BST36SS "Slingshot" Carb Question

[TxGSrider]

Ok, since my bike is up and running fine, I decided to mess with it again... I bought a new pipe for my old GS and I thought I'd try my hand at making some 36mm "Slingshot" carbs work on it again now that Ive got a better flowing exhaust. I was told the carbs were from a 89 or 90 GSXR-1100 (ahh... ebay), so I installed the stage 3 Dynojet kit listed for that (the kit came with emulsion tubes). Last year I tried to get them to work but I couldn't really work out the jetting (too rich at idle, stumbling at part throttle, great full throttle), so I boxed them back up. So now Im going to use my wideband O2 scanner and get it set right... I hope.

So here's my question... I believe that none of the GSXR1100 used the little pilot jet plugs, but several of the other models did, and since I am not 100% this is a GSXR1100 carb set, is there an easy way to look at the carbs to see if they need those plugs or not?

Thanks!

 

[geol]

Look into the pilot well and if there is a hole across to the main jet well, they need a plug; if not, they don't use a plug. When the pilot well is plugged, the pilot jet draws gas through that hole across to the main jet well and not directly into the pilot jet well hanging down into the bowl.

 

[TxGSrider]

Look into the pilot well and if there is a hole across to the main jet well, they need a plug; if not, they don't use a plug. When the pilot well is plugged, the pilot jet draws gas through that hole across to the main jet well and not directly into the pilot jet well hanging down into the bowl.

Thank you, I was kinda thinking the same thing but wanted to confirm it.

 

[Carter Turk]

I've messed with 90 Gixxer 11 carbs many times on my 1150.
Not even close to an expert, but I do think it's important to lift the carbs up higher than where they want to rest.
If you look at a side view of air/oil cooled GSXR, notice the angle of the intake ports and the angle of the float bowl gasket surface. I fabricated some crude carb holders that mount to two holes on the old airbox bracket on the frame.
Float height is around 14.6mm stock, but I think that'll need to be leaned out a hair or two to compensate for the straigher intake tract on a 1100. Just a theory.

 

[Buffalo Bill]

A good theory.
I have an 82-GS1100G and 92-GSXR 1100 engine in a 90-Katana.
I can make a suggestion about tuning the jets, start at 115 mains, and work up from there.
I used the Katana BST36SS and started with Dynojet needles 120 mains, just bit smaller than the 122.5 GSXR mains.
Enormous torque for now, but it can use a bit more top end. I will start testing larger mains when I need something to do.

 

[TxGSrider]

Good advice guys.
I'm going to mess with them this weekend. I know if I can get it to start and idle (even a fast idle) I can get the jetting figured out pretty fast with the wideband. The only problem here is that today it's 103 and the humidity is high, which makes it miserable to work on, and if I get the jetting right, it'll be way lean when the temps drop down into the 70-80's here this fall (AKA -Riding season here).

 

[geol]

Carb assemblies on later bikes had the carb bowls canted at an angle to match the angle of the engine which is laid forward to get more weight on the front of the bike. These carbs are hard to make work on a bike like a GS1100 and the floats are at the wrong angle the carbs will starve for gas under normal acceleration... you would have to gin up some intake manifolds that tipped the carbs so the bowls are parallel to the ground. I am not sure if the early BST carba are this way but I am thinking they are not. If they are, you may not want to mess with them.

 

[TxGSrider]

Just an update. It was ONLY 92 and really humid (showers in the area) yesterday, but even so I got some testing done. I ended up with 40 pilots and 2.75 turns out (I didn't have any 42s to try, but 45s were way to rich to idle with the screws turned out at all). I'm using the dynojet kit for gsxr1100 (1990), and with the needle in its leanest position its still rich and gets worse from 1/2 throttle up. The smallest mains in my kit was 155 and they show rich readings at full throttle (in the 10.5 range). Of course none of my mikuni jets fit the Dynojet emulsion tubes so I ran out of options to try.
I may try a kit for the gsf1200 as they seem to use a less aggressive needle and have 150 main jets.

 

[Carter Turk]

I started with a used Dynojet and K&N's on used 90-11 carbs, before I realized the emulsion tubes were ovaled out and shot.
160 mains that looked drilled out and 30 pilots and funky hourglass needles with really blunt ends. Fouled many plugs.
Decided to try Factory jet kit and emulsion tubes. The needle was way more tapered, nothing like the DJ's.
Middle clip on the needles or one down, 142.5 Mikuni mains, 32.5 pilots, 2.5ish on the a/f screws.
Changed all the o-rings a few years back and gained 10-12mpg.

 

[BurntKittyForge]

^^^Now I'm really wanting to change the O-rings/rebuid carb. (I get pretty bad mileage).

There was a rare GSX1100G ('91, '92,or'93(?)) stock with the same BST36 slingshot carburater so I was interested in this
topic mostly.
My '93 has Mikuni RS installed by a previous owner. (I imagine/wonder the RS is atleast comparable to, or better than "slingshot" in terms of H.P. output gains(?))...

ALSO: I searched and searched for information on whether the (rear) suspension modification I made would affect the carb angle enough to need readjustment one time . But found NOTHING anyplace on internet regarding that.

I replaced a homemade hardtail steel bar (discovered after purchase ,rear tire sat few MM's from fender) with a RF900 shock (sat opposite, all the way up tail, opposite from previously,needed kickstand extension)...

Once finished the bike would not run more than seconds, turned out to be dirty carb though.
(rusty tank cleaning unsuccessful, went with caswell, cleaned carb 2nd time).

My First thought was float angle/ carb needed adjustment, but it's been fine so far.
Planning on adjusting it properly soon though.

Sort of interesting IMO, not a single post I could find regarding suspension causing potential carb issues is all. (?)

-Dang reply too long but Also been wondering whether having a fuel-pump VS. no fuel pump changes the jet sizes much(?) (I have no fuel pump, it's been removed by a PO) so I don't want to tell anybody w/ stock bike what jet combo works OR take advice on it either. It's just questionable information otherwise.
Thanks for any feedback on that all...(back LATE from out of town, I better sleep before work).

 

[TxGSrider]

I haven't checked around here, so there may already be a thread that covers this, but maybe we could start up a thread that people could list their carburetor jetting? Maybe post some brief information like engine size, mods, exhaust type, carb type, air filter type, altitute and how you tuned it. It would be good to list what brand jets/needles used (dynojet numbers are different). I'm just thinking it would make it easier for folks to get into the ballpark.

 

[Buffalo Bill]

Just an update. It was ONLY 92 and really humid (showers in the area) yesterday, but even so I got some testing done. I ended up with 40 pilots and 2.75 turns out (I didn't have any 42s to try, but 45s were way to rich to idle with the screws turned out at all). I'm using the dynojet kit for gsxr1100 (1990), and with the needle in its leanest position its still rich and gets worse from 1/2 throttle up. The smallest mains in my kit was 155 and they show rich readings at full throttle (in the 10.5 range). Of course none of my mikuni jets fit the Dynojet emulsion tubes so I ran out of options to try.
I may try a kit for the gsf1200 as they seem to use a less aggressive needle and have 150 main jets.

Why don't you try genuine Mikuni components?
PS: I forgot to add that I'm using the stock airbox, filter and exhaust system.
The carb tuners over at katriders.com insist the BST36SS carbs need the airbox and standard filter for the carbs to work. Without that slight intake restriction, they don't work well.

 

[Guest]

If it helps - I have a box full of 89 gsxr1100 carbs parts - basically everything except the carb bodies

the bodies were damaged beyond practical repair but diaphragms, slides etc were good.

just want them out of the "mountain of spares" so they're free - I'm in Katy so can post or meet halfway

 

[TxGSrider]

Why don't you try genuine Mikuni components?
PS: I forgot to add that I'm using the stock airbox, filter and exhaust system.
The carb tuners over at katriders.com insist the BST36SS carbs need the airbox and standard filter for the carbs to work. Without that slight intake restriction, they don't work well.

I'd sure like to use the mikuni jets, but Dynojet in their wisdom seems to have created their own jets that will fit in their emulsion tubes. The mikunis are a smidgen larger in thread diameter.

 

[Carter Turk]

Why don't you try genuine Mikuni components?
PS: I forgot to add that I'm using the stock airbox, filter and exhaust system.
The carb tuners over at katriders.com insist the BST36SS carbs need the airbox and standard filter for the carbs to work. Without that slight intake restriction, they don't work well.

I can't say mine are working perfectly, been blowing off vacuum caps lately #2-#3. Currently #2 blew off on the last ride. #3 on the ride before.
The timing is slightly retarded, to ease start up. Don't know how that helps start up, but figured if it starts easier, then why not. Going on 15 years with pods, made it to Michigan with them actually. They don't like going 25-30 mph, I'll admit that, though haven't had an airbox on any GS since 1988. The BST's get better mileage than the stockers with pods, by quite a margin, even with pipe and bigger pistons.

I've always wondered if inserting velocity stacks inside the K&N's (like the stockers in the airbox) might improve small throttle openings at lower speeds, maybe help direct the air more efficiently, before mixing with the gas.

 

[limeex2]

I'm running gixxer 11 carbs on mine, so here's my 2 cents worth, It may only be worth 1 cent though... The needle and emulsion tubes will almost always be worn out. The nylon slides that the carb pistons slide up and down in are a trouble spot, check closely. The carbs can be tilted enough, with float height adjustments to get it were you need to be for proper running. Use NEW carb boots and a bracket really isn't ness., but for peace of mind a brkt fabricated to hook into air box brackets on the frame work well. I can not help you with jetting. I did use a dyno-jet kit, but am unsure where the tuner ended up with for jetting. I dyno all my bikes. It runs perfect and carburetes like a new bike

 

[TxGSrider]

OK I had a little time to mess with it this weekend. I took some of Factory Pro's website advice and lowered the float level 1mm and leaned out the O2 readings allot but it still a little rich... but allot closer. It actually is running really good. Next weekend I may try lowering it another 1/2mm and see if it cleans up the readings some more. I also found some 150 DJ mains and my O2 readings at full throttle from 7000 up are allot closer. I will keep everyone posted as I keep experimenting with the settings.

 

[geol]

If vacuum caps blow off (I had a GSF1200F that had this issue), your can buy little tiny vinyl vacuum caps at an auto parts store that will stay on small vacuum fittings. Rubber caps lasted about a day or two before flowing off and those that lasted longer usually cracked and leaked soon anyway. I think I bought those little vacuum caps in the "HELP" section and they were red.

 

[Carter Turk]

If vacuum caps blow off (I had a GSF1200F that had this issue), your can buy little tiny vinyl vacuum caps at an auto parts store that will stay on small vacuum fittings. Rubber caps lasted about a day or two before flowing off and those that lasted longer usually cracked and leaked soon anyway. I think I bought those little vacuum caps in the "HELP" section and they were red.

Never heard of anyone else mentioning this happening. Not sure why it happens, seems like a timing issue or when the starter clutch snatches at start up.
My bike doesn't seem to light on the first attempt, as if residual fuel is left in the combustion chamber. My valve guides particularly on #3 need replacement among many other things. There's a fair bit of slop on the exhaust side of the valve stem. I just bought some caps with the fussy clamps at my favorite hardware store. They stayed on, on the last ride. When one blows off it runs like sh*t. Most folks on the GS site don't have to worry about it with stock CV or older carbs.

 

[TxGSrider]

A little update: I replaced the DJ Emulsion tubes and needles (with a new set of DJ emulsion tubes and needles), replaced the intake tubes, and replaced all of the rest of the O-rings in the carbs that I hadn't already replaced. Now it idles really rich (I was using the 40 pilots that were in the carb when I got them). I rechecked everything and as near as I can tell everything is set correctly so I'll have to pick up some smaller pilot jets (I think they came with 32.5 or 35's, so that's what I'll try). So now I'm waiting on parts.
Good thing I have a 3 day weekend this weekend to mess with it some more...