Interesting phenomenon with my CVK. You FCR guys feel the same?

I just finished my glorious CVK swap. I rode all 65 mph highway to the ladyfriend's house yesterday to test cruise fuel econ, and I noticed something interesting...

With the Mikuni in there, it seemed to struggle more to cruise at that speed with my 15/39 gearing. Now it sounds all open and free and doesn't make as much noise pulling me along with the CVK. I have solid proof that both are tuned better than most people's bikes ever are thanks to my fancy gadgetry, so it must be related to the new carb rather than a difference in tuning. My only thought is that the percentage being used of the total horsepower available at that RPM is now lower, (since the bike makes more HP) so it sounds happier. Do the FCR's do the same thing?

Of course, I'm pleased with this massive improvement, I just don't know exactly what the reason is....

the fcrmx makes more power everywhere.3-4 peak.because it's a pumper type carb instead of a cv the difference is more dramatic in terms of throttle response and acceleration.the only reason for the mikuni bsr36 is emissions to satisfy the epa.

i noticed the same thing with mine immediately. prior to, i would wack the throttle to pass someone or fool around and be surprised at how much throttle i already had open. with the CVK i cruise around with WAAAYY less throttle. i dig it.

bum these guys are running the 40mm CVs

so how does the fuel economy compare jimmy and whits

The CVK40 is a bigger carb, so you expect it to give you some more grunt....but with no accelerator pump, the throttle response not as good as an Fcrmx .....

The CVK40 is a bigger carb,

I'm not sure it is, it's a bigger number but doesn't have bigger effective area.

At full throttle there is still the butterfly valve in the venturi but with the FCR at full it's just got the needle.

In fact I'd guess the FCR39 flows better than the CVK40.

i remember way back when i think eddie said that a cvk would have to be a 44mm to be the equivalent of a fcr39 in terms of flow.

the butterfly is not that big of a deal. its still a HUGE improvement over stock and with the popular slide mods the throttle response is great. my mileage has been hard to nail down since i cant stop fooling around on it, but the last two tanks have been around 45mpg with plenty of wheelies and WOT play.

the butterfly is not that big of a deal.

the throttle body on the 09-10 crf 450 had to made 50mm to flow like a 40mm fcr because of the "butterfly".

the throttle body on the 09-10 crf 450 had to made 50mm to flow like a 40mm fcr because of the "butterfly".

thats cool, but i ride a stock motor'd drz, not a 55hp crf450

the simple truth here is: a CHEAP cvk40 is a huge improvement over stock and far far far from the price of the fcr, ie: the butterfly is not a big deal....

50hp. about what a big bore,cams,pipe and fcr drz makes.

so your saying a cvk wont support 50hp? post up a dyno sheet or flow data on the carbs

where did i say that?

but since you asked.....

i used to build klx650r's before i got into drz's and i gained 6hp going from a the 40mm cvk to a 41mm fcr.

there is nothing wrong using the 40mm cvk if that what you wanna do,but its not a fcr.

ok, again i ride a drz, not a klx650r, and yes on a motor that size going up from 40 to 41mm carbs better make a difference.

i dont want to be a dick, but in almost every carb related discussion i can find you seem to have the mindset of "fcr or its junk", but i cant find where you've posted any dyno numbers with a jetted cvk40 ON A DRZ.

not everyone has 600 bucks to throw at a TT kit or even 400 at a used fcr. We dont all race or need race bikes. the cvk IS an improvement and it IS cheap, i dont care about the butterfly, i dont care about a fuel injected honda. i bolted this carb on, and the bike goes faster, simple as that.

ok, again i ride a drz, not a klx650r, and yes on a motor that size going up from 40 to 41mm carbs better make a difference.

i dont want to be a dick, but in almost every carb related discussion i can find you seem to have the mindset of "fcr or its junk", but i cant find where you've posted any dyno numbers with a jetted cvk40 ON A DRZ.

not everyone has 600 bucks to throw at a TT kit or even 400 at a used fcr. We dont all race or need race bikes. the cvk IS an improvement and it IS cheap, i dont care about the butterfly, i dont care about a fuel injected honda. i bolted this carb on, and the bike goes faster, simple as that.

Like to see your before and after dyno post then :-)...

i bolted this carb on, and the bike goes faster, simple as that.

done.

I'd be interested to see a direct comparison too. I doubt the CVK has the throttle response of the FCR. How does hp compare down low and in the middle. I've seen a lot of dyno's where the FCR doesn't improve hp until after 6000 rpm. One thing I wonder about the accerator pump on the fcr is if I am wasting fuel every time I open and close the throttle when I shift?

same offer as always,any one that needs to dyno a set up to compare and post here gets free dyno time.

ive got no time to argue with people any more about this stuff. so when ever i post its never in a attempt to incite argument,only to state facts.

some of the accusations made towards me here are just ridiculous with no proof to support it.

my reputation stands on its own.:smirk:

Whitsdurz, I think you're just reading into Eddie's comments too much. He said that there is nothing wrong with you using a cvk, but just to understand it won't give the same performance as an fcr. I think you understand this too and it sounds like you're ok with this. No one's trying to be rude here, but Eddie has more experience than anybody when it comes to these bikes... so he'll lay the facts down straight (albeit bluntly sometimes) to keep people from getting confused. He only aims to help :smirk:

Good to know that the same effect is felt.

For me, the purpose of my CVK was a little fun for a low price, and that's all. I have 2 other bikes, both with FCR carbs on them. IMHO, it is ABSOLUTELY "FCR or it's junk" in terms of thottle response. I can't explain the difference between my two FCR equipped bikes and my vacuum slide DRZ, but when you've used an FCR, you appreciate it. What really is important here is that I'm currently into this $150 for everything, and got a very noticeable performance gain. It's definitely not the best available, but it meant some fun times in the shop and on the lathe, and a task I'm proud to say I did as well as can be done. I don't get to say that often in life, so I take em where I can get em. :smirk:

I DO have before and after "dyno" numbers, but am extremely resistant to release them because of some inconsistencies I suspect. When I finish my wideband data logging system, get my bike perfect-as-possible by myself, and do a "real" pull, I'll inform further. It's still in the project stage in my mind.

I wished I lived in CO... for various reasons. I want a track, I want dyno time, I want mountains, I want DH mountain biking, I want snowboarding. If I make it out there with the sumo I'll let eddie have at my bike if he thinks it will be of use to him.

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