P-38, what is it and what does it do?

12 replies to this topic

Posted July 10, 2004 - 04:46 PM


as the title says, what is a P-38 and what does it do? also, will it work on a '00 yz-426? thanks for the help.

  • Unibomber

Posted July 10, 2004 - 05:33 PM


P-38 Lighting was a WWII fighter bomber, I think it had the split seating fuselage. :thumbsup:


Posted July 10, 2004 - 10:03 PM


P-38 Lighting was a WWII fighter bomber, I think it had the split seating fuselage. :thumbsup:

haha, very funny. i could have told you that as well. but, what i was looking for was the part the has to do with the carb(i think). i saw it somewhere and i cant remember and was just curious as to what it does.

  • Benjitis

Posted July 13, 2004 - 05:40 PM


P-38 is also an old German 9mm Pistol made by Walther i believe.


Posted July 13, 2004 - 07:46 PM


I believe its a small metal ring that hooks to your carb, its supposed to boost low end punch. it should work on your bike. A friend had one on a 2001 YZF 426, he felt the boost given was barely noticeable. He told me not to bother. I have a 2002 YZF 426. hope this helps. :thumbsup:

  • Rick_Kienle

Posted July 13, 2004 - 09:01 PM


The P-38 is a replacement accelerator pump cover that is aimed at curing the off-idle bog. It has a larger reservoir, and a small pin in the bottom that limits the AP diaphragm travel. The ports are also slightly larger. The net result is a shorter duration AP squirt. There is a more complete description in the current issue of either MXA or Dirt Bike (can't remember which one).

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  • DrThumper

Posted July 14, 2004 - 07:54 AM


The net result is a shorter duration AP squirt

...not really, its an atomizer that cures the problem of the off-idle bog the same way as a shorter duration spray. By atomizing the AP spray it burns leaner and more powerfull. I use one, I love it. I have no bog whatsoever....the P-38 when used with a PowerNow (I made the FreePowerNow) is very very effective! The PowerNow increases the velocity of the air in those low-throttle position events where the bog would be most apparent, so the faster air combined with a finer (atomized) spray gives you that lean burst of power. :thumbsup:

And, it looks cool! It comes in blue, red and other colors (I think). Looks pretty swank next to a anodized idle jet screw, like from Storm or Zip-Ty.


Posted July 14, 2004 - 11:35 AM


so since ive done the bk carb mod i wouldnt need this? or would it be better to have the P-38 instead of the BK carb mod?

  • RJB

Posted July 14, 2004 - 06:21 PM


Check out the MXA mag this month - got a whole piece on accel. pumps and a bit on the P-38 - otherwise I could copy it in here if you want


Posted July 14, 2004 - 10:14 PM


if theres a site that would be very helpful or if you just want to copy it that would be great too. otherwise i will just have to try and find it. thanks for the help.

  • RJB

Posted July 15, 2004 - 05:51 AM


Okay - here is the article in the mag (verbatim, or as good as my typing skills permit):

The P-38 is an accessory accelerator pump produced by Factory R&D. The P-38 differs from the stock cover in these ways:
1) The P-38 reservoir is 20% larger. It is not larger so that the diaphragm pump can squirt more gas, but to keep the accelerator pump primed during repetitious on-off throttle situations.
2) A timing pin in the centre of the reservoir restricts diaphragm movement. Factory R&D presets the length of the timing pin and tunes the duration of the accelerator pump squirt to best accommodate engine characteristics.
3) The inlet gas circuit is larger and the outlet is smaller. Gas fills the reservoir more easily, and the diaphragm squirts more forcefully.
4) It keeps the depressed diaphragm under greater pressure so it can spring back harder. The reservoir fills with gas faster and the accelerator pump resets quicker for the next shot.
Factory R&D's P-38 modified Keihin FCR shoots a more forceful spray of gas for a shorter duration of time. They claim that the stronger stream of gas atomizes more quickly, lessening the chance of engine flooding. For info call (949) 206-0894
<end quote>

MXSouth have it online for about $74.00 P-38
...now, if you want the full breakdown on what the accelerator pump does....well, in short, it is needed for 4 strokes to get the fuel at low RPM's, thus preventing a combination of too much oxygen and not enough gas; which would/does result in bog.


Posted July 15, 2004 - 09:27 PM


thanks so much for that. i have been out of the house busy with work and other BS so i havent had the time to really look. that cleared it up for me and maybe i will try that instead of messing with the BK carb mod i have done. thanks again for all the help ive got from all the TT members.

  • RJB

Posted July 16, 2004 - 08:26 AM


No problem - when I get a free moment, I'll scan the whole article and post a link for you to read

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