Is this fuel starvation?

[Darkstar]

After WOT in gear 5, if I pull the clutch, RPM's drop below 800 momentarily, almost stalling, then recover to proper idle 1300. Tank is clean as a whistle and carbs were cleaned 2000 miles ago. Jets in order. Pulls hard all the way up. Previous top speed was 105, now it's 110, and front wheel hops a bit coming into 2nd gear    

[user11235813]

Why would you pull the clutch in, if you at WOT in 5th? As you hit 8000 or thereabouts you'd just give a a tiny blip to upshift to 6, yes? no? Or if going down you'd leave the clutch engage then give it a quick blip as the revs dropped to downshift.

You might also find some clues in this thread where I was having a WOT stumble but it turns out that maybe it's just bad throttle action. http://gstwins.com/gsboard/index.php?topic=72399.0

[mr72]

After WOT in gear 5, if I pull the clutch, RPM's drop below 800 momentarily, almost stalling, then recover to proper idle 1300.

Assuming you are talking about a bike that's FULLY WARMED UP (that is, run on the road >15-20 minutes), then...

No, that's not fuel starvation.

You've heard of "hanging idle", well this is the opposite, "idle dip".

It means your idle mixture is slightly off (lean) and your throttle stop ("idle speed knob") is set too high to compensate. I'd turn the idle mixture needles out 1/4 turn and then reset your hot idle speed for more like 1100 rpm, NOT 1300. If you make it more rich and try to set the idle speed to 1300 you'll get "hanging idle".

IF the bike is not fully warmed up, then this is probably normal if everything is set up right. It's normal for a cold engine to have a little idle dip, you may have to nurse the throttle a touch to keep it from stalling. In that case the problem is you are riding it way too hard before it's fully warmed up. Of course if you're trying to wheelie in 2nd gear and measure the top speed you're riding it way too hard anyway. Expect a top end rebuild to come knocking real soon now. Get a water-cooled bike and a lot of life insurance if you are determined to do that.

[Kookas]

Why would you pull the clutch in, if you at WOT in 5th? As you hit 8000 or thereabouts you'd just give a a tiny blip to upshift to 6, yes? no? Or if going down you'd leave the clutch engage then give it a quick blip as the revs dropped to downshift.

Because clutchless shifting is risky if you mess it up.

[Darkstar]

tiny blip to upshift to 6

i didn't install my 6th gear yet, i'll be doing that right after i rotate my tires

[Darkstar]

It means your idle mixture is slightly off (lean) and your throttle stop ("idle speed knob") is set too high to compensate

This i what I came here looking for, makes sense. Thanks. And yes, this occurs when its fully warmed up, but the temps have been swinging from 65 to 85F throughout the day, so i think thats why this has been happening,. To clarify, Im not doing top speed wheelies all day in 2nd gear, i was just explaining that I ride it hard. But from what folks say at the track, this engine holds up well at extended high RPM rips, correct?

[mr72]

It means your idle mixture is slightly off (lean) and your throttle stop ("idle speed knob") is set too high to compensate

This i what I came here looking for, makes sense. Thanks. And yes, this occurs when its fully warmed up, but the temps have been swinging from 65 to 85F

Ambient temps are not really related. It's engine temp.

Remember, ideally the engine will idle with the throttle stop set so the throttle is completely closed. It should get enough air through the pilot air inlet at the throat of the carb (bypasses the throttle plate) and the amount of fuel is set by the needle position in the pilot jet. So if it is idling too slow, then it's getting too little fuel, it's lean.

If you open the throttle with the throttle stop that allows more air in that doesn't flow across the pilot jet. Now, often times one might set the idle very rich and then open the throttle plate to allow more air in to match the too-much-fuel and you wind up with a high idle and subsequently hanging idle. I think in your case what's more likely happening is it's lean on the pilot but you have the throttle stop set high enough to actually lift the slides a little bit and get some fuel from the main jet, so it's not really idling, it's running on main just very slowly. When you suddenly close the throttle the slide drops all the way and causes it to briefly run on idle only (closes main jet), and once the idle "dips" vacuum increases a little, lifts the slide a touch, more fuel from main, and voila, you're back at your high "idle".

I still suggest adjusting the idle by closing the throttle all the way, backing the "idle speed" knob all the way out, then adjust the idle mixture screw until the idle stops increasing. With any luck that's >1000 rpm and you're done. If the pilot air orifice is clogged or gummed up at all then you will have no choice but to add some air via the throttle stop, and set the idle mixture too-rich just to get the idle up to 1100.

And my point before, riding hard at high revs all the time you have no choice but to accelerate wear.

[Darkstar]

Because clutchless shifting is risky if you mess it up.

this clutch is very light and forgiving, very hard to mess up

[Watcher]

tiny blip to upshift to 6

i didn't install my 6th gear yet, i'll be doing that right after i rotate my tires

So long as you're talking GS500 you should have a 6th gear.

If you aren't talking GS500, then maybe being less of an ass and explaining what bike you're on would be a good idea.

[Darkstar]

Ambient temps are not really related

Really? Then why do I have to adjust mixture in winter when temp is 30F vs 90F in summer? People re-jet for these situations.

[Darkstar]

If you aren't talking GS500, then maybe being less of an ass and explaining what bike you're on would be a good idea.

HA, you're right. I was being an ass. Long stressful day, Im not thinking. Sorry about that

[mr72]

Ambient temps are not really related

Really? Then why do I have to adjust mixture in winter when temp is 30F vs 90F in summer? People re-jet for these situations.

The only reason you'd need to do this is because of air density difference between 30F and 90F but it's really not different enough to warrant adjustment or certainly not rejetting.

The bike will warm up faster in warmer temps. It will take longer in cold temps and cool faster, requiring more choke more often when it's cold out.

Regardless of theory, my objective experience is that the bike runs perfectly fine with zero adjustment difference at 25F or at 100F. In reality due to density (and humidity!) it will run somewhat leaner when it's very cold out than it does when it's very hot, but you can't really compensate for any of this because it's so dynamic, not without a closed-loop FI with lambda sensor.

In truth we run GS500s so rich across the board that they are rich when it's cold and more rich when hot. AFR of 14:1 when it's cold and 12:1 when it's hot are both rich and will not appreciably affect the way the bike runs.

[Watcher]

Ambient temps are not really related

Really? Then why do I have to adjust mixture in winter when temp is 30F vs 90F in summer? People re-jet for these situations.

I never have, and living in Chicago I'd see lows less than 30 and highs sometimes over 100.

[Darkstar]

Ambient temps are not really related

Really? Then why do I have to adjust mixture in winter when temp is 30F vs 90F in summer? People re-jet for these situations.

The only reason you'd need to do this is because of air density difference between 30F and 90F but it's really not different enough to warrant adjustment

this changes a lot for me. im glad that i asked. thanks

[user11235813]

I'm still not getting this.

So you're riding along in top and what, you need to come to a sudden stop so you pull the clutch in and hold it while you  stamp the gears down to 1? I can't see how else it would drop down to idle.


BTW here's the definitive video on clutchless downshifting. I can assure you that it works you can downshift with butter smooth shift on the GS, but only down to 3, I wouldn't try it lower than that. He explains it with the actual gears.

And here's someone else talking sh!te

[Darkstar]

I'm still not getting this.

Actually, Im not asking about how to shift without clutch. My post was about an odd symptom that occurs in the moments that Ive had to grab the clutch when Im in WOT

[user11235813]

Actually, Im not asking about how to shift without clutch. My post was about an odd symptom that occurs in the moments that Ive had to grab the clutch when Im in WOT

The clutch shifting was brought up by someone else so I thought I'd answer that.

But what I'm not getting is that why you are holding the clutch in at WOT long enough for the engine to drop down to idle speed, to what purpose are you doing this. I'm assuming that you must take it off WOT. Or are you saying that you are holding the throttle open in top and even though you are still at WOT when you pull the clutch in and take load off the engine your revs drop all the way down to idle while you've still got the throttle at WO.

Or are you simply doing a hanging idle test but you like to do it accelerating in top instead of stationary in neutral.

[Darkstar]

I see now. To clarify: Im not riding around for long periods with WOT and clutch pulled in. There have been a few instances recently where I happened to be on WOT and it was better to pull the clutch in at the moment, as opposed to downshifting/braking. One of these moments was going down a long hill where I saw a green light turn red far ahead. The road was empty and I knew I had enough space to coast on down, so I thought that instead of burning through more of my front brake, I'll just pull the clutch in and put the bike in neutral, so I can coast down to the red light, to a rolling stop. Does this make sense?

[user11235813]

snip... Does this make sense?

Is this a trick question? No, it makes even less sense now that you've explained. it.

Let me summarise, basically your problem seems to be that if you are stationary in neutral and the bike is idling and you give it some throttle and close the throttle the engine drops below idle then returns to idle but sometimes it drops so low that it stops. That is your problem and that should have been your question and this has been answered.

Everything else in your post is crazy, it will not make sense to anyone. If it makes sense to you then that explains your first post to me.

Let's analyse this...

Im not riding around for long periods with WOT and clutch pulled in.

Well that's good but you should not be riding around with the clutch in and WOT for shorts period, or in fact any periods of time at all. Why the hell would you, if you did that you'd be at 12000rpm and on the verge of blowing your engine up almost instantly.

There have been a few instances recently where I happened to be on WOT and it was better to pull the clutch in at the moment, as opposed to downshifting/braking.

The only instance I can think of would be an emergency brake situation but that's debatable.

One of these moments was going down a long hill where I saw a green light turn red far ahead.

Really? Right so as per your OP, you're riding along minding your own business in a high gear at WOT, that means you're travelling at 100mph OR you are accelerating fast in a high gear approaching 100mph. You're definitely not in a low gear at WOT because you'd be redlining.

Now you're either already going downhill and suddenly see a distant light change to red. OR you've just crested a hill and see a distant light change to red. You're travelling at a fast speed, now any normal person who knows how to ride a bike at this point would shut down their throttle causing instant engine braking with no danger of stalling. So you've already begun to slow down and you have not touched your brakes yet. At this point anyone who knows how to ride a bike would just work their way down through the gears and soon they'd be travelling at a normal speed and would continue to downshift and slow to the red light and/or apply some gentle braking.

But not you, when you suddenly see a the green light turn red, you go "sh!t, I'm travelling at 100mph, this is going to wear my brakes out, what will I do, I know, I'll not use my brakes and instead I'll coast to a stop by disengaging the engine.

Let's have a look at some high school physics, probably the most important equation in the history of the world. No not e=mc^2 the other one f=ma or in this case it might be better to write f/m=a

In this case m is your bike. f is gravity there's also some f in the form of friction of the tyre against the road and in the wheel bearings, but assuming your wheel bearings are not rusted out we can ignore both of these and just see the f as gravity.

The a is acceleration so seeing as the mass of your bike is not changing and you are going downhill thus gravity is the force that is operating so you are going to accelerate, you are not going to coast to a stop, especially as you are travelling at close to 100mph so you already have a large momentum.

The only time that makes sense to me to coast downhill in neutral, is when I've been on a road through a rainforest and I'm going at a slow speed maybe 20-30kph and I will turn the engine off and coast just so I can have some peace and admire the forest. Or if I think it's dangerous to have the engine off then I'll leave it in a low gear at a low speed and feather the brake to keep the speed down.

The GS500 has excellent engine braking, it's one of it's most useful characteristics, by not utilising engine braking you are going to wear your brakes out more not less. Now I'm not saying you should use engine braking per se but you are the one who is saying you are trying to avoid wearing out your brakes and the way to do that is by using engine braking whenever you can. For the record I'm still on my first set of pads and I've done 50,000 kms and it looks like they are 1/3 used. I actually wish they'd wear out quicker so I can put my new Ferodo semi sintered pads on that I bought last year.