carbs gs1000

[Anonymous]

there's three extra pipe's running off the carbs . i dont have the original tank or airbox. i have what looks like an z750 tank with a suction tap . i'm wondering if the gs is the same or do these lines run back into the airbox.

 

[Keith Winter]

The 3 hose's on your Mikuni's are;
One hose, I think it's on #2 carb, is the vacuum line for your fuel valve on the tank. I don't think it matters what tank you have so long as the fuel valve is in running order.
The other two hoses are float bowl vents. These route up anywhere under your tank. The function of the vents are too keep atmospheric pressure inside the float bowls the same as outside so the fuel can be drawn up the main jet tube properly. Do not block these off.
I would have to go look at my bike, but I think that the two vent tube's are attached down around the float bowl area and are on carbs #1&3 and the vacuum line is mounted up by the throttle bore. The two vents are at a different spot than the vacuum line anyway, so If you look close it should be easy to tell them apart.

 

[KEITH KRAUSE]

What year 1000? If they're the VM carbs...'78/'79, then the vacuum nipple for the stock petcock is on the left side of carb #3. The two floatbowl vent nipples are on the left sides of #2 and #4. If you run pod filters, take the vent tubes off. This will increase the venting ability. A vortex is created in the tubes because of the increase in air flow. This vortex causes resistance to proper venting. Without the tubes, the jets can draw fuel easier. If you leave them on, you'll experience fuel starvation, especially on windy days. Jet kit makers also recommend this.

 

[Keith Winter]

Well there it is.
My memory is crap isn't it. I should have looked at mine first I guess. And not buying a jet kit, I didn't know about the vent trick. Thank's Keith, if it stops raining here today I'm going to take off the vent tubes and take it for a ride.

 

[Anonymous]

for those running the CV carbs you can do the same vent trick if you have replaced the paper element with a foam or k&n single.

 

[KEITH KRAUSE]

Well there it is.
My memory is crap isn't it. I should have looked at mine first I guess. And not buying a jet kit, I didn't know about the vent trick. Thank's Keith, if it stops raining here today I'm going to take off the vent tubes and take it for a ride.

I made a topic a long time ago about removing the vent tubes if you run pods. It was part of the jetting requirements from my Dynojet kit. I thought the same thing. How would the average person know about the venting trick? So I posted it. Did'nt get much in the way of responses. I don't know, maybe I'm a little more picky or "in tune" to what my bikes doing.
All I know is I sorta doubted that leaving the tubes on would have such an effect. I did what I was told to and removed the tubes while I got the jetting right. One day I decided to test it and see if there was any noticable effect. I went down the long quiet back road where I like to do my jetting tests and of course the bike ran perfect. I then pulled over and stuck the tubes back on and went down the road again. Within 1 mile at a steady 50 mph the bike started hesitating and showed obvious fuel starvation or fuel flow problems. Just like when you start to go on reserve and it's letting you know.
I pulled over and removed the tubes and took off again and it ran perfect again. I could'nt argue with those results. I still called Dynojet to ask them what was happening and they explained as I said earlier. They said if you leave the tubes on on a windy day or ride in crosswinds, the problem worsens. You can even get spitting out the carbs. I can't imagine anyone not noticing this if they do the same test. You won't really feel it if you're at varying throttle positions/changing gears, etc. It's at a steady speed that you can feel it happening. Maybe some people mistake it as lean jetting and try to go richer on their jetting to get rid of it. Of course, you're not going to get rid of it, just a poor compensation. With the bowls not venting their best, the jets can't draw fuel as easy. Putting in a larger pilot jet will seem to help but you're just over jetting. The larger jet will allow more fuel to enter the carb throat but the increased fuel flow won't atomize correctly, so now you're too rich.
Anyways, by the lack of responses I got, I guess there's not very many people out there that notice this. Maybe it varies some from bike to bike?
We also tried this test on my new friends '76 Kawa' Z1 900 and he too was surprised over the difference. He did'nt buy a jet kit either and he just thought it was something he had to live with. His bike was'nt as picky about it as mine, but still noticable. Maybe because I have K&N's and he uses those Emgo pods. The K&N's flow more.
Hope you benefit from this. And don't be concerned over the vent nipples being open. I havn't had any problems with dust or dirt getting in them.
I suppose a spider looking for a nice place to live could screw things up though. :lol: But that could happen even with the tubes still on too.

 

[Keith Winter]

First rate stuff Keith;
I knew you were as fussy as me! I am a border line obsessive about thing's like this, if it's not as perfect as I can get it I don't even like starting it up. I have always been this way. I've had boat's when I lived on the coast, motocross bikes(I was alot younger) cars, and street bike's, and I've been the same way with em all. I'm going riding tomorow and I can test this. I wish I had seen your posting on this before I jetted the bike, as after reading what you said I've probably without knowing it over compensated. But hey I have not had to do any carb work for over 2 years now, so I guess I'm due! Thank's again and I'll get back to you about the result's.
Keith

 

[KEITH KRAUSE]

Well, if you can remember any hesitation/fuel starvation especially noticable at steady speeds of 30-70 mph in top gear, then poor venting would be at least partially to blame. The effect can be mistaken for the jetting being too lean, which in a sense it is. I mean, the jets just aren't drawing fuel well. But in this case, it's not the fault of the jet size.
Some people start their jetting too rich, which is the safest way to start. They may end up still rich after they decide their jetting is completed. This would compensate and possibly hide the fact that their bowls are not venting correctly. Without the jet kits instructions to tell me to remove the tubes, I would also have known no better and tried increasing my jet size or needle height. In my bikes case, I started with Dynojets suggested "base settings" which I found out were ridiculously lean by the way.
You say you're obsessive? My wife thinks I am too. I deny it. I just happen to absolutely, completely and totally love my bike.
I'm the original owner of my '79 GS1000E. 120,000+ miles so far. She's in pretty good shape and she's a runner.
If interested, check out my website and tell me if I'm obsessed. :wink:
Just click the WWW below.

 

[Keith Winter]

I actually do remember some hesitation, kind of, when I started my quest to jet the bike. It was mostly at the lower end of the rpm range. At 50 to 70 mph it would make alot of noise, but lacked power as in like you said, lean. This is how it went, took off stock air cleaner put pod's (not K&N) on. Bike was completely unrideable. Plugs white. Took out #95 jet's and replaced with #102, moved needle clip down 1 notch. Test ride, idle to mid rpm range good engine would rev or lug, noise but power dropping off past the top-middle of rpm range. Plugs coffee and cream color to mid rpm, then whiteish at constant higher rpm's. Replaced 102's with #115's and moved clip down another notch. OOP'S why did I move the clips? Put clip's back to one down from stock and now we are cooking all the way in the rpm scale. Now for the odd stuff. My plugs are a coffee with almost no cream color,so you say hey man your a little rich. The problem is, and some people-not you- have a hard time understanding what I'm up against here in Calgary. I'm 4000 ft above sea level here, so instead of 14.7 psi I have about 13psi to work with in air pressure. But when I ride out to my beloved west coast I'm back down to sealevel 14.7. Going over the Rocky's at 6000 ft in some spot's,ok it just run's rich and you don't want it lean when you get to the coast. So not wanting to carry the stuff and rejet out there, it run's a little rich here. And by the way, those plug's are the perfect coffee and cream color on the coast, and the engine really does make more power out there too! I almost hate to come back to Calgary. Anyway's that's how it went, and now I'm going to check the vent thing. If it does change thing's I'm going to have to keep that in mind when I ride to the coast this summer.
Keith

 

[KEITH KRAUSE]

Removing the vent tubes WILL allow your jets to draw fuel easier. So your present jetting will run richer. How noticable it is on your bike may vary from mine. It's a little interesting that you only had to raise your jet needles one position. That would show that your pods are not flowing as well as mine. That would also mean that my bike would show the venting problem much more. There are of course other factors but the filters are the main thing.
In the past when switching to pods, my friends and I have tried jetting with the stock needle and in every case we had to raise the needle a minimum of two positions or it was just too lean. Like you said, jetting in Canada is different. That's the one thing I really havn't spent much time reading, air pressures and such.
Down here it hasn't been a problem lacking that knowledge.

 

[Anonymous]

Performance mods

Performance mods

Tried it today,she runs noticeably sweeter.Good thinkin' Batman!

 

[KEITH KRAUSE]

Re: Performance mods

Re: Performance mods

Tried it today,she runs noticeably sweeter.Good thinkin' Batman!

Don't mention it Robin! Just happy to help a fellow GSer in distress!
Back to the bat-cave! 8)

 

[Anonymous]

carbs gs1000

i'm amazed at the responce to my little question. i had the all the tube's bloked up while i had the the bike ticking over in the garden . it's a pretty windy day here in dublin . i noticed the bike's rev's riseing and lowering as wind blew . it is also spitting back sometimes . you hit the nail on the head with all your points. it's smoking like a steamtrain now i'm wondering if i messed up the bore. the last time i had it started the smoke died off when it warmed up . my guess it's just the oil ring's seized . ps thank's for the help this site is like the samaritun's for gs owners

 

[KEITH KRAUSE]

With pods, blocking the tubes would be even worse than leaving them on. No venting at all. Stock bikes can keep the tubes as long as they remain open. Pod filtered bikes benefit from removing the tubes. The better your engine flows, the better the benefit.
Your bike will idle with no venting, but when opening the throttle the performance will suffer.
A simple (I hope) way to describe what's happening: If you take a jug of water that is not vented or properly vented, turn it upside down, you'll see the water come out in spurts (glugs?), very uneven. If you increase the venting or the ability to vent, the water coming out will be much smoother. It's the same thing with the floatbowl venting. The jets draw fuel easier and the fuel passes more smoothly and consistently when there's adequate venting.
The pods increase the intake. The existing vent system can't keep up with the increased flow. This increased flow causes a vortex in the existing (tubed) vent system that compounds the resistance. We can't practically increase the size off the carbs venting chamber/passages, but we can minimize the resistance and remove the vortex by removing the tubes. This will help the jets draw fuel better.
How much better and how much more noticable will depend on your particular engine set up.
Even with the tubes removed and the venting at its best, riding through crosswinds can/will cause some hesitation and brief/minor fuel flow problems when pods are installed.

 

[saaz]

I haven't run vent tubes on the bike since the early 80s...so I forget what it is like with them! Cross winds, rain etc seem to make no real difference to running..and I have been through a bit of weather in my time....

 

[KEITH KRAUSE]

I haven't run vent tubes on the bike since the early 80s...so I forget what it is like with them! Cross winds, rain etc seem to make no real difference to running..and I have been through a bit of weather in my time....

It depends on your set up as to how much you'll be effected.
I have the tubes off, but if I hit a good crosswind the bike will act like I hit a sudden headwind and slow just a moment. If the crosswind continues, I'll experience the effect longer. Otherwise, it's perfect.
The Dynojet instructions require the removal of these tubes and warns California riders specifically.
I have the K&N chrome ovals and they have the ability to be mounted so they are not all exactly in line with each other. I turn the middle two "up" and have the outer ones "down". This helps the middle two flow a little better in my opinion. The filters don't block each other as much. What I really want to mention is the crosswinds seem to have less effect now. I don't know why the different arrangement helps, all I know is it does. It's not a big deal either way. The main thing is having the tubes off in the first place.

 

[saaz]

I have K&N chrome ovals, but they are one filter to two carbs..a big oval shared filter. maybe this makes the difference. I have not noticed any cross wind effect in 20 years, well at least as far as tuning goes..some of those winds do make the bike lean over and move around a lot!