Carburetor master needed

[Kowl]

Greetings fellow forum members. I'm seeking some help with the bst33ss carbs that came on the 1992 gs500en I'm trying to get running right for somebody.

They promised me a good condition 01 gsxr750 if I can do it. I saw it and I want it so bad despite nothing gets power when you turn the key on. He said it was fixed before by replacing the main fuse in the starter solenoid but he had someone else do it and doesn't know about it. It's now doing the same thing again so he offered to me as payment for finding him main air jets for an Cr special 37mm carbs AND if I could get his GS500 running. Found the jets for his drag bike but I made the gs500 run worse 💩

The first time I was there we struggled because I just kind of allowed the owner to show me what they know. The bike would rev to 7,000 rpms if it would even start. After a little bit I noticed there was no throttle play. I checked the cable at the carb and sure enough it was set so closed throttle position was actually making it rev up on start up. After I set that the bike ran alright but a little weak like it needed cleaned and balanced. He wanted to play with the idle knob but I said don't bother it needs a clean and balance so I took them home and rebuilt them. Had to reuse the needle jet and starter jet/choke plunger because those parts were not an exact match. The bike will now only run on choke and through refurbishing the carbs I discovered the pilot jets are not found on any Keihin or Mikuni I'd chart. They look like Mikuni vm pilot jets but are not stamped and have a bleed hole in the top slot area but vm Mikuni carbs (and others) don't have a bleed hole in the top of their idle jets. It has the lunch box and 150 mains. That unstamped jet that looks like a vm series pilot is not the correct one for bst33ss carbs but it did work initially. He keeps pouring gas into the fuel hose because there's no tank on it yet and it comes out of the front of the carb sometime. Plugs keep getting blackened when checked but not wet. The needle was shimmed with two washers and the throttle plates were off a little. After perfectly refurbishing them and balancing the throttle plates and setting them to bisect the foremost idle hole as a starting point it should be like all the other cv side and down draft carbs I've done. Warm it up and idle drop it. I've swapped 142 mains in, aftermarket needles that are skinner and sharper, tried each position and checked and rechecked everything. Checked for vacuum leaks, and have the primary carb vacuum hose plugged per the manual instructions for starting after a carb rebuild if the tank isn't on. Only thing I have not done but will be doing when I get them in 1-2 more days is try using #40 Mikuni pilot jets for this carb. I forget the series number. I am very desperate at this time and about to order new floats out of my pocket too because I really want that gsxr he promised me.

The floats are at 14.6 mm or just over half an inch when tilting the carbs so the float tang just barely rests on the needle valve pin. When the bike would warm up with full choke it would do that back spitting out of the carbs that will actually make them shake sometimes. Some people call it backfiring but there's no flame when this bike does it. I had a bandit 1200 that did the back spitting during warm up and hard acceleration and it was the intake boots but it's not the case here. They are not cracked up and besides the bike ran almost good enough to ride after initially just resetting the throttle play but it was a little weak of an idle. But at least it could idle with no choke and you could rev it up like normal. It just didn't instantly rev up like a brand new bike. There was a split second hesitation during the throttle snap before it revived up. He got the bike with a spare set that was lacquered up frozen solid. I redid those and tried them with the same results. They have 142 mains in them though.

The owner does things the book says not to like open the throttle during start up or before the engine gets warm but that's the only way it was starting sometimes. It acts like it won't get gas during idle now but the plugs keep coming out sooty but not wet. I already know jetting up to #40 pilots is not going to solve the whole thing but I'm hoping it will at least get it to idle without choke. I have tried the pilot screws it came with and the replacements at 1-6 turns out and none of it made it idle without choke. Each time I came over I started at 2  turns out and worked to 4 which is where I found them to be originally turned out to.

The spare carb sets pilot screws were turned out to 2.5 but like I said neither set of carbs or any configuration of needle position or # of shims for the needles that don't have slots will get the bike to run like I've done with many other cable and cv carbs. I'm stumped and don't want to give up but completely defeated at this point. I am accepting any advice or criticism like if it's not broke don't fix it but the bike really wasn't good enough to ride before I did any carb cleaning. It was about 90% I'd say and most people would've ran it but it wasn't running 100% so I did the carb. The spare set of carbs had the bowls with the drain screws facing each other and I knew that couldn't be right because you'd barely be able to get at them while on the bike that way. So I switched them during the refurb. There's also some weird toggle switch on the left handlebar control that's labeled start and race lol.

Please help he mentioned he's going to move the gsxr to his son's house and I feel like I will lose the opportunity although he's already said it's my bike because at the end of the day it's not yet and it's not in my name. I have pics but it's not allowing over 500kb for some reason.

Sidenote I youtubed gs500 backfiring out of carbs and found a video where they sneezed until they shat the bed and popped off the intake 🤣

[ShowBizWolf]

Welcome to the forum!

The lunchbox is notorious for being a pain. I've come across several instances where people ditch it entirely and go back to the stock airbox and filter to make things easier.

Not sure if this will help at all but it might be worth a look (specifically the tables that start about halfway down)...
https://wiki.gstwins.com/index.php?n=Upgrades.Rejetting

Pictures are most successfully shared by hosting them on another site (like imgur for example) and then using the Insert Image button (the one above the emojis that has a little Mona Lisa pic on it).

Have you got a linky to that video you found? 

[Kowl]

Thank you and here's the link. Watch til the end for a chuckle. This person said in the comments he just turned his pilot screws out a little to solve his problem. I have tried starting at 2 and 2 1/4  but have been to every setting up to 6 turns out lol
https://youtu.be/z_NJedqUXg0

I checked that jetting/mod table and the way I found the first set of carbs was pilots were at 4 turns out and missing the orings and 1 of their washers. It wasn't stuck inside it was just not present. 150 mains. Unstamped idle jets that look identical to ones used in Mikuni vm/tm/tmx carbs yet they have an extra bleed hole in the top of the jet near the slot. 2 washers under the needle that I'm guessing are #4 washers. He never rode the bike like it was. Just bought it this way and couldn't get it to run so he took the carbs off to look inside the bowls that's all. He put it back on and when he did he had the throttle cable tightened like a screw instead of set in the correct place then locked with the nut. His throttle plates were open so I guess I should've just left it alone after doing the free play reset. But a cable adjustment honestly isn't worth enough to accept a 2500 dollar bike for fixing a simple mistake and ordering him main air jets through sudco. Now I'm desperately trying to get these carbs to work at least close to how they were when all I did was fix the throttle cable. I even sealed all the tiny pipes at the joints with a dab of fast drying super glue. The choke circuit and vacuum port balancing pipes because they can leak apparently and cause a vacuum issue. No glue was out in the pipes just around the joints.

It's a cool bike that someone was racing or trying to race because it has a track body kit and strange mods like the extra on/off toggle switch on the left handlebar that says start/racing hand written on it lol. It does nothing that I can tell but is wired into the right handlebar switch. The bike sparks like a mf so I don't think it's anything with that. .

What I'm not getting is I put the carbs back how I found them (excluding reusing the old needle and seat) before cleaning and even that didn't get the slightest improvement. This bike does have an unrestricted pipe on it. I didn't check if the exhaust collector/header was stock or aftermarket. The only carbs I could never get to work 100% besides these ones were on a cb650c 1981. I could get it to run fine beyond idle speed but not idle well and tried everything with it. Now I'm literally stumped by these carbs and can't get it to do anything but run on choke. It will start right up on choke now but before it warms up enough to see if it will idle without choke he starts opening the throttle plates with the twist grip full throttle and then pouring gas into the main fuel inlet hose until it squirts out the right hole in the air side of the carbs which I believe feeds air to the needle jet. I tell him to stop and feed it fuel a little at a time then try starting but he thinks it needs that much fuel to run.

He treats it like the kz1100 drag bike he has with crs carbs that I had to order main air jets for. That bike really will suck down a quart of gas in a moment or two with a few redlines like he was doing. The only thing left I can think of doing is starting over with new floats and size 40 idle jets. Perhaps those unstamped vm looking idle jets are size 40 but they don't say and it didn't work any better than a size 37.5 idle jet that I know is the right dimensions along with turning the pilot screws out half a turn each start attempt starting from 2 turns out. He said he is confident I will get it but I've been there 4 times now and barely moved a sliver back towards how it was when I reset the throttle play. It was slightly weak and seemed out of balance but it would idle on it's own and rev up decently clean... unless that's just because he kept pouring so much gas in that it wasn't actually working off the main and idle circuits but was just choking down gas from the air side of the carb as it pooled in the carb body. I don't think so though because it ran well enough that most people would think it was good to go.

He said he would sell the gsxr to me for $700 because he likes me then I said I could do $700 and he quickly responded that he wants my help and time with his project bikes...I still would but let me secure that minty 01 gix first please lmao. I don't want to give up because I'll look like more of a loser than I do now.

Oh and if it helps I looked inside the intake and the valves are completely black with a lot of build up on them.  Have not done a compression test or anything like that because it ran like it just needed a clean and balance when I initially fixed the cable.

[mr72]

Do a compression test and put the original airbox back on before beating your head against the wall anymore, IMHO.

See my signature for basically all the info you need.

Those jets are not hard to find. There's a sticky post somewhere here with links. Buddha will sell you the right jet kit for the setup for less than you can get them for building a kit yourself, and if you haven't screwed something else up, they will work.

[Kowl]

Thank you and sorry for any confusion I created by talking about irrelevant things. I ordered this gentleman main air jets for a set of keihin cr special carburetors that are on a kz1100 drag bike. His were missing and that was just the easy objective and only available through sudco because the guy is the only one that imports the specific long hex head main air jets for those carbs.

I will do a compression test but as I said the bike ran almost good enough to run and ride when all I did was reset the throttle cable slack because there was none and the throttle plates were being held open. I should've left it at that and taken the gsxr home as payment but I felt like his GS500 carbs would be perfect after a clean and balance. I know just because I've done this exact thing many times before with success doesn't mean I didn't mess up somehow but I did what I always do. Disassemble, dip, blow dry and assemble. Balance the plates with the service manual method and then put them on the bike for an idle drop and final balance adjustment if need be. I couldn't get any further than warming the bike up with choke because something is wrong besides the fact the owner keeps opening the throttle plates and pouring gas into the fuel inlet so much that it shoots out the right hole in the air side of the carb. This means he's filling the bowls with so much gas and pressure that it's rising up through the main jet tube and squirting out of the air hole that feeds air into the main jet tube.

Clearly somewhere I did something that's causing a vacuum leak I think because it will only run on choke and carbons up the plugs if he gets any revs out of it. The carbs were set up how the forum recommends when all that's done is a lunchbox and open pipe. 150 mains (unstamped idle jet that looks like a vm series idle jet) pilots 4 turns out (some say 3 out) 2 needle shims and that's it.

I will wait for more advice because I don't think I need any jets. I have two sets of stock and one set of 150 and one set of 142. I have stock idle jets and #40 idles on the way. Idk what to do but I will check compression today or tomorrow.

Oh and yes I came across your links when I began searching for troubleshooting information. Everything you mention has been checked over many times and yes I am going crazy but I know it's carburetion/vacuum related because it ran okay for most people when I just reset the cable and I knew it could be better but I've made it worse.

[ShowBizWolf]

This should help you with posting pictures. I'd be interested in seeing some pics.

http://gstwins.com/gsboard/index.php?topic=15370.0

[Kowl]

Thank you. I need help bad lol. Maybe it's the float height. Some say when the float seam is level with the bowl flange it's right but that would not be 14.6mm from just making contact. Float tang to needle pin. It ran like it needed a carb clean once the throttle play was set correctly. Last carbs I did before these were a bandit 600 and 99 R6. They worked great on start up and idle dropped to perfect idle after warming up the bikes. I have done many side and downdraft cable and cv carbs but got something messed up I keep overlooking I guess. The cr37 special carburetors I had apart ran his kz1100 drag bike and that thing was bought from a shady seller in unknown condition. The bike acts like it's not getting fuel from the idle circuit but you can clearly see fluid exit the pilot holes from the well in the bowl and if you squirt something through the left hole on the air side of the carbs. You see it rise in the 4 idle holes behind the throttle plate and the one idle hole in front of it. It must not be getting enough air into the opening to make fuel flow up and to the idle holes. Through a combo of choke and throttle twisting the owner has gotten it to rev up but it mostly lean bogs. Or at least that's what it sounds and acts like but when removing the plugs they're covered in soot deposit. Idk what's going on.

This bike ran and revved before doing the carbs. Just not 100% clean and crisp.

[The Buddha]

Those bleed style pilots dont work on any GS, pre 00 had non bleed, 01+ have a completely different type of pilot.
Cool.
Buddha.

[Kowl]

I see well they did work pre removal and cleaning of the carb once I had reset the throttle cable play during the first visit. It had the throttle plates half open lol. Thank you for your response and I have #40 arriving by the 13th. All the reading I've done says this bike actually needs to be ridden with choke for several minutes before it's considered warmed up all the way and able to be adjusted for proper idle speed and pilot screw settings. This is probably still true with jetted and modded air/exhaust mods right? And notice the bleed hole on top of the idle jet screw slot area. No Keihin or Mikuni idle jet that I could find on their charts have that bleed hole. I knew these idle jets were not the correct dimensions and they're not stamped at all. I checked with a 40x loupe for markings or etchings.

I never get more than a minute of running on choke and the pipes start to get hot before the owner starts to force fuel into the carbs making it shoot out the needle jet air feed hole. Do the float heights look okay or did I maybe measure wrong?

Also his other set of carbs had 37.5 idle jets of the correct series (dimensions) in them and I used new 37.5 idle jets of the correct series when refurbishing them. If they wouldn't work because it's stock size (apparently one size too lean from factory) and because the bike has airbox and exhaust mods then I'd understand. But I had those pilot screws 6 turns out at one point for both sets of carbs, with correct idles and the other with incorrect and it just would not idle even a little bit. But the most time I got with it running on choke to warm up before he starts forcing fuel in is only a minute or so. I feel like during my warm up and idle drop procedure he keeps fouling the plugs making it even more difficult to see if it will idle.

Every Suzuki I've ever had or worked on could throw a spark with an electrode literally worn down to nothing and the plug could be fouled up. It seemed the ignition on those Suzukis did not gaf lol

[Kowl]

Could someone tell me how the bowls are supposed to be put on please? I had two pairs of carbs. The ones that were on the bike had the bowl drain screw heads facing outwards. The spare set that was lacquered frozen had the bowl drain screw heads pointing inwards towards each other. And in a lot of videos available on the internet it shows the bowl drain screw heads pointing or facing to the right side of the bike. The manual only shows the left side bowl with it's drain screw head facing outwards or to the left side if your sitting on the bike. I didn't do a compression test because I didn't buy a tester and the owner doesn't have one. The bike seemed to idle and rev OKAY once the throttle cable play was reset but now only runs on choke after a clean and balance. It ran on only one cylinder for a minute last time I was there and filling the bowls so before they both filled and ran together He forced a bunch of fuel in the carbs and the plugs keep coming out black. He also doesn't have the stock air box unfortunately and that's probably the only good suggestion given here. Both carb repair kits had different pieces that were not identical to bst33 carbs. One has different needle and needle jet tube as well as starter jet. The other had the correct needle jet tube but not the correct needle and of course a different size starter jet again. First was too long the other was too short so in both carbs I had to reuse the parts that didn't have an identical replacement. They were starter jets, needles (both carbs had stock needles but one had grooves. The one without grooves had 2 shims) and one needle jet tube.

I'm asking because of the mismatch visual examples available in write ups with pics and how to videos. And because two pairs of the same carbs had them opposite before I worked on them. Just looking at them it seems they should be mounted with the bowl drain screw heads facing outwards for easy access and even though they can be reversed it seems this way is the correct way but I'm not sure due to the various ways they're shown in write ups and how to videos. Half of them are incomplete anyway and don't even show removal of slide valve support and needle jet tube. I doubt this is causing the problem I'm having of it only running on choke and barely being able to rev after getting hot but I still want to know what's the right way.

Hopefully a master of these carbs and bike doesn't mind being a hero by sharing the correct information and some problems that might occur but aren't the normal issues with a failed clean of bst33 carbs.

[The Buddha]

TL;DR. The drain screws face outwards.
Cool.
Buddha.

[Kowl]

Thank you for confirming that for me.

I did get the bike to warm up enough on choke to where it would rev to any rpm but if you cracked the throttle hard and fast like the owner was doing it would not settle to the correct rpm. It would dip low getting weak and stall. Mists of gas were puffing out of the lunch box but it was revving up good and almost idling correctly.

I think the biggest change was the owner was preoccupied with another guest and I was able to warm the bike up for a long time on choke and the only one controlling the fuel to the carbs. I was able to give it tiny amounts at a time as it warmed up. But as soon as he saw it was almost idling right and revving up a little he came over and pegged it redline and repeatedly revved it hard. It started running out of gas so he squeezed a bunch of gas down the carb inlet hose and flooded it then it stalled out and wouldn't start back up for awhile. I looked in one cylinder with a light and saw what looked like a fresh triple chocolate brownie layer on top of the piston which was visibly wet. Hydro locking to some degree due to gas flooding the carbs and pouring down the intake into the cylinder? The plugs came out wet but much cleaner like a Carmel color with no black sooty deposits.

I'm transporting it to my garage right now to work on it alone and hopefully get it running right by Sunday evening. I will be doing the compression test today since I have a tester now. I'll also use my vacuum sync gauges today that I've had for years but never used to see if I balanced the throttle or butterfly plates well like I think I did.

I got 125-130 on the left cylinder and 130-140 on the right cylinder. I keep getting random no ignition on both cylinders. I used a cheap advance auto tester then borrowed a matco from my neighbor. I was not able to get the engine fully warmed prior to the test and the carbs were off instead of having them on and opening the throttle.

Sometimes the right fires and heats up and sometimes it's the left. If you let it run long enough the cylinder that won't fire starts to ignite but then cuts out again.  I put dpr7ea9 plugs in to see if that would do anything and it didn't. The right one is the one that decided not to fire today. But only a few times did  it run on both cylinders for a few seconds.

I also found that the floats would hang up a little bit. The tube or base of the float assembly has two arms that seem bowed out a little and make the actual float part not drop down all the way as if the bowls were empty unless you tap the side of the carbs sometimes. I floated the floats and they float lol. I got se 4mm clear tubing and checked the fuel level after I think I primed enough gas into the bowls. Left side was about 3/8" under the bowl flange/seam and the right side was about a half inch under the bowl flange. If I held the hose up too tight the level would go even lower. Never had the much trouble and I'm doubting that the bike would've actually run good enough to ride if I had just left it alone. I think it was just so full of gas and kept having it forced in that it seemed to run because it was borderline flooding to flooding during the first visits. I'm gonna order floats I guess and I have a hand drill bit set for jets but the closest idle jet bit I have to #40 is #50 lol.

I did not hook my vacuum gauges up yet because I haven't got it to idle yet today. I have been keeping the idle stop screw all the way backed out so there's a slight gap between the screw and throttle actuator. It starts easier on full choke this way. And when I was able to warm it up without interference last time it's how I had it almost idling on it's own but the owner flooded it while I was trying to finish warm up and idle drop/pilot screw settings. I know I have to ride it to be considered fully warm but I'm not able to because idk where his seat is and the brakes are a bit sticking in the back. Plus I can't get his tank open to clean out and try using on the bike because his only key does not open the lock. It goes into the cylinder though.

I don't want to give up but I might have to move on to a gs750 drag bike he picked up.





Right side

Left side

[Kowl]

I got it. One of the carbs floats are shot they can't be adjusted to work right because the base of the two piece has bowed out arms that won't allow the middle float part to operate correctly 100% of the time. It comes slightly dislodged and stays down causing flooding and sometimes it goes crooked and sticks up only allowing a fraction of necessary fuel to drop into the bowls apparently because I have one set of carbs working perfectly now. The base arms do not bow out so much and the pegs on the middle float actually stay in their holes better as it travels up and down.

Main is a 142.5 with #40 pilot jets and pilot screw are 3 turns out apparently. Needle position on stock needle copy with grooves is one up from the bottom. I think I will raise it one more notch because I suspect sudden and wot throttle revs would become a little faster/smoother. They sound almost lean strained as if it's close but needs a hair more fuel from the main circuit. I did not check with the vacuum gauges yet but it could be throttle plates are slightly off.

Before I fixed the problem I got the engine warm enough to get 125 psi from both cylinders with a cheap advance auto gauge and a matco gauge borrowed from my neighbor. It came out to 125 on both multiple times with both gauges after I had a little user error at first. Had leaks. I did it with the engine warm and throttle plates open. And also engine warm with the carbs off. If I was reading the correct free online manual it said 1989-2000 should be between 149-200 psi. Good universal psi from what I'm aware of is about 140-150 at the lowest but I'm aware engines can run okay with less.

Does anybody know if 149-200psi is the correct range for this era gs500? Sounds high to me even for a 0 mile one. I'm assuming the number given is for new engines not the average or good used engine value.

I tried to put a video on imgur so I could move it here but it must be too big or something. No offense but this forum is annoying due to the host pics on another site thing. No actual comprehensive help. Just a jets sales pitch and go back to stock when I mentioned this is someone else's bike and I came here because I was stumped. At least I got a confirmation on the bowl screws. Compared to other motorcycle forums this one absolutely blows because of those reasons however I can see some absolutely love it which is cool. But I didn't really get anything out of it.There was no good information here on Mikuni bst33 carbs and no useful advice given so it was kind of a waste of time to join this one for help.

[The Buddha]

The float - Your description seems a little crazy, but I'll check if I have a spare. Your pics are huge, I cant make out what they're showing.
Anyway the bike will run with 125 compression and run rather well too. Just watch oil consumption. You really didn't get it as hot as it will be under full operating temp I'll bet. Also a screw in gauge will get you more accurate than the press on gauge.
Cool.
Buddha.

[Kowl]

I said I fixed it in my last post. I do apologize to any readers though because I do try to relay a lot of information and in detail so sometimes I misspell or lack proper punctuation. Sometime autocorrect errors slip by the proof read too.

Anyways I have the bike running excellent now and finished cleaning two tanks for it. I am thinking about bypassing the frame Petcock to save myself the headache of trying to find rebuilding kits. A brief scan of the forum shows it's a p.i.t.a affair. Is it okay to run tank petcock only if it works well? Which I suspect the two I have don't because they came out of lacquered tanks. A tiny dribble from each in the off position means it's not okay (tank tap) and I haven't vacuum tested the tank fuel taps. They may leak gas without vacuum for all I know. The owner does not like the idea that at least one tank will need a new fuel tap. I already had to replace the gas cap in the worse tank because it was oxidized and lacquered frozen.

Sorry about the pics I don't know why they were so big. I saw other posts like that and thought it was normal. This is the only forum I've been on like this so far and having to host pics remotely. It is frustrating I apologize. The only bright side is they're pretty clear I think.

I appreciate advice like you've just given it's more helpful.
It is running well now but I agree although it now easily starts and warms up and indeed got pretty hot, it's probably not quite the same as if it's been ridden around then idle dropped and a/f mixture screw adjusted. There is the tiniest delay during the decline of rpms after throttle snaps/revs. Not a hang or pause or anything and it's hardly noticable. But I wonder if it's a little more mixture screw adjustment needed or possibly the needle needs to be one position higher (so clip must go one spot lower which will be the lowest and it's a stock needle copy but has grooves like an aftermarket) to take care of that barely noticable delay as the rpms reach the lower side close to idle. It's not your typical lean hang or idle screw turned in too far when warm.

Anyways the plugs came out a light and even tan/Carmel color on the flat end of the threads and no staining on/in the center around the insulator I believe it's called. The electrode and the top of the plugs were very clean. But maybe it could be a little darker in color because like I said it's a very light tan color almost a hair lean looking. Also the plugs are the dpr8ea7. At least I think that's the "hotter" plug option for the engine. Also I think it shares the same floats as some gsxr bikes so I would order floats in sets of 4 if I wanted some which I kind of do.

[Kowl]

How do these look? $hitty? Clean, too lean? The tank took some damage. Sorry quik chix🙁 at least it functions again and cap works nicely.

[mr72]

inside the img tag you can set the size with the 'width = 400' parameter. set the number of pixels in width.

like this:






Please do this