Flatslide carbs

[RJ]

Given the same size carbs, how much of a difference in performance is there between the CV and flatslide carb designs? What mods does an 1100E need to have to make a jump in carb size worthwhile? My current set of BS34's works just fine with pods and 4into1 but I am contemplating performing some upgrades in the future.

[scotty]

Sometime it may be necessaary for you to do some internal mods before you can get that bolt on to really do its job well. Like head work.

[lhanscom]

I think it depends which flatslide you're talking about. The GSXR CV Flatslide has a modest improvement, as the only benefit is the slightly better flow. If you're talking about the RS carbs, they're a huge improvement. You not only get the flat slide, but also get rid of the CV part, and therefore the butterfly valve. You also get an accelerator pump, and are able to be tuned more accurately. The biggest thing is that they give your bike 'snap', when you twist the throttle you're directly effecting the slide instead of waiting for the vaccum to lift it. RS's make a huge improvement once you start modifing other bits, like getting rid of the air box, because the CV carbs don't react well to pods.

Only downside to the RS carbs is price, about $600 I think. They're worth it though.

[oldschoolGS]

GSXR CV flatslides are pretty good carbs, any of the air/oil model bikes will fit your bike. I would think that 36's would be perfect for your 1100. Price - about $200 off ebay or a salvage yard. I have used GSXR carbs w/Dyna jet kit on my '83 GS750ED for 15+ years. They were a great improvement over stock and worked excellent with a big bore kit and aftermarket cams.

RS flatslides, as Luke said, are the real deal- full out aftermarket race carbs that will offer max performance. Down side is cost- About $400 used or $600 new. You will also need a push/pull throttle. These carbs and a set of aftermarket drop-in cams will rock your 1100.

Depends where your budget lies. Ride On, Ed.
1983 GS750ED

[RJ]

Is there any compromise in low end power with the RS's? Most mods that improve all out power usually demonstrate some loss at the bottom end.

[gsbill]

Just dont get them too big...Bigger isnt always better when it comes to carbs...Engine size(cc), divided by 35.48 = carb size in mm. Got this from a old tuning book I have. For CV carbs add 2 mm.

[katman]

That formula makes my 1166 size carbs 32,86mm?

[gsbill]

Works out to about 33mm...CV's work out to 35mm...This is just a fromula to use as a guide..I had 38mm carbs on my 1200cc bike which, by that formula were too big...There are a lot of variables...My bike had to run good wide open only. That it did..The tuner who's formula is offered here, supplies charts using different sized carbs. His testing showed an increase in power & et with smaller carbs on the test bike than big ones.

1100cc test bike, mild port, drop in cams

35mm carbs= 10.35
31mm carbs= 10.08

[scotty]

Works out to about 33mm...CV's work out to 35mm...This is just a formula to use as a guide..I had 38mm carbs on my 1200cc bike which, by that formula were too big...There are a lot of variables...My bike had to run good wide open only. That it did..The tuner who's formula is offered here, supplies charts using different sized carbs. His testing showed an increase in power & et with smaller carbs on the test bike than big ones.

1100cc test bike, mild port, drop in cams

35mm carbs= 10.35
31mm carbs= 10.08

Your formula really caught my eye Bill.because my machine is going to be a street rod.
my intended 1266cc came out to be just under 36mm. Th mechanics were talking about 37 to 38 mm flat slides perhaps because i said i didn't mind a sloppy bottom en as long as it pulled like the devil when running flat out.
Anyhoo since you posted this formula, I will spend a bit of time withe the engine builder discussing carbs.
I listen and often hear many things i never knew.
Thanks BILL

[gsbill]

Scotty,

That formula came from an old book I have. Its called A Guide To Motorcycle Drag Racing, by Mike Nelson. Its a good basic and then some guide to building motors and racing.

[scotty]

Scotty,

That formula came from an old book I have. Its called A Guide To Motorcycle Drag Racing, by Mike Nelson. Its a good basic and then some guide to building motors and racing.

I think i have it--yellow soft cover 8X11 and maybe 1/2 inch thick

[gsbill]

Sounds like it...S&K drag bike on the cover. There is a lot of good info in there...

[Craig]

Flatslides

I talked to the guys at Sudco and with a fellow who has been doing dyno work for the last 20 years. I put in the 1166 pistons. cams, adjustable cam gears degreed at 108, and it was suggested that a set of 36mm Mikuni RS Flatslides would be the carbs to get. Haven't got it to the dyno yet, but the bike sure sounds nice!!!

Kind regards...Craig

[RJ]

Yeah this sounds kind of along the lines of epoxying the intake runners to reduce volume and increase velocity. That carb formula works out to around 33mm CV's for my bike as a stocker. If I could pick up a set of 32's (did they ever make Mikuni's in that size?) for real cheap I think it would be an interesting experiment to compare them with my 34's and see what happens. Anyone got a set?

[katman]

boy that's good. Glad I didn't just spend a load of cash for nothing....

He didn't happen to mention the pilot settings, mainjet size and needle position for that setup did he?