Strange loss of power

[Anonymous]

Sounds like you're running into a lean condition, fuel tank vent, petcock, vacuum hose to petcock, or carbs. Also everything to do with the air filter, its box and associated hoses. Also the orings between the carbs and the head if this bike uses screws insted of clamps. Are any of the header pipes turning gold or blue? Check the plugs also. Most of these bikes sat a long time at some point during their life, the carbs definately needed tanked.

[HiSPL]

Just for giggles, try replacing your vacuum hose from the #2 carb to the petcock. I had an intermittant problem once where the vacuum line would get hot and crimp off the vacuum. It didn't happen all the time and took me forever to find.

Just a guess, but its cheap 'n easy..........

[nabrams]

I have to agree with Kieth on this one - I also think it's electrical. In your case I think it's the regulator-rectifier and/or stator (or bad/dirty/corroded wiring connections to either). I say this because my old GS450 would die at random and then start up fine after sitting for 10 minutes. When a bad RR starts to heat up it can become a big resistor, impeding current to the coils, leading to gradually weakening spark as the resistance in the RR increases. After replacing the regulator-rectifier that problem went away. Then I had a different problem - the bike battery (brand new) would drain after a few rides - In this case it was a bad stator.
Another problem I found on my friend's GS450 only after a very tedious process-of-elimination was that his signal generator had frayed wiring, preventing a strong spark to the spark plugs. This one was especially hard to find because the bike would run all day but with reduced power. As soon as I replaced the wiring to that signal generator, the bike ran perfectly, but I spent at least 10 hours checking tons of other things.
It can also be faulty coils (gradually building resistance as they heat up).
I think the only way to pinpoint your problem is the time-consuming "process-of-elimination" method.
First of all, I'd ride the bike without the gas cap on, to make sure it's not a venting issue.
Then I'd carry a spark plug wrench with me so I could check the plugs immediately after the stall. Verify that they're getting strong spark. If they're not, then wait a half hour till the bike cools down. Then check the spark again. If the spark looks good at that point, I think your problem is narrowed down (namely, faulty electrical components preventing strong spark when heated up). If so, run the bike till it stalls (again) and measure voltages for each component (while the bike is still hot) to pinpoint the weak link in the electrical circuit.
At this point, if you've verified that all electrical components are functioning properly even after the stall (bike is still hot), then it has to be a fuel problem (because all cylinders stop firing). The only think I can think of that would gradually worsen the fuel flow to all carbs (besides the venting - which we've eliminated by riding without the fuel cap) is some kind of blockage at the internal petcock screen that worsens with heat.
Sometimes, just taking that petcock off the tank can reveal the truth.
Let us know if you try my troubleshooting steps and what your findings were.
Good luck - you'll figure it out.

[KEITH KRAUSE]

I have a couple of ideas that might help.
When it does it again, try turning the petcock to prime as you're riding.
If this stops the problem, then you know its either a bad vacuum tube, or bad diaphragm, or a dirty petcock.
If the problem remains, then at least you know the vacuum tube and diaphragm are not the cause. You could still have a dirty petcock but I don't think so.
Another easy fuel related check would be to pull over as soon as it does it and check for fuel in the bowls. Put the bike on the centerstand and drain each bowl into a small cup. If you can see that one or more of the bowls had less fuel in it, you may have a blockage at the float needle valve/seat.
If you try this, be sure to take a rag with you. Use a cup that is "see through' and mark the level of fuel, dump it out and go to the next bowl.
If you see different amounts you know you have a low fuel level problem in that carb.

[Anonymous]

Monday night I so nearly set my bike on fire when the vaccum hose wouldn't quit pouring gas all over my exhaust pipe. I called 911 but fortunately, the thing never caught fire. The gas boiled off the pipe, though. Sooooo close. The bike sat, not running, for a bit before this happened, so the pipes weren't as hot as they could have been. Thirty seconds earlier and I might be a former GSer. The fire engine gave me a ride home and I came back the next day with a trailer. One of the firefighters was a Harley rider, so you know they're not all bad.

Anyway, be careful if you're going to have loose gas around a hot bike.

Michael

[Billy Ricks]

Monday night I so nearly set my bike on fire when the vaccum hose wouldn't quit pouring gas all over my exhaust pipe. I called 911 but fortunately, the thing never caught fire. The gas boiled off the pipe, though. Sooooo close.

Twice a couple of weeks ago when filling up with gas the pump didn't shut off like it should and at least a quart of gas spilled all over my hot engine and exhaust. I just stood back as the fuel vaporized. Luckily it didn't light up.

[Anonymous]

Could the blue smoke be related to incomplete combustion due to poor spark/ignition? This might answer both the loss of power and the smoke.


Ummm, I missed the whole second page of responses, pardon the gaffe

Catnthehat

[Anonymous]

Power Loss

Tyler,

sounds like a familiar story ... one which almost had me selling the old GS (oh and cussing a lot).

Question: How's your battery? Make sure it has a full charge ... if it does that'll get ya about 60 -120 mi even if your stator is dead.

As the battery starts to die (because it's not charging) you'll start getting weak spark and eventually the plugs will fuel foul. Usually one the ones on the weakest coil will go first. When that happens (your now running on 2 or 3 cylinders, and the bike will run, at speed, smoothly just low power) the non-firing cylinder remains cold (relativity) the oil control ring doesn't expand and small amounts of oil will leak into the cylinder and blow past the exhaust valve into the still hot pipes and burn off (a little blue smoke).
After the bike sits a bit the battery charge will come up some ... maybe enough to get you further down the road. Let it sit over night and you'll swear that you've fixed it and it's good to go ... until you get down the road about 20 miles and it craps out on you again.

My 2 cents ... check your battery ... if its weak or dead ... check your charging circuit.

Kurt

[Anonymous]

Kurt,

I don't think it's a problem with the battery or stator, although it could be something elsewhere in the electrical system that is causing the symptoms you describe.

I usually ride far enough to encounter this problem when driving back and forth to school, so I don't get to test it much. I just had the problem again as I came home though.

The battery is strong, and able to crank the engine many a time even in the cold without any noticable decrease in power. Also, when I encounter the mentioned problem, the battery is still able to crank the engine considerably, but the engine just doesn't want to catch (unless I let it sit for about 15 minutes). That kind of leads me to believe it's not something with the battery or stator (I believe I have the original stator on there, but don't know for certain).

Also, this past time that it happened, it was near freezing, and I only went about ten miles before it happened. I was going up a slight hill, and just started to feel it die. Similar situation to before...start to downshift...keeps losing power...eventually stalls out and I drift off the road.

--Tyler

[KEITH KRAUSE]

Tyler, to narrow it down to electrical or fuel related, try this.
The next time it does it, pull the plugs. If any plug is wet, then you know that cylinder is not sparking or has a very weak spark.
If all the plugs are dry, then you know it's not electrical. Take a plug wrench and also a piece of 5/16 or 3/8'' tubing. When the plug is loose you can put the tubing over the plug and remove/install without getting burned.
Let us know what happens and we'll go from there.