1978 gs1000 air/fuel woes

[Jangusmcbarley]

After moving to Tulsa, ok, buying a gs1k, minimal tools, cannot get fuel/air right. The bike sat for three yrs., guy I bought it from got it running. The old bird bogs and sputters until today, BUT, I am not sure where hoses from top of carbs connect. Disconnecting the center of the three top hoses, the one with the vacuum, from the tank, helps the bike run right. I'm not sure if that hose is supposed to mount to the small petcock hose connection, but if not where? When running it With the vacuum hose hanging free it runs "right," but the hose is making its own little backfiring noises, pops. This leads me to believe a carb rebuild may not be necessary at the moment, but what the heck do I know?!? Between the three top carb hoses, and the hose coming from the tank (overflow), and the fact it runs better now, knowing that vacuum line has to connect somewhere, I'm baffled. Does anyone have any advice? I'm proud to own this record winning bike, just hoping it will run like one.

[7981GS]

Hint,
If you introduce yourself in the GS Owners section, they tend to notice you much better.
If you list your location and bike that you own in your profile, more likely to find a fellow nearby GSer that is willing to help.

Just sayin'

Eric

[OldVet66]

Welcome to the forum. You have come to the right place and you have the right bike. You can have one of the nicest bikes you can get, or create the nightmare on Elm street, depending on how you approach it. It is a 35 year old motorcycle, so you need to park it and do the necessary maintenance to bring it back to where it is reliable and safe. That might not take too long depending on it's condition. Fuel delivery is critical, so you need to clean the tank if necessary and inspect the petcock for proper operation. Get that out of the way, and you won't be filling your newly rebuilt carburetors with rust, or dumping a tank of fuel in your oil. While the tank is off, adjust the valves, the single most important step that is most often skipped. Nothing runs right without that. The GS valves get tighter with wear. Proper carburetor rebuild is a must, along with new O-rings and possibly carburetor boots. The electrical system, needs a thorough check, brakes brake lines tires etc. There is more than enough expertise, and willingness to help you rebuild the whole bike if you needed to. You will find manuals, parts sources and everything else you need to do the job. Now I will step back and let the real pros introduce you to one of the best bike on the planet IMHO.

[Jangusmcbarley]

Thank you, Eric and Old Vet, I'm an old salty Vet myself. Will do as advised. Processes and results of the attempts have me confused. Obviously air intake is an issue, making progress nonetheless. It's good to have this resource for knowledge I definitely don't own yet. Any further input is very welcome.

Cheers!

[OldVet66]

Carbs from left to right are 1-4. #2 and #4 are vents. #3 is petcock vacuum. There are also problems associated with carb boots not sealing, causing vacuum leaks, boots to the air box and top of box not sealing causing a lean condition because of too much air. Try to get everything running right with the stock air system and exhaust. My bike came with a 4 into 1 exhaust and I switched to pods so I was in uncharted re-jetting territory already before I even learned how to rebuild the carbs. Needless to say, I spent a lot of time chasing my tail without a clue. After a long journey and learning to do it all myself, it purrs like a kitty and gives me a big grin every time I get on it. I ride it to work year round and really appreciate the 42MPG on regular gas. If pulling the vacuum line causes it to run better then it isn't surprising that the air adjust screws on the side don't do much. Turning them in will make it richer and out leaner. There are four fuel needles under the bowls, but they are painted in position at the factory. A bit of soaking may be necessary to free them up to get them out before the final soak in carb dip when you rebuild. You have blocked up passages in your carbs. It may have sat for three years, but how long did it sit before the previous owner got it running. Everyone seems to think carb cleaner spray and compressed air will do the job, but it won't. I'll guarantee those small passages in there look like a plumbing commercial.

[OldVet66]

Thank you, Eric and Old Vet, I'm an old salty Vet myself

Did a lot of H&I for the Marines around My Lai.

[MisterCinders]

After moving to Tulsa, ok, buying a gs1k, minimal tools, cannot get fuel/air right. The bike sat for three yrs., guy I bought it from got it running. The old bird bogs and sputters until today, BUT, I am not sure where hoses from top of carbs connect. Disconnecting the center of the three top hoses, the one with the vacuum, from the tank, helps the bike run right. I'm not sure if that hose is supposed to mount to the small petcock hose connection, but if not where? When running it With the vacuum hose hanging free it runs "right," but the hose is making its own little backfiring noises, pops. This leads me to believe a carb rebuild may not be necessary at the moment, but what the heck do I know?!? Between the three top carb hoses, and the hose coming from the tank (overflow), and the fact it runs better now, knowing that vacuum line has to connect somewhere, I'm baffled. Does anyone have any advice? I'm proud to own this record winning bike, just hoping it will run like one.

If your bike runs with the vacuum line hanging free, your petcock must be in the PRI position or is failing wildly. With no vacuum and petcock set to ON or RES, you should have no fuel supply.

If you are set to PRI and find it "running right" with the vacuum port open, then your jetting is too rich, causing the carbs to gobble up the extra air coming in through the vacuum port.

You won't be able to get the air/fuel right until you tear down the carbs and clean them fully. Otherwise you will have no baseline and have to chase gremlins in circles.

Good news, you are in the right place for carb rebuild help. I think you have VM26s on that bike, like mine. They are pretty easy to tear down and clean. BassCliff has a pretty good guide for VMs on his site.

You should also start through the basic maintenance list, valve adjustment, charging system, etc. These old bikes need maintenance that POs never seem to do. Once you tighten her up on those items, however, you'll really dig the bike.

[Big T]

If your bike runs with the vacuum line hanging free, your petcock must be in the PRI position or is failing wildly. With no vacuum and petcock set to ON or RES, you should have no fuel supply.

Plus, your crankcase may be filled with gas, how's your oil level?