FCR Flatslides for a GSXR1100L engine

[Wagola]

Hi All,

OK, just been told that a set of Keihin FCR41's that I was going to put on the Harris GSXR1100 are not suitable ! Apparently I have a set of downdraught carbs and these are not compatible for the GSXR1100 engine. Doh !!!

Can anyone on here confirm this please ? Or are there any suitable flatslides lurking about out there wanting a new home ?

Thanks all.

[Solcambs]

Keihins come in two variants for the GSXR - those that are horizontal and those that are downdraft. The downdrafts ones have an angled float chamber, and I have therefore always assumed that the float heights cannot be set correctly if you stick them on an engine requiring horizontal carbs.

Keihins go for good money ... so sell them on the bay! Or contact Frank MX who will I am sure buy them off you.

[Wagola]

It seems your assumptions are correct. These were a set of carbs I bought in a job lot with some Kawasaki ZXR400/750 race parts. I was hoping to use them on the GSXR1100 engine. Oh well, shit happens ! I'll hang on to the carbs for a bit as I do have a ZXR750 with a 900 engine in it that they might fit, although I have doubts about that now as well. I'll just have to look out for a set of horizontal FCR's or Mikuni RS's. Cheers for the reply.

[Gixer1460]

The downdraughts are also a different spacing so x2 not fitting

[Wagola]

Yeah, I knew that I was going to have to re-space them but was hoping they were the right ones. Guess I'll have to find another project for them to go on.

[Solcambs]

Even if they had fit, in truth the 41s are probably a little big - OK for WFO, but not very good about town, based on what I've read!

Edited May 30, 2017 by Solcambs

[Wagola]

Hi, yeah I was thinking that too but was going to try them anyway as they look soooooo damn cool ! They came with a load of ex-race bits from a zxr750 or zx7r so one of those may be my next project. Do you know what the recommended flatslides are for the GSXR1100L engine ?

[suzook12]

You really need 1340 or above to make FCR 41's work, you would be far better off with 37's or 39's for a road bike, 37's giving better low to mid than the 39's. I have 39's on my 1216 and they work really well, I came across a set of 41's from a 1216, they were sold as didn't work very well. I bought them for my 1340 motor, but a change of plans so I moved them on. These were all genuine race FCR's, not ex kawasaki items. There is no choke on the race carbs, but never been an issue as the pump puts plenty down the engine for cold starting

On the race carbs I beleive you just change the float bowls to make them downdraught/ side draught. Not sure if the same for ex kawasaki ones. Allens performance will be able to answer that......

[Wagola]

Hi, yeah that's what  I'm finding out as far as the carb sizing goes. I did contact Allens performance and he said it would be expensive to get them re-spaced to fit and not suitable anyway as they are downdraught. The engine I have is supposedly 1216 but not had the head off to check. Guess I'll have to look for a set of 39's.

[Oilyspanner]

One way to check whether different pistons are fitted without removing chunks of engine, is to remove a plug and shine a bright torch into the combustion chamber (when piston is near tdc). Std pistons have a direction arrow near the piston crown, if it's not there it has an after market piston and probably a big bore. I did this to mine, as the engine was oddly fit, turned out to have std pistons, but the inlet ports had been lightly cleaned up and the engine is just a healthy one.

[Wagola]

Thanks, I'll try that. Mine has worked on inlets as well.

[Gixer1460]

7 hours ago, suzook12 said:

On the race carbs I believe you just change the float bowls to make them downdraught/ side draught. Not sure if the same for ex kawasaki ones. Allens performance will be able to answer that......

FCR Side and down draught main body castings are completely different so the above doesn't work.

[Wagola]

I didn't think it would be that simple. It never is. 

[dupersunc]

9 hours ago, suzook12 said:

You really need 1340 or above to make FCR 41's work, you would be far better off with 37's or 39's for a road bike, 37's giving better low to mid than the 39's. I have 39's on my 1216 and they work really well, I came across a set of 41's from a 1216, they were sold as didn't work very well. I bought them for my 1340 motor, but a change of plans so I moved them on. These were all genuine race FCR's, not ex kawasaki items. There is no choke on the race carbs, but never been an issue as the pump puts plenty down the engine for cold starting

On the race carbs I beleive you just change the float bowls to make them downdraught/ side draught. Not sure if the same for ex kawasaki ones. Allens performance will be able to answer that......

So FCR41s are ok on a 750 kawa, but too big for a 1216cc Suzuki.

[suzook12]

1 minute ago, dupersunc said:

So FCR41s are ok on a 750 kawa, but too big for a 1216cc Suzuki.

Its all down to airflow, and the kwaks aren't using the full blown aftermarket race carbs and they do have forced air induction which probably helps. Many have tried and failed to get 41's running right on oil boilers of 1216 and less. I never got round to fitting them to my 1340 to find out how good they are on those but a couple of guys in the know said they would work, bearing in mind that was for a drag motor. The guy I bought them from certainly knew how to set a bike up (running 8's on gas) and he couldn't get them to work at all well. I decided the future was FI and turbo so, like I said, moved them on again.....

Think probably the air speed gets too slow to make them work properly when the tap is cracked, the 39's certainly work on these motors, my 1216 goes well with them although for road, as said earlier, would prefer 37's, but that's just personal preferance

[dupersunc]

I hear this "wisdom" all the time, yet it makes no logical sense.   I know they are fit to the kwaks to homolgate them for WSBK so were compromised on the road bikes, but they worked to an acceptable standard, on a 100bhp 750, yet a tuned 1200cc motor can't draw enough air speed??

Don't get me started on "ram air".

looking for some logic here not having a dig.

[Wagola]

Maybe because race motors are always in the top end of revs ? And not worried about town manners ? 

[suzook12]

1 hour ago, dupersunc said:

I hear this "wisdom" all the time, yet it makes no logical sense.   I know they are fit to the kwaks to homolgate them for WSBK so were compromised on the road bikes, but they worked to an acceptable standard, on a 100bhp 750, yet a tuned 1200cc motor can't draw enough air speed??

Don't get me started on "ram air".

looking for some logic here not having a dig.

I understand where you're coming from fella, I don't know what the exact answer is. 41's work on the kwak on the track, not necessarily the case on the street. There could be lots of reasons but higher rev limit, downdraught and ram air will all play their part, short inlet tract will no doubt play a part also. By all accounts they work well on R1 and gsxr thou motors too, so air path to the valves and increased RPM may well be the biggest part of it. Our old oil boilers have quite a long inlet tract and have to turn the draught through 90 degrees too...... Add to that the slower engine speed of some 2000+ rpm. Maybe they would work better on an m/n 1100 but 3mm is a massive jump in carb size, especially when the stock carbs are CV's at that for the L's on 38's....

Also bear in mind, Kawasaki would be throwing a big budget at keihin for a limited number of carbs to get them right. And the motor would have been designed with this in mind too.....

1 hour ago, Wagola said:

Maybe because race motors are always in the top end of revs ? And not worried about town manners ? 

I've not ridden a ZX7RR to comment too much but I beleive they aren't a bundle of joy on the road, so yes, I dare say you are right. Racing is certainly a different proposition to road bikes for the likes of you and me. However, even a drag spec 1216 wouldn't run them, hence how i got hold of a set as the guy knew I was building a 1340, there was no doubting his bike was quicker on 39's by lots....

Edited May 30, 2017 by suzook12

[Gixer1460]

I've a set of 41's that are for my 1460 so should be ok airflow wise LOL! A M8 tried them on his 1216 and whilst the top end was there, they were pants at 'non licence losing speeds' so i've given him some 36mm RS's which have just been set up by Sean @ Big CC and total transformation - road manners, lifts the front in 1st 3 gears on the throttle + 156hp top end = happy bunny!

[suzook12]

19 minutes ago, Gixer1460 said:

I've a set of 41's that are for my 1460 so should be ok airflow wise LOL! A M8 tried them on his 1216 and whilst the top end was there, they were pants at 'non licence losing speeds' so i've given him some 36mm RS's which have just been set up by Sean @ Big CC and total transformation - road manners, lifts the front in 1st 3 gears on the throttle + 156hp top end = happy bunny!

Yup, 36/38 RS's are good carbs. I prefer FCR's but I still have a set of RS's, allbeit 40's.... Just been offered a shedfull of gsx-r's and associated parts at maybe not quite rip your arm off price, but certainly "Don't waste time chewing" price lol, so kinda rueing the decision to sell my 38's.....