38mm Vs Flatslide Carbs

[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....

[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.

[Anonymous]

They are not smoothbores, but are the same size. They should give a lot of extra compared to the stock CV34 on GS1100. I can?t however see an acceleratorpump on them, but so does the SB33:s miss....That means that from idling RPM you can?t rev it up too quickly, since the gasoline is sucked directly from the throttle needle - main jet, sounded strange even to me but hopefully you know what I mean.
With pods and a 4-1 you can start with 127,5 main jets and go from there. On my bike I used that and it worked fine, ran a little rich in the midrange so I lowered my needles one step.

[Anonymous]

OK so here is yet another question 8O
I know a bit about CV and flatslades - i.e. I understand the differences and the pros and cons - and have riden bikes with both. But I do not know about smoothbores Can anyone fill in the gap in my knowledge What are the pros and cons of smooth bopres compared to CV and flatslides

[skip]

chrille_08 wrote:skip] :

Do you have a ported head on your beast?

Its mildly ported with boots matched to the carbs and the intake matched to the boots. mild porting inside the head and oversize valves it was a $ 600 port job at the time(not including parts) and I got a price break because the shop I went through got a dealer discount and passed it on to me

[Anonymous]

With flatsides and not beating it to death all the time, what kind of gas mileage should you get?

[skip]

Because of of the acceleration pumps if you twist the gas alot your milage will fall into the twenties but baby it a little or do some highway and you should be up in the forties

[GER144]

BikerShaun, here's the differences on the flatslides-smoothbores-CV's.
Basically the smoothbore name is applied to any carb that is not CV. You can have smoothbore flatslides, and CV flatslides. Smoothbore round slides, and smoothbore CVs'. Smoothbore flatslides are a hair more responsive than smoothbore round slides. All smoothbores won't have as nice drivability as CV's, but the RS's come damn close.
In a CV carb there is the throttle slide, and also a throttle valve. The throttle valve is connected to the throttle cable. Twist the cable, opens the valve (or butterfly) and the incoming vacuum rasies or lowers the slide. But that 'butterfly' -or valve, is always there so there is not a 'smooth bore' through the carb even when the slide is fully open. The valve is always in the way of airflow through the carb. Make sense?
There are basically 3 kinds of smoothbore flatslides. The Mikuni RS, the Keihin FCR, and the Lectron. My favorite is the RS's. I run RS40's on my 1428 dragbike, but I have also ran these same carbs on a completely stock '83 1100 Katana, and it carbureted and ran just fine. Different jetting of course. The FCR's are nice, but harder to find, and usually more money. The Lectrons are great too, but not good for the street. Dragbike only. I also have a set of Mikuni 33 smoothies with the rare accelerator pump kit on my '83, and they work pretty good, but not as nice as my RS's. If I were you, save your pennies and get a set of RS's instead of CV's. They work so nice, and their drivability is nearly as good as CV's when set up properly.

[Hoomgar]

GER144, can you give some info on where to find some RS's at a good price? And what size/type would I look for to put on my GS1000C. We bored it to about 1100 and port and polished the head. Was going with a set of 34mmcv's on it but would I be better of with the RS's?

Thanks for any info.

[Anonymous]

[/quote]can you give some info on where to find some RS's at a good price?

Take a look at these:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&category=35597&item=2457181676&sspagename=STRK%3AMEBWA%3AIT

No idea what they will go for, but the typical winning bid is around $350-$400USD.

Mark

[rosco15]

I can't help but think flat slides are the cheapest way to make a ton of power. 36 mikuni flat slides, stock pistons, stock (no porting) head, V+H drag pipe, good ignition made 113 HP. I put in an 1166 low compression kit and I got 128 HP. Seems Isaac has a comparable motor, but he runs Keihin carbs, aftermarket cams, and has his head ported and makes 129HP (darn near the same). I would think with a set of Mikuni's, the porting, and cams, his motor would make a ton more power than I got.
HOOMGAR, Just a note. The 36's on the stock motor seemed a little big. I did some head work and might put on my 38 flat slides, but am worried they are too big.

[skip]

I can't help but think flat slides are the cheapest way to make a ton of power. 36 mikuni flat slides, stock pistons, stock (no porting) head, V+H drag pipe, good ignition made 113 HP. I put in an 1166 low compression kit and I got 128 HP. Seems Isaac has a comparable motor, but he runs Keihin carbs, aftermarket cams, and has his head ported and makes 129HP (darn near the same). I would think with a set of Mikuni's, the porting, and cams, his motor would make a ton more power than I got.
HOOMGAR, Just a note. The 36's on the stock motor seemed a little big. I did some head work and might put on my 38 flat slides, but am worried they are too big.

i dont think the 38's will be too big with the rest of ther work you have. I have the 38's with a 1229 kit and g-4 cams and the combo runs great, my buddie has 38's on a stock 1150 with headwork and g-4's and loves it.