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'93 GS Tune Up/Overhaul

Started by tmbr_wulf, July 12, 2012, 09:01:22 PM

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So, this post is partly to keep a running log of maintenance that I'm doing on my bike for my sake, partly to vent, and partly to just share with the community.  Maybe some other new people can learn a thing, maybe the experienced folks can get a laugh.

I bought my GS a few years ago but it wouldn't start one morning, riveting I know.  Being my first bike I didn't really know what was going on and I didn't have the space to work on it so it just sat around for a couple of years.  Now I'm getting around to performing the maintenance that it needs and finding out what was messed up.  I'll try to post some pix, but some of the work is already buttoned up.

Summer '11 [Jump in the Wayback Machine]
The bike isn't running, but I've got the itch to start ripping into it.  Since it wouldn't start in '09 I figured that the carbs were bad, and that's where I started.  I tore the carbs off and opened them up without a rebuild kit.  Everything looked clean, there were some flakes [or sand] in the bowls but aside from that the innards were spotless.  The outside looks pretty gummy but I decided to let that slide.  Being in a rush and wanting to ride I simply reassemble the carbs and pop them back on.  At the same time I put new fuel hoses [I'm now suspecting they're to small], and I had a damn hard time getting everything routed and remounted, but it happened.  Popped a new air filter in, and put the tank back on.

I also took this time to install an Automotive Fuel Filter.  Whoops-a-do.  While it doesn't seem to be a huge detriment, my suspicions are that it's not helping.  After all that, the bike still doesn't run well, it's probably because it has 4 gallons of old fuel in the tank.  Me not being prepared, and it getting late in the season finds me not really draining the tank, just trying to top it off with fresh fuel [instead of draining it or using Seafoam  :cookoo:.]  Long story short [too late] the bike doesn't run on the road in '11.

Oh, it gets a new battery too, because that was dead.  New plugs as well, these seem to help despite the bad gas.

Spring/Summer '12 [Present day]
ALRIGHT, LET'S DO THIS AGAIN!!!  So  I start out by draining most of the old fuel from the tank through the carb drains.  I then pop 1/3 can of Seafoam in the remaining gallon or two of old gas and it FIRES UP!!  She runs strong enough to ride down to the gas station and load up with fresh fuel.  Over the next few weeks I put a few hundred miles on it commuting to work.

Nows when I start getting serious about maintenance.  At the end of June I do an oil change [fresh 10W-40, filter, crush washer], and it did need it.  I'm also concerned about the super spongy front end which has clunked and bottomed out a few times, and it worries me when I'm running at highway speeds.  I read a bunch of stuff on the forums, BeerGarage, and elsewhere to get prepped for the fork seal job.

Being a '93, I have the easier damper bolt configuration and build the giant 5/8" "hex key" out of threaded rod, it costs less than $10.  Though it's recommended, I can't find new copper washers that will fit so I just reuse the existing ones.

Problems discovered during the Fork Seal Change:

  • Oil is really black.  Really, really black.
  • Fork seals have a touch of rust on them, and the retaining springs do as well.  There's a little bit of rust stain on inner fork by the retaining spring, but it doesn't penetrate.
  • The upper fork legs have some rust spots from rock dings.  A little CLR and some grit clean them right up.  The toothbrush I used was also used to clean bicycle chains, I think that's where the grit comes from and I think I'm going to remember that trick in the future.  It seemed fine enough to not scratch the uppers, but rough enough to get the light rust off.
  • One of the bolts for the front brake has been broken or lost, and was replaced with a hex bolt of appropriate size and pitch.
  • If you don't work on one fork all the way through you end up trying to "slide hammer" the fork seal out of the fork you DIDN'T remove the damper from.   :cry:

The reassembly is fairly straight forward.  Used 15W-40 for the oil, reinstalled the stock springs, and filled them up to -99mm down from the top.  The uppers weren't put back to their original positions because I lost my markings, but they are set back to the same height.  While the bike doesn't sag anymore, I feel the 15W might be too strong for my ~165 lbs. as I can feel the bumps in the road a bit.

I also decided to investigate a buzz that I heard in the gauges.  I tear those open and discover that the PO mashed standard cap nuts onto the metric posts of the speedometer.  I'm forced to destroy a nut in the removal process, and find out that the post underneath has been totally stripped.   :mad:  I need to replace the rubber under the gauges and either get a new speedo housing, or a die to re-thread the posts.  I also discover that PO made their own rubber stepped washers that mount on the back side of the gauges  :icon_rolleyes:.

Well, at least the forks are safer so I can ride it....  WRONG!  The bike runs like crap now.  I don't know if it was because it sat for two weeks, or the new stance is disagreeing with the fuel line/carb setup.  The bike won't hit it's previous 1200 RPM idle unless the choke is partially open.  NBD, I was planning on syncing the carbs anyway since the tank was almost empty and easier to move.

Holy (*#@, this is a whole 'nother can of worms.

Get the tank off and look the carb over with fresh eyes since I've been doing some studying.  The vacuum caps are homemade, by forcing a small hose over the cap and screwing a screw into that hose.  I guess it's...creative?!  So I pop some hose [$5 sync tool without a cross bridge] on the ports and I am caught way off guard!!  When I fire up the warm bike the right carb almost immediately sucks oil 2 feet up and into the carb before I can kill it.  Great.  When I fire up the bike again without the hose on it and touch the open ports with my finger tips I can feel the right one is pulling more than the left.  So much for riding this weekend...

So now I'm contemplating my next move.  I'm thinking of doing a full carb clean and rebuild with a kit.  The left carb can form a small drop of gunky gas from the carb drain.  And I know that I'm yanking that in-line fuel filter because that doesn't seem like it's helping my situation at all, it's probably best to just get it back to stock.

Question for anyone that made it through this rambling mess:  Is the vacuum difference that I'm noticing indicative of a bigger problem?  I haven't pulled the plugs yet to check their condition, and I haven't checked them for spark yet, I'll do that tomorrow.  My fear is that there's a larger problem like a blown head gasket or cylinder issue that I'd have to hunt down as well.  I don't have the tools to perform a leak down or compression test and I'm not sure what they cost, or if it's even something I need to consider at this point.  But I think it's safe to say that it would be worth it to clean and rebuild the carbs and tune them from scratch to make sure they're running well.

I'll try to post some pics, and there will be more information coming forward later once I can get some parts in.  Thanks for reading if you read!


So before work this morning I pulled both of the plugs to see how they look.  As soon as I get to the bike I notice that the automotive inline fuel filter is full...which means that I left the petcock on Prime overnight.   :cry:  I just keep hurting myself...  Fortunately the tank is off so it was just the fuel in the lines draining down slowly.

I pulled the plugs and the left one looks whitish, a little lean I guess.  When I pull the right one it's wet, probably from sucking oil through the carb last night during my attempted sync.  The insulator has a touch of brown on it, and it generally doesn't look as lean as the left plug did, but I can't be sure of that due to the carb oil-suck incident.

Since I noticed that the fuel filter filled up I wanted to make sure that there wasn't any gas in the cylinders, and I figured I'd do it now while I had the plugs off.  I wadded a little paper towel into the plug holes in case gas shot out, turned it over real quick and they both :POP: popped out.  No liquid was present in the cylinders.

Since the bike is down for a while I'm going to order two carb rebuild kits and tear into the carbs with a little diesel or kero.  I'm also going to probably replace my fuel lines again now that I can look up the proper size, last season I eyeballed it and they seem to have too small an ID.  Now's probably a good time to check the carb-to-petcock vacuum line too.  I'm also going to comb the forums for info on that left cylinder too, I recall reading something about it when I was just browsing, but I'm hoping that it seems off because the carb isn't set up right.  Please be that.


Sorry, no pics.  I just don't have a great way to pull them onto a computer and I don't think to take them before I start a project  :dunno_black:.  Maybe I can post a couple retro-actively.

Tore into the carbs and found some issues immediately.  The left vacuum O-Ring [remember my really poor vacuum?] was crushed during my fake cleaning/re-assembly last season  :2guns:.  The left bowl gasket is pretty cruddy, and the right float needle seat O-Ring is rough [stuck, white residue].  Fortunately these are all issues that will be fixed with my two new K&L carb rebuild kits that I got from the dealer [good price, and a proper bowl gasket.]  I also find sandy crap in the bottom of a bowl even though I installed a crappy automotive fuel filter in the line.  I later find the source of that sandy crap in the threads of the emulsion tube underneath the main jet.  I also pulled the choke assembly, idle air screws, nothing bad there, both sets look good.

I dunked the main needles, carb body, and bowls into some diluted degreaser for a little while.  The degreaser that I'm using is not strong enough for this job.  It takes off some residue, but the caked on old gas, oil, grease, road grime can smear instead of leaving it squeaky clean.  I was also using an old toothbrush to help clean, but even with the degreaser the bristles went from clean to greasy in no time.  I'm going to the hardware or auto. store after work to get a new can of carb cleaner / good degreaser, I'll probably need it in the future for other jobs on this bike anyhow.

After cleaning layer of crud off of the removed main jet I find that I'm still running the stock 122.5s.  I've read about the 145s that people bump up to, so I was a little surprised that there's such a jump from the stock jet to the preferred/recommended jet.  But on the other hand, I don't understand what the carb numbers really mean, to me they're just relative to themselves. 

After thinking I decided against going to 145s right away, partly because I want to get this together and ride, partly because I don't want to change too much at once.  I've only ridden this bike a few hundred miles and it hasn't been in tip top shape, and I think I'd still like to leave it stock while it's getting its health back and I'm getting comfortable with it.  With the forks rebuilt and the carb properly tuned I can ride it a little harder and at the end of the season when we get back to indoor weather I can play around with giving it more guts [also do valve clearance and head maintenance.

So now the plan is, clean carbs again with more aggressive cleaner, clear out the idle air mixture ports I missed.  Re-assemble with stock pilot, jets, etc...  Install new O-Rings, gasket, needles, float needle seat from the kit.  Set floats, install, remove auto. fuel filter, balance, ride!


Great read sir!  :thumb:  I really like threads like this.  People think no-one cares to read all the little details but I think it is good stuff!  Good luck!  Watching,.....
"Its something you take apart in 2-3 days and takes 10 years to go back together."


Thanks for the feedback!  Still no pictures.

I finished the carb cleaning with a little wire to the idle air ports and a couple other areas.  During reassembly I was a little worried because my new float needle seats refused to bottom out due to the O-ring, it always wanted to push back out about 1mm.  It didn't seem like there was much I could do about it unless I tried lubing up that ring/port but I didn't want to do that.  Put the floats and new needle in, pressed down on the whole unit and measured and it seemed to be right at that 14-14.6 mm clearance.  Rest of the bowl reassembly goes smooth, including installing the choke, new o-rings on the floats and pilot needles.

Flipped it over to do the slides.  Put a little oil on the backside where the slide body forms a 90 degree L.  I installed the needle with one #4 stainless washer in this order: diaphragm body, plastic washer, stainless washer, e-clip, spring seat, spring.  My bike is a '93 so I only have one e-clip position on the jet.  Put the caps on after paying special attention to making sure the diaphragm boot was properly set in it's groove, because it did want to pop out a little.  The last thing I did was connect the vacuum hose back to the carb because that is way to tight to get into with everything assembled and in the bike.  Before bolting the airbox back on I tested the diaphragm for proper action and one wouldn't open!!  Turns out I didn't properly seat the diaphragm spring on the post in the top of the cap.  Easy fix, and I'm sure it saved me some despair and frustration later on.

Before connecting the airbox I replaced all 4 boot clamp JIS screws with regular phillips because I stripped the engine side heads on removal because they were tight.  With the airbox and carb connected I lowered the whole assembly down and it popped right into the engine.  So much easier than the last time when I mounted up the carb to the engine first and then the airbox to the carb second, doing it as one unit is the way to go.  Connected the main fuel line [sans automotive fuel filter   :oops:] to the carb and the vacuum line to the petcock, I then placed some fuel in the tank-to-petcock lines just to test it out.

The bike springs back to life after a few cranks!!   :)  After running it and giving it some throttle for a minute it exhausts the fuel in the line, that's it for the day.  The next day I hook the tank back up in a "temporary" fashion by hooking up the lines but resting the tank on a stack of crates, my goal is to balance the carbs before buttoning her up.  I let her warm up a bit [I have a fan blowing on the front end to keep it from getting too hot], and I close the choke and it's idling real low, and then dies.  I decide to open up the air idle from 2 turns to 3, on both sides.  She likes this a little more and I also adjust the idle screw so that it sits right around 1100-1200.  She responds really well to throttle, and only seems to be a little "hangy" with real short blips [2-3k] but falls fast when reved to 5-7k, sounds a bit more deep than she did before.

So finally we get to the hang-up, when I try to sync the carbs.  I tend to get a little impatient and when I do corners get cut.  I didn't fully build out the $5 sync tool, I only got a 6 ft. length of hose but no T connectors because the hardware store didn't have any for that size hose.  I didn't think that you really needed it, but I discovered that it probably is a good idea because it is very sensitive to decent sized vacuum differences.  When the engine wasn't fully warmed up I had the sync on and was fiddling with the adjustment screw a little, it seemed like there wasn't a big difference.  Than between the engine warming a bit more and me giving it some gas the left cylinder grew some BALLS, and sucked some oil into the carb!!!  F-ing great, I've done it again, only it was a different carb this time.  I pulled the sync off because the oil needs to settle [totally full of air because it was sucked up hard and fast], covered the ports and revved the engine to burn it out.  The exhaust is white for a few seconds but it seems cleared out pretty quick.  I let the oil settle back down, reconnect the sync [engine is hot now] and turn it over with no choke.  It wants to idle at ~1200, but it only takes about 3 seconds to suck the oil dangerously close to the left vacuum port.   >:(

With the sync tool oil totally impregnated with air bubbles I decide to let it sit and call it a day, I figure the air in the oil is going to make it easier to move and I won't get a good reading.  I'm so damn close to getting the bike back together I can taste it, and I really want to see how the new carb is going to handle.  This morning I read an old thread and I think it was adidas that was mentioning a different approach to syncing.  When I get home I'm going to warm the bike up, and then open up the vacuum ports one at a time to see the RPM drop.  Maybe I can rough-tune the carb using that method, and then really dial it in with the tube and oil.  I am happy that I seem to have done the carb reassembly properly as the bike fired up pretty readily.  There's nothing more dishartening that putting work into something that has a bunch of steps and then have it not work and to not be sure where something went wrong.

So tonight my plan is to go home, cook sausage, sync carb, button up the tank, test ride.  And I'm going to have to make some temporary vacuum caps because PO made their own, and they are bad and not reusable.  I think I can cut a small length of tube from my sync kit and melt it shut at the top.  I've got new ones waiting at the dealer and it'd be nice to be able to ride there because they aren't exactly close.


ROckin!  Anticipating the update to see how it turns out!  :)
"Its something you take apart in 2-3 days and takes 10 years to go back together."


Partially just a note to myself, partly for anyone else having balancing or syncronising issues, I found this in a thread from '06.  Since my carbs seem to be so far off each other and I'm not sure which way to start adjusting I was in a bit of a pickle.  At least now I can get an idea for what I'll be doing when I'm turning the screw, and I can start out by trying to move things over to the #2 cylinder.

Quote from: scratch on May 31, 2006, 03:32:38 PM
The hoses from the balancer hook up to the spigots on top of each carb; you have to remove the rubber caps first; usually the left hose is for the No.1 cylinder and the right is for No.2, or their respective carbs...

The screw is located on top of the throttle linkage in between the carbs, it is reachable with the tank propped up in the back by a 4x4 on top of the battery, using a small flathead screwdriver (about 4-5" in length).  Turn clockwise to raise the amount of vacuum drawn in the No.1 cyl, counter-clockwise to increase it for No.2.


Okay.  Got the carbs tuned pretty darned close.  I'm going to need to stop and get a couple T connectors for my sync kit because without a closeable connector between the two halves of the hose the loop is way to sensitive, and it's difficult to adjust.  I then cut two 3/4" lengths of my sync hose and melted one part closed to make a temporary vacuum cap until I can pick my new ones up from the dealer.  The PO made their own by screwing screws into a small hose and then sealed it off with some gasket maker I believe.  The gasket maker has worn out and gotten flaky and I don't want to suck that down into the carb.

I got the tank popped back on, all hoses reconnected [fuel, drain, airbox drain], and rode it to work this morning.  It seems a little better than it was, and I definitely worked out a flat spot that I had when rolling on the throttle, so that's good.  It used to bog out at 1/2 throttle, so if I wanted to accelerate it was either 1/4 throttle or crack it open.

After work I'm going to ride down to the dealer to get new dampers for my guages, a new dust seal to replace my compromised one [PO] and my new vacuum caps [PO again!]  I also need to pop the tank off because I [AGAIN] forgot to mind my front tank cushion during reassembly/removal, and I'm not sure if it's on my workbench, garage floor, or somewhere down the street.  I'm still feeling out the front forks and I think that I need to measure the fork sag.  I still feel some of the larger bumps on a couple of streets, and I do get some dive when braking, but overall after the seal job it is riding much higher and better.

Overall, things are improving, slowly but surely.  I'd like to ride it out to the end of the season, and then try to do a big tear down at the end of the season before it gets too cold to work in the garage [I have very limited options for indoor work.]  There's a small ding in the tank [PO] that cracked the tank and is rusting so I figure I should nip that in the bud, possibly repaint the whole thing [and more?].  After that I want to check valve clearances, head tightness maintenance.

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