Keihin PWK 30 Carb

[JerryHawk250]

Originally Posted by Megadan

You can also simply order a PWK30 without the power jet as well. It will work to more or less the same degree, though you may need a larger main jet to compensate. 4 strokes don't benefit from a power jet anywhere near as much as a 2 stroke, so you can go without it realistically.

Thanks Dan, I forgot to mention that. I've thought about capping it off just to see if there is a difference in performance.

[Megadan]

Originally Posted by Deryl

I was looking to get this pumper carb before learning about these carbs

https://www.amazon.com/TC-Motor-Acce.../dp/B01FA7K598

Since I am new to all this its kind of confusing to me. So the power jet carb has a pilot and main jet like normal and on the bottom side also has another jet which is the power jet? So you can leave your main on the lean end on purpose and you swap out power jets to get your carb dialed in? Are the power jets the same kind of jet as your main?

Trying to get info from some people who have them or know more about them than me to see which would be best for my hawk. I would be doing a port and polish in the future along with new exhaust and filter but not decking the head. If I am understanding this correctly sounds like the power jet carb might be a better fit for what I am looking to do, and the mix screw is accessible without removing the carb so you can adjust with the bike running.

I can break down the difference.

Pumper Carb: Has an accelerator pump tied to the throttle. When throttle is applied, the accelerator pump shoots a tiny bit of fuel into the throat of the carburetor as the slide opens. This combats the initial lean condition a standard carb sees between when the slide opens and the flow of air starts drawing fuel, of which there is a small delay between those events. This gives the engine an immediate response to rapid throttle changes, but only applies extra fuel when the throttle is opened past a certain point, usually past 1/8th throttle, and then adds no more additional fuel. Here is a great video on the timing and demonstration of a pumper carb.


Power Jet: Operates like a standard slide carburetor through most of the throttle range, but past 3/4 throttle under high RPM/Load the airflow through the carburetor draws extra fuel up from the bowl and mists it into the throat of the carb. The reason this is popular with 2 strokes is in large part due to how sensitive 2 strokes are to fueling. Too rich and they will bog down and lose power. When they are tuned leaner they make better power and are much more responsive, but go too lean and they will self destruct rather quickly. What the power jet allows is for guys to tune their carb on the lean side to get the better response and power under most throttle conditions, but at wide open throttle it ensures that the bike doesn't go too lean at high RPM WOT conditions, giving the best of both worlds.

Power Jet in action.



In theory, you could tune a 4 stroke to utilize the power jet, but not for the same purpose. By running a smaller main jet, in conjunction with needle jet tuning, you could tune the bike to have a leaner part throttle condition, which under cruising conditions can help give better fuel economy, with the power jet there to compensate for the smaller main jet at WOT high load conditions. The downside to doing this is that the jet transition between needle and main can also cause hesistation if you go too far into the lean spectrum - essentially exaggerating the lean condition that a pumper carb resolves.

Of the two, on a 4 stroke the pumper carb is the better of the two options.

I have the PZ30 Pumper currently on my Hawk and I absolutely love it in the short time I have used it. It was easy to jet and setup since the stock Hawk carburetor is also a PZ30, so the same jetting works on it as well. That said, the PZ30 pumper is a great upgrade for any CG engine as it really makes the bike feel much stronger.

One advantage of the flat slide carburetors like the PWK is the flat slide itself. The narrower slide allows for more laminar airflow with less turbulence resulting in a higher velocity across the jets, resulting in a stronger "draw". This results in a much stronger throttle response and more immediate fueling from the jets, which is why Jerry's bike has a stronger throttle response at lower rpm/throttle positions. In a sense the flat slide helps combat the same roll-on lean condition as a pumper carb does, but to a lesser degree.

One big advantage of the PWK30 is the smooth bore nature of the carburetor over the PZ30 with it's more traditional venturi shaped bore. It is capable of flowing more air, and thus will be stronger at higher RPM. This is especially beneficial with a ported head.

[Deryl]

Thanks Dan and Jerry, I think for now I am going with the pumper carb. Only thing that sucks is the air/fuel mix screw is on the bottom. Are you using one of these dan?

https://www.amazon.com/NICECNC-Motor...a-582226868816

I am also pretty sure it's not a real keihin but a copy. Will keihin slow and pilot jets be compatable with it like the ones sold on amazon?

[Megadan]

Nope, mine actually came with a mixture screw that had a small knurled end I could reach with my fingers or put a small length of tubing on to adjust it.

[Deryl]

Did you get the one I linked from amazon?

[Ariel Red Hunter]

Originally Posted by Megadan

I can break down the difference.

Pumper Carb: Has an accelerator pump tied to the throttle. When throttle is applied, the accelerator pump shoots a tiny bit of fuel into the throat of the carburetor as the slide opens. This combats the initial lean condition a standard carb sees between when the slide opens and the flow of air starts drawing fuel, of which there is a small delay between those events. This gives the engine an immediate response to rapid throttle changes, but only applies extra fuel when the throttle is opened past a certain point, usually past 1/8th throttle, and then adds no more additional fuel. Here is a great video on the timing and demonstration of a pumper carb.


Power Jet: Operates like a standard slide carburetor through most of the throttle range, but past 3/4 throttle under high RPM/Load the airflow through the carburetor draws extra fuel up from the bowl and mists it into the throat of the carb. The reason this is popular with 2 strokes is in large part due to how sensitive 2 strokes are to fueling. Too rich and they will bog down and lose power. When they are tuned leaner they make better power and are much more responsive, but go too lean and they will self destruct rather quickly. What the power jet allows is for guys to tune their carb on the lean side to get the better response and power under most throttle conditions, but at wide open throttle it ensures that the bike doesn't go too lean at high RPM WOT conditions, giving the best of both worlds.

Power Jet in action.



In theory, you could tune a 4 stroke to utilize the power jet, but not for the same purpose. By running a smaller main jet, in conjunction with needle jet tuning, you could tune the bike to have a leaner part throttle condition, which under cruising conditions can help give better fuel economy, with the power jet there to compensate for the smaller main jet at WOT high load conditions. The downside to doing this is that the jet transition between needle and main can also cause hesistation if you go too far into the lean spectrum - essentially exaggerating the lean condition that a pumper carb resolves.

Of the two, on a 4 stroke the pumper carb is the better of the two options.

I have the PZ30 Pumper currently on my Hawk and I absolutely love it in the short time I have used it. It was easy to jet and setup since the stock Hawk carburetor is also a PZ30, so the same jetting works on it as well. That said, the PZ30 pumper is a great upgrade for any CG engine as it really makes the bike feel much stronger.

One advantage of the flat slide carburetors like the PWK is the flat slide itself. The narrower slide allows for more laminar airflow with less turbulence resulting in a higher velocity across the jets, resulting in a stronger "draw". This results in a much stronger throttle response and more immediate fueling from the jets, which is why Jerry's bike has a stronger throttle response at lower rpm/throttle positions. In a sense the flat slide helps combat the same roll-on lean condition as a pumper carb does, but to a lesser degree.

One big advantage of the PWK30 is the smooth bore nature of the carburetor over the PZ30 with it's more traditional venturi shaped bore. It is capable of flowing more air, and thus will be stronger at higher RPM. This is especially beneficial with a ported head.

Yes, just the thing for throttle snappers. Nothing wrong with that style of wrist twisting, especially as most North Americans learned on cars how to drive. In my case, I learned on motor cycles before I ever drove a car, so to me it is more normal to roll on a throttle rather than to snap it open. That's because the bikes I learned on all had round slide carburetors and heavy flywheels, which don't respond to snapping the throttle open as well as "pumper" carbs or square slide carbs do on light flywheel engines of today do. So now you've heard a voice from the past...ARH

[SensuBeanCartel]

Hello new to the forum, megadan could you please post a link to the carb you purchased? Also can anyone address the fact that the tt250 250cc head is already decked compared to a normal stock hawk head or ebay head, I believe that jerry has alot more shaved off his head than you (megadan) or anyone else with a ported head since by comparison the tt250 head should have higher compression.
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[MDStroup]

Originally Posted by SensuBeanCartel

Hello new to the forum, megadan could you please post a link to the carb you purchased? Also can anyone address the fact that the tt250 250cc head is already decked compared to a normal stock hawk head or ebay head, I believe that jerry has alot more shaved off his head than you (megadan) or anyone else with a ported head since by comparison the tt250 head should have higher compression.
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Didn't even know that the tt250's head was decked or to check to see if the tt250 ran at a higher compression.

[JerryHawk250]

Originally Posted by MDStroup

Didn't even know that the tt250's head was decked or to check to see if the tt250 ran at a higher compression.

The TT250 head is not decked. The TT250 does use a thinner head gasket from what one of the members on here posted a thread on.
http://www.chinariders.net/showthrea...ght=tt250+head

[JerryHawk250]

I did some experimenting over the weekend. I capped off the power jet and went riding to see if it performed any different. I found that with the power jet disabled there was a slight dead spot from 3/4 to full throttle. I'm already running a 125 main which is the biggest I have on hand so don't know if a larger main would of made a difference. I hooked the power jet back up and went for another ride and it definitely runs better through out the entire throttle range.
BTW I check fuel mileage and got 69.98mpg running 55-60 mph.

[NzBrakelathes]

Originally Posted by Megadan

Nope, mine actually came with a mixture screw that had a small knurled end I could reach with my fingers or put a small length of tubing on to adjust it.

I'm fairly sure all Keihin marked are this way, I have a new unused PZ30B/Pumper and has that slightly longer screw.
I looked into getting CNC Air screws made - too much outlay for me at this moment and other factors like vibrations might cause issues.

My unit has more common jets in it - not that odd pilot like in the stock carb on the Hawk - yes it is for sale if someone wants it.

[JerryHawk250]

Originally Posted by SensuBeanCartel

Hello new to the forum, megadan could you please post a link to the carb you purchased? Also can anyone address the fact that the tt250 250cc head is already decked compared to a normal stock hawk head or ebay head, I believe that jerry has alot more shaved off his head than you (megadan) or anyone else with a ported head since by comparison the tt250 head should have higher compression.
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I've ported, polished and decked both the Stock Hawk head and The TT250 head for another member here. The main difference between the two head are that the stock TT250 head has a better casting and the exhaust and intake ports are less restrictive. The TT250 comes with a thinner head gasket which will bump the compression ratio a little more than the Hawk.

[SensuBeanCartel]

Want me to take a picture of a side by side comparison, the deck on the head of the tt250 is already a mm shorter then the ebay head i have (after decking it a MM), and definitely my stock hawk head. Measured them both, not being rude but theyre nowhere near the same in compression, the tt250 has way less of a deck surface stock. look at the area where the deck meets the rest of the head, the combustion chamber depth, and its circumference.

[SensuBeanCartel]

After decking the ebay head over 1mm its still roughly 4mms, while the tt250 is just around 3mm, you might wanna double check your compression and your math, before you get kind of rude.

[SensuBeanCartel]

The casting also isnt too different, the main difference i saw was the fact the valves were set properly, more recessed, and lapped to a larger face on each valve. The area between the valve was also nice having a well defined ridge, theres also some nice pillars that look like leftover thoughts but actually could help provide some support, however that was after machining and valves being placed in doesn't have anything do with casting, but on the other hand crappy machining. There is also a gigantic gaping exhaust hole in the tt250 head, the stock hawk head has the sub port filled, the ebay head has no sub port just fins which will provide better cooling for that section of the head (just like a computer radiator),

Not questioning your skills here dude, but you might wanna give that a better look over if you're going to be running that engine hard, I dont believe your at the compression you think you are.