SUZUKI GSXR750 Carbs Mikuni

[pggg]

Hey 57, those carbs look like the GSXR carbs to me. They'll be excellent. 200 bucks is a damn good price.

[underdog57]

Excellent

Thanks PGGG ,

I would of got them for under 170.00 delivered if I didnt get worried ...Lucky I still got them !! The guy was cool about it ...

Knowing this stuff is a real benifit !!

Do you know what designation this carb is , to get parts??
The guy saw no numbers . The numbers must be ink that wears off ??

They should be here mid next week , then will play with them ...

See ya
Bob

[pggg]

57, check out these diagrams for part numbers

http://www.slingshot.cc/tech/microfiche/index_5.htm

[underdog57]

Cool !! Thanks

I Looked in a few gsxr web sites , those guys are real carb heads also!!

Bob

[TopCatGr58]

Questioning the info from UK XS11 site!

Hey Dog and Rob,

I don't know about Slingshot carbs, but I was wanting to do a little research on ours before posting this!

There is NO PORT in the carb body that draws the slides up!!!!

The vacuum running thru the throat of the carb passes by the bottom edge of the vacuum slide. There is a little hole in the bottom of the slide, that hole goes thru the slide into the chamber ABOVE the rubber diaphragm. The lid seals that area above the diaphragm. The only way air gets in or out is thru that little hole on the bottom of the slide!

Below the diaphragm in the carb body, there's the large hole facing the INLET bell that goes to that curved vent! Looking down into the area that the slide fits without the slide, there is a hole around 2 O'clock, it's just a fabrication hole, it's plugged! The other hole is on the slope portion around 1 O'clock, it goes to the choke/fuel enrichener, and when the choke is closed, so is that hole!!

VENTURI effect is what draws the vacuum slide up, as you open the butterfly valves, the air passes thru the throat, a lower pressure(Vacuum effect) is developed above the slide due to the air being sucked out thru that little vent hole in the bottom of the slide. That lower pressure is what allows the HIGHER pressure air below the diaphragm to flow thru that large arced vent into the area below the diaphragm, and pushes upwards on the diaphragm lifting it up, raising the slide and the needle!

With obstruction to that large arced vent, the slide can't rise as much. Also with pinholes in the diaphragm, the vacuum can't buildup above the diaphragm, again preventing the slide from being able to slide up.

The Dyna-Jet mods are both lighter tensionsed springs, and drilling the slide hole a bit larger which allows it to create a stronger vacuum above the diaphragm quicker, and with less spring tension, they will slide up quicker/easier as well, which is how they state quicker throttle response.

So....I was just stating that the GXSR carbs definitely had the needed large diaphragm vent on the inlet bell side. From looking at the diagrams for the slingshot carbs, they have probably made changes "like" the dynajet mods, lighter smaller springs, and probably larger slide venturi holes which probably makes the slides more responsive.

BTW, I put a piece of tape over that slide hole, and applied a shop vac to the engine side of the carb, and the slide did NOT rise! Also, Without tape, with the butterfly closed, the slide did not rise.
T.C.

[pggg]

To hook up the XS vac advance connection, gotta also drill a half mm hole thru one carb throat, the tiny hole is only just exposed at the butterfly idle position. See the XS carb has a notch on the butterfly to allow for that. You need to drill a 5mm hole on the outside body to wedge in that small brass tube. The brass tube comes off the XS carb with pliers.

[79XS11F]

Re: Questioning the info from UK XS11 site!

Originally posted by TopCatGr58
Hey Dog and Rob,

I don't know about Slingshot carbs, but I was wanting to do a little research on ours before posting this!

There is NO PORT in the carb body that draws the slides up!!!!

The vacuum running thru the throat of the carb passes by the bottom edge of the vacuum slide. There is a little hole in the bottom of the slide, that hole goes thru the slide into the chamber ABOVE the rubber diaphragm. The lid seals that area above the diaphragm. The only way air gets in or out is thru that little hole on the bottom of the slide!

Below the diaphragm in the carb body, there's the large hole facing the INLET bell that goes to that curved vent! Looking down into the area that the slide fits without the slide, there is a hole around 2 O'clock, it's just a fabrication hole, it's plugged! The other hole is on the slope portion around 1 O'clock, it goes to the choke/fuel enrichener, and when the choke is closed, so is that hole!!

VENTURI effect is what draws the vacuum slide up, as you open the butterfly valves, the air passes thru the throat, a lower pressure(Vacuum effect) is developed above the slide due to the air being sucked out thru that little vent hole in the bottom of the slide. That lower pressure is what allows the HIGHER pressure air below the diaphragm to flow thru that large arced vent into the area below the diaphragm, and pushes upwards on the diaphragm lifting it up, raising the slide and the needle!

With obstruction to that large arced vent, the slide can't rise as much. Also with pinholes in the diaphragm, the vacuum can't buildup above the diaphragm, again preventing the slide from being able to slide up.

The Dyna-Jet mods are both lighter tensionsed springs, and drilling the slide hole a bit larger which allows it to create a stronger vacuum above the diaphragm quicker, and with less spring tension, they will slide up quicker/easier as well, which is how they state quicker throttle response.

So....I was just stating that the GXSR carbs definitely had the needed large diaphragm vent on the inlet bell side. From looking at the diagrams for the slingshot carbs, they have probably made changes "like" the dynajet mods, lighter smaller springs, and probably larger slide venturi holes which probably makes the slides more responsive.

BTW, I put a piece of tape over that slide hole, and applied a shop vac to the engine side of the carb, and the slide did NOT rise! Also, Without tape, with the butterfly closed, the slide did not rise.
T.C.

So any ideas where someone would find these "lighter" diaphragm springs for our carbs? I have never found and dyna-jet kits for 78 and 79 XS11s listed anywhere.
Rob

[pggg]

There's a few kits for the bike you can adjust the same with the stock parts too. I drilled out the slide holes like in dyna kits and it might have had slightly better response but too hard to tell.

[79XS11F]

Originally posted by pggg
There's a few kits for the bike you can adjust the same with the stock parts too. I drilled out the slide holes like in dyna kits and it might have had slightly better response but too hard to tell.

What size bit did you use pggg? I'm not to keen on altering the existing springs unless I have set of back up carbs handy.
Rob

[pggg]

3mm holes, about an extra half mm but you'd need a hotted up motor to feel any difference.

[79XS11F]

These carbs will in the end be installed on my 1179 big bore engine with the exhaust side ported and polished, New used 4 into one header and pod filters.
Rob

[79XS11F]

SILLY ... MAYBE ... MAYBE NOT?

I have been thinking about this carb thingee a lot lately and trust me .. I am no carb expert by any means. I can re & re all the parts and clean them no problem but tuning carbs is a true art unto itself.
Anyway. I was under the impression that the diaphragm was lifted by the negative pressure created by air moving past the air box side of the carb where that oval port at the top of the bell is. Now if it is true that one can have a better carb by having the diaphragm lifted by the suction of the engine by having the port on the engine side of the carb can this be done with the existing carbs?
My thinking is like this (watch out for smoke). Could one not plug the oval port on the bell side of the carb. Tap into the top of the carb above the diaphragm and run a vac line to the intake boot at the engine or even use the vac ports that are there to lift the diaphragm? Would that be too much vac or not enough. Could vac pressure be controlled with a valve on that vac line for fine tuning?
With some cutting and fitting could a vac line be run from the engine side of the carb to the existing oval port?

I wish I had a backup set of carbs to mess around with. i would try some of this sort of stuff
Rob

[mro]

carb mods???????

cart before the horse?

need a good running engine before trying to make mods. Once it's running good, make a single change, get it running good and move to next mod. Otherwise how ya know where problems are or possible to make adjustments in wrong places to compensate for a problem.

Tunning carbs:
"attention to detail" good info on where to start and a lot of patience!!!!!


mro

[79XS11F]

I agree...
The engine is running well. There is nothing wrong with the engine. It's a tuning issue / carb issue. I still think they are running RICH. I think that putting pod filters on them will lean the mixture out. I have cleaned and checked everything there is to check in regard to the carbs. I do not want to be buying an assortment of leaner jets at 5 bucks or so a pop when I know I will be installing a better breathing engine in the bike soon. That engine will be ready by fall I hope.
So instead of leaning out the jetting I will add more air and see what I get.

The other post is just what's on my mind for when I get the carbs running right in their current configuration.

It baffles me to no end because I added to my 78 XS11 a Kerker pipe and pod filters with a simple change in the main jet size and that bike HONKED and HONKED real good. This bike has stock jets and should be running lean but it isn't. I don't get it.

Rob

[mro]

can try lowering fuel level in bowl couple mm.
(raise float height when bowls off and carbs upside down)
_________
course could try and find a set of these




mro