1980 GS850g. Runs only with jumper cables.

[Guest]

I have a gs850G. The battery on it is bad but I can start it with jumper cables and it runs excellent but soon as I take them off it will idle fine but won’t accelerate at all it cuts out bad. Soon as I put the cables back on I can rev it like a new machine. I think it’s a bad stator because I’m only getting 5volts to the battery at an idle. Any suggestions will be appreciated thanks!!!

[Redman]

Welcome to the GSR.

Charging system on these GSes, even if working well, dont put out much at all with bike at idle.
So with a bad battery, and bike at idle, probably not enough voltage to fully operate the ignition so are probably haveing really weak sparks.

TO properly check the charging system, you will do better if have the battery charged first (even if it is a weak battery).
CAn you put a charger on it for a while...?

THEn check voltage:
- with ignition off
- with ignition on
- ruuning at idle
- running at 4k rpm

Report here.
IF determine is a problem with the charging system, then we can talk about troubleshooting that.

SO far, all we know is the battery is suspect.

[Redman]

Oh, wait a minute.

We cant help you till we see picture of the bike.

Yep, we need to know if that 80 850 is the maroon one or the black one.

[Rich82GS750TZ]

Welcome
Your bike isn't charging the battery. You'll need a new battery or known good battery to perform any tests on your stator and/or your regulator/rectifier (R/R). After that, the Quick test linked in my signature will show us the health or weakness of your charging system. There are tons of manuals and articles for everything else in the other link to BikeCliff's website.
Most likely, like most of use here, here's what happened:
Under-performing Shunt type R/R installed at factory has fried your stator:
leg-to leg test will probably reveal that you will need a new stator
Get a series type R/R like a Shindengen SH775 R/R - member Nessism buys used units, tests them and sells them at a great value to members.
There are many posts here om installing this new R/R, including leaving out the useless headlamp loop on most of these bikes.
Clean up your wiring, establish a SPG (single point ground)

Additionally, you'll want to put your bike specs in your signature, so you never have to repeat it.
The search function on this site is your friend, but only if you click Advances, and search in titles only (top tip)
You have some reading to do.

And most of all, we like pictures. The best way to post pics to the forum is to set up a free flickr or imgur account. Copy the BB code and paste up to 10 pics in one post.

Others will be along with more info and help. Don't be afraid to ask question, but try using the search function as I've suggested as well.

edit: Dang it Dave, you're quick, you made 2 replies while I was typing my one.

[bwringer]

It's electronic ignition, and it's not going to run without a somewhat healthy battery and the ability to charge enough to stay ahead of the demand and keep the battery topped up.

Stop running it with a dead battery; you won't learn anything useful and you're only going to do more damage to whatever remnants of a healthy charging system you may or may not have.

Install a healthy battery, then test the charging system.