FCR Accelerator pump tuning

koko64 · January 13, 2019, 06:41:43 PM

Does anyone know if the hole in the accelerator pump arm which cranks the pump rod is oval or round? The arm is plastic and the hole in it is quite ovaled causing a pause in pump actuation. I wound in some safety wire to fill the hole above the rod and noted a clear improvement in immediate response from low rpm range. If you guys think an oval hole would be wear induced then I can order a spare part. I honestly cant remember if the hole is a slot or round shape.

Howie · January 13, 2019, 07:20:43 PM

Me neither, but I think you found the answer.

Speeddog · January 14, 2019, 11:05:17 AM

The FCR's I can get my eyes on right now have oval slots.

I wager it's so you can have that dead spot if you want it.
You can tweak the little stop for that plastic arm, get rid of the dead spot.

There's two holes for the pushrod up at the cable spool foro adjustment too.

koko64 · January 14, 2019, 12:30:01 PM

Cheers

Taking a close look, I can only see a horizontal post with locknut behind the throttle cam. It doesn't appear to touch anything. I know I can adjust via leak jet but can't see a screw anywhere that would roll the pump arm or take up the slack (which I've seen on Mikuni TM RS flatslides).

koko64 · January 16, 2019, 01:30:59 AM

Tested engine response by lowering the pushrod 1mm and reverting back again. This showed clear results from getting the pump to operate a little earlier. Throttle response was immediate and strong, really increasing low rpm torque. It appears a disproportinate effect.

One has to be careful to avoid having the pump squirt too early causing the fuel stream to hit the throttle slide.

It is definitely worth a few bike lengths in acceleration and the immediate torque is satisfying.

koko64 · January 16, 2019, 07:00:38 PM

Spoke with the importer and they have a selection of leak jets but the leak jet for the Ducati carbs is already blocked as delivered to give maximum volume, so no extra gain there. They did have diaphragms with a taller centre nipple, 2ish mm taller so I ordered one. The MX guys like these raised diaphragms for more immediate response. There was only one length pushrod available.

koko64 · January 18, 2019, 12:34:01 AM

They sent an incorrect diaphragm which has the nipple facing down not up towards the pushrod. This would bottom out the stroke early and reduce pump volume. It is designed for a different pump boss. They are looking for a slightly longer push rod which I can trim if required.
My spacing of the current pushrod will suffice for now. The response is immediate and excellent.

ducpainter · January 18, 2019, 03:17:20 AM

Why are you fussing over immediate and excellent?

Are you trying to fix it until you break it?

koko64 · January 18, 2019, 03:52:38 AM

It shits me how such a high end carb doesn't have an adjustable accelerator pump. The MX version does.

ducpainter · January 18, 2019, 03:58:53 AM

Quote from: koko64 on January 18, 2019, 03:52:38 AM
It shits me how such a high end carb doesn't have an adjustable accelerator pump. The MX version does.

So use a couple of MX carbs as split singles on short manifolds if you want problems.

koko64 · January 18, 2019, 07:27:07 AM

Quote from: ducpainter on January 18, 2019, 03:58:53 AM
So use a couple of MX carbs as split singles on short manifolds if you want problems.

I've always wanted to build a short manifold Supersport motor for the track. Oem manifolds are great for the street.

koko64 · January 18, 2019, 08:10:02 AM

I got the response "immediate and excellent" with my bodgy safety wire mod. Removing the slack in the system commences the stroke earlier removing a pause in response. I would rather adjust a screw.
It must be perfect

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FCR Accelerator pump tuning