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mixxer

Keihin PD Super Pumper Carb/ TURBO

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Catchy title....lol

I know RickyRacer started a nice info thread on an oem PD Pumper Carb...

NEODS and I decided to try the knock off route / asian PD Pumper Carb knock-offs from eBay, new, for about 43 bux... I have since seen them for $38...

NEODS had posted up some solid info on his.... And I just got mine today...

I wanted to have one cohesive carb data bank and decided to start this thread.... 

The CRF230 comes stock with a Keihin non-pumper PD carb...  I don't know when the PD series of 4 stroke carbs came into being, but I know I first encountered them in my dirt biking youth in the 70s...

The PD has a main characteristic of having an oval bore/ venturi... Reason being to increase throttle response by having a more steady/ linear progression of open bore per amount of throttle twist from one quarter to three quarters throttle... Yet still have a decent amount of total flow area at wide open with it's taller-than-wider oval bore....

With all my involvement in motorsports... For whatever reason... Until recently I was unaware of there being a pumper/ accelerator pump version of the PD carbs... 

The carburetor is an elegantly simple device... Using a series of fuel metering circuits ... All using vacuum assisted velocity and pressure drop to pull fuel into the airway based on throttle opening and engine speed/ vacuum....

A fast/ large opening of the throttle can create a less fuel than optimal condition for a brief time while the engine speed comes up to pull enough vacuum to pull the correct amount of fuel to match the air flowing in the larger opening... Until the air/ fuel ratio is correct there is less than optimal power being produced...

The Keihin pwk 28 mm carb is not accelerator pump equipped, but has a slide designed  to allow for better/ sharper vacuum signal use/ sharper throttle response.. quite a few members use them and love them...

Accelerator pump carbs  have a feature that mimic a syringe shooting a gasoline stream into your venturi ... A squirt gun like shot.... In response to quick openings of the throttle... Which makes for better/ faster throttle response and power until  the vacuum is enough to run metering circuits...

The accel pump carbs allow you to use a bigger carb that would normally cause a bigger lag in pull from low rpm due to rpm having  to climb to make enough vacuum to make the carb work properly...

The pump shot adds needed fuel until rpm rises to a good enough rpm to make the carb ciruits function properly.

I will start posting pics and info tomorrow... Ricky, NEODS please post up some of your excellent info here...

 

Anyone with carb info of any kind, please post and share....

 

 

Edited by mixxer
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With respect to autos and boats...

Venturi design has a tremendous impact upon throttle feel and response and TQ delivery.  A great example is the booster venturi on the old Rochester Quadrajet (Q-Jet).  Particularly the pre-75 750 CFM models which have smaller primary venturis than the later 800 CFM models.  When jetted properly on an average engine (i.e., no big cam) these carbs need almost no pump shot and deliver exceptional throttle feel and response and TQ delivery.  Put a 750 CFM square-bore Holley on the exact same engine and you need a pretty good pump shot to get some sort of response.

On pump shots...  Capacity,  duration, and volume are critical to best throttle feel and response as well as fuel economy and 60-foot times.  Too little and you have backfires, stumbles, inconsistent traction, etc.  To much and you have stumbles, inconsistent traction, etc.  Some of this can lead to 60-foot time issues due to lack of consistent full power.  Pump shot is critical and with big aggressive cams it becomes even more critical, as does idle circuit fuel capacity.

While a Holley can be made very good it will never be Q-Jet due to its simple venturi design.  While the simple design may win a WOT dyno war it will not yield the same great throttle feel and response.  The booster venturi on the Q-Jet pays a penalty because it becomes restrictive at very engine engine speeds.  All things come with some sort of price/penalty.  For all-day WOT work square-bore Holleys are great.  For daily-driving part-throttle work Q-Jets are great.

The Q-Jet is so sensitive it is almost ridiculous and I have to believe the PWK is delivering something very similar due to its unique slide design.  The problem with a Q-Jet is that it can be so sensitive you are rewarded with too much wheelspin and a lack of traction.  I have had guys come to me with their POS 600 CFM Holley not happy and I put the original Q-Jet back on (jetted and massaged) and they can't believe the difference.  More bottom.  More top.  Better throttle feel and response.  They are now happily burning tires with what they were told is a junk carb.

Anyhow...  Point is venturi design and pump shot capacity, duration, and quantity is critical to netting the most power out of any engine.

Edited by VortecCPI
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First thoughts out of the gate while fondling my genuine imitation PD Pumper Carb....

You get what you pay for with manufacturing in countries where the workers are paid "3 fish heads per week" salaries.... Copies don't have to carry on the pride, engineering, or reputation of the original manufacturers... They have nothing at stake... They are copies...

So far I believe my carb will be serviceable.... But I am less than impressed with the manufacturing....

First and most irritating .... And already addressed ...is that the throttle cable cam/plate is not clocked properly on the axle that operates the slide crane assembly... Such that the throttle stop.tab hits the limiter boss on the carb body before the throttle fully open the venturi aperture .. about 3mm shy by eyeball... The clocking can't be re worked, but the stop tab can be cut to allow correct opening, which I have already done... wishing my irritation mode didn't have to be activated so soon on my new performance toy...

More nit picking and bitching to come... But I have a busy day before I can get back to carb detailing... So far nothing has been a deal breaker... But it definitely isn't bolt on and go for me...

NEODS and Ricky.... Come in and help me out with some pics and observations... Ricky has OEM model with larger than knock off bore size... NEODS has a new knock off like mine...

Original carb is from 78-83 ish xl/xr250

 

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9 minutes ago, mixxer said:

First thoughts out of the gate while fondling my genuine imitation PD Pumper Carb....

You get what you pay for with manufacturing in countries where the workers are paid "3 fish heads per week" salaries.... Copies don't have to carry on the pride, engineering, or reputation of the original manufacturers... They have nothing at stake... They are copies...

So far I believe my carb will be serviceable.... But I am less than impressed with the manufacturing....

First and most irritating .... And already addressed ...is that the throttle cable cam/plate is not clocked properly on the axle that operates the slide crane assembly... Such that the throttle stop.tab hits the limiter boss on the carb body before the throttle fully open the venturi aperture .. about 3mm shy by eyeball... The clocking can't be re worked, but the stop tab can be cut to allow correct opening, which I have already done... wishing my irritation mode didn't have to be activated so soon on my new performance toy...

More nit picking and bitching to come... But I have a busy day before I can get back to carb detailing... So far nothing has been a deal breaker... But it definitely isn't bolt on and go for me...

NEODS and Ricky.... Come in and help me out with some pics and observations... Ricky has OEM model with larger than knock off bore size... NEODS has a new knock off like mine...

Original carb is from 78-83 ish xl/xr250

 

Three fish heads per week???  When did they get such a raise???

This is the big problem with much of the "Pacific Rim" goods -- Complete lack of consistency due to lack of QM.

Makes me wonder if any two will be the same and if we will end up with various different jetting requirements due to inconsistencies with respect to dimensional tolerances.  Simple little things, such as needle jet ID, could end up being a nightmare.  The Keihin PD carb may be a very simple device but it is surely a high-quality device.

"2mm DIA. +/- 1mm" is not a good thing...

Edited by VortecCPI
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Agreed... 

NEODS had posted that his throttle at WOT had the slide open 2mm above the throttle venturi bore... Which is good for me to open the venturi to max size/ flow potential,.. while on mine the slide stopped while blocking 2mm at top of venturi... Since we each pain $43 I think we even purchased from the same vendor .. Caltric on eBay...

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Is interesting...  Many people in this great country don't seem to care much about quality today...  It's all about quantity and little about quality...

Junk News...  Junk Food...  Junk Tools...  What happened?

One thing about Japanese fabrication/manufacturing as taught by W. Edwards Deming...  You don't have to make the most (HP, TQ, Cargo Space, Fuel Economy, etc.) but you MUST strive to make each and every product exactly the same.  No anomalies.  No revisions.  No changes.  No problems.  No surprises.

One thing we know about our clunky old Keihin PD is that (with proper float level) jetting will almost always be 100% predictable for us.

Sorry...  Bit of a tangent there...

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The only pictures I got are in the thread I started. I will have more after the 19th as I will be starting the stroker build. I don't want to take it apart again. I can say from the pictures I can see the difference in quality. I did notice it looks like the aftermarket version has a removable leak jet for the pump. Mine is fixed. Maybe I should scoop up another factory carb before the 230 community wipes out the supply 😂 I hope it runs well as mine is incredible 😁 I need to look up the float level. Just eyeballed it😳 When I put it together. 

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"The quality of it and the aesthetics are not very pleasing to the eye, but you get what you pay for" -NEODS girlfriend...  Granted she is a Die Press Operator and knows her castings...

Poor fill, blisters, overspray in the casting, and the consistency in the assembly is to be questioned as well. I still do think there is a lot of potential for gains with a little elbow grease. I think finding a good OEM example like Ricky, for the right price could be a very long waiting game, we'll find out soon enough if it would be worth the wait.

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Is there a drain screw on the bowl like the original?  

Mine still has the original pump diaphragm decades old.

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I decided to pull the choke assembly off of mine ... More CFM, no question since a power now wing kills 2 hp on a 450...

Epoxied up the axle holes.... Pulled all choke stuff..cut off part of accel pump linkage that worked with choke... Cleaned up the look a bit...

 

IMG_20170805_133339994.jpg

Edited by mixxer
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Also adjusted limiter tabs for a more solid pump shot...

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4 hours ago, Baja Rambler said:

Is there a drain screw on the bowl like the original?  

Mine still has the original pump diaphragm decades old.

Yes, still a drain screw on the bowl.

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4 hours ago, mixxer said:

I decided to pull the choke assembly off of mine ... More CFM, no question since a power now wing kills 2 hp on a 450...

Epoxied up the axle holes.... Pulled all choke stuff..cut off part of accel pump linkage that worked with choke... Cleaned up the look a bit...

 

IMG_20170805_133339994.jpg

That looks unobstructed.  Any way to keep the idle-up ramp with the choke cable.  It's nice for doing a walk-around flight check while the bike is warming itself up.

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Wow this new thread has me LOL.

Where we used to call it China made Crap, we are now being so polite and cautious with conversations about China made Crap.

 

As Mr Green stated about the origin of manufacture of the Pro Com.

"Oh the humanity"

 

 

 

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3 minutes ago, adnohguy said:

Wow this new thread has me LOL.
Where we used to call it China made Crap, we are now be so polite and cautious with conversations about China made Crap.
As Mr Green stated about the origin of manufacture of the Pro Com.
"Oh the humanity"
 

I hope it doesn't just look like a carburetor.

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15 minutes ago, Baja Rambler said:

That looks unobstructed.  Any way to keep the idle-up ramp with the choke cable.  It's nice for doing a walk-around flight check while the bike is warming itself up.

Maybe you could have... But I already went all out and epoxied and chopped linkages... That ship sailed today..  I wasn't thinking about it...

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34 minutes ago, adnohguy said:

Wow this new thread has me LOL.

Where we used to call it China made Crap, we are now being so polite and cautious with conversations about China made Crap.

 

As Mr Green stated about the origin of manufacture of the Pro Com.

"Oh the humanity"

 

 

 

Cautious? Holy crap! Lol

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