accel pump diaphragm 07 450

5 replies to this topic
  • slinkster

Posted May 24, 2015 - 07:51 AM


I need to order a new diaphragm however it looks like I have 3 options to choose from. 



. .Diaphragm, Acc Pump (Dph#25) AP
. .Diaphragm, Acc Pump (Dph#35) STD
. .Diaphragm, Acc Pump (Dph#45) AP


Bike is heavily modded. Stock one is done. What are the differences between these 3?


Was also thinking about the R&D bowl but i have been out of the game for awhile and don't know if i want to justify that expense until i start racing again. But will go ahead and order it if the consensus is that it should be added. 




P.S don't let the first post fool you. My old account got deleted and had to create a new one. 

  • grayracer513

Posted May 24, 2015 - 09:29 AM


The difference is the length of the rivet, or button, on the bottom of the diaphragm, which limits the maximum pump stroke, and thus, the delivered volume of the squirt.

The lowest number in the third set of characters (xxx-xxxxx-17-xx, for example) has the shortest button, and thus the highest output volume.

If the bike ran well with the original diaphragm, then chose the one listed as standard. Diaphragm selection is one of the designed in ways of tuning the accelerator pump, along with timing and leak jet selection.

The R&D bowls don't do anything that can't be accomplished by normal means with Keihin parts, but it can simplify the selection of leak jet size, since that feature is externally adjustable. On the other hand, it may also encourage the use of leak jet size to control things it's not intended to, somewhat as people will use pilot jet size to compensate for the wrong needle diameter.

  • slinkster

Posted May 24, 2015 - 04:23 PM


Thanks Grey,


The bike ran great when hot. The typical B to start cold but as soon as it lit it was a beast. 


Would changing the Diaphragm help starting at all? The jetting was nearly spot of prior to the diaphragm going south. 

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  • grayracer513

Posted May 25, 2015 - 06:37 AM


Won't really help, no.  Do you prime with the throttle before a cols start?

  • slinkster

Posted May 26, 2015 - 09:30 AM


I usually give it a twist of the throttle. Or i will do a few soft kicks before starting. I contribute the hard start to the head work and high compression piston. It needs a nice firm kick that goes completely through the stroke to light. Im going to swap out the spark plug to something a bit hotter and see what that does.


I run Vp4.4 on race days and 110 on practice. 

  • grayracer513

Posted May 26, 2015 - 10:04 AM


Give it more than one twist (as many as 4, if that's what it likes).


The correct procedure with auto decompression is to push the engine up against compression (the "hard spot"), then reset the kick crank to the top and kick from there.  Auto decompression positions the crank just short of TDC (about 20-25 degrees BTDC), so a kick from there gives you the full, though shortened, compression stroke and pushes past the point of ignition at the same time.  You can kick from just anywhere, but your results will be much more random as to whether you push it through ignition or not.

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