1981 GS850 runs... but like a bag of worms.

[DPeanut]

Hello again all! I got my free GS850 running. Dunked the carbs, cleaned them all. Bench tested them all and made sure all was in good working order. Float height was fine, at stock. Got it to sputter and fire for the first while, then after a few more tries, ran somewhat better. After I got it to stay running for more than 5 secs (I assume just clearing out airlocks in the carbs) I could slowly work up the throttle to about half --tach does not work-- then it would just seem to drop down to nothing. I could either let it die, or work the throttle back up a bit. Any ideas what would be causing that?

I am using a different tank on this to just 'bench' test the bike. The petcock only has one outlet for the fuel line, where the stock tank, too dirty to use, has 2 lines coming to the petcock. The one large one goes to the main fuel T, and the other smaller line goes to the top of the center left carb. When I cranked over the bike, it would seem to pump air in and out of this small fitting on the carb. If I left it be, the bike would stutter and pop while wanting to start. But if I plugged the fitting with my finger, it would fire up fast and would get rid of some of the half throttle problem. From what I can conjure up as a conclusion, this fitting on this carb needs fuel to it so it can run properly?

Last thing for tonight. I am using a car battery for the bike. To crank it over because the battery in there was old, and dead. Is it normal for these bikes to need the battery there to keep running? When I unhooked the jumper cables from ground, it would run like crap. Would not rev up at all, just die. I guess it needs the battery there to keep things in check, the stator can't put out enough power to be self-sufficient.

Any help with the carb problem, the fuel line to carb thing and battery issue would be greatly appreciated.

[MelodicMetalGod]

Disclaimer: I'm not an expert these days (far from it), but I'm in the process of pulling my carbs for cleaning for similar issues, so I'm beginning to recall what I used to know.

RE: Half throttle/stalling issue:
I've had the same problem and the suggestions that I've gotten range from "dirty carbs" in general to "a dirty/clogged choke circuit" or a "dirty/clogged idle circuit". I'll be cleaning my carbs over the coming week, so I don't yet know for certain if that's my issue or not. I think you'll need to provide more information and greater detail to allow some of the GS experts here to narrow down the likely problem(s).

RE: Smaller line from carb to fuel tap:
On my bike that second line from the stock fuel tap connects similarly to one of the carbs. However, I believe that it's a vacuum line, not a fuel line. Carbureted fuel delivery systems usually use vacum in one way or another. I'm not sure if it's critical to carb operation or if it's needed for the stock fuel tap to deliver fuel properly. I'm sure that someone here will be able to provide a more complete answer on this.

RE: Battery/Need one to run?:
It is my understanding that motorcycle charging systems in general do not generate enough current at idle to charge the battery (unlike cars), which means that there is no excess current available until a high enough engine speed is reached. In addition, the electrical/charging system on these bikes is apparently their Achilles heel anyway. Therefore, without a battery installed, it is likely that something isn't getting the juice it needs. Again, someone more knowledgeable will hopefully elaborate.

I'll be watching this thread to see what other GS-ers have to say.

Good luck!

[mark]

Is your airbox on? Won't run well at all without the airbox on and well sealed. The smaller line from the stock petcock to the carbs is a vacuum line and needs to be plugged if its not hooked up, its NOT a fuel line. When the bike is running the smaller line applies vacuum to the petcock so that gas will flow into the carbs. And yes, the battery must be in place and in good working order for the bike to run.

[Nessism]

As Mark said, plug the vacuum line until you get the real fuel tank on there. These GS bikes don't run for crap until they are fully warmed up, and won't hardly run at all w/o the choke when cold. Also, the carb boot O-rings dry up and should be replaced or you will get air leaks which will be very noticable at idle - idle will hunt between 0 and 3000 rpm.

Good luck.

[Steve]

Have to agree with all previous posters.

The second (smaller) line to carb #2 is a vacuum feed to the petcock. DO NOT put fuel in here. Keep it plugged while using your "test" tank, be sure to connect it to the petcock when you put your "real" tank back on.

Yes, a (good) battery is necessary for proper running. Besided providing the necessary electricity for the ignition, it is also necessary as a reference for the charging circuit. When the regulator tries to regulate, it needs to know how much.

'80 and '81 bikes seem to have the worst problems with idling, because of the then-recent changes in the EPA laws. If you are reasonably certain that you did a thorough cleaning of the insides of the carbs, fire the engine, nurse it along to operating temperature (where you don't have the choke on) and do a vacuum sync of the carbs. Also be sure to set the mixture screws properly. If you change them much, might want to check the sync again, just to be sure.

My wife's '82 850 is a pleasure to ride after all these checks. It starts easily and idles with no choke after about 30 seconds of choke. Can't complain about that at all. \\/


.

[sissonk]

Just a point about carbs , I have found that the settings of the mixture screws needs to be very accurate , so that the engine runs properly so as to be able to produce vacumm to smoothly flow through the pilot circuit into the needle circuit. If you had these out they need to be adjust properly first before you will get a good sync . If you didn't take them out maybe some of the passages still have muck in them.

[deves3000gt]

Frist I'm no pro. but, my 78 750 was doing the same thing as far as the reving and idling. It turned out to be i hook the wrong line to the petcock vaccume line. It seems like you should double check to make sure the gas is flowing freely. I don't know if your bike is differnt from mine but when to battery was dead i kick started it and it ran and reved fine. Again your year might be differnt. Good luck. Let us know how it's working out for you.

[DPeanut]

Alright. Thank you for all the info. I went and picked up a battery today so I can run it w/o needing a car battery to jump it :? What are the settings for the mixture screws?

[Nessism]

Set the mixture screws to 1-3/4 turns out from fully seated. After the bike is running well you can tweak them a little to achieve the best idle smoothness.

[DPeanut]

Awesome! Thank you for that. I set them at 2 turn out from snug. So I guess I wasn't that far off. I'll try that after classes today and see how that works. That is, if the weather holds out.

[dcn32459]

wow

Hello again all! I got my free GS850 running. Dunked the carbs, cleaned them all. Bench tested them all and made sure all was in good working order. Float height was fine, at stock. Got it to sputter and fire for the first while, then after a few more tries, ran somewhat better. After I got it to stay running for more than 5 secs (I assume just clearing out airlocks in the carbs) I could slowly work up the throttle to about half --tach does not work-- then it would just seem to drop down to nothing. I could either let it die, or work the throttle back up a bit. Any ideas what would be causing that?

I am using a different tank on this to just 'bench' test the bike. The petcock only has one outlet for the fuel line, where the stock tank, too dirty to use, has 2 lines coming to the petcock. The one large one goes to the main fuel T, and the other smaller line goes to the top of the center left carb. When I cranked over the bike, it would seem to pump air in and out of this small fitting on the carb. If I left it be, the bike would stutter and pop while wanting to start. But if I plugged the fitting with my finger, it would fire up fast and would get rid of some of the half throttle problem. From what I can conjure up as a conclusion, this fitting on this carb needs fuel to it so it can run properly?

Last thing for tonight. I am using a car battery for the bike. To crank it over because the battery in there was old, and dead. Is it normal for these bikes to need the battery there to keep running? When I unhooked the jumper cables from ground, it would run like crap. Would not rev up at all, just die. I guess it needs the battery there to keep things in check, the stator can't put out enough power to be self-sufficient.

Any help with the carb problem, the fuel line to carb thing and battery issue would be greatly appreciated.

im so glad i found this post!!! my 81 gs850 has these exact same problems! this is a huge help... but i think my battery is ok , i probly just killed the starter, the lights and all come on nice and bright when ign. is on , but my starter wont work for crap without jumping it off