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Change in Engine Noise at Highway Speeds

  • Thread starter Thread starter sztandanga
  • Start date Start date
S

sztandanga

Guest
Hey all,

Since I'm a fairly new rider and I just started taking my GS850 out on the highway, I noticed something weird happening. Every now and then the pitch of the engine noise changes at around 55 to 60 mph. At constant throttle, it'll be making one pitch, and then suddenly it drops to a lower pitch for a second or so and then it goes back up to the normal pitch for that RPM. Then it happened s again a few seconds later. It usually happens when I week more crosswind, but I'm not exactly sure of that. It seems to me like the engine is being starved of air or fuel. Interestingly though, this doesn't happen when I'm putting around town around 30 to 40 mph.

I first thought it might be cross winds "stealing" air away from the intake, but I have CV carbs and the stock airbox, so I don't think that that's likely to be the issue.

Next I thought that maybe there's an air bubble in my fuel line that's preventing good flow of fuel. When I set the petcock to prime and ride it's seems to help, but no conclusive results. The petcock I have is a replacement from the forum recommended eBay seller. Interestingly though, the fuel and vacuum lines face the rear of the bike, whereas the original petcock hat the lines face the front of the bike,so my fuel line is a little long. It looks like I can pull the nipples and plugs out and reverse them. Has anyone done that? I wouldn't want to throw 50 bucks out the door doing something that can't be done.

I have new carb and intake boots. I have a new, well oiled K&N air filter insert. I cleaned the carbs over the winter and replaced all of rings (I unfortunately had to use K&L float valves and valve seats, but I changed out those o-rings). I just recently installed new spark plug caps. I just did a valve clearance check. I'm running 130 to 135 psi on all cylinders.

Has anyone experienced anything like this before? Could it be the fuel line or the float valves? Could it be both?

Thank you for any help. And sorry for the wall of text.
 
Last edited:
Does the speed change when this sound appears? If so that could indicate a fuel or ignition problem. Have you checked the plugs after this happens? In other words, the next time you hear this sound, stop immediately and pull the plugs. If there is anything funny with fuel or ignition it should show on the plugs at that time. The petcock vacuum line you should be able to pivot 180 to face front. There are 4 small screws holding the diaphragm cap on, just remove those, careful not to disturb the rubber and rotate towards the front of the bike. Be careful with the small spring and make sure its seated properly. That's it. I did that with my petcock and saved all that tubing.

Assuming timing is correct, spark advance working smoothly and electrical system working properly (read the stator papers) the focus should be carbs and fuel system.

We are here to help, glad to see a new member. Welcome.
 
The CV carbs on the 850 setup are extremely vulnerable to crosswinds. Get the rubber boots and airbox stuff all sealed up tight and I bet your trouble will disappear.
 
The change in pitch happens so quickly and is so short. Would it register on the plugs? It's one second low and then back up, and then repeat. I do feel a change in speed. At least I think I feel one.

And I didnt think it was that simple. Doing so doesn't affect the settings of the knobon the front?

Thanks wymple. I didn't know that either. I though that the airbox and carbs were sealed up pretty well. I've got weather stripping everywhere on the inside of that airbox and new carb and intake boots. It did look the was some silicone or other sealant on the old airbox boots. Is that something I should try?
 
Try the old trick of spraying a bit of starter fluid or even carb cleaner around the intake boots and airbox rubbers. Let the bike idle and spray; if idle changes you have a leaking or defective seal at that manifold. I also did not know of the crosswind problem with 850 CV carbs. Now I have to ask, does this crosswind also affect CV carbs on my GS1100E? Is this something to be looked at with any of the CV carbs?
 
I have ridden through some nasty crosswinds, not to mention passing many trucks on the highway, with each of them pushing its own version of a crosswind off the front bumper and have never noticed any change in the way the bike runs. I have done that with all four of the GSes in the stable, as well as the Wing, never a hiccup from any of them.

Now, I will have to qualify that a bit. :-k It might be because I accidentally got all the carbs perfect, or it could be that my butt just isn't calibrated enough to notice. Two bikes (wife's 850L and son's 1000G) have stock pipes and airbox. My 850G has stock airbox and a header. Other son's bike (650L) has EMGO pods and a header. The bikes with a stock airbox all have K&N filter inserts.

Personally, I would bet on the non-calibrated butt theory, but all the bikes seem to run well, so I leave them alone.

.
 
Steve said:
I have ridden through some nasty crosswinds, not to mention passing many trucks on the highway, with each of them pushing its own version of a crosswind off the front bumper and have never noticed any change in the way the bike runs. I have done that with all four of the GSes in the stable, as well as the Wing, never a hiccup from any of them.

Now, I will have to qualify that a bit. :-k It might be because I accidentally got all the carbs perfect, or it could be that my butt just isn't calibrated enough to notice. Two bikes (wife's 850L and son's 1000G) have stock pipes and airbox. My 850G has stock airbox and a header. Other son's bike (650L) has EMGO pods and a header. The bikes with a stock airbox all have K&N filter inserts.

Personally, I would bet on the non-calibrated butt theory, but all the bikes seem to run well, so I leave them alone.
Click to expand...

Good to know, thanks. I have never noticed anything different when I have ridden among crosswinds or passing large trucks, does that mean I too have a "non-calibrated butt?"
 
Crosswinds made a lot of difference on all three of the CV carbed GS Suzukis I've owned. So much that just moving the knees in or out from the bike is noticeable. My 850 was horrible when I got it. Sealed up intake systems cleaned them all up nicely. Recently my son had the same issue resolved on his 83 GS1100.
 
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