I had been reading up on the DR650 on the net - I think it'll make a nice street single - and came across a lot of talk of it being necessary to change or mod the carb. The carb mod seems simple enough and improves the throttle response in the low and midrange. So I thought I'd try it on the GS...
With the tank off I took the top off the carbs, pulled out the slides and drilled the holes either side of the needle 1mm larger taking care to level the burr on the hole from drilling. In my 2009's carbs the slide springs sit over the holes effectively halving the holes area...
I bolted it all back together and took it for a test run. As advertised the throttle response from 3-5000 rpm is better and now I can ease the throttle on at 2500rpm and not have the bike shudder badly - still shudders a little though. For a $0 mod I'm happy with the result so far.
I'll ride it like it is for a week or two and if I feel it'll be of benefit I'll do the next stage of the mod which is backing off the spring preload on the slide by trimming the spring.
Cheers
Interesting modification. Did anyone ever say if you go bigger than 1 mm if it negatively affects the response? Anything else that needs to be done as far as jetting etc.?
Interesting , thanks for the data point. is jetting all standard?
This is a common Harley mod. But there are as many sites for it as against it. I cvonsidered it but fixed my juddering problem by taking bike back to stock (leaner)
I'd be interested to know the effect at WOT around 5k RPM.
Quote from: jar75 on January 20, 2021, 07:53:35 PM
Interesting modification. Did anyone ever say if you go bigger than 1 mm if it negatively affects the response? Anything else that needs to be done as far as jetting etc.?
I went 1mm bigger because that was the next size up drill bit I had. I would have gone 0.5mm bigger first if I had the drill bit. In the slides from my 2009 carbs there wasn't really the room for the extra 1mm diameter but I forced the issue.
The idea is to have the slide react a bit quicker to throttle openings but going too large with the holes would have it reacting too quick which could cause fuelling issues. The fuelling is still controlled by the needle and seems to be fine with the 1mm increase. The next stage of the mod is to back off the slide spring preload by shortening the spring and needs the needle to be lowered since the slide will sit higher for a given air flow.
Quote from: herennow on January 21, 2021, 12:55:46 AM
Interesting , thanks for the data point. is jetting all standard?
This is a common Harley mod. But there are as many sites for it as against it. I cvonsidered it but fixed my juddering problem by taking bike back to stock (leaner)
I'd be interested to know the effect at WOT around 5k RPM.
My bike is totally stock, haven't even had the carbs off the bike.... The GS500 isn't really meant to be accelerated from 2500rpm which is the only time I get any shuddering. I'm lazy and try not to downshift when in city traffic. The biggest noticable difference is rolling back on the throttle at 3000rpm in 6th - pickup is smoother and quicker. Haven't found a drawback yet.
Here's (https://www.youtube.com/watch?v=aN1aU0G4YQE) a link to a vid showing the carb mod for the DR650. This is the accumulation of years of experimenting on the DR carb and won't translate exactly to the GS carbs.I can't find anywhere on the net where someone has done something similar for the GS but there are other bikes where the details have been sorted out. That's why i'm approaching it one step at a time and evaluating each step.
The DR slide spring is 112mm long stock and they cut it to 100mm - the springs in my GS carbs are 100mm stock so after a couple of weeks getting used to the first stage I plan to cut one loop of the spring off which will be about 5mm and test that out...
cutting that spring will actually make it stiffer. FYI. The "preload" affects how much force (vacuum) is required to begin moving the slide. Cutting it will result in less vacuum required to begin moving it but more vacuum to move it further. This will really affect mixture across rpm and throttle openings making it progressively leaner across the range as throttle and rpm increases. But it will be richer at initial opening and very low rpm and throttle.
Good thing internet users of dr650s know more about carburetor design for a bike they are not even working on than Suzuki engineers did when they designed the gs500.
Oh, this could be at work in the 02 carbs I could never get to run right especially past 1/2 throttle. Now in an 89-00 the slide comes up far too fast. That's our biggest problem, its solved by blocking 1 hole. But this may be at play in the 02 rack I have. I "solved" the problem by switching back to the older carb.
Let me check that video. Thanks guys.
Cool.
Buddha.
https://www.youtube.com/watch?v=aN1aU0G4YQE
I watched that video. That's a slightly different version of the 89-00 carb on that DR with 1 hole in the bottom of the slide.
I'll be careful applying its "lessons learned" to the 01 and later GS carb. The 89-00 carbs sure - except the GS has 2 holes in the slide and a well documented case of slides coming up too fast especially if we remove any restriction like pipe. So I'd say the DR setup is the opposite and they're trying to create a problem we already have. Maybe we could trade those guys our slides and get theirs in exchange.
BTW a carb trying to feed 650 cc's at 8K redline has a whole different situation than one trying to feed 250cc @ 10k. The CFM's are nearly 2X on the single, but they cant increase the venturi diameter to match. Then the bike will be unrideable at low revs. So they fit too small a carb on it anyway. That leads to a bunch of other problems like slide rising too fast etc.
Cool.
Buddha.
Quote from: herennow on January 21, 2021, 12:55:46 AM
...
I'd be interested to know the effect at WOT around 5k RPM.
I don't normally ride WOT but tested this out coming back from the shops when the bike was warmed up.
In first then second then third I held the bike to a steady 5000rpm then slammed the throttle wide open. Pickup was instant and it revved out fine.
Quote from: mr72 on January 22, 2021, 05:19:48 AM
cutting that spring will actually make it stiffer. FYI.
Should be a recommended budget fix for the soft fork springs then I would think.
Quote from: mr72 on January 22, 2021, 05:19:48 AM
...
The "preload" affects how much force (vacuum) is required to begin moving the slide. Cutting it will result in less vacuum required to begin moving it but more vacuum to move it further. ...
More vacuum is provided by the larger holes in the slides as mentioned in the first post.
Quote from: The Buddha on January 22, 2021, 09:50:56 AM
... a well documented case of slides coming up too fast ...
I'd like to read about that. Can you point me to any info on this?
Cheers
Quote from: moe_tunes on January 22, 2021, 05:15:36 PM
Quote from: mr72 on January 22, 2021, 05:19:48 AM
cutting that spring will actually make it stiffer. FYI.
Should be a recommended budget fix for the soft fork springs then I would think.
It is a cheap way to make a spring stiffer, except you don't know how much stiffer the spring will be. Its much more a guess and check thing. Better to spend the $100 on a known spring rate and be done with it. Maybe a physicist could tell you, does cutting a spring in half make it twice as stiff? Its probably a more complex relationship than that.
Now you want to introduce guess and check into your carburetor without an objective way to measure the results (dynometer)? Have at it if you like pulling the GS carbs off over and over but you are more likely to kill your fuel economy than get any measurable gains in HP.
Bluesmudge, if you had read the first post you'd know it isn't about "gains in HP".
Cheers
Quote from: moe_tunes on January 22, 2021, 05:15:36 PM
Quote from: mr72 on January 22, 2021, 05:19:48 AM
...
The "preload" affects how much force (vacuum) is required to begin moving the slide. Cutting it will result in less vacuum required to begin moving it but more vacuum to move it further. ...
More vacuum is provided by the larger holes in the slides as mentioned in the first post.
no it's not. Vacuum that pulls the slide up is above the diaphragm. That hole is a controlled leak. Air coming through it actually goes into the cylinder, making it leaner, mostly at idle. But there main purpose of that hole is damping, the larger the hole, the slower the slide comes up, and the faster it goes back down. A stiffer spring will also put the slide down quicker. This is all a delicate and precise balance where each change interacts with everything else. Very rarely can you change one thing and have no deleterious effects.
IMHO this is a misguided solution in search of a problem.
Quote from: Bluesmudge on January 22, 2021, 05:50:56 PM
It is a cheap way to make a spring stiffer, except you don't know how much stiffer the spring will be. ... does cutting a spring in half make it twice as stiff? Its probably a more complex relationship than that.
Actually it is exactly like that, pretty much. For active coils, it is precisely linear. It's easy to approximate inactive coils. With a calculator and a micrometer you can easily calculate spring rate as long as you know the spring material.
Problem with the GS spring is that it's so soft to begin with, you have to cut like 40% of it off to get it stiff enough and then it's too short to not impede travel. When you cut coils you also shorten the entire spring, reducing the space between coils available for movement. You make this up with a spacer but at some point you end up with coil bind bottoming the fork before you have used up all of the mechanical travel.
I did exactly this, cut about 1/3 off of my stock springs, and they were better but the .90 Sonic springs are way better. We'll probably put the cut down GS springs in my dad's TU250x. It doesn't have as much travel to lose and can handle softer springs.
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 :dunno_black:
Quote from: moe_tunes on January 22, 2021, 05:22:02 PM
Quote from: The Buddha on January 22, 2021, 09:50:56 AM
... a well documented case of slides coming up too fast ...
I'd like to read about that. Can you point me to any info on this?
Cheers
Dynojet offers plastic plugs to constrict and/or to close off those holes. I actually dynoed my bike with 1 hole closed off, it still showed signs of the slide coming up too fast. I trained myself to open the throttle slower.
When you whack the throttle open and the bike falls on its face when it was running along fine, and if in that same rpm/speed/gear it reacts fine when you open the throttle slowly, that's a sign the slide is coming up too fast.
Cool.
Buddha.
Quote from: mr72 on January 23, 2021, 05:49:00 AM
Quote from: moe_tunes on January 22, 2021, 05:15:36 PM
Quote from: mr72 on January 22, 2021, 05:19:48 AM
...
The "preload" affects how much force (vacuum) is required to begin moving the slide. Cutting it will result in less vacuum required to begin moving it but more vacuum to move it further. ...
More vacuum is provided by the larger holes in the slides as mentioned in the first post.
no it's not. Vacuum that pulls the slide up is above the diaphragm. That hole is a controlled leak. Air coming through it actually goes into the cylinder, making it leaner, mostly at idle. But there main purpose of that hole is damping, the larger the hole, the slower the slide comes up, and the faster it goes back down. A stiffer spring will also put the slide down quicker. This is all a delicate and precise balance where each change interacts with everything else. Very rarely can you change one thing and have no deleterious effects.
IMHO this is a misguided solution in search of a problem.
Where do you think the vacuum that raises the slide comes from?
I don't think you quite understand how CV carbs work. Have a look at Benoulli's Principle (https://en.wikipedia.org/wiki/Bernoulli's_principle). It might help you get that bit sorted.
Cheers.
Quote from: sledge on January 23, 2021, 07:58:58 AM
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 :dunno_black:
I'm suprised you didn't tell me to get a different bike ! (http://gstwins.com/gsboard/index.php/topic,73615.msg883816.html#msg883816)
Cheers.
Quote from: The Buddha on January 24, 2021, 11:27:07 AM
Quote from: moe_tunes on January 22, 2021, 05:22:02 PM
Quote from: The Buddha on January 22, 2021, 09:50:56 AM
... a well documented case of slides coming up too fast ...
I'd like to read about that. Can you point me to any info on this?
Cheers
Dynojet offers plastic plugs to constrict and/or to close off those holes. I actually dynoed my bike with 1 hole closed off, it still showed signs of the slide coming up too fast. I trained myself to open the throttle slower.
When you whack the throttle open and the bike falls on its face when it was running along fine, and if in that same rpm/speed/gear it reacts fine when you open the throttle slowly, that's a sign the slide is coming up too fast.
Cool.
Buddha.
So it's not documented somewhere that you can point me to? I would have liked to read about that.
I know there are plugs for the slide holes that are used on four cylinder race bikes where low and mid range fuelling is less important.
I'm trying to have the 2009 GS500 I have now fuelling like the GS450 I used to have. That bike wasn't leaned down to meet Euro emissions and would rev from 1500 to 9000. The 500 is basically the same engine so should be capable of a similar rev range once the carbs are sorted. Changing jets and mixture screws is just a part of the solution...
With the first stage of the mod I have 1000 extra usable revs, a crisper pickup and more smiles per mile.
Quote from: moe_tunes on January 26, 2021, 12:52:44 AM
Where do you think the vacuum that raises the slide comes from?
I don't think you quite understand how CV carbs work. Have a look at Benoulli's Principle (https://en.wikipedia.org/wiki/Bernoulli's_principle). It might help you get that bit sorted.
Cheers.
wow. Welcome to my ignore list. You can screw your stuff up and I won't get distracted by it. We all go home happy.
That does seem a bit sensitive, I was just trying to help...
For a simple $0 mod I have an extra 1000 usable revs and crisper throttle response. Not really screwing any stuff up at all.
Cheers
Quote from: moe_tunes on January 26, 2021, 01:12:09 AM
I'm trying to have the 2009 GS500 I have now fuelling like the GS450 I used to have. That bike wasn't leaned down to meet Euro emissions and would rev from 1500 to 9000. The 500 is basically the same engine so should be capable of a similar rev range once the carbs are sorted. Changing jets and mixture screws is just a part of the solution...
With the first stage of the mod I have 1000 extra usable revs, a crisper pickup and more smiles per mile.
A 100% stock 2009 GS500 will rev from 1200 rpm to 10500 no problem. There may have been an issue with the carb that you are trying to bandaid.
I believe you are getting a different throttle response as a result of the mod..............not necessarily a better one
Quote from: Bluesmudge on January 26, 2021, 11:56:11 AM
Quote from: moe_tunes on January 26, 2021, 01:12:09 AM
I'm trying to have the 2009 GS500 I have now fuelling like the GS450 I used to have. That bike wasn't leaned down to meet Euro emissions and would rev from 1500 to 9000. The 500 is basically the same engine so should be capable of a similar rev range once the carbs are sorted. Changing jets and mixture screws is just a part of the solution...
With the first stage of the mod I have 1000 extra usable revs, a crisper pickup and more smiles per mile.
A 100% stock 2009 GS500 will rev from 1200 rpm to 10500 no problem. There may have been an issue with the carb that you are trying to bandaid.
Yes I also found the comment about extra rpm surprising, especially considering that originally the statement was made that WOT is rarely used
It's like nobody bothered to read the first post...
If you read through this forum you will find that over the years there has been a consistant opinion that the GS500 isn't very usable under 4000rpm which to my dissapointment I found was true with my stock GS. Nothing like I expected it to be. Even from 4000rpm it feels pretty anemic, not anything like these engines are capable of which is obviously due to Suzuki leaning out the fuelling to meet 2009 Euro emission limits.
When I started this thread I knew I was interacting with the internet of 2021 and was fully aware there would be people who hadn't tried the mod who would poo-poo the idea just because they had nothing else to do, didn't like the idea of someone doing something to their bike, didn't like that someone else could have something positive to contribute to the community or some other petty reason. That's our modern internet...
Over the next few months I will, step by step, experiment with what's known to work with other bikes to see what works with the GS because no one has done much to sort out the weak spot of the GS, the low to midrange fuelling.
Cheers
The stock GS exhaust and airbox keep air flow down to a point that the 2 hole slide isn't your limiting condition. In fact the exhaust is the first limiting condition, specifically the can.
Take that out and you instantly run into the next limit. The airbox.
If you were running say 3K and whacked the throttle open and have the bike seem to gasp and want to stall, that means your slide is rising too fast. Open slowly and it reacts better, open fast and it seems to just gasp like you opened the window on a car going 100 and stuck your head out the window.
Now with a K&N and pipe and closing off 1 hole I had my bike dynoed and there was a flutter they said was a slide still rising too fast. I didn't bother partially closing off the other hole. I just trained to open a little slower.
The 89-00 GS does not need more holes.
That DR carb video doesn't apply to the 01+ GS, the slides, springs etc etc are different. Yea suzuki fixed a problem no one was having and ignored all the problems people were having. Exactly what we needed was 3 jets with smaller holes.
Cool.
Buddha.
After 2 tanks of fuel, no change in fuel consumption and only benefits from the first stage of the mod it was time to try the second stage.
As mentioned previously the slide springs in my 2009 carbs have a free length of 100mm. For the first step I cut them down to 95mm. Throttle response down low has improved again and going from a closed throttle to a slightly opened one mid corner is much less snatchy. Very happy with the improvement. I'll put a couple of tanks of fuel through it and then see if taking another 5mm off the slide spring free length is an improvement or a bit too much.
Cheers.
Have you told Suzuki and Mikuni about this revelation yet?
I think you should :thumb:
Today was my first chance since the second stage of the mod to do some country road scratchin' and it's great not to have to be constantly changing gears to have some acceleration on the GS.
During the last week I performed a couple of tests on my daily commute to various parts of suburbia where i am limited to 60 km/h to check out how the fueling is now with the mods. My normal mode of riding is to filter to the front at a red light and take off briskly to get away from the half asleep, myopic, facebook reading tin top drivers and change up at around 5000 rpm's from first to fourth, change into fifth and cruise 'till the next set of lights. On Tuesday I didn't go higher than fourth and Wednesday no higher than third. Each day the the fueling was fine, the bike rode great and was very responsive but there was an obvious difference compared to my previous 17 months with the bike. Towards the end of the commute I felt heat from the engine on my lower legs which I hadn't had before and after parking the bike I could smell the extra heat coming off the engine, moreso when fourth was my top gear for the day rather than third. Sure signs of the bike running lean in the midrange and probably why the DR guys from the vid grind a taper on the needle for the DR's carb. When I drilled the slides in the first stage of the mod I noticed the needles were closer to having parallel sides than a taper which I attribute to Suzuki constantly leaning out the fuelling for a carb'd bike to meet increasingly restrictive Euro emissions. So instead of the next stage of the mod being removing another 5mm off the slide spring free length it makes more sense to add some taper to the needles. Following the $0 mod ethos of this thread I'll use a grinding wheel to add the taper to the needle. As a starting point I'll reduce the tip by 0.5mm and taper it up 20mm 'cause it's easier to take more off later than add some back... I'll put another tank of fuel through the bike and retest what happens with fourth and third being the highest gear I use to confirm things.
I'm sure sledge won't be happy to read about someone using a bench grinder to add a taper to the carb's needles and I'm OK with that, hope it gives him something to fill his day. From what I've read on this site and others the GS500 provides a low cost of entry to the motorcylcing world and plenty of low cost opportunities to experiment and learn and personalise a bike.
Cheers
You use a bench grinder to change the needle taper ??? While you're at it brush your teeth with bench grinder too.
Needle taper can be changed by putting the needle in a hand drill and spinning it with wet emery paper between your fingers.
You're using an atom bomb to squish that little ant at your foot. BTW the stock needle is in short short supply, so you grind it up and we'll all connectively say ... WTF, you ground up what ???
And stock needle is nearly ideal as well, ofcourse you can grind up any part you like. Its your bike.
Oh yea you want a hacked up needle - look into dynojet, atleast that way you have a way back, those guys also drill and tap and this and that the slides too.
Cool.
Buddha.
exactly what Buddha said. Plus, the stock needle I probably aluminum, which will go bad real fast if you try to modify it. I have some stainless steel needles that are probably dynojet, already screwed up for you and much more forgiving when you try to modify them.
The thing Buddha didn't mention is that the tremendous value of the collective wisdom from three decades of GS500 owners experience is tossed out the window once you try re-engineering the carbs. That's probably the most valuable aspect of that bike.
Every day i ride the bike I become more and more happy that I took on the challenge of being the first to try this mod on the GS carbs. After a year+ riding the bike I have developed some habits, a way to ride the bike, which now that the bike is much more responsive on the throttle has me constantly backing off the throttle to slow the bike down and get back to the speed limit on our speed camera infested roads here. A sure sign to me that positive progress is being made.
This week I have repeated the two tests from last week during my commute and while each time the engine was a bit hotter than normal it was never to the extant of last week. Last week was full of pretty good weather and this week has been heavily overcast and raining so that has played a part. The engine still showed signs of being lean in the midrange and that will only become worse with the colder weather of winter approaching so on the weekend I'll take a long runup and a bench grinder to the needles to add some taper to them ;)
Happy times :)
For a visual representation of how unscary and undangerous this is have a look at the vid I linked to early in the thread. All that's needed is a bit of patience and a medium level of coordination.
Cheers
;)
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. :hithead:
slide rising correctly in proportion to the air volume and corresponding needle profile is preferable. That's what you get stock. But when you screw up one thing, the whole system is out of balance and then you'll be chasing every other thing trying to get it to work wack-a-mole style.
OP solved a problem that didn't exist, created new problems, and now is trying to solve them, calls this "improvement". Maybe more charitable to say the OP misdiagnosed a problem and applied the wrong solution and now is in the spin cycle. Happens all the time with carburetors. I have done this myself many times.
It's hard enough with modern gas to keep stock carbs working correctly, and the easiest way to get them working right is stock.
Quote from: Henrico123 on February 21, 2021, 05:35:50 AM
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. :hithead:
Your '91 was built before Suzuki had to start tuning the carbs for emissions instead of ride quality so this mod won't be necessary for you.
It's not about fast moving slides just a faster moving slide in my 2009's carbs. Smaller holes in the bottom of the slides for less vaccuum to lift the slides, a stiffer spring to slow the slide lift and a needle with bugger all taper means less fuel entering the engine, 2009 emissions levels met and crap throtle response...
If the early 90's carbs were 34mm instead of 33mm I'd just throw a set of them on.
Cheers
Quote from: mr72 on February 21, 2021, 06:13:03 AM
slide rising correctly in proportion to the air volume and corresponding needle profile is preferable. That's what you get stock. But when you screw up one thing, the whole system is out of balance and then you'll be chasing every other thing trying to get it to work wack-a-mole style.
OP solved a problem that didn't exist, created new problems, and now is trying to solve them, calls this "improvement". Maybe more charitable to say the OP misdiagnosed a problem and applied the wrong solution and now is in the spin cycle. Happens all the time with carburetors. I have done this myself many times.
It's hard enough with modern gas to keep stock carbs working correctly, and the easiest way to get them working right is stock.
It's like you haven't read anything I said...
Cheers
Well, I do have you on 'ignore'.
But what you have said is just wrong. So there's that. That's why I put you on 'ignore' in the first place. This thread is actually kind of funny because to me it looks like a weird conversation of nothingness between three or four people I have on 'ignore'.
Quote from: Henrico123 on February 21, 2021, 05:35:50 AM
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. :hithead:
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.
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
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.
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.
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.
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 ;)
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!
Thanks for the kind words Guru :)
Quote from: sledge on January 23, 2021, 07:58:58 AM
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 :dunno_black:
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 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.