Keihin FCR Accelerator Pump operation

Nezbert · Jul 29, 2004

Hi there!

I have a question, i am rebuilding the Bearings of the acceleratorpump. and i recognized that there are two positions for the Link lever of the pump. Please look at this diagram, the linklever i mean has the Number68:

http://www.sudco.com/Diagrams323728/expfcr.gif

If u look at part number 12, u see two positions, one will let the pump operate sooner ("faster"), one later (slower).

So, wich position is better? Wich do u use? At the moment the link lever is attached to the "later" position, wich is the one more close to the axis of number 12.
If somethings unclear (i guess so

), please say!

Greetings!

Nezbert · Aug 3, 2004

Helloooooo

Nobody Home? Everybody on vacation?

sacberg · Aug 3, 2004

Your link took me to the Sudco main page. I assume the diagram your are referring to is the FCR side draft diagram. I have seen articles on bending the linkage, it makes sense that changing the cam hole would have a similar affect. On the 2004 carb looks like theFCRMX diagram on the Sudoc site iit has a stop screww that limits the accelerator pump squirt.

Try this articlce: http://www.4strokes.com/tech/ktm/jetmods.asp

LINEAWEAVER · Aug 3, 2004

Hi Nezbert,
For what it may be worth:
When the FCR is properly tuned I have obtained the best overall results with the accelerator pump completely disabled.
Sincerely,
Dale

Taffy · Aug 4, 2004

here here mr lineweaver!

Taffy

maichusa · Aug 4, 2004

I was told that the Yamaha 250f had better powerdelivery with the TPS disconnected. Nothing to with the accelerator, I know.

LINEAWEAVER · Aug 4, 2004

maichusa said:
I was told that the Yamaha 250f had better powerdelivery with the TPS disconnected. Nothing to with the accelerator, I know.

Often is the case that more tractable power delivery is had by using ignition timing ******** from that of full power. The TPS when disconnected from the loom emulates WOT with a consequent reduction in spark advance.

Hope this helps.
Best Regards,
Dale

Nezbert · Aug 5, 2004

Hi again!

I talked to a german Husabergtuner, who trold me to use the 2. Position, letting the pump operate sooner and faster.

btw, do u guys also have problems with the berg-vibrations and the pump-linkage?
I have now replaced the standard linkage bushings with miniature-ball-bearings, im curious about how long it will last...
Greetings!

Chas · Aug 21, 2004

Hi Dale,
I was under the impression that the TPS function when connected was to ****** the ignition advance at WOT in order to limit preignition, and therefore when the TPS is disconnected that full advance is retained at WOT. I would be interested in a discussion of how TPS operates and of the pros and cons of disconnecting the TPS function on FCR carbs.
Thanks for the advice.
Sincerely,
Chas Moser

LINEAWEAVER · Aug 31, 2004

Chas said:
Hi Dale,
I was under the impression that the TPS function when connected was to ****** the ignition advance at WOT in order to limit preignition, and therefore when the TPS is disconnected that full advance is retained at WOT. I would be interested in a discussion of how TPS operates and of the pros and cons of disconnecting the TPS function on FCR carbs.
Thanks for the advice.
Sincerely,
Chas Moser

Hi Chas,
The ignition timing is viewed as a 3D map consisting of load (as indicated by the TPS), Engine RPM and Ignition Advance.

All else remaining equal most often is the case with high output four cycle singles that ignition timing is advanced during light load operation to compensate for a less dense and often times exhaust diluted fuel mixture.

By unplugging the TPS timing will go to the default setting eliminating light load advance with a consequent reduction in throttle response.

Hope this helps.
Sincerely,
Dale

husabutt · Dec 16, 2005

LINEAWEAVER said:
Hi Nezbert,
For what it may be worth:
When the FCR is properly tuned I have obtained the best overall results with the accelerator pump completely disabled.
Sincerely,
Dale

Hi Dale:

I understand why you feel/know that A/P pump removal is the way to go on big bore singles (450-650) but what about a 250 4s.

Have you found that the 250's can benefit from the A/P as the FCR was originally designed for multi cylinder street bike's with 250cc or so of displacement per cylinder?

Would a 250 need the A/P due to the large carbs they are running?

LINEAWEAVER · Dec 16, 2005

Hi Husabutt,
Personally, I have found the pump to be of little use. A 250 "performance" single makes so little power off the cam (unlike a 1 Liter multi) that low rpm with heavy throttle opening is discouraged simply by design.

.
Hope this helps.

Sincerely,
Dale

husabutt · Dec 17, 2005

LINEAWEAVER said:
A 250 "performance" single makes so little power off the cam

Off the cam?

Hmmm....... I don't really know what that means.

Someone please enlighten me

LINEAWEAVER · Dec 17, 2005

husabutt said:
LINEAWEAVER said:

A 250 "performance" single makes so little power off the cam

Click to expand...

Off the cam?

Hmmm....... I don't really know what that means.

Someone please enlighten me

Horsepower is a product of torque and rpm.

In order to produce more power from a given displacement one must fill the cylinder more frequently (increase rpm) and / or provide forced induction (Turbo, Supercharger, N2O, Etc.).

In order to extract 35 plus RWHP from a naturally aspirated 250 single peak engine rpm is elevated. To achieve good filling during high rpm operation valve timing must be long and with considerable overlap. Unfortunately, with such high rpm attributes comes a reduction in low rpm efficiency. IE "Not much power below 6,000 rpm".

Hope this helps.

Sincerely,
Dale

Chas · Apr 22, 2009

LINEAWEAVER said:
Chas said:

Hi Dale,
I was under the impression that the TPS function when connected was to ****** the ignition advance at WOT in order to limit preignition, and therefore when the TPS is disconnected that full advance is retained at WOT. I would be interested in a discussion of how TPS operates and of the pros and cons of disconnecting the TPS function on FCR carbs.
Thanks for the advice.
Sincerely,
Chas Moser

Click to expand...

Hi Chas,
The ignition timing is viewed as a 3D map consisting of load (as indicated by the TPS), Engine RPM and Ignition Advance.

All else remaining equal most often is the case with high output four cycle singles that ignition timing is advanced during light load operation to compensate for a less dense and often times exhaust diluted fuel mixture.

By unplugging the TPS timing will go to the default setting eliminating light load advance with a consequent reduction in throttle response.

Hope this helps.
Sincerely,
Dale

Sorry for resurrecting such an old thread, but there is still a problem lingering in my mind over the TPS control over the default advance curve when the TPS is connected vs when it is disconnected. I realize that the primary function of the TPS is to add advance to the default curve in several stages, from a maximum amount at low rpm/ small throttle opening to a minimum amount (zero) at full throttle and high rpm. My concern deals with Dale's comment that, quote 'By unplugging the TPS, timing will go to the default setting eliminating light load advance, etc'. Intuition on my part and feedback from other sources seem to indicate that when the TPS is disconnected, the total advance would revert to the default advance curve plus the small throttle maximum advance added by the TPS therefore leaving the default advance curve with the additional maximum TPS advance throughout the rpm range regardless of actual throttle position. If this is the case, then simply disconnecting the TPS could easily lead to too much total advance while the engine is being operated under full throttle conditions. You can see the dichotomy between Dale's original statement and with my comments here. Please help me out.

steve · Apr 22, 2009

Not sure I can help much as I haven't really tried to analyse it. What I do know is that based on Dale's advice I played with my 650 and decided that the throttle response was more linear and predictable with it disconnected so that is where it is. For bush work there is very little WFO however. I do however run a small amount of AP as that does help. Once jetted properly you don't need much. Currently I'm at about 0.2 mm.
http://www.husaberg.org/index.php?set_a ... _photo.php

Steve

LINEAWEAVER · Apr 22, 2009

The TPS merely provides a means of adding additional advance during light load conditions.

RPM based curves are most often the same.
I.E. Pre TPS vs TPS unlugged = similiar curve.

Back in the day.......
Ignition systems had a mechanical (rpm) advance and a vaccuum (load) advance.

http://www.classicchevytrucks.20m.com/vacuum.htm

Hope this helps.

Dale

Chas · Apr 23, 2009

Thanks for the response. I am aware of the analogy between the function of the TPS vs the function of vacuum advance. I am still having a difficult time visualizing why the TPS wouldn't be 'locked in' to the maximum light load advance when it was simply disconnected. Since the disconnected TPS wiring is still connected to the CDI, why wouldn't the system then consider this as a permanent light load condition??

LINEAWEAVER · Apr 23, 2009

The safest path.
That of no load based advance.

Dale

Chas · Apr 23, 2009

Delete.

Keihin FCR Accelerator Pump operation

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