38mm Vs Flatslide Carbs

[Anonymous]

OK my GSX1100 already has a set of big pistons and a bit of head work. I will be buying a dyna 2000 ignition and slotted cam sprokets for it (winter upgrades).
The carbs fitted are still the 34mm OEM fitted carbs.
I understand the 38mm carbs form the L&M GSXR750 work very well. But I also see mention of some GSXR flatslides in this site. I am looking at E-bay to get the carbs.
Which carbs work best to give me most power but still maintaining good ROAD driveability? If the flatslides work well what size do I need?
I'm also told that the 38mm CVs gain a lot from a dyno jet kit. Is that the same for the flatsides?
Currently the bike is putting out 105bhp on the dyno. I want this up to 125 bhp this winter.
All advice would be happly recieved.

 

[biker66]

Get the real thing at once instead.
I'd buy these: Mikuni RS36

They're good for up to around 155bhp and are quite driveable, I love my set.

 

[RifRafRacing]

38 mm flatslides

38 mm flatslides

the 38 mm flatslides compromise midrange/low end performance but the topend hit is worth it

 

[Billy Ricks]

Don't mistake stock CV flatslides for RS flatslides. Two different animals.

 

[skip]

how big is your piston kit? if you are over 1166 I would go with the 38 rs flatslides, they are smooth easy to tune and as you do more mods they will still be enough carb. my bike is 1229 cc with other mods and the carbs are great. if you plan on keeping the cc displacment smaller go with the 36 rs flatslides

 

[Anonymous]

Thnaks for the advice. Where any bikes fitted with these RS36 or 38 carbs as standard? If which?

 

[biker66]

Not that I know of, but tuning shops sell them. Or look for them on ebay like the link in my post above.
Considering your goal of 125bhp I'd definitely buy a set of RS36:s, I've used them on 1168, 1200 and 1300cc engines and are very pleased with them.
When my rear wheel puts out around 150-160bhp:s I'll switch to RS40:s, not until then.

 

[Anonymous]

OK so after much looking it seems that the RS carbs are expensive and the 38mm CVs are as common as rocking horse shit - but the 36mm from the bandits are common and cheap. I currently have 34mm is it worth the bother of changing to 36mm? I've also seen some 40mm CV for sale would these be too big for a mildly tuned GSX1100?

 

[Addy Leung]

Hi Club Members,

After read through the posts of this topic, I have a question.
If it is going to use the RS38 flatslide carbs, dose it need to change the 4 rubber intake boots(maniflods between carbs & engine)? If yes. where can find the right one?
Also, is it the RS36 just fit to the standard intkae boots of GS1100?
Addy

 

[skip]

my 38 flatslides fit right into the stock boots

 

[RacingJake]

Yeah I just bought a set of GSXR 38mm CV carbs for $75 bucks. Compare to Flatsides at $600 bucks it's a no brainer. If I don't like them I can always put them on E-Bay and get $150 out of them. They fit the OEM boot on my 1100E but I'm going to grind out the inside to match the intake port.

Jake

 

[Anonymous]

Jake what year are the GXSR carbs for your GS11

 

[Anonymous]

Trouble is I can not even find any 38mm carbs
Some 36mm flatslides did come up on e-bay but at ?280 that was too rich for me!
So I now have three choices;
Leave the current 34mm on the bike and wait for some 38mm CV or 36mm flatslides at a reasonable price.
Fit 36mm CV (loads about and very cheap) but will this give me any power increase? Will it be worth the bother? :?:
Fit 40mm (seem to be a few around) but will these be too big for a 1170cc engine with a mild tune?
Oh I forgot the fourth choice Fit 33mm Flatslides (again common and cheap) but will these be any better than 34 or 36mm CVs.
Too many choices and too little money 8O

The answer to the previous post is 38mm CV were fitted to GSXR750L & M I think they where 90 and 91

 

[RacingJake]

Jake what year are the GXSR carbs for your GS11

I really don't know. The carbs I bought from this guy said he had then on a GS1100E too. They are Mikuni with number 18D3 K198 printed on the side if that helps??. I do know that they are bigger than my OEM CV 34 carbs.

i'll post a few pic's on my www site.

Jake

 

[RacingJake]

I posted a few pic's of the carbs, to view just tab on my www button below.

I would guess that my carbs are 90's to 95's.

Take a look at StripBike.com they have a lot of stuff on that web site too.

jake

 

[Anonymous]

I shopped for carbs last year so I know how confusing it can be. Most people I asked said 33mm smoothbores or up to 36mm flatslides were the best.
I have an 83 1166 gs with cam motion G3 (.345 lift) mild porting and V&H 4-1. It puts out a smooth 129Hp.
Some people I talked to said it's hard to go too big. That partial throttle is partial throttle on any carb and the more air/fuel you can flow at wide open, the better. I found some Keihin 37.5mm smooth bores $350.00 I think from e-bay. Just a tiny bit sticky when I open them after deceleration. Worn slides I think. I have a set of 33mm's that I'll try soon to see if I pick up any bottom end.
I'm pretty sure any set of carbs you get will need jetting to suit your motor. So if you're going to invest in the time and $$ it takes to do that....Put it this way: After reading The Sportbike Performance Handbook, If I ever buy different carbs I'll save up and buy the Mikuni RS36 flatslides. In theory at least they are more responsive.

Then again $75 for 36mm CV carbs will get you a little more flow.. :?

Can you tell I'm a terrible descision maker?
Long winded too.

Just my 2 cents.

-Isaac

 

[Anonymous]

No that is great, thanks for the help, if i get used cv's should i buy a jet kit and rebuild kit?

 

[Dink]

No that is great, thanks for the help, if i get used cv's should i buy a jet kit and rebuild kit?

Absolutely Definitely
Dink

 

[Anonymous]

Best value for yor money is definetely the old smoothbore 33mms. They are cheap and increase power a lot. But the RS carbs are smoother to drive, maybe because they are fitted with an accelerator-pump. They fit like a glove, but a little job on the boots should be done to get a smooth ride for the mixture. What it all comes down to is size that is equal to your inlets. On a stock GS1100 head the manifold is about 33,5mm and the boots somewhere there too with a terrible fit to the inlet aswell as to the carbs. If you want to go bigger, port the head first. I have a st.2 ported head wich now measures 35,5 mm in the beginning of the manifolds. I can?t see why going larger than 36mm on the carbs should be of a benefit for me. However, if my thought is wrong I would be very happy if someone could explain it to me, since I haven?t talked to anyone really. What you want is an area which get smaller nearer to the valves inside. To produce a high velocityspeed on the mixture. That I know.
skip] : Do you have a ported head on your beast?

The benefits of RS36-40 are the lack of throttlevalves, just the throttle moving up and down. Measure the area of your manifolds. And then measure your carbs minus the, I?m not sure of the right word, axlearea for the valve. In % it?s quite a lot. Thats why RS and the old smoothies increase HP so much. I?ve heard that the SB33:s equals at least a set of ordinary 36mmCV:s. The carbs should be a little larger.
Fuzzy? Hey, I?m confused now.... :lol:

 

[Anonymous]

The lin kbelow is to some carbs currently for sale;
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=2453662788&category=9946&rd=1
Are these smoothbores?
The guy selling them says they are from a '86 GSXR750.