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#76 | |
Moderator
Join Date: Oct 2016
Location: Houma, La.
Posts: 11,593
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2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel |
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#77 | |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,065
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Quote:
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.
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Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124 |
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#78 |
Join Date: Apr 2018
Posts: 68
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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? |
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#79 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,065
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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.
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Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124 |
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#81 | |
Join Date: Jun 2016
Location: akwesasne, NY-13655
Posts: 2,220
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#82 |
Join Date: Feb 2019
Posts: 74
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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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#83 | |
Join Date: Apr 2016
Location: Chesapeake, VA
Posts: 207
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Quote:
Last edited by MDStroup; 02-18-2019 at 01:18 AM. |
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#84 | |
Moderator
Join Date: Oct 2016
Location: Houma, La.
Posts: 11,593
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Quote:
http://www.chinariders.net/showthrea...ght=tt250+head
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2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel Last edited by JerryHawk250; 02-18-2019 at 06:08 PM. |
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#85 |
Moderator
Join Date: Oct 2016
Location: Houma, La.
Posts: 11,593
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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.
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2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel Last edited by JerryHawk250; 02-18-2019 at 03:36 PM. |
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#86 | |
Join Date: Jun 2016
Location: Hell
Posts: 2,408
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Quote:
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. |
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#87 | |
Moderator
Join Date: Oct 2016
Location: Houma, La.
Posts: 11,593
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Quote:
__________________
2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel |
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#88 |
Join Date: Feb 2019
Posts: 74
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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.
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#90 |
Join Date: Feb 2019
Posts: 74
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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. Last edited by SensuBeanCartel; 02-18-2019 at 01:23 PM. |
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