1981 Suzuki GS750 Restoration Story from Ramses


This is my story of the restoration of a vintage Japanese motorcycle. This blog is intended for grease monkeys that like to read stories about mechanical work on motorcycles. It’s mostly notes on what I did to get it running. I hope it helps other mechanic enthusiasts and by sharing this information, that it will help revive the interest of vintage Japanese motorcycle restorations. I hope for this to be a good point of reference for those of us up to the task.

Barn Find

Mid August 2013 on Craigslist.com I saw a motorcycle listing: a 1981 Suzuki GS750L, with 4100 miles, and title, for $200. The bike looked OK in the single picture advertisement. The short description said that it sat for many years but it was garaged kept. It was a no-starter but the engine does turns over. The 180 mile day trip was well worth it.

I was immediately curious about this vintage bike with so few miles accumulated. I called the seller and asked about the history. He said it sat for 30 years. His past neighbor’s son bought it in the early 80’s and rode it for a few months, but he left for the military, moved to another country, and then the bike sat in a garage for about 15 years. The neighbor eventually gave it up for free to the second owner, the seller, the guy that sold it to me. The seller said the bike never ran right for him. He tried to make some changes to get it going, about 15 years ago, but eventually he gave up, and it sat “again” during all that time.

When I got there the first thing I noticed was a little corrosion; and it’s understandable for a bike that age. The first place where I look for in an old bike is under the fenders. That part always get rusted on vintage bikes. This one had it but not as bad as I thought; it was only surface wear with no pitting. After that I walked around it and got an overall look - not bad. I then looked at signs of neglect such as scratches from falls, big dents, torn seat, broken lights - there where none. Next I looked closely for signs of oil leaks - none. The exhaust had very little rust as did most of the small parts near the middle compartment, typical. It had all original parts. I rolled it onto my trailer and away we go.

The Bath

This bike had crust of sitting dirt everywhere. There wasn’t a place that you could touch without getting your hands dirty. Looking at it made you want to sneeze. I got up early, covered the intake with big plastic bags and carefully cleaned it with a power washer. Next I used a whole bottle of de-greaser. I let it dry the rest of the day. It looked really great the next day. After drying with a rag you can see the shine in some parts. It’s a lovely bike.

First Dance

The next day I started to take it apart. The tires looked new even with the little nipples still. I could not believe it, but looking closer I noticed that the front tire had signs of wear, a little dry-rot between the threads. The tire was from 1997. The back tire was fine. The front brakes where completely frozen and the lever was stuck open; the back one still worked well. The throttle was completely stuck and would not roll at all. The caburetors had a little surface rust and the throttle wheel was also stuck like it was glued.

The battery was dead. The gas tank was somewhat rusted inside and it smelled like burned cockroaches. After a closer look I noticed it had gunk inside about a quarter of the way from the bottom, as if gas was left there to dry for 15 years. I would not dare show a picture because it was depressing; but with some hope it could be turned into a thing of beauty, as was the case.

I installed a new battery and checked that all the lights worked. The brake light was not working. I cleaned corrosion from several electrical connections and absolutely all electrical components worked after that. I opened the timing sprocket engine cover and was able to turn over the engine by hand. Tried to start it after that and the engine did turn over - a very good sign.

Opportunity Rings Twice

By luck I found another phuked-up 1981 Suzuki GS750E on craiglist for $100, no title, 36k miles - unbelievable! This one was truly in bad condition but it made for a good “sacrificial bike” and more than 95% of parts where interchangeable with my “L” model. Very few insignificant hardware was missing. I brought that one home and now I had two sister bikes that made my garage look like a junk yard. A dumped sacrificial junk bike or two are always good to have.

Carburetor from Hell

Began taking apart the carburetor. It was missing the original air box and instead the previous owner installed cheap air pods. I know for a fact that on these bikes changing the air box for pods will make it run poorly - could be the reason why he said “it never ran right”. I had some carburetor work to do. I disassembled and cleaned the carburetor by first boiling it (only metal parts) to break away gunk and residue. Next I cleaned all parts with a brass wheel grinder, carburetor cleaner, a little sand paper.

The carburetors where in fair condition except number four had a broken float valve handle. It was crooked and glued together. Hence the float was sideways. I swapped it with another carburetor from the sacrificial bike.

The First Start

After cleaning the carburetors it finally turned on. However, It idled well for about 2 minutes then it bogged down and turned off. After that it would not restart for another half an hour. I tried starter fluid and it started but turned off right away after a few seconds.

The next day it started up right away. It also idled for a few minutes then died - a sign of too much fuel mix. You could also smell it and the exhaust was smoking (a sign of too much fuel being burned). I waited half hour and tried again. This time I opened the throttle to test all the jets, but the motor could not go beyond 4000 RPM; it would bog down and turn off. The air/fuel mix was not tuned for sure. However the bike did start - good progress for now. Tomorrow will be another day.

The Fuel Tank

This part caused a lot of work. The fuel tank was rusted mostly inside but especially it had gunk from dry fuel left over a very long period of time. The first thing I did to remove the rust and the gunk was to dump the fuel tank in a my molasses tank for a few days. I use 10 parts to 1 molasses and water in a 55 gallon tank. This combination will remove rust slowly but it is truly amazing. I had to rinse the fuel tank and dump it again for a whole day a few more times until most of the thick rust was gone.With a pressure washer I removed more pieces of rust from the inside and the original paint also came off nicely. I dumped it again a few more times in the molasses. I like to use molasses, a natural way of removing rust; much slower but less contaminating and corrosive, compared to chemicals.

About 80% of the rust was gone before I dumped the tank in another solution, a 5 parts to 1 big bucket of phosphoric acid and water. After one hour i took it out an a lot of fine rust had been removed. Longer than that and the metal could eventually disappear since phosphoric acid disintegrates metals. At the end I dried the tank and applied some WD-40 to avoid surface flash rust. The fuel level plunger was toast; I cleaned the gunk and tested but it was dead. Replaced it with the fuel level from the sacrificial bike and it tested OK.

I assembled the tank and turned on the bike. Noticed that the engine would bog down after about 20 seconds. Also the exhaust was blowing white smoke - a sign of too much fuel going into the cylinders. Looking underneath there was a small gas leak coming out of the little breather hole in the middle of one of the exhaust headers, signaling foul play at the carburetor.

I waited 30 minutes and was able to turn the bike on again - typical of a flooded engine. Looked closely at the carburetor and notice that gas was flowing in through the clear vacuum line. The fuel petcock or the fuel tap was leaking gas into the vacuum port of the carburetor, flooding the cylinders vacuum with gas during each down stroke. I opened the fuel tap and noticed that the diaphragm was deteriorated. I put it up and could see the light through it. I order a fuel tap replacement kit. After a few days, reassembled the fuel tap and tested - no more engine flooding. Now it idles for ever, with no bogging down and no turning off. However the idle sometimes goes up and down on it’s own. There must be a carburetor synchronization problem.

Through all the testing I kept smothering the fuel tank on the outside with WD-40 to void flash rust. I decided to paint it but first I would treat internally with an epoxy liner. I removed 95% rust from the inside of the tank. But there was still a little bit in spots that would just not come off. They where small thin layers of rust and it’s hard to get to them being inside. I did some research and found that other people just simply cover the inside with epoxy lining. It can especially cover the remaining pockets of oxidation and close them off forever.

I ordered Caswell Expoxy Gas Tank Sealer from http://www.caswellplating.com. It worked very well. I used a little bit of paint thinner per the instructions which was recommended in several blogs. First I covered all the holes in the tank, but the main one, with masking tape. I put temporary bolts in the fuel tap holes and removed the fuel level plunger. I kept turning the tank over to different positions every 1 minutes for an hour; used a light to observe the epoxy slowly spreading inside. The next day the epoxy lining was hard as a rock all over the inside of the tank and it smelled great, like new. I assembled the fuel tap and fuel level plunger and began plans for the external paint.

Carburetor Tunning

The engine could not run beyond 4000 RPM. I read through some forums that this bike was built very lean from the factory, and a jet enhancement was crucial in order to increase horsepower and engine acceleration. I ordered Dynajet Kit 3315 Kit from dynajet.com. I increase the main jet size from 112 to 124. I also drilled and increased the slider vacuum holes, and decreased the main jet air passage with a tiny washer according to instructions. I reassembled the sliders and after that the engine would quickly accelerate past 10,000 RPM in a split second. However, engine started to bog down, again, after 2 minutes of idle.

The bike also was displaying symptoms of a rich fuel mixture. White smoke was still coming out of the exhaust after 30 seconds of acceleration together with the bogging down and turning off after 2 minutes of idling. I had to play around with the slider needle adjustments in order to enhance the air to fuel mix, not to lean nor rich, just right. That meant having to assemble and reassemble the sliders several times - what a pain!

I took the bike for several test runs and was able to determine the needle adjustments in both extremes, lean and rich. I found the sweet spot after about 5 test. This took several days of tinkering and it was the most difficult adjustment task by far.

I took the carburetors apart one last time and synchronized them by hand, using a pin needle to match for the same stickiness on all four butterflies. I reassembled it and gravity fed fuel about two cups into the carburetor bowls. It turned right on with no problem and the idle had a much more stable sound.

The last tuning I performed was formal using the carburetor synchronizer from MotionPro.com. It worked great and I will never tune another motorcycle carburetor without it. I was able to get the idle down very low and steady, The bike sounded like it was going to turn off but it kept on going at what sounded like maybe 200 RPM; it almost sounded thrice faster than a heartbeat. The idle at 1000 RPM sounds very smooth - I could tell the engine was in sync. You could hear it and you could feel it.

Starting Problems When Cold

I noticed this bike had a very annoying problem. It did not want to start when it was cold. It was very difficult to get it started 9 times out of ten only when the engine was very cold after many hours of standing. I had to use starter fluid in order to start during the morning after it sat in the cold night 60F or lower. After that it would start great as the day got warmer. I hated having to carry starter fluid with me just in case.

What I had to do was enlarge the jet for the enrichment circuit. I opened the carburetor bowl and looked at the choke jet and noticed that it had a very tiny hole. I wonder how the heck fuel enrichment could get through such a tiny hole - impossible. I don’t know what the Suzuki engineers where thinking. Solved: I drilled the tiny little hole and made it bigger. Now the bike fires up fine with the choke during very cold starts.

The Exhaust

I spent a long time tuning the carburetor again and again. Riding I got a good sense of how it feels and sounds when running lean or rich. I kept adjusting the needles, the air and fuel mix screws; changed different size of jets, different size of needles. But I could not get the bike to run right no matter what I did. The low and middle throttle range where OK but at full throttle I could only get the bike to run stable at 65mph or below. Once I surpassed that speed it would hesitate and slowly loose power until it bogged down after a couple of minute. I then had to wait about 5 minutes in order to turn it on again. At a stop it smelled like there was too much gas fumes coming out of the carburetor and out the engine vacuum line also - a sign of a rich mixture.

However, the problem was with the exhaust causing too much restriction of air. The engine was not able to push out the output gasses quickly enough during continuous full throttle operation, causing the cylinders to flood with a very rich gas mix. What I did was drill the back of the exhaust. The baffle on the end of hte exhaust has two plates. The outer most plate has 6 holes and the inner plate in front of that is solid with the main big hole of the baffle thought the center. I inserted a thick 1/2 inch bit in each of the 6 holes of the outer plate and then drilled the hole through the solid plate. Now the baffle would not be able to restrict so much air. I went for a ride and it was like the difference between day and night. The next day I took a 80mph ride to work for the hole 45 mile ride, with no hesitation - the engine was finally breathing right. The problem was the closed up exhaust all the time. Drill baby drill… The exhaust was a little louder but too loud and the motor sounded much better - you could tell that it could breath and there was no more asthma. LOL


Some idiosyncrasies typical of this bike I found in forums after some first hand experiences. This bike needs to be warmed up before it can idle steady. If you take off after a few seconds it will idle unsteady at the light and may even turn off - not safe. I rev it a few times and let it idle for 60 seconds steady; as in let the old toaster warm up to better cook the wheat.

When decelerating from full throttle down to idle it goes below 500 RPM and bogs down for a few seconds. I usually blip the throttle twice as I’m about to stop at the light and that fixes it. I think that is one of the consequences of swapping the original air box for the popular air pods. The air flow vacuum is interrupted too much when decelerating, causing too much fuel to continue down the intake, then causing a temporary bog. By blipping the throttle it mixes the fuel/air a little more even before switching to the idle jets.

The front brakes are not as firm as I am used to. But my point of reference comes after having ridden for months my previous motorcycle, a high performance 1994 Ninja ZX9 tuned for track racing; the comparison is drastic. The performance is just what can be expected but there is room for enhancement. Hence, my future tinkering to be continued.

The Brakes

I took all brake calipers apart and completely disassembled them. Noticed some gunk especially on the front calipers. Most of the rubbers where in good shape after cleaning. I ordered and replaced the inner rubber seals. Painted the calipers red with VHT paint. The brake shoes where almost brand new and with very little wear.

The brake lever was shot. I thought about ordering a restore kit but for ten dollars more I could get a whole new chink master cylinder. That is what I did and it works very well, except it took 2 weeks to deliver.

The brake lines had gunk inside. I cleaned them using a coaxial cable inner core. I created a video about it and uploaded it to youtube.com. There is very little information and/or recommendation on cleaning old brake lines. Most people advise to get a new stainless steel brake lines but I like a challenge. So I cleaned them as mentioned before while using WD-40, brake cleaner and an air compressor.

I fit the lines and calipers and bleed the brakes. At first they where spongy but I had to keep bleeding them via push and pull of the fluid until the press became firm. The back brakes where even easier to complete. I went out for a test and all breaks where functioning. However, I’m still not completely convinced about the front brake. They feel a little impotent. I ordered stainless steel brake lines and will fit them and post the difference. If that does not work I will try using brake calipers from other Suzuki bikes. I heard of people fitting GSXR, Katana and Bandit brake calipers from the 1990’s onto the GS750 and GS1000 from the late 1970s and early 1980s. I noticed on many blogs complaints about brakes on the GS bikes from this era; too spongy with no wood. I will work on that and post my findings after trying all best alternatives.

The Tires

The front tire was worn so I had it replaced. But I went up a bigger size. Apparently the size for this old tire is very hard to find. The original size is 90/90-19 and I installed a 100/90-19. The back tire was intact, with no signs of wear and the threads looked as if they where made yesterday.

The Chain

The chain was rusted and stiff and the sprockets where dirty. But they where all in good condition with no apparent mechanical wear at all. I had to cut the chain off with a grinder then ordered a 630 o-ring master link for it. I put the chain in a molasses bath for a few days, cleaned it up and then left it inside a bucket of thin gear oil for a few days. Afterward I loosened every link back and fourth thoroughly and back into the gear oil bucket for a few more days. I then took it out cleaned it real well and checked for any kinks. I put it on the bike with the new master link. I lifted the rear tire and idled it in first gear to see any signs wear. It ran through very even with no kinks; it did not whip like bad chains do usually. The original chain stays. Incredible after 30 years it is back to life.


I took off the insignias from the side covers and sanded them a little bit just so the primer sticks well; same for the fuel tank. Spread the primer lightly every 30 minutes about three times then let it dry. The next day I sprayed the blue paint lightly on the covers and gas tank outside every 1 hour and let it dry. The last day I sprayed clear coat lightly, also about three times every 1 hour. I let it dry till the next day. At the end I left it as is. I may polish the clear coat later on. For now the bike looks great with this color and the metal fuel tank is protected from corrosion inside and out.

The Forks

The forks felt hollow with no suspension at all and the would dive during breaking; cornering was a little shaky too. I took them apart and the oil was still pink and very little amount. It had some strips of black gunk come out, which looked like an egg had rotten in there. I took all the tubes apart and cleaned them. The seals where still in very good condition but I used new ones that I pre-ordered anyway. I fit everything together and used half and half of 10W30 oil and ATF oil, 3/4 of a cup per the repair manual. The forks are now nice and firm.

The Ride

My first impression was that the seat and the stance are very comfortable; both aggressive enough for an attack ride to work and comfortable enough for a long lazy weekend ride. The engine is huge and its size matches its strength at 80 horsepower, which is not too shabby for a bike of that age. I dislike very much the stock buck handlebars that came with this bike so I put on a more forcefully sporty handlebar that I had lying around. Shifting is very smooth. I love the gear indicator and the fact that you can turn the headlight completely off. All instrumentation is very easy to use with the glance of the eye. Passenger comfort is excellent. Exhaust is quiet but has a nice rumble when blasting. Acceleration is great especially when surpassing 5000 RPM. These engines love be revved very high and it’s true what they say that the best horsepower comes at those engine speeds. Tilting is very smooth for such a heavy bike; the foot pegs are just right and don’t rub during hard cornering. High speed stability is excellent with nice stiff frame, it moves very straight with no wobbling at all. The bike feels very nimble once you get going despite it’s weight. Handling is excellent all around. The only pessimistic comment that I have is the spongy braking which has many complaints, even way back straight from the factory. An alternative replacement stainless steel lines and later year Suzuki calipers should do the trick. More on that later.

This old bike was a record setter in it’s time. Suzuki came out with the GS750 in 1977 - the fastest of it’s class. In 1980 they upgraded the engine head to 16 valves. In the US the title continued as model GS but in Europe and Australia the model name was changed from GS to GSX. In 1985 The GSX-R was born out of this engine - or the famous gixxer. The engine is high revving and it is at best in mid range acceleration - just like racing sportsbikes. I’ve ridden this bike very comfortable between 5500 to 7000 RPM from Orlando, FL to Miami, FL and it is very comfortable and handles very well. It has a 60 inch wheelbase which is short enough for sport performance but long enough for long range comfort. The frame is very rigid and it handles very straight during high speed. The shifting is very smooth and putting it in neutral is very easy.

Cafe It Yes or No?

A lot of people are converting these great machines into cafe racers, bobbers and flat trackers; a very fashionable thing now. I’m not the trendy type but I also have an itch to convert it into a cafe racer. I will leave this one as is and instead do that to my smaller 1977 Suzuki GS550, which has been lying around for about 10 months in my garage - more on that later. These GS bikes are very easy to “cafe” them. The basic modification consists mainly of clip-on handlebars and a homemade wimpy epoxy flat seat with a race imitation rear hump; lower the forks about 2 inches and you’ve got a cafe racer. Sexier enhancements begin from there.

Why I Did This

I love old inline-4 Japanese bikes from the 1970’s and 1980’s. They where fast as hell, overbuilt and indestructible with good care. They are formidable machines, durable, with excellent handling and performance. They have their own look and style which I really like; a morphic combination of cruiser and sportsbike mixed together which makes for a very comfortable but sporty style of riding. They call them UJM (Universal Japanese Motorcycle). To me they are works of art. When I look at one I see power, sophistication and simple but excellent workmanship. These machines are by far the best motorcycles ever built and there is enough evidence to prove it.

Updates as of 5/2015

I made many updates which improved the performance of this motorcycle:

  • Replaced carburetor pods for 52mm velocity stacks from Dime City Cycles. This change improved the performance of the carbs especially at high RPM. More air was entering the cylinder as a result. I had to downsize the jets from size 125 to 117 to get the right air/fuel mix.
  • Replaced front brake lines with stainless steel. It made a big difference.
  • Took off the tire tubes. The magnesium wheels do not need tubes inside the tires but this bike came with tubes. I changed the front tire with a tube thinking it was required. As a result of the tubeless change the tires where harder and stiffer with improved handling. Got a new back tire also. Shinko Tourmaster brand is fine.
  • Changed handlebars for shorter forward more aggressive ones. It made the bike look more sporty and the stance felt better especially at high speed.
  • Took of the plastic windshield. It vibrated a lot during high speed. I created a bikini fairing myself with thin sheet metal from Lowes. I bolted it to the light brackets. It reduced the wind even more than the windshield because it sat flush with the headlight and much more forward. I recommend that mod to everyone. I will post pictures about it.
  • Replaced sprockets and chain. Went from 15/40 to 16/38 sprockets and 530 riveted chain kit from JT Sprockets. The bike performed very well with this mod. Acceleration was very smooth. It produced almost 1000 RPMs less. I liked it. I could do 82mph at 5500 RPM, which is the range that the engine sounds the best. I would recommend a 15/37 if you are worried about low speed acceleration. I am not a drag racer so smooth acceleration is fine for me; plus with this drastic sprocket ratio I can still take all the cars at the light.
  • Created my own side covers from thin metal and strapped them using metal tie wrap. It looked good. I lost the right original side cover because it deteriorated and fell of while riding. The originals are made of plastic and they do brake off. Tried to find one on eBay but they were asking $60 - no way!
  • I sold the bike two weeks ago to a vintage motorcycle enthusiast. I was sad to see my old girl go. I am currently working on two other projects and am running
    out of space in my garage. I have 3 motorcycles and a bunch of parts. I am restoring a 1977 Suzuki GS550 and a 1998 Kawasaki Ninja ZX6E. My daily ride is a 1999 Bandit 600S.

    I hope you enjoyed my grease monkey motorcycle story. If you have any questions or would like to share comments let me know and I will copy them here.


    Ramses Soto-Navarro

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