Carb Slide Mod

[The Buddha]

So I am confused now, what is preffered, a fast rising slide or a slow rising slide? I am contemplating just switching to a set of Keihin flat slides. 2 stroke carb tuning gave me less of a headache. 

Its neither - rising at the just the right speed is desired. Goldilocks slides and needles. More or less isnlt the answer. Just right is.

Stock 89-00 slides rise too fast. But stock airbox and pipe prevent that from becoming the determining factor because they dont let the vacuum build fast enough for slide to rise too fast that you notice it.

You take out the pipe and put a slipon or full system. The slide rises too fast, with the airbox putting the check on it that it can.
You remove airbox and you're definitely in rising too fast territory. The best option I have noticed, you train yourself to open the throttle just at the right speed. In spite of that a lot of people have had the bike feel like it falls on its face.

Remember this is independent of needles, jetting or any of those. You cant fix this that way.
If you cant open slow enough and some bikes dont respond to that slow open of throttle, the best option is to block/constrict holes in the diaphragm to let it rise just fast enough.

Now we have someone who has drilled more holes and acheived some magic after looking up a DR650 video from the older style carb with 1 hole and applied it to the newer style carb (which already has 2 holes) and shaved the needle etc etc.
Well we have no idea except what he says, if more people start drilling and shaving their slides and needles and did more scientific experiments we may know.

But AFAIK, GS slides rise too fast. Many many of us have had that issue in 89-00 as well as 01-09 carbs. Most people never had issues with the needle taper, and those that did DJ usually remedied it by swapping back to stock needles.

So I'd like some others to step up and try these before confirming a faster slide and a shaved needle work. And what other mods were done need to be replicated.

PS: 91 US spec bikes were subject to EPA. That's why we got 122.5 mains and 37.5 pilots and non adjustable needles while the rest of the world, including canadialand got 125/40 and adjustable needles. Same needle just with 5 slots to lift/lower them.

Cool.
Buddha.

[moe_tunes]

It has been a great week riding the GS.
Last weekend I added some taper to the needles and am so happy with the result. With the combination of the three mods I can now gently roll the throttle on at 2000rpm (which was unthinkable before) and the bike accelerates, albeit slowly. Any throttle opening above 2500rpm has the bike leaping forward with an enthusiasm I hoped for but didn't really expect.
It's not like there's an extra cylinder or 200cc giving more power, the bike now works like a four stroke not an anemic two stroke that has to clutch-slipped into the power band. No more opening the throttle and waiting for something to happen... It is great how responsive it has become at any revs.
I repeated the two tests and the extra heat I was feeling from the engine has gone so adding some taper to the needles was the right approach in every respect.

For those that commented when they had no clue the needles are made of a very hard stainless steel and took some patient work on the bench grinder to alter.

Cheers

[The Buddha]

SS needles You have a DJ kit ? Stock US bike needles have visible wear from dirty filters if you put too many miles on em with dirty filters in a dusty area.
Cool.
Buddha.

[mr72]

Yeah AFAIK stock needles are alloy on US bikes.

If you have SS needles, well that may very well be the root cause of whatever issue you were trying to tune out.

I had SS (probably DJ) needles in my carbs and could not make it run correctly, had a stumble/hesitation you could not get rid of coming off about 2K or 2500 rpm at small throttle openings. I documented the process of finding and fixing this in detail elsewhere on the forum.

But whatev. We have a new super expert here. Let's throw away decades and hundreds of users' experience, we were all doing it wrong. We should have been on the DR forum instead.

[The Buddha]

For a while DJ was advertising their needles were Titanium. If you look in the cycle world mags of the 90's those little square things in the last 3 pages of sponsors ... Does anyone remember those ? Or am I too old for this forum already. I need GSJack now. Sheesh.

On bikes like vulcan 1500 and GSXR 1127 and 1052 (aircooled) where needles would hit the emulsion tube and wear, they made Ti needles. So in short order you can replace the brass emulsion tube LOL.

Cool.
Buddha.

[moe_tunes]

After about three months riding with the modded carbs it's time for an update on my real world experience with it.
I initially thought that by adding more fuel with the carb mod I'd have a reduction in fuel economy but I found that with the mod I had to use less throttle to go the same speed ... and economy wasn't affected much at all.
Over the 14 months I had the bike before the mod I'd settled on refueling when the trip meter was around 360 km's which kept me from needing to swap to the reserve and was around 15 litres to fill up, around town or with highway use. After the mod around town I've never needed reserve before 360 km's and on the highway I can now go 390 km's before needing around 15 litres to fill up.
So to sum up: The mod has made the bike so much more enjoyable for me. I have 1000 more usable rpm in the low range, throttle response is better all through the range, fuel economy has stayed the same or improved depending on where I'm riding and since I already owned a JIS screwdriver, tape measure, wire cutters and a grinder it cost me $0 !
The only down side was just after the mod the inputs to the bike that had become habit had me going faster than was appropriate so I had to learn to do less. Not really a problem at all

[Guru]

Hello to all,
I registered to this forum only because I was looking information for tunning the bst 33 carbs. I own a dr800. This bike use two bst 33s, almost same as the gs500 carbs. I had previously read all the thread about tunning the bst40 by the Dr 650 guys and I was wondering if anyone did the same to the bst33s. So thanks moe_tunes for all the feedback despite all the negative answers from the members here. I did the same tunning to my dr800 for both the bst33s and the bike is awesome now with open filter and exhaust off course. Moe_tunes my friend you are a totally old school biker who likes to use the tools in the garage and keep his hands on the motorcycle. Thank you!

[moe_tunes]

Thanks for the kind words Guru

[Hang Fire]

Ask yourself a question..................

If the very easy (and cheap) placing of a tiny hole in the slide in the way you describe gives such an advantage.........why didn't Mikuni and Suzuki with all their combined years of in depth knowledge and experience do it themselves before the bike even left the factory?

I will leave that one with you 

Ah, the good ol' Appeal to Authority.

I've worked with a bunch of former Detroit automotive engineers, sitting around shootin' the bull about all the crap they passed into production. Nothing comes out of a factory perfect, just a (hopefully) reasonable set of compromises between efficiency, emissions, safety, performance, and cost.

Think about it, how many long model runs of motorcycles finished with exactly the same revision of part numbers they started with? How many had zero TSB's? Pretty much none. Why didn't they 'get it right' the first model year? Maybe they are learning, too.

Guys have been modding motorcycles since the first one was sold. Not all mods are great, not all are useless.

[The Buddha]

The thing about a GS carb rack, while me and Dynojet dont agree on pretty much anything, we do agree on the problem that the slide rises too fast. That much is proven.
The airbox and stock filter and exhaust keep it in check, or atleast becoming the main driving factor. If you swap the exhaust can you tend to run into the problem with a little ability to control it with your right wrist. Now you remove the air box and all bets are off. No idea what a DR800 is like, but I cant see how it works on a GS. It may well work on the DR family of bikes.
Cool.
Buddha.