Question about FCR fuel pump diaphragm

DaleEO · Apr 23, 2006

Why is there a difference in the height of the stop located on what would be the bottom of the fuel pump diaphragm?

I recently replaced mine when I put the quick shot cover on as per the directions. And the replacement the local shop had a significantly longer stop than the stock Husaberg one. I asked one person at the shop and they told me the difference was that the Japanese bikes, as well as the KTM's have a bleed jet, where the Husaberg's do not.

Can anyone shed any light on this?

Thanks,

berger · Apr 23, 2006

I don't have an answer for you on the bleed jet. What I have heard is that the jap pump with the quick shot cover is the way to go. I believe it has less volume and the cover reduces air in the stream. I was considering that mod until I ended up going with Lineaweavers jet kit

buckwheat5679 · Apr 23, 2006

May be this will help. I had to go thru this when I installed a FCR from a 2004 CRF 450 on my Berg.

When you twist the throttle, the AP linkage pushes a rod down against the AP diaphragm which pushes gas through a passage going to the carburetor venture. The squirt of gas compensates for the big gulp of air the carburetor sucked in. The sudden drop in vacuum causes less fuel to be sucked through the normal jets. To help in fine tuning this squirt, there are adjustments. The leak jet is like a bleed hole in the AP squirt passage. A slow twist of the throttle will push a small amount of gas through the leak jet (which is the path of least resistance) and almost none will make it through the whole passage into the venturi. If you twist the throttle quicker, it tries to force more fuel through the passage which can't all go through the leak jet, so the rest flows through the whole passage and squirts into the venturi. The timing screw (on the external linkage) lets you time when the squirt starts and to some extent the duration, i.e. earlier squirt equals slightly longer duration. The length of the rivet on the diaphragm will also control the duration. A longer rivet will cause the diaphragm to bottom out sooner and limit the travel of the diaphragm, therefore reducing the duration of the squirt. A shorter rivet will allow longer travel and therefore a longer squirt duratio

Taffy · Apr 23, 2006

buckwheat is technically spot on. can't complain about that. what i would say is that everyone from the beginning has tried to reduce the squirt length and intensity.

so you want the diaphram you've been sent. you won't notice any difference i expect but what you do would be for the better. the mod on the mk1 carbs is called the Taff mod and on the MK2s forwards it's called the BK mod. those mods try to imitate what you have just bought.

regards

Taffy

Johnf3 · Apr 23, 2006

If you happen to be looking to reduce your squirt time, an easy way is to fit the diaphram that Honda uses.

My squirt time on my FE 550 was a solid three seconds--way too much. With the Honda part fitted, it is barely one second. This mod had an extremely positive effect on fuel mileage.

I went to a richer needle at the same time, decreased the main and the the bike rips.

Question about FCR fuel pump diaphragm

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