Technical Information on Suzuki GS series bikes

I’ve heard that the valve clearances are important on this bike. More so the exhaust than intake. I’ve never adjusted mine, but I suppose I will before I sell it.

Charging System Gremlins

The Suzuki charging gremlin has hit the only one of these I’ve worked on. There was a lot of extra electrics on this one, but it may have been sold to my friend in the chunked-out state. The alternator on these doesn’t do a very good charging job if the revs are held low for a long period of time. My friend who owned this bike had constant problems with it charging its battery. When I borrowed it, I never did. She was very gentle with it, I let it rev quite a bit. Shift later and running the revs higher will help a lot. If you poke around town short shifting this bike, it's just not going to charge its battery

Petcock (fuel valve) Problems

The petcock on this one is not one of Suzuki’s best designs. There’s something about the vacuum not starting right away that doesn’t open the fuel valve right away so that if the bike doesn’t start right away, it won’t start. The workaround for this is to start the bike with the petcock in the Prime setting. Replacing the vacuum hose and intake boot are options that are progressively more expensive, and it could be that the diaphragm in the petcock body is hosed, too. This is not replaceable, but the gasket around the dial is. The whole unit is pretty spendy from Suzuki, but not too bad from boneyards. If you get one from the junkyard, be sure to bring your old one with as Suzuki used several different designs and bolt patterns for their petcocks. Beware!

I’ve had the pleasure of working on several of these bikes.

Choke Cable

Not much you can do here but replace it. I had to do mine two times a year. The factory part is pretty cheap, but they’re available elsewhere for less dough. A good switch is to get earlier slide-pull carbs that have the choke on the side of the carb body.

Carb Diaphragms

Be careful cleaning these carbs because if you aren’t the slider/diaphragm piece is about $50.00 a throw.

Inlet Rubbers

They do get old and crack. This can lead to lean running and holed pistons, so ignore them at your peril. The easiest way to test them is to squirt a flammable liquid on them while the bike is running. If the revs change, you’ve got leaks.

Handlebar mods for L models

I would say that about half of the GS750s sold in the US were the "L" model. This was the "cruiser" style variant of the GS line. They usually had "mag" wheels, stepped seats, chrome rear fenders and a thinner waist. Their frames were much thinner across the top and back and therefore ran different side covers. I think the thinner frames were so they could easily accomodate the "King and Queen" cruiser style seats. They have dubious "cred" as a cruiser, and they are not that great looking. They also have something I consider a cardinal sin for controllability: "Buckhorn" style handlebars. Some folks also call them "pullback" bars. I find these very difficult to use as they force me back in the seat giving me less of a sense of control of the bike. This is not so good. Due to my experience swapping these "buckhorn" bars with regular "TT" bars, I've found that the GS750L models work very well with these TT bars on them.

TT bars are kind of like dirtbike handlebars except for that they don’t have a crossbar. The problem one runs into is that the brake master cylinder hose is too long and the clutch cable needs to be re-routed. This is no real big deal and the tradeoff is a much more controllable bike. The buckhorn bars the "L" models came with push you back in your seat. This made my back and arms ache because I was fighting the wind and trying to hold myself up against it. That sucked for comfort and control.

The front brake hoses are by now pretty much shot. Drain the system and install braided steel brake lines. You'll get better braking performance while avoiding the life-treatening inconvenience of blown brake hoses.

To swap to the 4 valve head or not

There were two different kinds of heads for the late ‘70s and early ‘80s GS750s. The two valve and the four valve per cylinder heads. Believe it or not, folks, but for performance and reliability, skip the four valver. The performance gains are negligible and the hassle factor goes way up. Sure, there are performance gains to be made, but there just isn’t any reason to do a head swap for the meager performance this swap offers. Sure, if you’ve just blown your head gasket and you have a four valve head sitting around, go for it. Don’t bother otherwise. Also on the four valver, watch your tolerances and be sure to change your oil ever 3,000 miles. If you don’t, you’ll see grooves appearing on your cams.

Tires

Run the best tires you can afford on these bikes. The handling isn’t magical even with the best tires, but it gets better with good rubber. These bikes handled OK for their time and were a whole lot better than most anything at the time they were built.

Fork Seals

Fork seals blow. This is a fact. This job is such a pain in the ass that I’ve gladly dished it off to my local shop. Trust me, if you’re worried about bushing wear, they’re sure to tell you about it. It means extra money to them to have you have them replace/recondition them. Get your seals done soon after the telltale grime starts to appear around the bottom of the sliding area of the forks, or you risk fouling out your brake pads and hosing up your braking performance. Don't bother with aftermarket seals, go with the factory ones.

Head Race Bearings

For some reason the headstock on the ’81 Suzuki GS750L was so weird that they didn’t even bother publishing a how to fix it in the Haynes/Chilton’s manuals I got for my bike. Take that one to the shop as well. All the others seem to have pretty traditional ball bearings and races. Do those yourself or hit the GS Resources page to see what you need to convert it to tapered rollers.

Seats

Seats deteriorate from use and sitting in the sun. Get the best one you can afford. You’ll enjoy your ride so much more.

Clutch

The Barnett clutch pack for this motor might be overkill, but you’ll probably never have to replace it again. A word of caution: Tighten and loosen the clutch cover bolts in a criss-cross pattern and just a bit at a time or you will break the clutch cover. Not an expensive part from the junkyard, but a pain to acquire none the less. When replacing the clutch, pay attention to the pivot arm that extends the clutch rod. A friend of mine went with new discs and springs and ended getting stuck a couple of times due to the arm starting too far up its ramp and then getting jammed at the top. This locks the clutch out and makes it hard to get home.

Battery

Tend the battery on these bikes. Charge them out of the bike at least a couple of times a year and watch the fluid level. If it needs some electrolyte, add DISTILLED water and don’t over fill. Be sure you route the overflow tube to a place where it isn’t laying against or over a painted or chromed surface. Plumb a new line if you have to. You will screw up your paint if the battery cooks. And it will.

Charging System

Check the GS Resources page if you need a new stator or rotor. They have produced a new one for this bike that is superior to the factory replacement.

Ignition System

Older bikes in this series have breaker point ignitions. Dump it and get an electronic ignition. Set it up carefully or get a shop to do it for you. You won’t regret it. You will be rewarded with quicker starts, and less chances of migrating timing putting holes in the crowns of your pistons. Food for thought.

Airbox

Re-oil your filter frequently. Change paper element filters frequently. If you scrap the airbox and install pods or K&Ns, REJET! This holds true for putting aftermarket pipes on it as well.

Chain and Sprockets

Needless to say, replace these as a unit unless you really like working on this part of the bike. When you do replace the chain, get an O-ring chain. It’s quieter and will last much longer if cared for. And you MUST care for it. Save the installation information that came with the chain and follow it religiously. If you do, you chain will last for 25,000 miles plus. If you don’t, you’ve just flushed $150.00 of parts down the toilet. Also, be aware that the hash marks printed on the swingarm of the bike are probably not that accurate. Find some other way of aligning your chain. There are several out there. I like the string method.

Swinging Arm Bearings

If your bike is chain driven, test the slack and play in the swingarm bearings at the beginning of each season. The test is easy: Put the bike on the center stand and with the bike off, grab the back of the wheel right under the taillight. Pull it back and forth towards the exhaust pipes. If you notice some side to side play, consider replacing the bearings. There may be some side to side play on a bike with good bearings, but more than a millimeter or so and you're looking at fried bearings. Replacing these bearings will make life much easier on your chain and make the handling of your bike much more predictable.

These bikes are more of the same as their smaller bretheren. They are big and heavy. Shafties are clean and even heavier, chainers are more performance oriented. All these bikes are pretty reliable, comfortable, big in every sense of the word and a pretty nice scoot for both town and touring duty.

Final Notes

Just about everything I’ve said for any of the GS series bikes applies to all of them. Don’t you just dig those digital gear readouts?