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I have read many threads on jetting an accelerator pumps but have not heard this one come up yet. Honda uses a short stroke ap diaphragm. Has anyone put in a long stroke diaphragm like used in the ktm's? Pros and cons? Looking for imput before I mod mine.

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I have read many threads on jetting an accelerator pumps but have not heard this one come up yet. Honda uses a short stroke ap diaphragm. Has anyone put in a long stroke diaphragm like used in the ktm's? Pros and cons? Looking for imput before I mod mine.

Here's the scoop:

All Honda's past 2003 use the short rivet. It is the correct one, as it fills the pump cavity completely. Lower performance motors (KTM) did not need it, and they were getting issues with too much squirt, even with a large leak jet, so Kiehin offered a 'restricted throw' pump diaphragm.

All Honda's past 2007 have a different apump lever and pump system than all other FCR MXCR 39-41 carbs. These are built for Honda only. They don't need any mods, just tuning, as the pump circuit and mechanism have been updated.

THE BEST tricks for the pre 2008 carbs:

1. Merge racing or R&D apump detent spring upgrade: instead of the o-ring mod. It's permanent, and works much better. Keeps the apump working along with the throttle slide, instead of always being late. Prevents binding (oring, safety wire) and possible wide open throttle problems (safety wire)

2. Leak jet: 50 is usually close enough for most people. If you head is ported with a 2002R cam, you might need a 40.

3. Linkage adjustment: lots of info here and on youtube on adjusting this.

Your goal:

Getting .8 - 1.1 sec of apump squirt the never hits the slide, and always shoots right into the head. Leak jet size determines distance and volume, apump linkage adjustment determines timing to miss the slide.

Tilting up the subframe, re-installing the gastank, and watching the apump in action through the bell of the carb, is the best way to know exactly what is going on. You adjust the linkage on the side of the carb throttle wheel, to change the timing. You can see it change. If you video tape the apump action, it's easier to see than trying to turn the throttle and watch at the same time.

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Thanks for the info Krannie. Mine is already timed and jetted properly. Was just going to experiment with a longer duration and see where it landed.

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My carby is the same as the left 1 and my friends 2008 is the same as the right 1

I also recorded a video of my ap squirting if you want to see it ?

Thanks I want to do a lot of searching before I have to buy new parts for my carby

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My carby is the same as the left 1 and my friends 2008 is the same as the right 1

I also recorded a video of my ap squirting if you want to see it ?

Thanks I want to do a lot of searching before I have to buy new parts for my carby

 

I think you have that backwards, because the carb on the left is the last updated version of the FCR carb.

 

I supposed it's possible that some years got different carb updates, but not according to Honda.

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I think you have that backwards, because the carb on the left is the last updated version of the FCR carb.

I supposed it's possible that some years got different carb updates, but not according to Honda.

no that's how they are... when you throttle it pushes his instead of it springing up on its own like mine

Mine is 01/07 x and his is mid 08

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