Burning smell at full throttle and engine knock

[BossMaverick]

I am having a slight rubber burning smell under full throttle at 5,000+ RPM's. At first I thought it was my leaking oil cooler hoses, but I replaced them and the smell continues. I'm not using a significant amount of oil (a quart or less every 2,000 miles), I don't have any oil leaks anymore, and I don't have tire rubbing. If I hold a steady 5,000+ RPM at mid throttle, there is not a smell. Anybody have any ideas? I'm more curious on this problem than concerned since I'm not having any spark plug fouling or exhaust smoke. It runs smooth but I know it could stand a carb cleaning.

Also, I'm having a engine knock noise that is best described on Yamaha's OEM parts website under the first TSB. To summarize, it's a knock at partial throttle cruising situations between 3,000 to 4,000 RPM's. It's an annoynance with my fairing bouncing the noise back to me. It doesn't knock under acceleration but just at steady cruising. Strangely enough, it gets better with a can of seafoam. Yamaha's TSB says the noise can be reduced with a different vacuum diaphragm assembly, part #3h5-81683-09-00. Strangely enough, that is the only diaphragm part number that they list now. Anyone have a simple fix for this problem or a source for a cheap upgraded diaphragm assembly? The knocking is driving me nuts.

Thanks!

[trbig]

Under full acceleration, you could be getting a larger amount of blow-by than normal, which would force these gasses into your crankcase and out the vent line.. with possibly some of those fumes getting back up to you. As stated, you have a fairing, and that tends to swirl the air from the back side of the bike to the front which would help them get to you. This is all just a guess though. Since you are likening the smell to burning rubber, just keep an eye on your tires and carb boots to make sure they aren't getting hot looking spots.

As for the knock, I would try to rule out a crank or rod bearing. If it's possible to replicate the knock while off of the bike, get a heavy glove and take turns pulling the spark plug boots off of the plugs one at a time.. then back on. If you find a cylinder where you pull the boot off and the knock goes away.. I would lean towards bearing problems.

But.. since the problem goes away with Seafoam and you are burning oil, it could be a matter of carbon formation in the head/cylinder getting built up to a point to where it's raising your compression past your current fuel's antiknock properties and that's what you're hearing. Seafoam would raise the octane rating high enough to get past that point. A pinging engine means there are hot spots in the cylinder that are igniting the air/fuel mixture before it's time and prolonged.. could cause lots of problems.

It is hard to describe or diagnose a sound on here though, but maybe this is something to look at.

Tod

P.S. Another quick thought.. when was the last time you checked/changed the fluids in your middle/final drives? Maybe the grease is burnt and harder acceleration causing hotter/harder work for them and smelling THAT out of the vent? OK.. Stabbing in the dark here.. but thought worth mentioning.

[Crazcnuk]

I am having the same problem since I rebuilt the top end.

It's not really a 'knock' but it feels like detonation right around 4000 rpm (exactly where it sits at highway speed limit).

Decelerate or accelerate and the noise/vibration goes away.

The fairing really amplifies the noise. I also get a wierd sickly sweet smell while it is doing this. It smells sort of like a charcoal BBQ (w/o the steak!).

[TopCatGr58]

Hey Folks,

Cruising at 4K rpm is right where the vac. adv. pulls the timing very far advanced for fuel economy, but it may be just too far advanced for the grade of fuel you're running? As Tod stated, the Seafoam most likely raises the octane, and helps it to NOT preignite in the very advanced timing state.
When you crank the throttle open more, the vacuum decreases, and the timing actually drops back to LESS advanced to take advantage of the richer fuel/air mixture for more power!

The simplest test would be to put in some 89 octane if you're running 87, and see if the problem persists, or diminishes.
T.C.

[tarzan]

My SG,the one I just sold has the exact same problem.I'm pretty sure it is the vacuum advance.I put about 3500 miles on it last year and the knock never changed in tone or loudness.Always from 3000 up to like 4500 it would do it.
I found the TSB on the advance when I was trying to diagnose it and deciced to leave it.BTW mine only has 4100 miles on it and runs great,so I dont think it has a bad bearing.

[bikerphil]

noise at 3-4K under light load

Kinda have the same problem on my 79SF. Higher fuel octane seems to help, a little. I also tried backing the timing down a little, this made the problem disappear, but power disappeared also. I advanced the timing back up and then decided to shorten the travel limit of the vac. advance unit. this did help a lot with no power loss or rattling. The only other thing I'm not sure about; I'm running a centrifugal advance from a Standard on this Special and it's possible it advances further than the Special one does.

[Crazcnuk]

"The simplest test would be to put in some 89 octane if you're running 87, and see if the problem persists, or diminishes. "

This is what I was going to try. I know Yamaha already knew about the problem back when these bikes were new. They also said it is NOT harmful to the motor, just annoying.

Mine didn's have this problem, though until after the rebuild. I assume it is due to the increased compression, and a lack of oil raising the octane!

[fredintoon]

Lose the fairing?

They only throw the engine noises right back at you.
Posts here have said the noise is not harmful, only annoying.
My dear old father-in-law used to claim he could get another 10,000 miles out of a Hillman Minx engine if he turned off his hearing aid while he drove it.

[BossMaverick]

I should have clearified my meaning of knock for this thread. When I say knock I mean more of a detonation sound.

I normally use the premium gas (91 octane). I've found that if I run 87 the engine actually has a little more power and is generally smoother running; however, the knock gets a little louder (even more annoying). I would compromise with 89 octane but the 89 has ethanol at the gas stations around here and the 87 and 91 doesn't have ethanol. Again, it doesn't knock at idle, acceleration, or deceleration, just at a steady cruise between 3,000 to 4,000 RPM. My problem is exactly described by the Yamaha TSB. I'm not concerned so much about the knock causing problems (according to the TSB at least) but it is very annoying with the fairing. I wonder if a slightly firmer advance spring would keep the advance just below the point of knock

I would really like to find a solution to the knock so I can use 87 octane gas since I run smoother with it, and so I'm not annoyed by the dang noise anymore.


I think I thought of possible cause and cure for the oil burning smell. I'm going to clean and reoil my Uni filter and use actual Uni brand filter oil in case my current cheapo filter oil is being sucked into the engine under wide open throttle.

[cywelchjr]

They only throw the engine noises right back at you.
Posts here have said the noise is not harmful, only annoying.
My dear old father-in-law used to claim he could get another 10,000 miles out of a Hillman Minx engine if he turned off his hearing aid while he drove it.

Actually some of us actually like the look with the fairing, and a few more like the ride better. I also like the storage that the fairing, bags and trunk give me. Then again maybe I'll try putting a sidecar on my next 11, then the wife might even come with me on rides.

[fredintoon]

Actually some of us actually like the look with the fairing, and a few more like the ride better. I also like the storage that the fairing, bags and trunk give me. Then again maybe I'll try putting a sidecar on my next 11, then the wife might even come with me on rides.

Hi Cy,
regarding fairings, you like 'em, I despise 'em and we are both right. Or at least firm in our opinions.
As you say, if you had a sidecar you could get by without the fairing storage but if your wife wants to ride along you'd best keep the bags & trunk, eh?
My own dear wife always refused to ride pillion but happily rides in the sidecar.
As the phrase "chick magnet" is not always appropriate let me say instead that a sidecar is a great social lubricant. Many have noted that while folks in parking lots tend to hastily walk away shielding their children from solo riders they will go out of their way to speak to a sidecarist even if he is the same unshaven leather-clad figure as he was on his solo bike.

[cywelchjr]

Hi Cy,
regarding fairings, you like 'em, I despise 'em and we are both right. Or at least firm in our opinions.
As you say, if you had a sidecar you could get by without the fairing storage but if your wife wants to ride along you'd best keep the bags & trunk, eh?
My own dear wife always refused to ride pillion but happily rides in the sidecar.
As the phrase "chick magnet" is not always appropriate let me say instead that a sidecar is a great social lubricant. Many have noted that while folks in parking lots tend to hastily walk away shielding their children from solo riders they will go out of their way to speak to a sidecarist even if he is the same unshaven leather-clad figure as he was on his solo bike.

Maybe I could figure out a way to setup a sidecar rig that is easily detachable so I can attach it for SWMBO and detach it for solo riding.

[fredintoon]

Warning!

Maybe I could figure out a way to setup a sidecar rig that is easily detachable so I can attach it for SWMBO and detach it for solo riding.

Hi Cy,
sidecars are an addiction. There is no cure. And we all start like that. Just undo 4 bolts and unplug the lighting wires to ride solo.
Well, you will most likely leave the subframe still attached and the best way to mount that is on the centrestand mounts but still, it's a solo again.
Then you realize that you haven't taken the chair off once this year and then you get into flat-tread tires and reduced front wheel trail and the inability to give up all that carrying capacity and the way that riding on gravel or ice has become hardly a bother rather than white-knuckled terror and then it's too late. You are hooked. And what was the other thing?
Ah yes, you start evangelizing the things worse than a JW.

[Bigleo]

pre ignition knock

Hi, I too had this knocking problem. I disconnected the vacuum advance entirely. This is not a performance enhancing piece of equipment, it is only used to advance ignition timing at low engine loads to increase gas mileage. To make up for the loss of ignition advance, I advanced the initial timing to 15 degrees BTDC. The bike starts way better now, and has much better low end torque. I also suspect the vacuum advance is the main culprit in causing the broken ignition wires near the pick ups. Just take off the ignition cover and start the engine. The vacuum pulse is from only the one cylinder, it sure causes the vacuum can to yank the timing plate back and forth. This is what I think ruins the wires after a period of time.
Leo

[BossMaverick]

Bigleo, did you notice any change in gas mileage with your mod? Also, did you lose any top end performance?