427d.jpg

[dquarton]

Originally posted by dabeechman
No, it's actually called a power jet.

Works off of the amount of air that comes across the carburetor. The more air that passes by the siphon tube, the more fuel it pulls.

This is mainly used for drag racing, although it can be used by anybody. Main purpose is to compensate for climate/elevation changes. You'll see these on just about any alcohol carburetor, as that is where they are most effective.

Although, whoever installed it did a terrible job. That siphon tube needs to be centered in the throat of the carburetor.

Oh boy, I listed it as having a dial a jet, I take it I should probably end the auction?

[HondaPohl]

I had a power jet on my banshee. Worked good for me on jetting.

[wilkin250r]

Then Dial-a-Jet would also be considered a "Power Jet", because what you guys have looks and works just like a Dial-a-Jet.

A traditional power jet is exactly as I described earlier, a secondary jet that shuts off at high RPMs. They came stock on the CR250 for a couple years, and several other 2-stroke dirtbikes. They were all electronically controlled and shut off at high rpms.

Like I said, normal 2-stroke carbs will get rich in the upper RPM. The same jetting that is spot-on at 6000 rpm will be really rich at 8000 rpm, and you can't adjust it because it's all the same throttle position (WOT). The overly-rich mixture will cause a drop in power.

To fix this, some carburetors come with a small secondary jet that can be turned off at high RPM. This allows the carburetor to have two different mixtures at the same throttle position, the secondary jet obviously having some sort of power applied to it to activate it. Without an overly-rich mixture at high RPM, the power stays strong in that range.


Now, I'm not here to get into an argument about semantics, a quick Google search reveals several products similar to a Dial-a-Jet, all indeed advertised and described as "Power Jets". I'm just here to educate that the traditional powerjet that came stock on the CR250 and other dirtbikes is not the same as the powerjet shown and described here.

So, dquarton, I don't think you have to end the auction. It might not actually be a "dial-a-jet" brand name, but it is indeed the same thing.

[HondaPohl]

Originally posted by wilkin250r
Then Dial-a-Jet would also be considered a "Power Jet", because what you guys have looks and works just like a Dial-a-Jet.

A traditional power jet is exactly as I described earlier, a secondary jet that shuts off at high RPMs. They came stock on the CR250 for a couple years, and several other 2-stroke dirtbikes. They were all electronically controlled and shut off at high rpms.

Like I said, normal 2-stroke carbs will get rich in the upper RPM. The same jetting that is spot-on at 6000 rpm will be really rich at 8000 rpm, and you can't adjust it because it's all the same throttle position (WOT). The overly-rich mixture will cause a drop in power.

To fix this, some carburetors come with a small secondary jet that can be turned off at high RPM. This allows the carburetor to have two different mixtures at the same throttle position, the secondary jet obviously having some sort of power applied to it to activate it. Without an overly-rich mixture at high RPM, the power stays strong in that range.


Now, I'm not here to get into an argument about semantics, a quick Google search reveals several products similar to a Dial-a-Jet, all indeed advertised and described as "Power Jets". I'm just here to educate that the traditional powerjet that came stock on the CR250 and other dirtbikes is not the same as the powerjet shown and described here.

So, dquarton, I don't think you have to end the auction. It might not actually be a "dial-a-jet" brand name, but it is indeed the same thing.

Oh I see what your saying. I had a dial a jet than not a power jet. Gotchya!

[wilkin250r]

Originally posted by HondaPohl
Oh I see what your saying. I had a dial a jet than not a power jet. Gotchya!

Essentially. It doesn't help that the term "Power Jet" is used to describe two different things. There are indeed systems that are called "Power Jets" that look just like that.

http://www.thunderproducts.com/thunder_powerjet.htm
http://www.thunderproducts.com/TPJSmallUpright.jpg

Notice, it looks almost identical to a Dial-A-Jet, and that's because it IS almost identical. However, if the manufacturer calls them PowerJets, then I suppose we are forced to call them powerjets as well.

http://www.thunderproducts.com/dial_a_jet.htm
http://www.thunderproducts.com/images/photos/dialajet2.jpg

[atv fan 28]

When i hear power jet i think of something like this.

http://lectronfuelsystems.com/carburetor/lectron_48mm_power_jet_carburetor.html

[wilkin250r]

This is a photo of a traditional powerjet. I believe this is a stock 98 CR250 carburetor. Notice the electrical plug on the top, it connects to the CDI to turn off the jet at high RPMs, I don't know the exact cutoff range. (I never tested this carb, I bought the set for the ignition sysem.)

While the housing is built into the carburetor, the actual jet orafice extends into the middle of the carb and looks really similar to the Dial-A-Jet and related products, so it's not too suprising that they would call them "Power Jets", because they look really similar.

[wilkin250r]

Originally posted by atv fan 28
When i hear power jet i think of something like this.

http://lectronfuelsystems.com/carburetor/lectron_48mm_power_jet_carburetor.html

And as mentioned by dabeechman, they're common with Alcohol carbs, because alcohol needs to flow SO much more, you either need to drill out the main fuel passage to make it larger, or get an additional jet to add extra fuel.

[dabeechman]

The emulsion tubes on alcohol carburetors are drilled anyway.

The PJ's on alcohol carburetors are required because the carbs are pretty dirty on the bottom generally and require more fuel on top.

The PJ's main function though is jetting on the top end where performance is most noticed and motors are typically burned down. A half turn on a PJ can be the difference in a 87mph pass and a 92mph pass for me in 100 yards or a running motor and a seized one.

[woodsracer144]

Originally posted by atv fan 28
The power jets should be set up like my 48 Lectron. This carb will be feed alky through a fuel pump that runs off vaccum from the motor.

http://i39.tinypic.com/1h427d.jpg


HOLY SMOKERS! that things bowl is huge! I thought my bowl I got was big on my lectron...