End of FCR size discussion?

[greenmonster]

Probably not....

But a interesting test & report from Brad again:

http://bradthebikeboy.blogspot.com/2010/12/900ss-with-fcr-39-and-41-carbs.html

I bet the 41 would make a pony or 2 more w 155 mains.


Thanks to Brad f sharing another test again!  

[Drunken Monkey]

Someone should give Brad an award for "most arguments settled" or something 

[ducatiz]

[junior varsity]

good stuff

saw the comparo graphs yesterday

[greenmonster]

ducatiz,
what does your reply mean?

[ducatiz]

ducatiz,
what does your reply mean?

"here's to you"

[koko64]

Another example of Brad's data for me to store.
Glad I listened to Chris Kelly and got the 41s.

With porting and an open air box my bike is wanting quite a bit of top end fuel (big main jets) with the 41s. The A/F ratio comparison was interesting and may well explain why.

[koko64]

C'mon people don't let the thread die.

I have had two 900s with high comp pistons, open air box, advanced cams (7deg), porting, light flywheels and clutches. One had FCR 39s, one had 41s. The bike with the 41s had more substantial porting, while the other bike had slightly higher comp due to a skimmed head. Both had JE high comp pistons (actually the same set, but that's another story). Both Brad Black (Bikeboy) and Chris Ognenis (Raceperformance) have done work to both bikes. A free plug to them as they are the guys I trust with motor work.

I have had conflicting advice from people I respect as to whether there was much performance difference between the two carb sizes. The opinions varied from the 39s being stronger down low, more responsive with small throttle openings and hardly if any difference in the top end, to no difference down low but the 41s being better for peak power and modified motors. I have also been advised that with modified motors the differences are negligible, and I've been told the opposite. It's interesting to note that the bikes in Brad's test are pretty stock. The power figures are low so I wonder if he used a different dyno than usual. Maybe a Factory Pro rather than a Dynojet.

My experience from the saddle with the two bikes was as follows.
Bike with 39s was stronger off the bottom, wheelied easier, but was harder to get on the gas with lean angle off slower corners. It would spin up the back wheel off corners very easily. It would lift the front wheel through a series of S bends. You had to be careful not to highside it. WOT from 50-60mph was instant power. It was more responsive with small throttle openings.

Bike with 41s felt smoother off the bottom letting me get on the gas earlier with lean angle off the corners and not as snappy down low, but had a bigger rush into the higher revs. WOT from 50-60mph was a slight wind up before a storming top end (well for a two valver). Being smoother in pick up I can get off the corners better with the bigger carbs, but the smaller carbs are better for wheelies.

Brad's test makes me feel better about buying the bigger carbs.

Both required big main jets with the 41s a little bigger again (no surprise).

Both were excellent real world street motors that with the mods were well served by the FCRs.

[greenmonster]

So which is best, koko, 39 or 41?
You didn`t say.... 

WOT from 50-60mph

Which gear & RPM?

Have you Dynoed both?
Which bike accelerated fastest from 3-7000 revs?

[koko64]

So which is best, koko, 39 or 41?
You didn`t say.... 

Not sure, 39s were more respnsive at small throttle openings, but 41s were smoother down low. (I could be saying this to keep the thread going) 

Which gear & RPM?

I tried 4th and 5th from 50mph/80kmh, and 6th from 60mph/100kmh

Have you Dynoed both?

No, not with the FCRs, but they will be as one is owned by a friend now and we plan to do dyno runs. My friends bike now has Titanium valves, Ignitech ignition, JE 944 kit with K&N pods. Direct comparisons are now impossible leading to more conjecture and argument, but stay tuned .

Which bike accelerated fastest from 3-7000 revs?

I think in top gear roll ons the 39er pulled hardest from 3 to 5, and the 41er pulled hardest from 5 to 7. In the lower three gears I could not pick a difference. But being seat of the pants comparisons I could be mistaken.


If my answers appear evasive and uncommitted it's because I have worked for the public service for 20 years  .

[671M900]

Here's my $0.02: just get a set, 39's or 41's. Tons of fun either way.

[koko64]

+1

Leaving headwork out of it. Probably the single best performance increase to a carbed Monster apart from increasing compression.

[junior varsity]

man it did do wonders to my bike. but i also really liked the bigger coils, and the lightweight flywheel.


its getting hard for me to say one is better than the others, because i'm used to them all and I believe that's how it is supposed to work

[koko64]

man it did do wonders to my bike. but i also really liked the bigger coils, and the lightweight flywheel.


its getting hard for me to say one is better than the others, because i'm used to them all and I believe that's how it is supposed to work

Oh yeah
That's true, the big coils and lighter flywheel also made a big difference. I suppose that's why I went for the package of all those things. That package kind of updates the bike and brings out it's potential.
A satisfying street package.

By the way, did you get my PM about the K&N A/F ratio monitor?

[junior varsity]

i think i did - i have it where the wires are long and flexible enough to 'whip it out' from under the seat to view it while on a dyno, but really it would be very nice to disassemble its inner workings and attach the display's lights to my dash somehow, so i can get real time results while i am riding.

perhaps when it gets bitter cold.


alternatively, if i could find one that's the same size as the stock tachometer, i might replace the tachometer with the a/f gauge, and replace the speedometer with a nice speedo/tach combo.  still have a stock look, but more information