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GS1000G carb settings (again)

  • Thread starter Thread starter feelergaugephil
  • Start date Start date
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feelergaugephil

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OK, here we go, 1981 GS1000G, K&N standard air filter (cleaned properly) Harris 4 into 1, shimmed correctly, carbs balanced.
After e-mailing and getting valueable from Keith Krauss, I was going to P.M him, but I figured some people might have the same problem....
After the GS was run in (rings) I checked the air scews (on the top) which were all roughly at 2.5 turns.
I reset them to approx 1.3/4 and it would not idle, then at 2.3/4, still the same problem.
Eventually they are all at 4 turns out, the GS runs mint, idles perfect, and runs out at 136mph..............
I have ridden with a few friends who ALL tell me it smokes pretty bad when I start going at warp speed, if I ride at normal speeds, it doesn't smoke, only when I get on it.
If I ride with the Mrs on the back (dare I go fast,,,,,) it uses NO oil.
On my own at quicker speeds, it uses oil.
But what I remember, GS's use oil when at warp speed.
So, Keith, if your reading this, how do I lean out my mixture and make it still idle properly.
The plugs look OK too. Phil.
 
Is the heavy exhaust black? If so, at full throttle you're completely on the main jets. If the bike has been tuned correctly and is in good mechanical condition, then your mains are too big.
And 4 turns out on the mixture screws seems too far out to allow for just a pipe mod'. I would have to say this is compensating for something else wrong, something causing the pilot circuit to run lean. I think your bike should idle well with the mixture screws at around 2 1/2 turns out. Maybe an incorrect float level(s)?
 
Thanks Keith, the main jets are 117.5 and under full throttle it is heavy black, more noticable at night with car lights behind me.
If I ride it normal, it doesn't smoke.
Should I bring the jets down to 115 (standard) again?
 
Going up just one step, 2.5 on the mains, allowing for the pipe, (if it really does flow better) wouldn't cause heavy exhaust. A good flowing pipe alone should require a full size up (5), or sometimes more.
Something else is causing it.
I just re-read your first post, you say "shimmed correctly"? What do you mean? Shimming the stock needle jets? Shouldn't be necessary for just that pipe, if the air box is completely stock, no holes cut, lid off, etc.
A rich needle will cause heavy exhaust. Even though it may appear to be a main/full throttle problem, a rich needle setting will take time to burn out of the cylinders, but it should clear if you hold the throttle open for a few seconds.
 
Shimmed as in Engine shims (003-008) airbox is standard with K&N in it, all airbox is tight, but refuses to run right with covers off....
 
Refuses to run right with covers off.

Refuses to run right with covers off.

It refuses to run right with the covers off. Hmmmmm. It seems to my limited diagnosis ability that there is a clue in there. And I'm not being sarcastic just cautious. When you take off the covers, don't you get a bunch more air in the mix? Maybe the K&N's are not as clean as you thought. Can you shine a light through them? We're talking about paper K&N's aren't we? (Here again, I'm showing my noviceness)
 
Well, we all have read here how the CV equipped models have problems when the air box isn't sealed right or a cover/lid is taken off. So the covers should stay on. Testing with them off won't prove anything.
Remember, we have to assume you've checked all the basis things that can cause your problems, carbs cleaned, good compression, spark...
I really doubt that a 2.5 increase in main size would cause black exhaust, but try going back to stock since you should still have them. If that Mac pipe is actually flowing less than the stock pipes, in combination with the larger mains, then your bike would smoke at full throttle.
The other thing funny you mentioned is how your mixture screws adjustments effected top end. If you study a diagram of your carbs, turning the mixture screws out further will NOT have any significant effect, if at all, on full throttle. Your mixture screws are meant and designed to have significant effect only at closed or nearly closed throttle positions. The pilot air jet and pilot jet combine to send mixture to a passage that's metered by the mixture screw that bypasses the throttle plate. Once the throttle plate opens beyond, say, 1/8 to 1/6 throttle, the mixture screw has little effect, if any.
I don't know what's going on with your screws, but yours would normally be about 2 to 2 1/2 turns out. 4 turns out should cause an idle problem and eventual stall and hard starting when hot.
 
I was referring to the airbox sides being off, as when I sent the sides off to be chromed, I thought I would go ride it.....NOT! it wouldn't pull past 1/4 throttle. Now they are back on again.
OK. with the screws set at 2.5 it refuses to idle and quits likes its choked up.
The only way I could get it to idle was on approx 4 turns out and it will idle all day on that, and when it's hot, it cranks over 1st push of the button.
Exhaust is a Harris which is designed for my model (G)
K&N is in tip top condition and very clean,I even used the K&N oil spray on it after I cleaned it.
Everything really is perfect, it rides supurb, just the smoke that pisses me off, as I spent a fortune rebuilding the motor.
 
Well Phil, as I said, I don't know what's up with the mixture screws needing to be that far out. Sounds like compensating for something else but I don't know, considering you're sure all work has been done correctly. Are the mixture screw the originals?
As for the black exhaust at full throttle, we all know that the main jet controls the fuel flow at full throttle. I can only wonder if the pipe you have is not flowing well and the slightly richer main is causing the heavy exhaust. At least that is logical.
You say everything else is good/checked. :?
Are you using Mikuni main jets? Are they new, or did you get them from someone and they could have been drilled larger?
And though this fits into the "everything checked" list, if you put a timing gun on the ignition, can you see the ignition advancing fully and the timing marks line up correctly?
 
The increased oil consumption and smoking at higher speeds are very likely related. I suggest you check compression using a compression gauge. Warm engine, pull plugs, OPEN THROTTLE ALL THE WAY and turn engine over a few times for each cylinder. Record your readings. Then put a teaspoon of oil in cyl #1 and repeat. Note reading. Repeat for other cylinders in turn. Don't pour oil in all of them at once or it will be blown into the air. Anyway, if you compression reading goes way up, your rings are getting marginal and you need to think about re-ring or new pistons depending on the piston to bore clearance you find when you tear it apart. The other common source of smoke is valve stem oil seals. These should allow a tad of oil through to lube the guides but when they wear or harden, too much oil gets by them and it will smoke. This generally occurs after the bike has been sitting and at start up but it can occur on hard throttle, I guess.

As far as your jetting, I would pull out a pilot jet and see what size it is. With your set up, it should probably be a #37.5. If it is larger, you may need to turn the air screw out to compensate to allow the air/fuel mixture to be right at idle. Four turns out means the air screws are barely in there and could rattle out. If you don't figure out what the issue is with the pilot system, remove the screws and stretch the springs some so they will provide more tension with the screws backed out that far.
 
wiredgeorge, his carbs don't have air screws, just mixture screws.
His problems go back to other topics too. He says his motor is rebuilt. New rings, etc.
 
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