Keihin FCR Carbs

[Kawasakifreak]

I'm looking to improve carburation on my streetfighter Kawasaki ZX7R P1.

Any opinions about Keihin FCR carbs & which size would be best ?

I'm looking to inprove bottom & mid-range response - engine standard cams & ignition timing at the moment.

Thanks.

[speedy sie]

for get this idea for a road bike as the crf's are for the track and will only make the bike worse,go over to redmonkey and there is a thred about this mod.

better of getting yours dyno'ed and set up right.

[spacemonkey]

for get this idea for a road bike as the crf's are for the track and will only make the bike worse,go over to redmonkey and there is a thred about this mod.

better of getting yours dyno'ed and set up right.

Absolute, unjustified cobblers... They are brill, plus much more adjustable than standard carbs. just make sure you don't use a set that is too big (35 or 37mm perhaps.) and get them properly set up on a dyno.

[speedy sie]

http://www.redmonkey.com/7r/messages.php?msg=23391.1

http://www.redmonkey.com/7r/messages.php?msg=23107.1

as it states,set up right they are great,but unless you are a master of the throttle,the things will bog the bike down,not the best mod for a rider who just wants a bit more ummppff,

and the fitting of the crf's in to zx7r air box is a bit more than you think,it is not a simple bolt out and bolt in....

iv had a zx7rr with the 41mm acselerater pump carbs and yes bloody great,but you have to understand about throtle aplication,as the rider has a greater imput to the air fule mix,and unless you understand wot the carbs are actualy doing then you can over flood the engine with a good fist full of throttle,and to little throttel can weken the mix ,so all in all a good mod for a proper experenced rider,but not one for the week end rider.

id say yes to the mod as i love flat slides,but get the bike a full akey,k&n and dyno and this is a better simpler tune up.

[Evilchicken0]

I wouldn'y look to fit flatslides for low down repsonse ... they're more track orientated, and although it depends on how they're set up you should find CV's better for road use.

If you want to make the bike more ridable low down consider a smaller carb diameter or lower the gearing

[spacemonkey]

http://www.redmonkey.com/7r/messages.php?msg=23391.1

So you'll have to enlighten me on what a logon screen proves.....

[Barry]

just make sure you don't use a set that is too big (35 or 37mm perhaps.) and get them properly set up on a dyno.

ZX7 N uses 41mm as standard. The ZXR750 K & M models use 39.

39's are better than the 41's for bottom end and mid range, pointless going smaller.

I have 39mm FCR's on my ZXR750M, and I'm also running a set of 39's on my 7R(N) track bike with ZX9 engine. Both carbs are now running all jets as per the race kit manual and pull like a train from around 2k rpm. Cost me around £300 to jet both sets of carbs to race kit spec.

[spacemonkey]

ZX7 N uses 41mm as standard. The ZXR750 K & M models use 39.

39's are better than the 41's for bottom end and mid range, pointless going smaller.

I have 39mm FCR's on my ZXR750M, and I'm also running a set of 39's on my 7R(N) track bike with ZX9 engine. Both carbs are now running all jets as per the race kit manual and pull like a train from around 2k rpm. Cost me around £300 to jet both sets of carbs to race kit spec.

I don't suppose you have dyno runs to compare with CV carbs?

Would you swap back to CV's or are you happier with the FCR's?

[speedy sie]

So you'll have to enlighten me on what a logon screen proves.....

sorry just press the guest button and it will then put this the up.

[spacemonkey]

sorry just press the gues button and it will then put this the up.

Sorry, I should've seen that guest button!

Still, that's one guy's opinion, he doesn't give reasons for his opinion, he possibly hasn't even tried them.....

He could be talking rubbish. It'll be interesting to hear more from guys that use them like Barry. I've got fantastic bottom end pull from FCR carbs before. There is absolutely no reason they should be rubbish for the road. In fact they should be better because you have more possible adjustments. The only thing I can think of that makes them less suitable that CV's is that they often don't have a choke. - But a couple of twists of the throttle and the pumps will give you a rich enough mixture for cold starting....

I've found most people who go around saying they are unsuitable for road bikes have either not tried them or they've tried carbs that are too big.

Sorry to come on a bit strong but loads of people just repeat stuff they've heard 82nd hand, and it becomes gospel when enough people say it. - Doesn't make it true though. It's like chinese whispers!

[speedy sie]

no problemo..once you have masterd the two pump to start,and get use to fethering the throttle i loved them,and would fit them over fi,but alas the fi does the stuff at 4 am every moring,but the flat slides do put the soul in to a bike,and as you have said,well set up they are brill.but to just add them to a bike and expect super power is a bit unreal.

riding a biike with well set up flat slides,and getting the throtle masterd is one of the best feelings in bikeing,in my view,but then a againe im gods own dispach ridder....

[spacemonkey]

no problemo..once you have masterd the two pump to start,and get use to fethering the throttle i loved them,and would fit them over fi,but alas the fi does the stuff at 4 am every moring,but the flat slides do put the soul in to a bike,and as you have said,well set up they are brill.but to just add them to a bike and expect super power is a bit unreal.

riding a biike with well set up flat slides,and getting the throtle masterd is one of the best feelings in bikeing,in my view,but then a againe im gods own dispach ridder....

Is there a 4 in the morning? :-o My sympathy!

I suppose nothing is any good if it is not set up right... EFI, CV carbs, flatslides, etc can all be made to work badly!

Not many things give such an easy power gain though! ... And they probably cost less than an Akrapovic or somesuch....

[Barry]

I don't suppose you have dyno runs to compare with CV carbs?

Would you swap back to CV's or are you happier with the FCR's?

No sorry, never had CV's on these bikes, infact I've not ridden a bike running CV's for ages now thinking about it!!

As long as you don't crack the throttle wide open at low rpm then you'll be fine with FCR's. It's all about progressive throttle control rather than just wack it open and let the slides take care of it with CV's.

I sold a spare set of 39's a couple of weeks ago for £300, which is what they usually go for, sometimes a bit more but very rarely for less. Unless the person selling doesn't know what they have!

Both my bikes are running the 39's (as mentioned) and both in carbon race airboxes. The jetting is way different than the normal road setup they they come with as stock, and low throttle responce on mine is amazing. As its been mentioned above, you need to get it setup really and the slightest changes to any of the jets can make a big difference.

[heds954]

As long as you don't crack the throttle wide open at low rpm then you'll be fine with FCR's. It's all about progressive throttle control rather than just wack it open and let the slides take care of it with CV's.

I've been told the very same by my local dyno man. When properly set up they do as Barry put it 'pull like a train' apparently, whereas a CV set will tail off FCRs will just keep going and going and going. Which is why I might be after a set of 33 or 35's for my steelie

[suspensionsmith]

One thing to be aware of on high milage FCR is how they have that trademark slide rattle at idle,the little rollers on the slides will over time wear grooves in the carb body that they roll upon,making off idle/part throttle control impossable...I have repaired a few with this problem.

Other than that these carbs absolutely rock when setup well.

[spacemonkey]

One thing to be aware of on high milage FCR is how they have that trademark slide rattle at idle,the little rollers on the slides will over time wear grooves in the carb body that they roll upon,making off idle/part throttle control impossable...I have repaired a few with this problem.

Other than that these carbs absolutely rock when setup well.

Ah yeah... Then they start busting slides.... But to be fair thins happens with a lot of CV carbs too. The slide guides wear and then the slides start to stick at low positions....

[eddie]

I have to agree with Barry. I have a zxr 750 K1, that has the FCR 39's on it, and it does pull like a train. It feels like it has so much more power than other bikes Ive had/ridden. Before I bought it, i read loads about the "bogging" down whilst pulling away etc,and how bad these carbs were on the road, but to be honest, I've never noticed it pulling away or at any other time. I only use the bike on the road.

. However there can be drawbacks

the small bit was rattling around on top of the valves! Bike was still running, and after a 3 month wait for a new part, it still does!

Paul

[fran9r]

Wow. Eddie, do your FCRs have a groove where the slide wheels have worn the carb body?

[Kayla]

FCRs are awesome. I've got a pair of 41s on my TRX and they are so much better than the standard CVs. There is more of everything, everywhere. My bike gets ridden on the road and it must be an urban myth that they're crap on road bikes.

[peter187]

There's nothing wrong with flatslides on a streetbike. If you are bogging them down you are just completely cackhanded with the throttle. My YZF runs them and I've had absolutely no problems riding on the road with them.

[hamill12]

I have a set of Keihin 39mm FCR on a GSXR K2 1000. Ive got to say its a lot of fun. Does what it says on the packet Race performance. Pulls well im happy with them.