New bike - 1981 GS750, a few issues, plus cafe racer suggestions?

[ChrisGuilday]

Hey guys, I am brand new to the forums, first post.

I’ve owned over 10 motorcycles in my life, I’m 26 and I’ve been riding since I was 16. I haven’t had a bike in about 4 years as I got rid of all of them as I was too young and was reckless previously and realized it was only a matter of time before I went down.

Anyway, I picked up a 1981 Suzuki GS750 that was listed as a 1980. I’ve done quite a bit of research, and am aware that this is the first year of the 16 valve. It was $1,800. Unknown miles.

The bike has been partially turned into a cafe racer. I bought this bike specifically because it cannot do wheelies, yet is still somewhat quick, and because it was cheap, reliable, and needed work (I like a project) and I wanted a cafe racer.

I literally spent 6 back to back hours trying to get the dang philips head bolts out on both covers. I used an entire can of PB blaster, I freezed them, hammered them, spit on them, and tried to use clamps. I managed to come out on top and only stripped two of them, in which I drilled them out, haha.

here’s a list of the problems, some of which I know how to fix and have already fixed, and some of which I don’t.

1) Clutch is toast
2) Running tail light (But brake light works?) - Don’t know what’s wrong. Not good with electrical.
3) Battery does not charge (Stator or rectifier, or maybe battery, probably rectifier)
4) Bike will not start with starter when cold, but will bump start relatively easy. Once it is warm it will start with the starter. This is with the battery fully charged. Battery looks somewhat newer.
5) Tach and speedometer do not work. Lights on gauges do. Cables seem to be screwed in properly. Maybe the cables are snapped inside? I have no clue what the issue is.
6) Overflow tube from petcock slowly drips gas. (Floats or inlet valve I assume?)
7) Bike has quite noticeable mid range hesitation, but flies up top.

Listed below is what I’ve bought for it. I haven’t had a chance to attempt to replace much yet as I only just got all the parts in the mail. Tomorrow I’m going to do a lot of work on it.

1) New clutch - installed
2) New stator - installed (Does it matter which wire goes to which? I spliced them in randomly)
3) New rectifier - TBD
4) New rear LED taillight / turn signal combo - TBD (I assume the light itself isn’t the source of the problem with the running light not working, but wanted new ones anyway)
5) Entire carb rebuild kit - TBD
6) New cafe racer seat - Doesn’t fit (Can someone guide me on where to buy one that does fit?)
7) New LED headlight - TBD
8) New bolts - TBD (To replace the damn philips heads)
9) New LED front turn signals - TBD

To be honest with you, I bought almost everything off eBay except the clutch and the bolt kit. The clutch is EBC.
I plan on really making this bike my own and fully stripping it down to the frame in the distant future, and properly building it. For now I just bought cheap eBay junk to make it road worthy.

here are my questions:
1) Why isn’t my running tail light working? The one on it is currently aftermarket. Doesn’t this usually occur when a light is out somewhere? All my lights work, but the turn signals blink as if I have a bulb out. Maybe it’s bad wiring on the aftermarket tail light? The wiring had become disconnected when I got the bike. I connected it back myself. It has some kind of electrical box that the existing wires from the harness go into, and then 4 connections that come out that lead to the tail light / turn signals. I am so bad with electrical stuff.

2) Why doesn’t my bike start with the starter? Could this be due to a bad rectifier? I replaced the stator, but that has nothing to do with the starter, right? The stator provides current to charge the battery and run the lights while the bike is running, right? and the rectifier converts the power from AC to DC, then charges the battery? Sorry, I wish I knew more.

3) Why doesn’t my tach and speedo work? Could this also be due to a bad rectifier? Or is there nothing more to it than the cables?

In addition, if any of you guys have any source for some aftermarket cosmetic parts / cafe racer parts, that would be awesome. I want to slowly start rebuilding this bike and slowly replace everything in time, but I want to complete the cafe racer look.

I am sorry for so many questions!! I am just eager to work out these kinks.

thanks a bunch!

[tom203]

“I’ve owned over 10 motorcycles in my life, I’m 26”

you’ve been busy .. I suggest you post specific issues in their respective categories to get some focus . Lots of maintenance awaits...your safety depends on it. Avoid buying more stuff...

[ChrisGuilday]

Well I am off to go do some work on it more.

Going to replace the rectifier, rebuild the carbs, see if there’s a loose wire somewhere that’s effecting the tail light, and I suppose I’ll unscrew both the cables for the tach and speedo and see if I can tell if their intact.

You’re right, lots of general stuff that needs to be done, and maybe most, if not all of my problems will be fixed with doing the above. I’ll report back once I’ve spent some more time working on it with more specific issues if I don’t have much success.

[gustovh]

Pull the carbs and tear them completely down and give them a good soak in a good carb cleaner, Napa has a good one. As far as a needing a carb kit, jets don't wear out, O rings yes ( contact Robert Barr), the rubber plugs on top the jets yes, and maybe the float valve. You probably have tight valves as well, they are so much fun to adjust.

For the electrical issues, clean and inspect, bad connections to ground or the stator wires are a one place to stare for charging issues. Look up the stator papers and the top 10 newbie mistakes.

Download a manual for your bike.

V

[ChrisGuilday]

Pull the carbs and tear them completely down and give them a good soak in a good carb cleaner, Napa has a good one. As far as a needing a carb kit, jets don't wear out, O rings yes ( contact Robert Barr), the rubber plugs on top the jets yes, and maybe the float valve. You probably have tight valves as well, they are so much fun to adjust.

For the electrical issues, clean and inspect, bad connections to ground or the stator wires are a one place to stare for charging issues. Look up the stator papers and the top 10 newbie mistakes.

Download a manual for your bike.

V

Does it matter which stator wires go to which? My new stator doesn’t have any color indicators on the wires. Also, the same question for the rectifier. Does it matter which wires go to which? Again, my new rectifier doesn’t have any indicators on the wires except for the positive one, and the ground. The others are all just plain yellow. I’ve already wired up the stator and the bike runs, but it was running a whole lot worst than before, but I think that’s because I didn’t have the air box secured. As of a few minutes ago I just wired up the new rectifier, but I have to go to ace hardware to get a longer screw for the new rectifier. I haven’t turned the key yet since installing the rectifier. I hope I’m doing this right.

I did download a manual. It doesn’t say anything about the stator / rectifier wires. I’ve been told it doesn’t matter which wires go to which since it’s a 3 phase, but that was for a different bike and I just want to make sure.

in regards to the carbs, I have a whole carb rebuild kit with everything. I’m going to tear into them tomorrow I think. I’ve done carbs many times so I think I can handle that part.

[fastbysuzuki]

the stator wires have no polarity so it does not matter which is connected to which, are you are saying that the rectifier has an earth and a positive plus some yellow wires?
The bike will not run well if you don't have the airbox fitted.
you would be better stripping dipping your carbs and fitting new orings from http://www.cycleorings.com/ Robert Barr a member here using after market jet kits can cause problems.

[Nessism]

Please check the Newbie Mistakes and carb rebuild tutorial linked in my signature. They should help you...

[ChrisGuilday]

Yes, the 3 yellow wires are what I’m referring to. Thanks for your help.

Here’s an update

I got the new stator in, and the new rectifier in. The battery was on a trickle charger for 6 ish hours and I went to start the bike and the Battery seemed super weak and then died moments later. I couldn’t get the bike started.

I went to autozone and got an identical gel battery, put it in, and the bike started right up. I assume the bad rectifier fried the battery as the battery was dated 07/2020, so it was a new battery, but it just wouldn’t hold a charge.

Like I said previously, the bike had bad hesitation at low / mid range RPM, but was pretty fast at high RPM. It almost seemed like an air leak. I looked at the box for the filter and there’s two large circular holes that don’t look stock to me. It looks like someone drilled them out? Is the box for the filter supposed to have two circular holes the size of a soda can on the bottom?

I put a towel in the holes and rode the bike and it seemed to run way better.
Also, I went to change the rear tail light and I can’t couldn’t seem to get it to work, so I put the original tail light back on and now I can’t get that one to work either. It used to light up when you hit the brake, it was just the running light that wouldn’t work.

theres 3 tail light wires, a white one, a brown one, and a ground wire. I checked with the volt meter and the white wire makes the volt meter fluctuate when you hit the brake, so that one has to be the positive wire, right? And the brown one is negative? I’m not sure why I can’t get the light to work.

So here’s the remaining issues

1) Tail light does not work at all anymore
2) Still some hesitation in low-mid range rpm. Are the circular cut outs in the air filter box supposed to be there?
3) overflow tube is leaking gas.
4) Tach and Speedo do not work. - haven’t gotten a chance to figure that out yet.

I’m going to rebuild the carbs tomorrow following Nessim’s link in his signature as he suggested.

[Redman]

Brown is Tail Light. Should come on with key in On position (powered by the Signal fuse) and should also come on with key in Park position (powered by Main fuse).

White is Brake light.

Ground is the black/white wire.

[ChrisGuilday]

Ok great, that makes way more sense. Thank you!

The original (aftermarket) tail light has 2 wires coming from it. I assume those are the tail light and running light wires, and the ground wire coming from the bike just grounds to the frame, right? That’s how it was originally setup.


When I disconnected the wires, I tested them with an ancient analog volt meter, and the white wire fluctuated high when I hit the brake, and the brown wire had a constant current, which makes sense based on what you just informed me of. I tried connecting the wires back in, and the original light didn’t work at all anymore, so I swapped the wires, still didn’t work. I then tested the wires again with a volt meter and I got no current.


I checked the fuses and they looked fine. The lack of current could be due to the ancient volt meter failing, or dead batteries in it, or maybe bad fuses / loose fuse and I just didn’t notice it. But if the fuse was bad wouldn’t it cause the head light and front turn signals to not work either? Or maybe it’s something else entirely.


I am going to buy a digital volt meter tomorrow just in case.


My new LED tail / brake / turn signal combo light has then following wires:


Red: Brake light (Goes to white wire)
Yellow: Running light (Goes to brown wire)
Blue: Left turn signal
Orange: Right turn signal
Black: Negative


The bike came with an aftermarket turn signal “relay”? Not sure what this is called. But it is currently wired up to the rear LED turn signals that came with the bike. I assume I’ll have all the wires necessary for my new tail light from these wires coming out of the turn signal relay thing.


If I connect all of it correctly like that, everything should work I assume, but I just have to figure out what I’m not getting current from the tail light wires.

[ChrisGuilday]

Good news!!

Bike runs like a TOP!

It starts up instantaneously when I hit the starter. Doesn’t even turn over one time before it fires up. I hit the button and the bike is idling smoothly.

I have full power throughout the whole RPM range.
I tore out all the prior aftermarket wiring crap and just wired it correctly and all my lights are working except none of my turn signals blink, they just stay solid. Has to be a bad signal relay so I’m going to replace that, I just don’t know where the relay is yet, lol.

I thought the two circular soda can sized holes in my air filter box was the source of my low-mid range hesitation / bogging, so I taped them up, but taping them killed all my power past 3-4K. Bike just fell on its face. So I un-taped them, went for my first real ride since replacing everything, and the bike runs perfect. I guess the bad battery or rectifier was the source of the poor performance.

So either those two holes are stock, or the prior owner drilled them out and then re-jetted the bike.

Anyway, just a few things left to do.

1) Replace signal relay
3) Tear into carbs (Gas dripping out of overflow petcock)
3) Fix speedo / tach

I bought a $60 aftermarket LCD speedo / tach that might be junk / not work, but I’m going to try to make it work lol. I’ll search around the forums and see if anyone else has done it. I know the OEM tach is analog with a cable, and this LCD one is not, but I think there’s still a way to do it.