1980 GS850G CV Carb Noise

[Guest]

I searched for a while but cannot find it my current issue.

On my GS850, The spring for one of my carb diaphragms is noisy. Kind of like tapping the spring with a screwdriver. It did this before I mounted the carbs and can definitely hear it when the motor is running. It functions fine. I can manually push up on each diaphragm and they all respond down at the same rate.

Is this a normal sound for these carbs?

I do have another set of carbs from a 1981 850 but those springs are about a 1/2" longer than my original ones. The 81 carbs are the same Mikuni 45110 model but had 170 air jets and longer springs. My current stock air jets are 190.

If the noise is normal, I will leave it but if it isn't normal and I change them all out to the longer 1981 springs, will it affect the performance of the bike?

[tom203]

"can definitely hear it when the motor is running."

you must have incredible hearing... Are these shorter springs same diameter as the longer ones?

[Kjpeter]

Same diameter on both springs and yes I can hear it rattling in the carbs. The other 3 do have a slight noise when they were off the bike but the 4th spring is louder. is it possible the springs are bad or would it be the slide sticking a little and vibrating causing the spring to make noise?

[Steve]

Well, I must say, ... your hearing must be a LOT better than mine.

With all the racket going on down there, how can you possibly isolate the sound of a single spring twanging away?

Not only that, I can't imagine what would be causing that noise. There is no airflow in that area, except while on "choke",
and there is too much inertia in the slide to have it bouncing quickly enough to agitate the spring.

Now, back to your question, ... The length of the spring isn't much concern, it would be more like 'how much tension is exerted?'
If you were to change them all, it probably would not make a noticeable change, but then, you noticed the spring twanging, what else might you notice?

.

[Kjpeter]

Why does it feel like I'm getting roasted when I ask a question??

It sounds like the old slinky going down the stairs. I guess I am mainly wondering if it is a normal sound to these engines and if I should be concerned about it or leave it be and fiddle with it later.

If I were to fiddle with it later, should I also change the jets to 170's or leave my original ones in?

I am very picky, OCD, anal retentive when it comes to things working perfectly. Sometimes its a curse, sometimes a blessing.

[Kjpeter]

Steve, I believe you are thinking of the spring in the choke assembly. The spring I am talking about is the return spring for the slide diaphragm with the needle on the end on the Mikuni CV carbs.

[Steve]

Oh, I know exactly which spring you are talking about.

Look at the airflow for the "choke" assembly. Air enters in that oval port at the top of the carb intake, passes under the diaphragm (right past that spring) and goes through the little hole at the front, where the "choke" plunger will allow it to mix with fuel and go to the cylinder when it is opened.

Yes, the diaphragm spring is in the airflow for the "choke" system, but there won't be any aiflow (or pulses of air) in that chamber unless the "choke" is activated, so, as previously stated, I can't imagine what would tickle the spring enough to get it to making noise.

Nobody is "roasting" you, it's just that nobody has ever commented on hearing that spring before. I know that I have certainly never heard it.

In the event that you do change the springs, I don't know why there would be any need to change the air jets.

And, just for the record, I used to have OCD. I have gotten over that and now have CDO.
It's a lot like OCD, but it's alphabetized, as it should be.

Also 'for the record', I do have a bit of a hearing loss in one ear. It is frequency-specific. I discovered that when I tried listening to my old analog watch that had a mainspring. I could not hear the "tick, tick, tick" of the escape mechanism, but I could hear the "sproing, sproing, sproing" of the spring on the balance wheel behind it. That loss of high-frequency hearing should allow me to hear that carb spring behind all the other ticking noises, but I have never noticed it.

.

[geol]

Why does it feel like I'm getting roasted when I ask a question??

It sounds like the old slinky going down the stairs. I guess I am mainly wondering if it is a normal sound to these engines and if I should be concerned about it or leave it be and fiddle with it later.

If I were to fiddle with it later, should I also change the jets to 170's or leave my original ones in?

I am very picky, OCD, anal retentive when it comes to things working perfectly. Sometimes its a curse, sometimes a blessing.

My suggestion is to mention you have a brat bike with a skateboard seat and have chopped off the end of your frame, mounted dog bone risers and operate the bike with no mufflers. Then you will get a better perspective on a true forum ROAST. I am just kidding, of course, I don't think it possible to hear the springs but you may have better ears than I. If the springs rattle, it makes absolutely no difference in the operation of the slides in any case. The function of the springs is not all the important as the slides will re-seat when engine vacuum lessens as you roll back rpms. Not all CV type carbs even use springs and the gauge of the wire in springs varies greatly.

[storm 64]

Now I know why my dog looks at my carburetors with that funny, confusing look. He's hearing the springs rattling around in there! Haha, just kidding☺

[Steve]

The function of the springs is not all the important as the slides will re-seat when engine vacuum lessens as you roll back rpms.

Not quite accurate. The operation of the slides has nothing to do with engine vacuum. If it did, they would be wide open when you close the throttle at high RPM.

What raises the slides is the vacuum in the venturi caused by high air flow. When more air is flowing through the carb, the slides will lift. When the throttles are opened to cause "more air flow", the engine (manifold) vacuum will be nearly ZERO.

.

[Kjpeter]

ok so if it is not those springs I am hearing or not hearing.... Is there a quick check to make sure the chain tensioner is doing what its suppose to? Without removing the carbs and or side cover? My side cover has an engine guard over it so its a little more time consuming and also I do not have a garage. Working in the dark is not always easy even with a trouble light.

BTW ever have an old TV that is on but not showing any picture just a black screen? I can hear the high pitch squeal from that. I remember asking a teacher to turn the TV off and the class looked at me like I was on drugs until they pressed the power button haha

[geol]

OK... you don't need to remove side covers to check to see if the cam chain is the culprit. You need to remove the crankcase vent cover on top the cam cover, then remove the cam cover. OR, you can remove the carbs and leave the vent cover in place. Once you can see the cam chain guide up on top, you can lift it with your finger; should not come up too much... it will come up a tad but not much. If it comes up a bunch then the tensioner isn't working as it should; probably not set correctly when last installed OR the cam chain is stretched.

[AMK]

"And, just for the record, I used to have OCD. I have gotten over that and now have CDO.
It's a lot like OCD, but it's alphabetized, as it should be. :-\\"

GMO Steve, that's classic.