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Mixture Screws

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

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GS1000G 15K, 1981. rebuilt engine/rings. Just run in, (1000miles)
The problem seems to be that it is running a little rich, (rear of 4 into 1) is pretty black and the plugs are black aswell, but it runs great.
How many turns from stop should I turn out the mixture screws, I have no idea what they are now, as I had it all set up a few weeks back, but had to rebuild it due to worn out rings. Phil.
 
If you are referring to the pilot screw at the top, headside of the carbie, the servive manual I have says 1 5/8 turns back from its seated position. hope this helps.
 
1 1/2-2 turns will generally get them right. If you go more than about 3 turns you're off the jet and have the circuit wide open.
 
Billy Ricks said:
1 1/2-2 turns will generally get them right. If you go more than about 3 turns you're off the jet and have the circuit wide open.
Click to expand...
Ditto.
 
OK guys that replied to my question here, so, I took the tank off and checked how much the screws were turned out!
From left:- 4.5 5.0 4.3 5.1 it ran good but as I stated that the plugs were blackend as well exhaust end.
So, I turned them all in, then backed them out 1.5 turns and cranked it up, on idle it ran ultra crappy and would not hold idle.
So I turned up the idle screw and managed to get it to hold at approx 1100 revs, then it would go lower and lower and cut out.
STRANGE! So I turned them all out to approx 2.5 turns, it ran a little better but would not hold idle, it would rev sort of clear but back down to idle would make it quit.
So, 3.5 turns out (on all carbs) it now idles, and revs clearly!
So I pose the question of, why at 1.5 turns out it ran awful, but now at 3.5 turns out it's mint?
I have not checked the condition of the plugs since I cleaned them, I am hoping they are not black!
I suppose I will let you know how they are tomorrow, as I am going for a 200 mile ride on it in the morning.
 
Well, it obviously wants a richer mixture/more fuel at idle if the bike runs better with the mixture screws set at 3.5 instead of 1.5.
At idle, you're running on the pilot circuit.
If the carbs are out of synch, that will cause a poor idle too. Regardless of how you set the mixture screws, the idle will still not be optimum. The carbs have to be synched or the plug reads will not be accurate.
Carbs have to be completely clean too. Air jet too. Black/sooty plugs will allow the spark to intermittently "track" down to ground. Instead of jumping the gap, the spark takes the path (the soot layer) of least resistance. This too will cause a poor idle.
 
Thanks Keith! I think you should change your name to "Carb Man"
The carbs were checked a few weeks ago on a manometer and showed the carbs were in "sync"
It seems to run fine on the 3.5 setting, I'm just a little worried about the plugs being black again.
All I am going to do is trial and error, if they are still black I will turn them in half a turn and ride again.
Oh, carbs were cleaned out properly, new main jets (117.5) new float valves and seats and cleaned out properly K&N which has the k&n fluid on it.
Thanks again Keith.
 
Phil - A couple other reasons your plugs soot up... if you are running K&N filters, the gauze material needs to be misted with the spray oil... if you soak it, you decrease air to the mixture and hence the sooty appearance. It is common for folks to adhere to the "more is better" thinking pattern. I would clean those filters and reoil them lightly. The second reason your plugs can get sooty is that they are not in the right heat range. Check your manual and select the correct NGK plug. It is pretty common for folks to pick up a set of plugs at an autoparts store based on a cross reference they have and end up with plugs that are not hot enough to burn the crud out of the combustion chamber. The last reason plugs can carbon up is a weak spark. The power to your coils is VERY round-about. It goes from your fuse area, through your ignition swtich through your kill switch to a connector where it then goes to the coils or something along those lines. Over time, the switches wear and the contacts get a tad dirty. Put a multimeter in 20VDC scale on the coil lug where your power is connected (one probe to the power and one to the frame) and turn your key on. If you get less than 12VDC, which is very common, your WILL have a poor spark. It doesn't matter if you have spiffy aftermarket coils/wires and a great electronic ignition. Symptoms of weak spark are sooty plugs (not enough charge to burn crud out of combustion chamber), a few backfires through carbs while at normal running speeds and a bit hard to start. I sell and rebuild VM series carbs for a living and when I hear the "sooty plugs" symptoms always have customers check out these things first. If you are interested in powering your coils where they will provide max spark, check this link:
http://www.kzrider.com/ignition_upgrade.shtml
 
WOW! What a reply!!
With the K&N filter, I did not soak it, I was told to use the k&n lubricant stuff for the air filter, of which I did, I sprayed it so that it was all covered in the red lubricant.
Plugs are NGK B8ES which are gapped correctly, Coils are standard and show a bright warm spark when out on the head.
I rode about 160 miles today, A friend of mine was behind me on a Yamaha R6 and when we got on it, mainly rounds long curves when I gave it a fistful it ran perfect, but he said that when I gave it gas out of the curves the exhaust was smoking "White"
No black smoke though!
No oil used either, I checked the plugs after the ride out.
They are black on the inside outer edge, but the main part where the spark is, is a tan/brown color
It ran wonderful, one quiet stretch I managed to get it up to 135mph, So I know it's running great, the R6 passed me a few times though!
 
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