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Berg's In the garage a long time,,,

Joined Nov 2008
17 Posts | 1+
Campbell CA
FX550e

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This passion started a while ago, back with a 94 FE501, which owned twice, I used to live in the desert offroad mecca of Ocotillo Wells / Borrego Springs area of Socal. Hard starting when hot, a big problem in the boiling 110F days and extremely risking riding on your own ( which did most of the time ) I ended up buying the very first FE650e, so you no where that ended with all of its problems
in hindsight should have kept it but i wanted a work any time electric start.
but the the rides i did have on the 650 are etched on my mind, even though i still think my blueprinted 501 was probably faster than the stock 650 ???
so after a brief flirt with KTM 640 and ATK 605 I purchased this FX in Grand Junction CO it was advertised as a FX550 with 501 replacement engine and boxes of spare parts.
On getting home i found out the the replacement engine was the correct 550, a few years ago, Dale Lineweaver rebuilt the crank, lapped the cases installed shimmed roller bearings, rebuilt the cylinder head, re-jetted & removed accelerator pump on the FCR Keihin.
So after being in storage several years its finally about to see the light of day.
i have been going back and forth about making it a SM or offroad, after analyzing
i have decided to keep this as an off-road and build another 2nd Berg SM 650
So these builds will be posted in relevant sections.
 
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Looks great sean999r :thumbup:

I'll be interested to see what you think about the accelerator pump being removed in the real world. That's one of the main differences between the FCR and the Dellorto and I don't know why anyone would do it. I guess he is a well respected guy so there must be a reason but by the same token, Keihin are pretty clever also. The bogging can easily be sorted with an externally adjustable leak jet....

Looking forward to some pics of both of them.

Damo
 
lovely bike!

Here's a comment of Lineaweaver's which explains it:
http://husaberg.org/fuel/2950-tale-two-carburetors-06-fe450e-linea-berg-mod-report.html#post24840

"Why would one disable the accelerator pump? I thought it would be an enhancement over a non-pumper carb."


A smoothbore variable Venturi carburetor such as that of the Keihin FCR produces a very strong fuel signal even during acceleration. The accelerator pump is intended to cover holes in fuel delivery due to signal reduction during acceleration. Such is most noticeable in a fixed venturi carburetor.

The FCR 39 mm and 41 mm carburetors were originally designed for use on high rpm multi cylinder engines with each carburetor feeding a displacement of only 250 cc - 300 cc. Needless to say a pump shot was required in such an application to compensate for signal loss during acceleration from low (off the cam) rpm.

Regarding a large displacement single:
Venturi signal will remain strong even during rapid throttle opening as a result of the increased displacement.

Regarding Husaberg:
The pump remains in place to help cover the OEM lean carburetor settings.

In addition technical riding is enhanced as a result of a proper and more consistent A/F ratio. Such is the result of eliminating the constant pump dribble which comes from slight throttle movements.

I'm pretty sure the pump is not the only difference - the FCR is a complex high-precision design which meters well and flows well, and is easy to adjust.
 
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Hmmmm, interesting thoughts. I would've thought the problem would've been exacerbated with a large capacity piston with one carb feeding it though. Lots of extra almost instantaneous air flow and with the fuel flowing out the main taking a little longer to accelerate to match. I don't know of too many competition bikes that don't run a FCR pumper carb. It is universally noted for crisp throttle response and in part due to said pump. I do realise it's not the only difference, I didn't say that actually.

Anyway, I'm sure he would've tested it and I respect his knowledge.

I'm just interested in what it rides like, in the real world

Damo
 
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Damo

I think you have misunderstood the basic premise of a carb. if I have a 650 and it is a single, i don't have a cam that is ever 'off'...it is always working, so there is no flat spot.

secondly, a 650 at low revs is sucking hard, way harder than a 250-300cc cylinder, that means the air speed is far higher and there is a strong signal to the jest to 'come on up'.

the APJ is kept for closed to to go off of a closed throttle. just that first 'bang'. after that....they don't need it. remember, dirt bikes are undergeared and therefore more likely to have faster crank speeds than an SM.

regards

Taffy
 
Ok, fair enough....

From what I was thinking though, the accelerator pump is designed to work when 'cracking' the throttle open hard. Not a smooth transitional opening of it where the pilot circuit will come into play.....

Closed/light throttle = closed butterfly = high manifold vacuum but not a lot of air speed.
Opened throttle quickly = open butterfly = high air speed. But the fuel is not discharged in an instant like the air speed is, hence a small, metered injection to compensate.

That was my thoughts on it though...

Not trying to argue here, just talking it out as I find it quite an interesting modification :)

Damo
 
but it is far worse for a 250 or 300cc cylinder. the bigger the carb and the smaller the cylinmder the more your premise comes true.

Taffy
 

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