The O-RING mod


32 replies to this topic
  • MotoGoalie

Posted February 18, 2008 - 01:06 PM

#1

What size or diameter of O-ring do you use?

I've checked about 2 dozen links and nobody says exactly what size o-ring to use....:applause:

  • William1

Posted February 18, 2008 - 02:21 PM

#2

Plumbing store/Lowes/Home Depot
#78

  • Family Man

Posted March 14, 2008 - 10:31 PM

#3

what do you think about using and oring from an oring chain, say a regina orn-6?

  • William1

Posted March 15, 2008 - 03:16 AM

#4

Not having the oring dimensions, I cannot say.

You are aware a box of 10 #78's is like 2 bucks....

  • DBMX 925

Posted March 15, 2008 - 03:19 AM

#5

I wired mine. That worked well.

  • BergArabia

Posted March 15, 2008 - 04:44 AM

#6

Confusing post...
:confused:
OK.. carburator mods..:excuseme:

  • William1

Posted March 15, 2008 - 05:30 AM

#7

I wired mine. That worked well.


Wiring works but... you have make sure the AP diaphragm rivet does not bottom out hard when WOT.

  • grayracer513

Posted March 15, 2008 - 08:28 AM

#8

A far better solution is to use the stiffened accelerator pump drive spring from Merge Racing. This corrects the problem within the design parameters of the AP system, as the O-ring mod does, but is more durable and functional, and allows much more tuning latitude than wiring does.

Wiring requires the removal of the diaphragm stop button to prevent linkage bing up. That in turn increases the the AP output to the point that it is too great, leaving the tuner to have to use the leak jet to reduce it. Leak jets were not intended for this purpose. IMO, wiring the linkage is a patently Mickey Mouse approach.

  • bg10459

Posted March 15, 2008 - 12:47 PM

#9

....That in turn increases the the AP output to the point that it is too great, leaving the tuner to have to use the leak jet to reduce it. Leak jets were not intended for this purpose.

If leak jets were not intended to alter AP squirt volume and/or duration, even though alternate size AP diaphragms are available, what was the intention?:confused:

  • angellmxer

Posted March 15, 2008 - 01:26 PM

#10

Has anyone done this mod to an 08 with significant results? I heard that the 08 carbs are turned pretty well from factory and this may not be necessary.

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  • William1

Posted March 15, 2008 - 02:18 PM

#11

Has anyone done this mod to an 08 with significant results? I heard that the 08 carbs are turned pretty well from factory and this may not be necessary.


If you have no bog, then you are fine.

Though... every year, the news is the jetting is right till people start to complain. Unless the factory ran every bike and tested it, there will always be jetting issues. Every bike is different. Now, if they ran a EFI with all the sensors (and an additional 30 pounds was not a issue) then they would all run perfect from day one to day zero.

  • grayracer513

Posted March 15, 2008 - 03:03 PM

#12

If leak jets were not intended to alter AP squirt volume and/or duration, even though alternate size AP diaphragms are available, what was the intention?:confused:

The leak jet is included to reduce or eliminate the accelerator pump shot during slow or partial throttle openings. Read:

http://www.thumperta...330#post4415330

Has anyone done this mod to an 08 with significant results? I heard that the 08 carbs are turned pretty well from factory and this may not be necessary.

One of the differences in the '08 carb is the stiffer AP spring is already installed at the factory.

  • Ga426owner

Posted March 15, 2008 - 03:38 PM

#13

I am 100% happy with my wired AP. Yea there may be better ways /more expensive ways to acheive the same result, but I have never ridden any stock yami 400-450 that did not have any jetting issues to sort out or a bog or, excuse me a delayed response if you want to call it that, of some sort. Go ride any 07/08 Honda 450 they are like 2strokes when it comes to WOT starts...and I want this type of instant accelleration. The wired method came from YOT and Zipty still does this as part of their mod. The ORing AP mod is a cheap way to get similar results.

  • Windseeker

Posted March 15, 2008 - 03:41 PM

#14

One of the differences in the '08 carb is the stiffer AP spring is already installed at the factory.


The other is a modified diaphragm (with shorter knob thing in the middle)....:confused:

  • grayracer513

Posted March 15, 2008 - 05:05 PM

#15

The other is a modified diaphragm (with shorter knob thing in the middle)....:confused:

That's not really a mod so much as a change in specification. Keihin makes diaphragms with stop buttons in several different lengths as a method of controlling/adjusting the total volume delivered by the pump. Sudco sells the entire line, and you can basically duplicate the '08 carb changes in any earlier FCR.

  • TCCRA RACER

Posted March 15, 2008 - 06:52 PM

#16

our 08's don't bog or hesitate from idle at all!!! Get the jetting correct and all is well!!!

  • bg10459

Posted March 15, 2008 - 07:04 PM

#17

Since the leak jet is there, however, it does make a convenient way to dial in the strength of the AP discharge, and it's actually easier to do it that way than by the intended adjustment methods (AP cams, diaphragm button length, spring tension, and nozzle size.)

I think it's so much easier to dial your AP with LJ's and diaphragms that it has become the most widely used and perfectly acceptable method of doing so.

  • grayracer513

Posted March 15, 2008 - 08:00 PM

#18

Diaphragm button length is not only acceptable, it's the design intended means of varying the duration of the pump shot. Together with the timing screw, and the linkage spring tension, this is how the designers had in mind that the beginning, duration, and volume of the squirt would be adjusted. The leak jet is used to prevent the AP from over-enriching the engine when the boost it gives isn't fully needed, but it can be used to trim back an AP squirt that has simply been made too large.

The use of leak jets to adjust pump volume became popular with the advent of the wiring and other mods that eliminated the AP linkage spring. The solid linkage was an improvement because the AP springs previously used were weak. Because of the weak spring the delivery rate of the pump output was slower than it needed to be. But the use of a spring in the linkage allows the AP linkage to be stopped by the diaphragm stop button before the throttle is completely opened. The use of a heavier spring, as Yamaha and Honda have both now done (or an O-ring) accomplishes the goal of creating a stronger pump shot while still allowing the duration to be limited by the diaphragm stop button.

But, if the linkage is wired or solid, the diaphragm stop button would stop the throttle from opening unless it is cut off to its minimum length as it is in the wired AP mod. Cutting back the button in combination with a solid or wired linkage produces a bigger pump shot than the engine can possibly deal with, so the modifiers turned to the only means they had remaining to them to reduce this massively over-enlarged pump discharge: the leak jet.

Nevertheless, this method is not "perfectly acceptable" to everyone, and I think you will find that Eddie Sisneros in the Jetting Forum agrees with that. It's a shortcut method, at best, and far from perfect.

  • Kasjok

Posted March 17, 2008 - 01:34 PM

#19

FYI I found that it is great to use an O-ring with outer diameter of 7mm and 2mm thick (the thickest I found).

  • bg10459

Posted March 17, 2008 - 03:15 PM

#20

Diaphragm button length is not only acceptable, it's the design intended means of varying the duration of the pump shot.

Is diaphragm stud length the only method of adjusting duration? All else equal, will different LJ's not also have an effect on duration?

Together with the timing screw, and the linkage spring tension, this is how the designers had in mind that the beginning, duration, and volume of the squirt would be adjusted

I’m not aware of any alternative OEM springs for the AP lever. If this was the design intent, it seems they did not intend on making the volume adjustable this way. Besides, Keihin designed the carb, not Yamaha, right? They did, however, offer various LJ's and diaphragms for adjustment.:confused:

Guys like Merge Racing, JD and lots of members here (you included) think “outside the box” and adapt to design flaws. Do you prefer the “design intended” oil filter, engine oil or suspension (air cells??)?

The use of leak jets to adjust pump volume became popular with the advent of the wiring and other mods that eliminated the AP linkage spring.

While I’m aware that this type of AP mod is not so new, I think it became popular when it was introduced as the “Redbeard AP mod” about 2 years ago. I’m pretty certain there were lots of people tuning with LJ’s prior to this. I was.

The use of a heavier spring, as Yamaha and Honda have both now done (or an O-ring) accomplishes the goal of creating a stronger pump shot while still allowing the duration to be limited by the diaphragm stop button.

But, if the linkage is wired or solid, the diaphragm stop button would stop the throttle from opening unless it is cut off to its minimum length as it is in the wired AP mod. Cutting back the button in combination with a solid or wired linkage produces a bigger pump shot than the engine can possibly deal with, so the modifiers turned to the only means they had remaining to them to reduce this massively over-enlarged pump discharge: the leak jet.

Nevertheless, this method is not "perfectly acceptable" to everyone, and I think you will find that Eddie Sisneros in the Jetting Forum agrees with that. It's a shortcut method, at best, and far from perfect.

I re-read your post and think this is where we may have a misunderstanding. I agree that hard wiring and grinding off the diaphragm stud is "caveman" (no offense to any real cavemen:smirk: ). I think, though, that there is merit in the O-ring mod and in adjusting the duration and volume via the available range of diaphragms. Based on this, I also think it is perfectly acceptable to further tune your AP with LJ's, especially when you tune for various seasons, something the O-ring or stiffer spring still do not allow.

Whether the LJ is used to reduce or eliminate (or even increase) pump shot or to alter squirt volume and/or duration is semantics.





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