p-38 lighting ?

11 replies to this topic
  • onyxxx

Posted November 11, 2002 - 06:24 PM


I came across a website (MXSouth.com) that is advertising a p-38 lighting which is suppose to reduce the gas flow like what the BK mod does. I searched for info on this site and not much out there. I was wondering if anyone knows anything about this. Will this achieve same results as bk mod? Any info will be greatly appreciated.


  • Jekel

Posted November 11, 2002 - 06:33 PM


It will have the same effects as the BK mod. The BK mod will let you adjust the squirt and the P38 wont, it is just a bolt on item. I run the P38 on my 99 400 and am impressed with it. With your bike I would probably do the BK and save some money :) my .02

  • sabin

Posted November 11, 2002 - 10:39 PM


approximately what is the timing of the p38 squirt?

  • Hick

Posted November 12, 2002 - 07:27 AM


I searched for info on this site and not much out there.

Are you kidding? There must be 1,000 posts on the P38 running around on the TTalk server. Most are bound to be very old, the BK mod and its later incarnations for other Keihin carbs sort of rendered the P38 obsolete.

I don't know that anybody ever determined the P38 stroke or timing, but it is probably still delivering more fuel than the most members BK settings...

  • onyxxx

Posted November 12, 2002 - 08:14 AM


I ended up finding older posts mostly from the yz forums. When I first did the search, I only did wr forum, and came up with only 4 hits. I could not find anyone knowing the timing of the squirt, and came up with mixed reviews. The p-38 got my attention because instead of drilling, I would rather bolt on, because if I want to get it back to stock or sell it, I could unbolt it without having a hole in the tap. However the bk mod is making the most sense at this point unless proven otherwise.

  • Guy

Posted November 12, 2002 - 09:32 AM


I think you'll find the P-38 merely limits the duration of the stroke and NOT the timing, as stated above it is fixed and not varialbe, which is fine if it matches your bikes requirement , but otherwise........


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  • Hick

Posted November 12, 2002 - 12:44 PM


You can alter the pump timing on the Yamaha Flat CR carb, P38 or no, there is a screw for this just under the slide pulley that butts the pump arm (that is connected to the pump rod).

On non-Yamaha FCRs, you can alter the timing by spreading (increase delay) or tightening the gap in the fork-shaped pump stop that is cast onto the carb body.

With the BK mod, especially at very low settings, an additional amount of pump delay (in on the Flat CR screw) is helpful in my experience.

  • freestyle111

Posted November 12, 2002 - 03:17 PM


i have p-38 on my wr400.i love t it was well worth $75.on the otherhand you can go with taffy mod or bk mod for a lot cheaper and get same results.i chose p-38 because it was more convenient.installation is simple but you still need to play with jetting to fine tune p-38.another plus is it looks cool Posted Image

  • onyxxx

Posted November 12, 2002 - 04:12 PM


Thanks for the info. Freestyle, just wondering when you installed it, what did you have to do to your jetting, richer or leaner and what did you have to change? Also, does carb have to come off to install?

  • freestyle111

Posted November 13, 2002 - 12:39 PM


its been a while since i installed p38 but i believe i went with bigger main jet and went smaller with pilot.i think i also moved needle clip down 1 notch.i know i posted changes i made on tt when i installed the p-38.if you search thru my post you could probably find topic on p-38 installation and tuning.its been abpout a year since i would of posted it

  • Guy

Posted November 13, 2002 - 12:52 PM


:DNot on the 99 model of FCR hence the Taffy mod to limit the squirt and altering the length of the rod to alter the timing....the screw was only 2000 onwards as far as I know :)

  • freestyle111

Posted November 13, 2002 - 02:41 PM


Also, does carb have to come off to install?

if can you get diaphram cover off accel.pump without removing carb then you can probably install p38 without carb still on bike.it only takes couple minutes to remove carb and will make install easier.


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