36mm slingshots slide holes drilling

[gsBert]

hi, i have a set of gsxr slingshots on my 1150 engine and was wondering about the air holes at the bottom of the slides:

mine have 2 holes for the air (next to the needle) and one was epoxied shut. i was told these affect how the slide comes up.

more/bigger holes make the slide come up faster or slower?
and in which way do these holes affect performance? throttle reaction?

thanks for any advice you can provide. my bike's still running super rich all over the range, so i just changed everything in my carbs:

- smaller emulsion tubes and needles (normal taper, it had double tapers)
- 36 idle jets (had 40)
- 140 main jets (had 147.5)
- needles at their lowest position
- pilot screws are 2 turns out

i'll check the float heights as soon as i can make some adapter to measure it with a hose. and im keeping a set of 130 mains in my pocket just in case.

also i noticed that on the stock 1150 carbs the jetting is 130 for the 2 outboard cylinders and the 2 inside ones are 132.5. i'm guessing this is so those inside cylinders run cooler because they naturally get less airflow. should i emulate this in my flingflops?

[RacingJake]

I'm not 100% sure but I think it's just the opposite. The smaller the hole the faster the slides raise.

[Anonymous]

I don't know much about jetting a GS1150; especially with the "slingshot" carbs you are talking about. What are these carburetors? I am not familiar with the term.

In any case, it was curious that your bike is jetted "RICH" across the entire range of operation. How did you determine that? Did you do a plug chop to determine if the plugs were rich on main jet? How did you determine they were rich in mid-range when running on the jet needle/needle jet? How did you determine the pilot circuit was rich?

What type air intake are you running? OEM/stock or aftermarket pod filters? What type pipes? What is the basline jetting in the slingshot carbs?

OK last question... what plugs are you running? If the plugs are not the right heat range, the mixture will not combust entirely and leave mucho soot in the combustion chamber. What type fuel are you using? The lowest octane range your manual calls for is correct. High-test in engines that don't call for it will cause sooting. Octane in gas retards combustion and is intended for high-compression engines. Some folks use this stuff when not needed and their combustion is retarded and this leaves unwanted soot. Last, your spark may be weak... do you ever get backfiring when cruising at a set speed? This is also a sign of weak spark which will leave soot on the plugs. The reason for a weak spark is that the path for power to the coils is very circuitous. It starts at the battery; through a fuse to the igntion switch, to the kill switch and then back to the coils. A number of switches and connectors decrease the power that was originally available to the coils. I power ALL the older bike coils on my bikes through an automotive relay run directly from the battery. This usually gives me significantly more power to the coils and thus a hotter spark. Since I test carburetors for a living and many are jetted far too rich for my test bikes, this keeps me from fouling carbs. I generally get over 10K miles per set of plugs with this mod. This tip is documented at:

http://www.kzrider.com/ignition_upgrade.shtml

One of the symptoms are "rich across full range of operation".

[Billy Ricks]

Less controlled vacuum leak means the slides are going to rise faster and quite possibly remain higher under vacuum thus richer readings across the rev range.

George, the Slingshots came on the second generation GSXR's. They were designed to give a shorter, straighter shot of fuel mixture into the combustion chambers.

[gsBert]

george: bs36ss are the slingshots (flatslides, still vacuum controlled), you know those?
hah: i didnt need to do a chop test on the plugs, the smoke told me enough... that's how rich the bike ran.

the pilot's rich becuz the bike smokes at idle (fuel fumes), the midrange is rich cuz the bike smokes at 1/2 throttle and wot is rich cuz i cant see through the smoke in the mirrors(and the bike slows down), it was a miracle the bike ran at all, oh and the fuel consumption was at 10-12 liters for 100 kms.
and the ninja 500 my buddy is learning on, well i can't catch up to it.

the exhaust is stock, but ill swap in a supertrapp once i get the carbs working (should be small adjustments from then on) i run k&n pods (1 pod for 2 carbs)
i'm running stock plugs for the 1150 and as far as octane goes, unless it pings and it's timed properly i'll always run on 87

i'm not talking "my plugs are dark" here, i'm talking "my plugs are wet and i got more gas than oil in my crankcase" rich.

billy ricks: by "less controlled vacuum" do you mean bigger/more holes in the slides or less/smaller holes?

smaller holes will raise the slide faster or slower?
and if it rises faster, i get better throttle response as long as my mixture richens as my revs climb right?

[KEITH KRAUSE]

Drilling out the vacuum passage to the diaphragm chamber is a requirement mentioned in jet kits. They even supply the drill bit. The larger hole is to increase/improve throttle response.

[gsBert]

so a larger hole will raise my slide faster then. right?

just want to be clear on this before i remove the epoxy that's blocking one of my slide holes (the slingshots are supposed to have 2 right?)

[KEITH KRAUSE]

I'm not familiar with the slingshots and the number of slide holes.
I don't know why plugging one is useful either. Seems
"backwards" to me, but may be some racing tip or ? that I'm not aware of.
As for a larger hole raising the slide faster, I've always read or heard that enlarging the hole improves throttle response which I would understand as making the slide react faster to the throttle plate opening, not actually rise faster.
I'd check out some carb tune sites and find out for sure about why you have a hole plugged.

[mike J]

Can you post a photo of these carbs? I have a set of carbs off of a GSX-R but I don't have a clue as to what they are. I would be interested in your results on the 1150. Mike J

[Billy Ricks]

The larger hole will let the slide react quicker. Plugging the one hole should have a tendency for vacuum to pull the slide higher and keep it higher thus raising the needle. The throttle plate and needle are out of synch giving you the rich condition across the rpm range.

[gsBert]

wow billy! thank you so much.
that makes a lot of sense...
it explains why it was pluggued in the first place, my carbs dont have stock needles for the bike they got taken out of (friend's drag bike that now runs mechanical slides) but totally wrong for my stockish 1150 motor.

thank you very much for keeping up with my various posts about these carbs. i get closer to a solution everytime i read your replies.

right now the carbs i'm about to try are thusly set up:
- stock float heights for the gsxr1100 (will adapt a clear tube to the bowls to figure out perfect height once it runs ok-ish, but this should be a good start)
- 36 idle jets
- 140 mains
- the emulsion tubes and needles are a mystery but smaller in diameter than the katanas. they are stock mikuni parts and they are matched.
- idle screws are 2 turns out
i'll keep the hole plugged for now to see how that works but if it's too rich, ill drill out the epoxy and hopefully that will get it working right.

i'm trying the carbs out tomorrow, tonight im recharging the battery and installing them as well as new plugs (not taking any chances). look for yet another puzzled post tomorrow or a victorious scream of joy.
(2 years without getting that bike to run)

[gsBert]

mike-j:
i dont have a picture, but they are easy to identify...

heres an accurate description:

- they have flat slides (still round but flat on the intake side)
- they use a single throttle cable
- they have a 36mm diameter at the engine side (other sizes exist also)
- they have 2 fuel lines going to them (1 for each pair right/left)
- the choke is not bar-mounted
- the diaphragm caps are plastic and there's a little o-ring under the vacuum nipples (3 of them should be capped)
- the diaphragm caps bolt on with 2 screws, not 4, same for the float bowls
- the float bowl drain plug is smartly designed, you dont pull it out, it's in sideways and the fuel drains neatly without spiling all over your screwdriver
- the air intake to the carbs is oval with a half moon on top to provide pressure under the diaphragm. the bottom part has 2 small brass air intakes.
- the idle screw is near the engine side underneath
- the floats are orange plastic
- they are very light, simple and elegantly designed
- they have a slight downdraft to them (ie: the intake is higher than the engine side when the bowls are level)
- they say mikuni on the side, mine also says 40C00-K9Y2
- the needles are adjustable

and best of all in my case, they're real easy to take apart

as for the results on the 1150:
my friend has those carbs on his 1100 and they kicked some serious arse when we tried them on my bike, getting them jetted right is a pain though, if i had the money i'd buy the same parts he has but i can't affort to pay 600$ for needles and emulsion tubes from discontinu-backorder-zuki-ed so i experiment with what i have (mix and match from 3 different carb sets)