Thought I had a vacuum leak, now I think it might be a clutch issue

[fyarl666]

I have an 81 GS 400L, and it went from running perfectly to running like crap in a matter of minutes.

The basic problem is, it is not throttling properly. It's slow to return to idle after revving it, the idle has a very low, loud sound to it, and trying to drive it is damn near impossible. You need to keep the throttle open just to keep it from stalling, it has zero power, and it won't go any faster than 60kph.

At at first I thought it might be my carbs, so I took them off and cleaned them.

Then I thought I might have a vacuum leak around the boots, but after spraying carb cleaner all over the place, I couldn't detect a leak.

Im wondering now if it's something with my clutch? It sort of feels like you're trying to ease the bike into a really high gear from a low speed, even when it's idling in neutral. Is my clutch not fully engaging/disengaging?

Im at a loss as to what I should try next.

 

[Steve]

Put the bike on the centerstand.

Make sure the transmission is in neutral.

Start the bike. The rear wheel will probably turn (that's normal).

Step on the rear brake. The wheel should stop, the engine should be unaffected. Your clutch is not dragging.

Try it again, but put the transmission in second or third gear. The wheel WILL be turning.

Twist the throttle, step on the rear brake. The wheel should stop, the engine should stop. Your clutch is not slipping.

.

 

[tom203]

"I have an 81 GS 400L, and it went from running perfectly to running like crap in a matter of minutes. "

If this is a two cylinder ,Sounds like one cylinder is not working- either spark or fuel issue.

 

[fyarl666]

So hypothetically, if it's not the carbs, it's not a vacuum leak, and it's not the transmission, what else could be causing this issue?

 

[Stuarth]

Not the clutch- that wouldn't cause the engine to be slow to return to idle. I would guess a problem with one of the CV carbs slides not moving freely, assuming that the bike has CV carbs. Perhaps some dirt is stuck, causing it to move slowly.

 

[fyarl666]

Yeah I'm kinda thinking that too. I just put the carbs back on the bike, really don't want to pull them off again to check, but I don't know what else it could be.

I'll check for spark on both cylinders, and if that's not it, then I guess I'll be doing the carbs. Again (grumble).

 

[tweebs]

Put the bike on the centerstand.

Make sure the transmission is in neutral.

Start the bike. The rear wheel will probably turn (that's normal).

Step on the rear brake. The wheel should stop, the engine should be unaffected. Your clutch is not dragging.

.

My girlfriend just bought a '82 GS400E, it was only released in Canada but very similar to the GSX400. After I got it running, I noticed the back wheel would turn when on the centerstand in neutral. I was just combing though the twin forum to find out what was wrong with it when I came across you post claiming that it's normal. Can you explain why it turns?

 

[Guest]

All the gears spin whenever the motor is running, but none of them are engaged to the output shaft. However, there will always be some drag from the gears spinning on the shaft, which is enough to turn the rear wheel.

 

[Steve]

There is some drag in the clutch and the transmission, due to the oil in there. As the gears are spinning in neutral, they are dragging a bit on their shafts, which will drag a bit on the output gears, ultimately turning the wheel, if there is no resistance. Step on the rear brake or put the wheel on the ground, the gears will simply slip on their shafts.

.

 

[Sandy]

My girlfriend just bought a '82 GS400E, it was only released in Canada but very similar to the GSX400. After I got it running, I noticed the back wheel would turn when on the centerstand in neutral. I was just combing though the twin forum to find out what was wrong with it when I came across you post claiming that it's normal. Can you explain why it turns?

Wow! Looks you guys were on top this already.

Two things. The first is that it has a constant mesh transmission meaning all the gears mate with there opposing gear all time. The gears are selected by sliding a sleeve that is splined onto the output shaft and engages into the side of the gear that is selected. So all the gears are spinning all the time even in neutral, just nothing selected. Second is the transmission and clutch run wet in the engine oil so as the input shaft is spinning there is a very amount hydraulics happening between the gears on the input shaft in the gears on the output cause it to spin slightly and rotating the rear wheel. An experiment would be to start the bike cold in neutral, on the center stand, idling with the clutch engaged and observe how fast the wheel is spinning and how hard/easy it is to stop with the engine oil cold, use the brake in this instance. Then when the bike is nice and hot repeat the same thing and the wheel, if it's turning at all, should be very easy to stop with the toe of your boot.