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1980 GS850GL Need some advice

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Ok... I've done this:

the valves are in specifications, I've replaced all the o rings, dipped and cleaned all the tiny air passages with compressed air and small wire, I've sealed the airbox, and have the air screws backed out to 2.5 turns..

Here's the are the symptoms after my first ride yesterday, Idle is great set at about 1100 rpm, on initial throttle up there's some sputtering, once I get past about 3.5k rpm it smooths out with PLENTY of power in the upper range of the throttle.

Once the throttle is back down in the 2k - 3.5k rpm I'm getting what sounds like a out of time miss. I've checked the spark plug wires and pulled the plugs. #1 #2 are clean and perfect... #3 #4 are black with carbon.

all the carbs were set at the same height on the sliders... Am I reading that #3 and #4 are too rich?
IMAG0081[1].jpg
 
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The sliders (guess that's not what you call them) attached to the diaphragms. I left them where the PO had left them.
 
the slides aren't adjustable, but the needles in the slides are. is that what you are talking about? the needle height?
 
yep, needle height. Somehow (because of Steve calling me on it with the idle mixture air screws...I'm afraid to call anything a needle valve anymore...
 
Forgot to mention that the carbs were sync'd using a Motion Pro carb sync tool. (all nice and even at 2000 rpm)
 
A bit of stumble just off idle would indicate a slightly rich condition. Your #3 and #4 plugs show this. Each carb is different, so, having all of them at 2.5 turns out may not be correct for your bike. Actually, each one may be a bit different than the others. I would turn the idle mixture screws in a quarter turn on both #3 and #4 and see how the bike responds. Keep checking those plugs until they are all looking a bit tan in color.

What does the bike do at idle if you "blip" the throttle ? Does it take a second to settle into idle or "hang"....or does it dip or "bog" before settling into idle ? Of course, settling into a nice idle quickly is what you want.

Keep in mind, all this tuning must be done with a completely warmed up engine. Good Luck with it, sounds like you're very close. :)
 
Uncamitzi said:
yep, needle height. Somehow (because of Steve calling me on it with the idle mixture air screws...I'm afraid to call anything a needle valve anymore...
Click to expand...

Well, a "needle valve" is a needle valve, that's all. But that only has to do with fuel height in the float bowls.

The slides are not adjustable, as mentioned. The needles inside them are somewhat adjustable, but should only need adjustment if you have modified the airbox and/or exhaust system to the point where you need more fuel in the mid-throttle settings.

Once all the jet sizes are selected and installed (probably all stock, in your case), there are only four adjustments possible. 1) fuel level in the float bowls, 2) pilot screws (also called mixture screws), 3) carb sync and 4) idle speed.

And, ... going back to the picture in your first post, #1 and #2 are not "perfect". They are ALL too rich, but we need to know under what circumstances those plugs were run. If you were cruising down the street, then pulled into your driveway, idled for a bit, then turned the key off, there is NO telling what you will see on the plugs. You need to hold one setting on the throttle for a while, then pull the clutch and hit the kill switch at the same time and coast to a safe place where you can pull the plugs to see what they say. That procedure needs to be repeated several times, at different throttle openings, to read what is happening in the different circuits in the carbs.

.
 
Picture may not do the plugs justice...unless motorcycle plugs and car plugs are supposed to look different. The plugs in #1 #2 had no depost on them and were light tan...looking very much the same as when I put them back in. The plugs in #3, #4 were fuzzy black with carbon. The ride yesterday was a mixture of street and freeway driving over 100 miles. I am cleaning the plugs now and checking the plug wires for any shorts or breaks. I've done a bit of searching here and couldn't find any references to left side, right side ... I would understand if say #1 & #4 were fouled and #2&#3 were burning clean....but nothing about one side fouling ... #3 and #4 had a pretty hefty carbon build up. I'm thinking mid range rich on one side...but don't know where to start.
 
Twist off the plug boots, cut a half inch off and put them back on. This cured my problem. It could be that you've a weak spark on those two and it's not burning off the carbon well enough. I kinda wonder if you're in the main circuit and not on the idle circuit at idle on those two carbs.
 
It seems my idle is odd... I may have screwed up something while rebuilding. As per tutorial I backed the air mixture screws out to 2.5 turns. Just now I cranked them back softly to the stops and my idle sped up to 3k rpm.. somehow I don't think that's right...
 
Turning them in...or to the right, will lean out the idle mixture....and the it will richen the mixture by turning them out or left. it's a delicate balance to get it spot on.

Leaning out the mixture will make the idle rise.
 
ok..then that's right... just was out playing with minute adjustments 1/4 turn and such... and getting better results. I did reduce the size of the main jets down from the huge open holes the PO had in... but they are still bigger than the #115 that are stock. But that shouldn't be evident in the idle and mid range throttle openings should it?
 
Ok...another ride tonight. Started out pretty good...after we started to warm up the idle was all over the place... and then it started to miss with a slightly open throttle.. the upper range was again smooth and steady but the idle was crap. As I was turning the idle down, as it kept increasing, I realized where that spring I had left over probably went... so. I've got some doubts that I put everything back where it belonged on the reassemble so I think I need to open up the carbs again and take some notes on how things are moving.
I'm getting really tired of the tank install/removal.... Somethings going to wear out.
 
Steve said:
The only way he is going to be on the main circuit is if he is over half-throttle. :-k

.
Click to expand...

You're right, sorry I was thinking about cars. So on these CV carbs can you have the throttle blades opened too much at idle? Is that even possible?


OP, what spring did you have left over? Did you put the one that goes under the mixture screws back in? If not maybe those screws are vibrating around and that would explain the erratic idle.

I would think if you screwed them all the way in and the bike was still running there is definitely something wrong. Mine dies if I screw it in more than 2 turns out.

Steve, is it possible that his needles aren't in the right notch and left a little open at idle allowing fuel to be pulled past them? Sorry for the nomenclature, I mean the needles that affect part throttle operation attached to the sliders.
 
81GS850 said:
You're right, sorry I was thinking about cars. So on these CV carbs can you have the throttle blades opened too much at idle? Is that even possible?
Click to expand...
Well, let's just put it this way, ... if you open them more than you need for idle, you won't be at "idle" very long. It does not take much of an increase in opening to get the engine racing.


81GS850 said:
Steve, is it possible that his needles aren't in the right notch and left a little open at idle allowing fuel to be pulled past them? Sorry for the nomenclature, I mean the needles that affect part throttle operation attached to the sliders.
Click to expand...
Evidently you don't have a full grasp of how these carbs work. Don't worry, you are not alone.

There is only one notch in the stock needles, so that should not be a problem. And, for those of us who DO have more than one notch or have raise the needle by other means ("shimming"), idle is not affected, so that shouldn't be a problem, either.

The needles are slightly tapered. As the slides rise with increased airflow, the taper on the needle allows more fuel to flow past it into the air stream. The tips of the needles never leave the jets, to ensure that they do not hang up by not fitting back down in the jet.

.
 
Ok, guess I need to brush up on how these things work, I'm trying to apply automotive carb theory and it doesn't work. ;)
 
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