Bike stalls

[Uncle Jetski]

I inherited a 1982 GS450T from a buddy that had been sitting in his garage unused for 5 years. We cleaned the carbs, tweaked a few things, and it started right up. The problem is that it stalls after going 100 yards, usually with a brief hesitation, and sometimes with a backfire. If I wait just 10 seconds, it will start right up, and go another 100 yards before it stalls again. This process repeats.

Here’s the fuel situation: It warms up fine on the choke; if I then try to run it warm on the choke, it will, of course, stall (but this case is obviously because it’s too rich.) If I spray starter fluid around the carburetor, it does not rev; i.e. there don’t appear to be any leaks. If I run it on a separate gas tank, it still exhibits the same behavior (i.e. it stalls after a few minutes, but will start after I wait 10 seconds.) After it stalls, if I immediately clamp off the fuel supply, the bowls are both full. There is no crud in the bowls. If I run it on prime, it still stalls. If I pull the plugs after it stalls, they are both dry. If I adjust the air screws, it has no impact within 1+ turn.

I am just starting to troubleshoot the electrical system, but the fact that it re-starts after only 10 seconds makes me doubt that it could be an overheated coil, etc. It does spark against a ground after it stalls, but I have to figure out a way to do the test faster (e.g. quickly pull the wire and put it on another plug.)

Does anyone have any idea what’s going on here?

[Dave8338]

Check the screens on your needle and seat combo...sounds like there and not allowing enough fuel to flow out to keep the bowls full. Are you running an inline filter of any kind? Also, if the float heights are set too low, it will have the same effect. If it were electrical, your plugs would be wet when you pulled them. If it only happened on the tank that is on the bike, I'd say it was you vent in the fuel cap. :?

[relic-rider]

Definetely carb problems. Like said, check the float level. It is lean. The mixture screws(not air screw) should be turned out at least 2 turns to start. How did you clean the carb? Did you remove all of the o-rings before using the cleaner? That stuff will swell up o-rings and there are tiny ones down in the mixture screw holes. 5 years of a bike sitting can wreak havoc on carbs. Probably wise to get some carb rebuild kits for it.

[Uncle Jetski]

Problem solved

Well, thanks for keeping me focused on the carburetors. With the help of some very knowledgeable friends, we tore the carbs apart, scrubbed everything with carb cleaner, pulling apart all the valves, seats, diaphragms, bowls, screens, you name it. Fortunately, any parts we had to replace could come from a spare carb. Somewhere along the way, whatever was causing the problem got fixed. Now I just need to put some bandaids on my knuckles.:-D

[Uncle Jetski]

Problem returned

Well, I just took the bike out for a ride, and it stalled again (with a backfire.) It went a little farther than before (which is why it fooled us last night into thinking it was fixed,) but it looks like there is nothing else we can do to the carburetor to get it to stop stalling. We took out every o-ring, jet, valve and part we could find.

The question is: What would cause the particular behavior? That is, it starts okay, and runs for a few minutes, but then dies like it's starved for fuel. (The bowls are full, and the plugs are dry.) It won't start immediately, but if I wait just 10 seconds, it starts right up. It will then go for another hundred yards, and then stall again - as if the bowls didn't refill. But we checked the float height, and put it back in spec. We cleaned the float needle valve, screen and sleeve. Also, remember it's happening (apparently,) on both carbs. There is nothing they have in common (except age,) after the fuel goes into the bowl, right? The air screws are set at 2 turns (but it stalls regardless of where we set them.) If I assume that it's running lean, for example, what would cause that other than the air screw? Is there some other mixture screw that might be set too lean (its a Mikuni BS34SS)?

Is there some electrical component that would cause this? If it were the coils (or the igniter), they would take a half hour to cool down, right? This is acting more like a cut-off switch that resets in 10 seconds. Could it be something that heats up, shorts, and cools down quickly (because it's small)? I agree that it still looks like a carb problem, but should I look elsewhere?

New data: After it stalled, I pulled the plugs. Both were dry, but the left one was white, and the right one was "dark" (i.e. not evidently fouled.)

[relic-rider]

Just sounds like the bowls aren't filling up as fast as the gas is being depleted. Are the vent hoses for each carb bowl clogged? Is the petcock flowing good ? Are you running with the air box on? These kinds of carbs don't run very well without an airbox. Gas tank cap vent open?

[Nightmare]

Tank vent is a good idea to check... when the bike stalls take off the gas cap and listen for a hiss of air which would indicate a plugged tank vent which can lead to fuel starvation... (worth a try, its really easy to clean the cap vent if that's the problem)

[Uncle Jetski]

Still no change

Well, I had the carbs cleaned (a second time,) (completely taken apart, acid soaked, replacing worn parts,) by a pro carb shop; drained the tank and replaced all the gas; and cleaned the petcock, replacing all the o-rings, etc. I checked the tank vent, which seemed okay - and, of course, it stalls with a portable tank, too. No improvement! It still stalls after 2-3 minutes, and every minute after that.

Hellllp!!!!

[chef1366]

I would think the petcock is suspect.

[Uncle Jetski]

Bypassing the tank, it still stalls

I just tested it again using a portable tank, and it still stalls.

Again - the left plug is white. Is there a way to make the mixture richer on that side? Could it be electrical?

[chef1366]

Do you have the airbox and filter installed? These bikes won't run without the airbox.

[Uncle Jetski]

Airbox is installed

The airbox is installed, with a new filter that has been treated. It still stalls.

[Bikeman982]

I have same problem

My bike started acting real funny today. It is a 1983 Suzukii GS750E/ES that I recently bought. It was running fine a few days ago, but not today.
It would stall and then not start right away. I did get it running and at different times it would start to die. It took awhile but I got it started and then it died when starting out in first gear. I got it going again and started out and it acted like it was running out of gas. It had over 1/4 of a tank, but I barely made it to a nearby gas station and filled it up. It ran the same - barely. I can't tell if one or both of the plugs are bad, the coils are bad, the fuel is blocked, or if something else is causing it to be very erratic on running. At times it would be great, then all of a sudden stall or act like it was not getting spark or gas - skipping and the engine would stop. If I was going along I would downshift and then pop the clutch after it stalled and it would run again. It was bad at stop signs and at red lights. Sometimes it would start up and then stall when I started to go, other times it would be dead and would not start for a minute or two. I would push it to the side of the road, then start it up and try to go again. Other times it ran normal and would idle fine. What could possibly be causing this kind of intermittent problem? I am almost afraid to try and ride it again. I don't want to be stranded somewhere. I don't have any way to get home, if it fails to start up or run again. Should I just start by replacing the spark plugs, maybe the coils, or check all the carbs for bad jets or clogged lines or bad fuel?? What could it be? It really has me baffled. Anyone have any ideas??