loud noise 1981 gs750l

[i57chevy]

new problem as the saga continues. Bike makes lots of loud noise when it starts. problem started yesterday. Does not make the noise when you're turning it over with the plug wires loose. Can't really tell what area, but it seems like the lower end of the motor. I have the valve cover off and everything looks fine. Any ideas where to start without disassembly

[cloudbreakmd]

You said with the wires loose.. Does that mean that the engine still fires or just turns over?

If just turning over and not running then it may be the starter, starter gear, or starter clutch.

[i57chevy]

I unplugged the wires so it wouldn't start just to try to isolate the noise, but it doesn't make the noise unless I let the bike start.

[Wingnut]

I unplugged the wires so it wouldn't start just to try to isolate the noise, but it doesn't make the noise unless I let the bike start.

Need more definition of the noise. Such as:

1. Does it make noise on start-up or continualy?

2. What does the noise sound like, tapping, grinding, clunking?

3. Does it make the noise sitting still in neutral?

4. Does it make the noise sitting still, in gear, with the clutch pulled?

5. Does the frequency of the noise increase when you rev the engine?

Try to use a long large screwdriver as a stethescope. Make your hand in the shape you would have it to hold the throttle grip, then turn it palm up. Insert the screwdriver handle in from the pinky end half way to your thumb. Clasp firmly. With the engine running, put your fist to your ear so your thumb is near your ear and touch the pointed end of the screwdriver to the engine. Down low and then up high. Move around to find where the noise is loudest. Granted, you will hear the noise anywhere you touch the engine as the sound travels through, but it should be louder in some spots than others.

Report results.

bob

[i57chevy]

I'll have to troubleshoot more tomorrow, but It's a loud knocking noise. It's constant as soon as it starts in neutral. I disconnected the clutch cable and had no affect. It was making the noise on the road yesterday, so it does it in gear. I disconnected on plug at a time and started with knock on 3 cylinders. I ran out of light, gas, and battery before cylinder no. 2.

[Wingnut]

I'll have to troubleshoot more tomorrow, but It's a loud knocking noise. It's constant as soon as it starts in neutral. I disconnected the clutch cable and had no affect. It was making the noise on the road yesterday, so it does it in gear. I disconnected on plug at a time and started with knock on 3 cylinders. I ran out of light, gas, and battery before cylinder no. 2.

OK. That's not sounding too good at this point. I don't mean to insult your inteligence, but not knowing you I have to ask:

It's full of oil right?

What's the history here?
You've been riding it and it's been fine until all of a sudden, or, it's a restoration and this is the fist time you had it running and it's making this noise?

The reason I ask is, generally speaking, nothing should go wrong like this without something to precipitate the problem. Did it get run low on oil? Were you twisting it to red line all day. I'm saying, something usually happens to make a problem like this. Hole shots? Maybe something bad was done by a previous owner? Was the crankcase full of gas at one time?

[i57chevy]

I moved everything from one frame to another. It's never been ran low on oil while I've had it. It made some slight noise before the work, but I believe it was the tensioner. I've been riding it the last few days with only some carb adjustment probs. It started knocking slightly then really bad before I got home. I drained the oil and it looks fine.

[earlfor]

It sounds to me like you crossed your plug wires. Check to see if the two plug wires on the left coil are going to the 1 and 4 cylinder. The left coil should be firing the 1 and 4 cylinders.

Earl

I moved everything from one frame to another. It's never been ran low on oil while I've had it. It made some slight noise before the work, but I believe it was the tensioner. I've been riding it the last few days with only some carb adjustment probs. It started knocking slightly then really bad before I got home. I drained the oil and it looks fine.

[i57chevy]

I guess that it would depend on which coil I put on what side, but the wires are actually lableled. I thought about that, too. According to the manual the cylinders are labeled left to right 4,3,2,1 facing the front of the bike. I have the left coil going to 2 and 3, but it's the coil with the yellow and black wire. What about water. would it knock and how loud? I filled it with gas the same day, but I had a good bit in it. I hosed the bike down also. I guess it could have sucked water in, but when would it start and how long would it last

[earlfor]

"Facing the front of the bike",.............does that mean sitting on it and facing the front or standing in front of the bike and looking at it? :-) :-) Lemme see if we are talking on the same wavelength. LOL When sitting on the bike, the cylinders are numbered 1,2,3, and 4 from left to right. On the right end of the crankshaft are the crank triggers (or points if you have points) The left crank trigger (located at 9 oclock) fires cylinders 1 and 4. It makes no difference which side of the bike the coil is mounted on. Usually it will be on the left side. Whichever coil the 1,4 crank trigger is connected to must have its spark plug wires connected to the 1,4 cylinders.

If you have reversed the coil locations, but not the wiring, the firing would be backwards.

Earl

I guess that it would depend on which coil I put on what side, but the wires are actually lableled. I thought about that, too. According to the manual the cylinders are labeled left to right 4,3,2,1 facing the front of the bike. I have the left coil going to 2 and 3, but it's the coil with the yellow and black wire. What about water. would it knock and how loud? I filled it with gas the same day, but I had a good bit in it. I hosed the bike down also. I guess it could have sucked water in, but when would it start and how long would it last

[i57chevy]

looks like the way I got it

[earlfor]

All righty. LOL

Earl

looks like the way I got it

[i57chevy]

looks like the problem is in the no4 cylinder. guess there's no easy way to see if it's a connecting, bearing, or etc. noise comes from that cylinder and I measured the top of the piston at tdc and it's about 1/8 difference than no. one piston. Don't know if that says anything