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Discussion Starter #21
Flywheel is light. From a 600ss. Those are really cheap mods.
I read everywhere that mounting flatslides totally frees up the bike. Together with my high comp pistons it will be fun to ride i think
 

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We used to mount FCR's with 944 kits most of the time but had a number of customers with just FCR's. We installed some for winter riders as the flat slides did not suffer icing as the oem carbs.
If the stock carbs are jetted right then the power gains will be small so do not expect to see much better "numbers".

That said , If no one showed you how little extra power they made you would never believe it from riding the bike. I consider FCR's icing on the cake, they just make a already great package better and are one of "the" mods to do if the price tag does not scare you away.
 

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as eric says, it doesn't much more power at all, but they feel a lot better. no one that i've fitted fcr for on an otherwise std motor has wanted to go back. i had an m750 owner tell me the fcr39 he fitted felt like they'd added 10hp. nope. maybe 2 or 3.

light flywheel, cam timing, gearing, light clutch even. light wheels will make a huge difference to it too. way more than most people who haven't tried it would think.
 

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Discussion Starter #24
Thanks ducvet and belter f
or your insights. Im not about numbers, im about feel and fun. And those carbs are sexy as hell too ofcourse lol.
 

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flatslides "feel" faster because the slides connect directly to the throttle cable. cv's have to wait for the slide to catch up with the butterfly. this is why flaties give the illusion of heaps more power. cv's wont bogg with a fist full of throttle, flaties do, even with the powerjet. cv's are very under rated and very forgiving, especially when on a big breather 1100m bored to 1340cc's. and in lots of cases can be made to react quicker with a balance between slide hole size, slide spring and a correct needle. lot of fucking around but can be done. different strokes for different folks.
 

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Very true, a well set up CV is a good carb. I continue to run the CV carbs on my 750ss simply because I have not felt the need on that bike to change them. that said if a set of 39"s fell into my hands they would get installed.

The 800 carby in the dyno run above was running stock CV carbs with no issues.

But..... does this mean we do not get owners to try brand-X carbs so we can "test" them? Come on someone take one for the team!

There was the Honda hawk large CV carbs, mikuni flatslides and a number of Delorto's to test!
 

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I’m going to be playing around with my cv’s to improve slide response. Have you any idea of the drill size to increase the slide hole diameter ? How about the springs, how many coils cut off ? It would be nice to have a place to start.
 

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The Mikuni TM41 flatslides do work well on a wide variety of engines. There are plenty of tuning parts for them. I ran a 750 F1 racer with them and they worked very well, but I never tried to get a reliable idle or worried too much about low end running. I ran a pair on my 900SS racer too, other than having to fiddle with the horiz. float level they worked fine, until a pair of 41 FCR came into my life. There are many BMW's and Guzzi's out there running them too so they can be made to act properly for street use [other than the slide clatter at idle]. But they will require the split manifold setup.
 

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You can get flat slides to take WOT from idle if you do your do diligence. Also your fuel economy will astonish you. I got so sick of the bad mileage on my old BMW with the Bing cv carbs that I did the unspeakable. They who know said it couldn't be done, so I did it. Put 37mm Keihin flat slides on an old 79 BMW R100RS. Got 15 miles a gallon more and incredible throttle response. Feels like a 10 hp increase.
As stated above, nobody that I have ever installed Keihins on has asked to have them taken off. There are no downsides to this upgrade.
 

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“There are no downsides to this upgrade.” Yes there is, how much they cost for how little gain.
I agree with ducvet, if a set fell into my lap I’d put then on. On bikes that I’ve set up with them, they’ve all worked well and I actually like the way they feel but I’m not under any illusion that I need to buy a set to make a quicker bike. I love my bling, this is why I have carbon wheels and other useless ornaments on my bikes.:)
 

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"nobody that I have ever installed Keihins on has asked to have them taken off." Yup, money spent is already gone, nobody would probably take them off.

However - if you are reading this and want to sell me your used ones for what you paid for them 10-15 years ago - hit me up! I'll even trade you low mileage Mikuni stock ones! Two pairs of them in fact,...

there is just no way I'm going to drop $1,500 plus on the FCR 41's but I do enjoy very much the way the throttle works with them.
 

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the problem i've found with making the cv more responsive is that ultimately the lack of pump compromises them in terms of what jetting you need to run. possibly ok for race bikes, but i've had some road bikes where you end up richer then desired on pilot and needle jet just to make them not bog, which then makes them crap riding in commute mode.

i've not tried doug lofgren's mod tho - bruce said it was the best "jet kit" he had used, and it used std springs. doug did send me the stuff to show me how to do it, but i never got to it.
 

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I’m going to be playing around with my cv’s to improve slide response. Have you any idea of the drill size to increase the slide hole diameter ? How about the springs, how many coils cut off ? It would be nice to have a place to start.
DON'T cut coils off! :eek: That shortens the effective length of the spring, and increases the spring rate. When I was running CV's, I had a good improvement in response from a Dynojet kit, which had softer rate springs in it. You may be able to purchase the springs only from Dynojet - the kits are still available.
 

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Steve, it reduces preload on the slide when you cut coils off a spring that was made intentionally way too long. This alters the amount of vacuum necessary too raise the slide, therefore the slide will rise a little sooner and quicker. It’s just like removing preload from your forks or shocks. The vacuum to the slide must overcome preload before the slide starts to move. I have some lighter rate springs for the CV that used to come with the FP kit but no longer do. Some kits for CV carbs actually come with instructions about how many coils to remove and a drill to increase slide port diameter. Thanks for the input though.
 

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doug's kit involves knocking out the "restrictor" bush (don't know what else to call it) in the main passage of the jet carrier and fitting a small brass tube with holes drilled in it above the main jet that converts the fuel pick up to a proper emulsion style.

he would also fit factory pro needles from a yamaha maybe fj jet kit. std springs, not cut.
 

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Dukvet, I have a 1991 900ss I too have thought of changing the carbs--I know Dellorto's very well I use them on my 1972 BMW R75/5 AHRMA race bike & other BMW's as well, I know BMW's inside and out but not so with Ducati's--For this 91 900ss if I wanted to use Dellorto's which ones would you recommend --The bike is basically bone stock and I am keeping that way mostly-But I am putting a better exhaust system on it & a stage 1 carb kit to smooth out the flat spots, --also If I changed to Dellorto's can I can I still use the stock air box? again trying to keep it as original as I can with just a few upgrades. Thank you
 

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Hopefully the model of Dellorto you are familiar with is similar in dimension to the SS carb. There isn’t really a lot of space available. If you’re going to go outside the box , you have a shopping list: a means of connecting carbs to manifolds, a means of connecting carbs to air box, a means of connecting carbs to your right hand.
 

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Those are minor things --cables- easy I make then-intake manifolds again easy-already looked and a BMW one will work I work mostly with the PHM Dellorto's
 
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