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Engine Dies at the Stoplight.

  • Thread starter Thread starter Rocketjock
  • Start date Start date
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Rocketjock

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My 80 750GS runs great in all ranges but after about twenty miles or so when it is really warmed up it will sit idling nicely at any stoplight or sign and the when I give it throttle, it just dies. If I bring the revs up slowly I can get away with a little coaxing but generally it wan't to quit. I have opened the idle screws successive quarter turns but as of yet, to no avail. I am up to 2 and a half turns and am beginning to wonder. Is it flooding or not getting enough gas? Or more specifically, do these jet actually let in more air or fuel? Because that would explain it. I am actually leaning out the mix by turning out the screws. But I always thought it was fuel and not air. Can anyone clear this up?
 
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Set those airscrews at 1 turn out. Back out your throttle stop (Idle Knob) till the the throttles quit turning back, then adjust them in 1/4 turn in. Get it fully warmed up and adjust the idle knob till it idles at about 11-1200 rpms. Adjust your clutch play to 1/8 inches at the lever and see what happens.
 
Rocketjock said:
My 80 750GS runs great in all ranges but after about twenty miles or so when it is really warmed up it will sit idling nicely at any stoplight or sign and the when I give it throttle, it just dies. If I bring the revs up slowly I can get away with a little coaxing but generally it wan't to quit. I have opened the idle screws successive quarter turns but as of yet, to no avail. I am up to 2 and a half turns and am beginning to wonder. Is it flooding or not getting enough gas? Or more specifically, do these jet actually let in more air or fuel? Because that would explain it. I am actually leaning out the mix by turning out the screws. But I always thought it was fuel and not air. Can anyone clear this up?
Click to expand...
The mixture screw on your CV carbs richens as it's turned out. It actually allows additional EQUAL amounts of air and fuel (that's why it's called a mixture screw) but it's considered richening as you turn it out, leaning as you turn it in.
These screws should be set to achieve highest rpm, using 1,000/1,100 rpm's as a base point while setting. On a stock bike, they are generally 1 1/2 turns out.
Can't be sure, but your problem suggests a rich mixture since rich mixture problems generally show themselves/worsen as the bike becomes hot.
Try adjusting the screws first. If no joy by the time they are 3/4 turn out, then you have something else wrong. Possible wrong size pilot jets? Do you know the carbs history? Did problem just show itself but ran fine with the same jetting before? Dirty air jets (at bottom of carb throat/filter side). Dirty air filter? The bike idles about the same rpm from cold to hot?
 
Ah yes, the carbs history. This bike pretty well didn't run when I picked it up for 500. There were lots of air leaks and the valves weren't seating as there was no tappet spacing. All that fixed and as I said it now runs great. There may be a tad more vibration than I'm used to (previous 850/1100G and GSXR owner) but I can't say as it's a problem. The previous owner did say her was told it has 1100 carbs on it. To me this would mean that there is a greater volume of fuel going in and perhaps has something to do with the idle mix. I have turned everything down to one full turn out and thought I noticed improvement. After it warmed up tho it still bogged a bit. I am now adjusting to 3/4 turn to see what that does.
Oop, I was wrong. They were set to 1 1/2 turns. Now set to 1. Let you know how it goes.
 
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OK, so that has really fixed my idle start problems. Virtually starts off without problems now. Screws set at one turn. Even after it warms up. But I do think I have a greater problem. I mentioned it seems to vibrate a little more than most. Well, as I was riding along waiting for it to warm up I was reaching down to feel the fuel bowls for warmth when I discovered that vib coming thru No.1 carb. So on to a new thread.
 
Bob called that one...one turn.
As for vibrations in general, poorly synched carbs can cause this. They should be synched as normal maintenance anyway.
Though they may be similar, there will be some differences in jetting between the 750 and 1100 carbs. That could cause a lot of driveability issues.
 
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