Hello, all. First post on this forum. I've scoured this forum and the 'net generally for a solution for this problem, but no luck.
Long story short, I purchased a GS500 a few weeks ago for $200.
Sticker on frame indicated build date of 08/89, so I'm guessing it's a 90 model.
Came (mostly) complete, two gas tanks (one rusty, one dented), 2 sets of carbs (original BST33 plus a later model one with more lines and a throttle body sensor/dual throttle cables) and a few boxes of parts and the Clymer manual.
The bike did NOT run when I bought it, but for $200, I thought it would be an interesting project.
Before I do anything else with the bike, I want to get the engine running properly.
The immediate problem is the engine will not rev beyond idle.
It will start (full choke), then settle down to reasonable idle. Both exhaust pipes get hot.
Applying any throttle, it stumbles like mad and eventually dies, but it will not rev up at all.
I've disassembled and cleaned the carbs several times. Jets are 37.5 pilot, 127.5 main, 3 turns out, no washers.
The plugs were very black when I pulled them. Spark plugs cleaned, gapped, and checked - good spark on each cylinder.
Compression OK - 120 PSI each side.
Replaced O-ring on intake boots and added hi-temp gasket seal outside the O-rings.
Having pulled the carbs off and on about a dozen times, I'm running it without the airbox for now, for convenience. Gas tank is off too, so none of the fuel or vaccuum lines are connected; I'm using a small "auxiliary" gas tank while I troubleshoot this problem.
I've yet to check the valve clearance. However, odometer indicates 19k km ( ~12,000 miles) on the bike.
I haven't cracked the ignition cover, I'm hoping no previous owner screwed around with the timing.
I can't fit the "later model" carbs on the engine, due to a "bump" with a bolt on the right side of the engine block, with interferes with the TBS mounting bracket on that set of carbs.
I'm heading to the shop to take the carbs off and clean them (again), just in case I missed something the previous three times.
Thanks for reading, and thanks in advance for any guidance.
Cheers.
In my short time here, this seems to be one of if not the most common problem. Cleaning the carb won't fix old, crusty, leaky, missing O-rings. Spend a few bucks and do a proper job of replacing the rubber bits to seal things up the way they should be.
Clean and inspect the diaphragms and slides thoroughly. Do NOT use carb cleaner on them. If the diaphragms have any holes in them, they'll need replacing.
Verify the float heights also. You can do this with a 6 inch or so piece of aquarium air tubing attached to the bowl drain. Hold the other end up to the side of the carb and open the drain valve. The fuel level should settle at or just below the bowl gasket when on the center stand.
Sounds like you have the proper jets for a stock setup. But it's running rich or possibly only on the choke circuit. The blackened spark plugs are evidence of that. Float height or leaky needle valve will definitely cause that. I fought the same problem myself recently.
Don't worry about the other stuff until you get the carbs sorted. The valves, ignition, etc, are all working well enough for it to run (poorly at the moment). You can deal with all that later. I just read today that The Buddha here sells the carb kits you need. Wish I had known that sooner.
Good luck and welcome!
Quote from: Coltrane on September 03, 2018, 09:10:32 AM
The immediate problem is the engine will not rev beyond idle.
It will start (full choke), then settle down to reasonable idle. Both exhaust pipes get hot.
Does it "settle down" when you turn off the choke? How long after starting?
Quote
Applying any throttle, it stumbles like mad and eventually dies, but it will not rev up at all.
Since you have it all apart, observe the slides. Are they coming up when you apply throttle? If not, then that's why it's not revving. Diagnose (vacuum leak, torn diaphragms, stuck, etc.)
If the slides come up, then I'd guess very low floats. Maybe clogged pilot jet or pilot jet fuel passageway.
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I've disassembled and cleaned the carbs several times. Jets are 37.5 pilot, 127.5 main, 3 turns out, no washers.
Hopefully you didn't spray carb cleaner into them with the diaphragms in place...
QuoteCompression OK - 120 PSI each side.
This is actually pretty low. Spec is 160psi IIRC. but the bike should run anyway, either just be very low on power or refuse to run when hot.
Quote
Replaced O-ring on intake boots and added hi-temp gasket seal outside the O-rings.
IDK why you added a "gasket seal", but it's not necessary or recommended. Those intake boot o-rings will seal fine unassisted.
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I've yet to check the valve clearance. However, odometer indicates 19k km ( ~12,000 miles) on the bike.
I haven't cracked the ignition cover, I'm hoping no previous owner screwed around with the timing.
Doubt those are related. Likely fueling.
Quote
I'm heading to the shop to take the carbs off and clean them (again), just in case I missed something the previous three times.
Check that the slides are coming up before you pull the carbs again.
And maybe give this a look: https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html
Thanks to both Kilted1 and Mr72 for replies.
Let's see.
1. I ordered two Elaborate Service carb rebuild kits yesterday from the "Carburretor Shop"
http://www.dellortoshop.com/contents/en-us/p1779_Elaborate_Service_Kit_for_Mikuni_BST_33_carburetors.html
Should be here in 10-21 days. Kits have
Rubber (Viton) Float Chamber Gasket
Needle Valve Set
Main Jet # 140
Idle Jet # 41.3
Needle # Y430 = 5E94
Needle Clip
Needle Jet # 584 0-2
Mixture Screw Assembly
Various Washers and Rubber (Viton) O-Rings
I expect the larger main and idle jets will make the mixture richer, but I hope to eventually ditch the airbox and go with a K&N lunchbox. However, that's way downstream. I want to make sure the engine is running well in stock kit before I start changing anything. Had I known about Buddha's carb kits yesterday, I would have contacted him to order the necessary parts.
2. when I disassembled the carbs, I cleaned the parts in an ultrasonic cleaner with pine sol, cleaned with distilled water, guitar wire, and can of compressed air (the cans of stuff they use for computer cleaning, not shop-level pressure off my compressor.) Never took carb cleaner near any of the rubber parts. Diaphragms look good - flexible but not punctured anywhere.
3. When I apply throttle, the slides "flutter" up and down rapidly as the engine stutters very very badly (to the point of stalling).
4. Measuring the floats, they appear to be at 15mm. I'll grab some aquarium tubing to check the level. However, that will have to wait until the rebuild kits arrive and I've installed them.
5. The idle "settles down" after about 90 seconds, with choke nearly, but not completely off.
6. re compression, Suzuki service manual (pg 3-1) indicates "standard pressure" should be 142-199 psi with the engine warmed up. However, as I haven't run it for more than 3 minutes at a time, I'll re-test the compression when the carbs are rebuilt and the engine runs properly.
7. re the "gasket seal", I read somewhere that with older intake boots, if the are getting old and brittle, they can leak. Recommended solution was to add a high-temp gasket seal to supplement the o-rings.
Thanks again for the thorough replies. I'll update in a few weeks after I've rebuilt the carbs.
Cheers.
First , those jets are probably too big in the rebuild kit. Try and make it run with the stock jets first. One problem at a time.
Secondly, a properly tuned GS will not idle easily off choke after only 90 seconds of running while parked. I suspect your idle mixture is actually way rich and idle speed set way too high and maybe the stumble is because it's way too rich. Maybe try backing the pilot needle to 2 turns out and loosen the throttle stop (idle speed) all the way. Don't take it off choke when you run it and see if it'll rev in that case. Don't worry about idle mixture and speed until you can get it working well enough to ride on the road for 15-20 minutes.
Mine idles quite happily off choke indefinitely :thumb:
I guess the carb specialist who cleaned and overhauled them a few months ago must have done something wrong!
You really do talk some rubbish
:D :D :D
Quote from: sledge on September 05, 2018, 11:21:15 AM
Mine idles quite happily off choke indefinitely :thumb:
On a cold start?
(https://i.imgur.com/AbUWe1d.jpg?fb)
Quote
I guess the carb specialist who cleaned and overhauled them a few months ago must have done something wrong!
You really do talk some rubbish
:D :D :D
At no point in this thread has anyone said that a carb specialist overhauled the carbs...
Who's talking rubbish now?
sheesh.
I CAN'T EVEN FREAKIN' TRY TO HELP SOMEONE OUT!
to the OP, if you want me to help you, I'm all ears. Unfortunately there's someone who thinks he's so smart that nobody else should be allowed to help anybody, so I'm going to get off this thread and you can contact me via direct message.
C'mon chaps. A bit more politeness / humbleness goes a long way in forums.
Thanks.
Hi, an interesting problem is your fuel level in float chamber correct? How many km on the bike?
As I understand it, if you have a vacuum leak on the intake manifold, the idle will be all over the place. So might not be that. A diapragm leak creates an artificial maximum throttle position (small leak, can almost reach max rpm ; larger leak can only reach 1/2 rpm, etc). If there is a very large leak the diaphragm would never rise off idle. BUT, opening the throttle would not cause stumbling/dying. This is because if the slide never rises there is no more air allowed than at idle, and the fuel mixture, which is governed by slide position, would also remain unchanged.
+1 for watching the slide rise /oscillate, but I suspect that the slides are rising and that for some reason your mixture gets super rich as soon as the needle jet takes over the fuel mixture control.
I would look very closely at the needle/needle jet to make sure nothing has been "modified" or worn and all is stock and to spec. I have managed to track down the part numbers of the specs of the needle jet if you need them.
Your black plugs supports this "too Rich" theory.
PS can you post a photo of the "bump" preventing you from installing newer carbs? I thought that they should fit.
Good luck.
Quote from: Coltrane on September 04, 2018, 09:40:07 PM
Needle Valve Set
Main Jet # 140 <------ Wrong for nearly any setup.
Idle Jet # 41.3 <------- Whatever the druck this is, if you remove it - its done for ...
Needle # Y430 = 5E94 <--- Needle cut to factory specs - well that's exactly what you have, and I would trust that more than this crap.
Needle Clip <------------ Yea we need a new clip. Sure we need that.
Needle Jet # 584 0-2 <------- We're getting 2 of these ? I thought it was 5E94 ? is this for the other carb ?
Yikes - you need a 125 mains and 40 pilots for a stock bike.
You said you have 127.5 - You sure its not a 122.5 ? cos 37.5/122.5 is stock US 89-00 size. 1 size over, with 1-2 washers under needle is what you need for a stock bike.
Now all buddha kit is all fine, except I cant find it (or its in my other house) or my dead truck, or my dead car or my container where I dunno where it is.
Cool.
Buddha.
Over the last 15 years I have said this many times and I am going to say it yet again.
There are many people in this forum who are desperate to help and offer advice but anyone looking for advice needs needs to focus on what is being said, not on who is doing the talking. Take the advice and use it as a basis for your own research.
I truly despair sometimes at the thought of people needlessly wasting time and money and compromising the reliability and longevity ofbtheir machines because they blindly accept what they read in here as hard fact and that the option presented is the only viable one open to them.
When I need to seek advice, not just in the engineering related issues I deal with as part of my job but in life in general I will ask the person concerned what makes them qualified and experienced enough to give me the answer I need. I only wish people in here would follow this example.
BTW if anyone wants to PM me for advice go right ahead and I will do my best to answer. However it will come with a disclaimer :D
Quote from: sledge on September 06, 2018, 08:38:27 AM
Over the last 15 years I have said this many times and I am going to say it yet again.
There are many people in this forum who are desperate to help and offer advice but anyone looking for advice needs needs to focus on what is being said, not on who is doing the talking. Take the advice and use it as a basis for your own research.
You say that, but then you say this right after:
Quote
When I need to seek advice, not just in the engineering related issues I deal with as part of my job but in life in general I will ask the person concerned what makes them qualified and experienced enough to give me the answer I need.
That's focusing on who's talking rather than the content of what they say. Plus, seems me that you always hyper focus on mr72's posts simply because he's the one posting them. You almost never reply so often and so strongly to anyone else. So, which is it? Do you really care at all about what is being said, or do you only care that people whom you've arbitrarily decided aren't as qualified as you are the ones saying it?
Quote
I truly despair sometimes at the thought of people needlessly wasting time and money and compromising the reliability and longevity ofbtheir machines because they blindly accept what they read in here as hard fact and that the option presented is the only viable one open to them.
Sure you do. :icon_rolleyes:
If that's really how you feel, why don't you actually offer some real advice? What, specifically, do you think the OP should do? To be clear, I'm not asking for a refutation of what others have posted, I want your honest opinion on what you believe the solution to the OPs problem is.
As expected, no parts yet, so the project is on hold until I receive the new o-rings and gaskets.
Buddha - thanks for the advice. I'll stick with the 40/127.5 jets and the factory needles when I re-clean the carb and install the new o-rings. I'll drop the other parts of the kit into my "I better keep this" box of stuff.
As for the "bump" on the engine, see photo, just behind the starter cover.
The "other" carbs are the later 3-jet Mikunis, with a few more lines on them and a throttle position sensor. It's a metal bracket on the lower right of the carbs that conflicts with the "bump". (I'll try to post another photo over the weekend with these carbs mounted showing the contact.)
Tiny pic. That bump has a big A$$ bolt on it - that ? I believe it was used during assembly.
127.5 may work if you have a pipe and a K&N in the airbox. Stock paper filter and stock exhaust, you need 125.
Cool.
Buddha.
HI,
IIRC, that bolt holds the neutral switch plunger in place. It should be nowhere near the carbs when you install them. Here is a picture stolen from the web showing the distance between the carbs and the bolt.
Maybe show us a picture of the bracket that fouls the bolt?)
Attached are three photos of the newer model carbs. They are snugged into the intake boots as far as they will go.
The last photo shows the bracket on the bottom of the right carb (throttle position sensor bracket?) directly on the head of the bolt on the engine. Although it just fits (barely), I'm not sure I want those two pieces of metal in direct contact all the time.
Hi, I've never used those type of carbs, I believe all that extra piping is for California clean air related issues. I believe they can be removed and plugged and that this is actually recommended. I think a search will bring up several hits. Hopefully someone who has done this will post soon and confirm.
Fourth photo, different angle.
I'd have thought there'd be no reason to keep the TPS unless you're also swapping out the CDI.
Hi all - I haven't updated on this for a while. It's been 6 weeks since i ordered a pair of carb rebuild kits (see above), but they are MIA. (ETA was 15-20 days.)
I know it's a noob question, but can anyone point me to a source for the proper o-rings to rebuild
(a) a pair of BST33 carbs (89-90);
(b) a pair of the 3 jet carbs for later models.
I have both sets of carbs, and as winter is setting in to northern Alberta, rebuilding both sets of carbs and getting the GS running would be a nice start to the winter project. Thanks in advance.
@Sledge,
The inter webs automatically come with a Caveat Emptor.
What I've always wanted to know is when starting with the choke, why it takes a couple of seconds before the rpm rises.
Quote from: user11235813 on October 20, 2018, 06:51:15 PM
What I've always wanted to know is when starting with the choke, why it takes a couple of seconds before the rpm rises.
I have also wondered this... :dunno_black:
Quote from: qcbaker on October 22, 2018, 05:28:29 AM
Quote from: user11235813 on October 20, 2018, 06:51:15 PM
What I've always wanted to know is when starting with the choke, why it takes a couple of seconds before the rpm rises.
I have also wondered this... :dunno_black:
I'd have to guess it is because it takes a second for the fuel to refill the bowls since starting with the petcock closed.
Quote from: mr72 on October 22, 2018, 06:58:19 AM
I'd have to guess it is because it takes a second for the fuel to refill the bowls since starting with the petcock closed.
That's possible, but I'm pretty sure it does the same thing even if I put the bike in PRI and let the bowls fill first. I'll have to check next time I ride lol.
interesting. I have never tried it starting on PRI.
Actually on my GS I sometimes have to bump the throttle to get things going when its cold. Then it tends to rev right up. It always seemed to me that the longer it had set, the worse it was, so I figured it was fuel depleted in the lines and bowls. But that's just a guess!
Quote from: mr72 on October 22, 2018, 11:55:53 AM
interesting. I have never tried it starting on PRI.
Actually on my GS I sometimes have to bump the throttle to get things going when its cold. Then it tends to rev right up. It always seemed to me that the longer it had set, the worse it was, so I figured it was fuel depleted in the lines and bowls. But that's just a guess!
I was gonna post about this earlier but completely forgot. I rode my GS to work today and I put it in PRI for a little before starting it, and the revs climbed to normal "choke on" levels much quicker. So, I think you're probably correct (or at least partially correct) about why the RPMs lag on cold start. :thumb:
The problem on your bike seems alike the one I have on my 17 y/o GS with 40+Kmiles, just for peace of mind, check sparks color, I found mine orangish before the plugs stopped sparking. For what I have reserched, on my bike the weak sparks won't fire up the fuel once there is much more than enough to idle. You don't even need carbs attached to test the plugs. Good luck.