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Tuning in VM Carburetor - 78 GS1000

Gregory

Gregory

Forum Mentor
Past Site Supporter
Hello All, before I call and pay an expert to tune this bike, I wanted to ask you first.

BTW, I have been using the VM Carb Tutorial, soaked carbs and replaced O-rings and added new fuel pilot screws and 105 main jets (to go with 4in1 and stock airbox), and checked and changed out valves to put them in spec's.

I am at the stage of tuning in the air pilots. (I started them at 1 1/2 turns out since the directions said 1 1/4 and a member on a previous thread told me to initially set them at 2 turns out.)

The new fuel pilots are all set at 1 turn out.

The bike started right up and idled fine. Turned it to 1100rpm and turned the each air screw out slowly and it increased rpm ever so slightly, but every time I open it more it seems like it slightly increases rpm (but hardly anything above 1100). At one point I started opening one up a lot, then I got a "power surge" (WAY-UP then back down) of dramatically increasing rpms.

BTW, I do not have a vacuum sinc and do not know anyone with one, so I am hoping that does not have anything critical to do with this phase of tuning. (all slides visually were the same height at fully closed and fully open)

I noticed two things that I thought may be unusual.

1.) #2 and #3 pipes were immediately a lot hotter than #1 and #4.
2.) Before I came in to type this, I reved the throttle and it did not go back to idle very quickly at all. (stayed fast)

Is there an order I should tuning the carbs in? I did them #4 to #1.

Is there a video of anyone doing this procedure?
 
1 turn open on the Fuel screw and 1-1/2 to 2 turns out for Air should be reasonably close. From there you should perform a vacuum sync and ride the bike and see how it performs. Needless to say, you need to perform all the bikes basic maintenance like valve and points adjustment before performing any fine tuning.

BTW, a surging and/or raising idle indicates a lean mixture, most commonly from an air leak from the intake boot O-rings. Needless to say again, maintenance will help there also.
 
Nessism said:
1 turn open on the Fuel screw and 1-1/2 to 2 turns out for Air should be reasonably close. From there you should perform a vacuum sync and ride the bike and see how it performs. Needless to say, you need to perform all the bikes basic maintenance like valve and points adjustment before performing any fine tuning.

BTW, a surging and/or raising idle indicates a lean mixture, most commonly from an air leak from the intake boot O-rings. Needless to say again, maintenance will help there also.
Click to expand...

Thanks Ed. I did the valves but havent done anything to the points yet. Guess I will be looking for the tutorial on that too.

Air leak sounds plausible --- i forgot to put the hose clamps on the airbox. I will go back out and re-try everything.

Is there a reason that #2 and #3 exhausts would be extremely hotter than #1 and #4?
 
Gregory said:
Thanks Ed. I did the valves but havent done anything to the points yet. Guess I will be looking for the tutorial on that too.

Air leak sounds plausible --- i forgot to put the hose clamps on the airbox. I will go back out and re-try everything.

Is there a reason that #2 and #3 exhausts would be extremely hotter than #1 and #4?
Click to expand...

If 1 and 4 are not firing properly, that would do it. When things like this happen in pairs, check the coils and/or the ignition timing. One coil is for 2/3 the other is for 1/4. They are timing in that pairing as well.
 
Much appreciated,things are feeling a bit over my head now. I think I am going to take a break from the tuning, timing, coils etc... for now and change over to doing the seals in the front forks. I am thinking that will be something I may be able to figure out.

I did take it out and drive it down the street and back. It seems to be doing ok although it feels about as fast as a moped compared to my buddies 82gs1100 that I also just rode down the street.
 
Like Ed said...valves, point gaps, timing, vacuum sync. 1 turn out on the PILOT ( bottom ) screws and 1 1/2 out on the MIXTURE ( side ) screws is in the ball park. And as many other threads have said, you tune VM carbs " from the bottom up"..What that means is you leave the MIXTURE screws at the 1 1/2 turns out and you lean the pilot circuit out first with the pilot screws. Plug chops will show the tale of the tape. Then you use the MIXTURE screws to fine tune each cylinder. If a cylinder is a bit lean you turn the MIXTURE screw IN ( remember it this way..(IN)RICHMENT...and (LEAN) OUT ) If its a bit rich, then you turn the MIXTURE screw out to lean that cylinder out.
 
man i am really confused now.
the instructions said to work the air screws first, not the fuel pilot screws.
i may have to hire someone.

My bike is not tagged or inspected yet so i reaLLY CANT TAKE IT OUT AND RIDE IT AROUND. It seems like there ought to be a way to tune the carbs on the bench (in gear with tires spinning) so that you dont have to go back and forth with this plug chop method.
 
As far as your pipes 2 & 3 being hotter than 1 & 4, you could do this,
swap your plug wires around, 1 & 2, and 3 & 4, then find the 4 leads feeding into your 2 coils, and swap the two leads from each coil to the other.
What you have effectively done is swapped the ignition circuit from 1 & 4 cylinders to 2 & 3. Then you could run the bike and see if the heated pipes change over, if they do, you know the problem is in the ignition circuit, if they don't then its the carbs, carb or intake boots. Air leaks will cause you big problems. Make sure your breather hose is connected on both ends, your air cleaner cover is secured, I use foam tape underneath the covers edge, and the connections to your air cleaner box and air box are tight. You should also check your sync ports to make sure you don't have anything leaking (I found a open sync tool tube in one of mine, it was sucking air!)
 
Gregory said:
man i am really confused now.
the instructions said to work the air screws first, not the fuel pilot screws.
i may have to hire someone.

My bike is not tagged or inspected yet so i reaLLY CANT TAKE IT OUT AND RIDE IT AROUND. It seems like there ought to be a way to tune the carbs on the bench (in gear with tires spinning) so that you dont have to go back and forth with this plug chop method.
Click to expand...

Yeah, it's called a dynomometer - about $10,000 should get you a decent one

As said above, you need all the systems working together to get it to run correctly. So far you did the valves and are close on the carbs

Check the timing and see if there's any sparking going on at the points when it's running. Be sure it's advancing when you rev it

You will need a vacuum sync,tho

Your buddies 1100 shouldn't be much faster than your 1000
 
Greg...1 turn out is close enough and is actually a bit rich on the pilot curcuit. It has been posted here in several threads that in order to be in "compliance" with the EPAs emissions demands they were at approx 3/4 out from the factory..but thats just a tad leaner than most like.
 
Big T said:
Your buddies 1100 shouldn't be much faster than your 1000
Click to expand...

I guess that depends on how you define "much." I think my GS1100E is much faster than my GS1000E. But the GS1000 will go if you wind it out!
 
[COLOR=green said:
Air leaks will cause you big problems.... Make sure your air cleaner cover is secured, I use foam tape underneath the covers edge,[/COLOR]
My cover lid is missing so i made a cover from a piece of plastic. The reason I originally didnt think this was an issue is because in the instructions for the 4 in 1 pipe, it suggested to remove the cover and increase jet sizes. And also, air sucks in through the large round holes in the beather box anyway right?
Click to expand...
Click to expand...
 
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Since you guys have been so helpfull I thought I would give you an update. I cant tell you enough how much I appreciate everyone on this site. I am finding this site so interesting and usefull - I certainly have been spending a lot of time on here.

I went out yesterday and ran the bike on the center stand and it now appears to be running better. I suspect that maybe the 2 pipes were cold because the bowl needles were stuck from the rebuild.

Anyway, I havent vacuum sinc'ed yet, but in researching the cost of the gauges (about $65) I decided to call a dyno shop here in the Dallas Fort Worth area. The will vacuum sync the carbs for $40 to $50, and they offer a dyno diagnostic run for $40.

Since I havent found anyone local that I can borrow vacuum gauges from, I am thinking of going ahead and doing it. This of course is after I clean up all the electronic connections etc.

Also, I took the timing cover off during and ran the bike and didnt notice any sparking, is that basically all I should worry about on the timing right now?
 
It's up to you, but if your going to keep this bike a long time, I would just buy gauge to sync. and it's pretty easy (especially on VM carbs). For the price of of one sync. at a shop you could pay half the price of the best sync. tool (Morgan), instructions should be in a service manual, or check on Basscliff's site. Also that way you'll know they were done right. terrylee
 
Gregory said:
Also, I took the timing cover off during and ran the bike and didnt notice any sparking, is that basically all I should worry about on the timing right now?[/COLOR]
Click to expand...

Nope -points need proper gap, proper timing and proper advance

Put a timing light on it
 
The Carbtune from England is a tad over $100 shipped and will be very easy/useful for a long time to come.
 
terrylee said:
It's up to you, but if your going to keep this bike a long time, I would just buy gauge to sync. and it's pretty easy (especially on VM carbs). For the price of of one sync. at a shop you could pay half the price of the best sync. tool (Morgan), instructions should be in a service manual, or check on Basscliff's site. Also that way you'll know they were done right. terrylee
Click to expand...


Ok I may. I keep hoping there is a North Texas member here that would like to go in halvzies or rent them to me. I cant imagine me putting more than 4k on a bike each year, probably less.

Nope -points need proper gap, proper timing and proper advance. -
Put a timing light on it
(i dont know how to do the double quote posting)

Thanks BIG-T, I do think I can find someone around here with a timing light, and I assume I can find the gap settings in my manual.

(tranferred info to new thread)
 
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Greg....Today i had the time to open up the carbs on my 78 1000C. It had been setting for a few months and when i rode it the other day i felt the pipes and number 2 and 3 took a bit longer to start getting some heat...thus prompting me to "refresh them". I took the pilot screws and all the jets out and gave them a good flush of carb spray and repoked all the holes. Gas had been sitting in there and was getting gunky and I knew it.

Anyway, I set the pilot screws ( bottom ones ) at 3/4 turn out and it ran every bit as good as when they were at 1 turn out. This isnt saying thats where your bike is gonna like them, but 3/4 didnt cause any stumbling or lack of throttle response and power. Just thought I would pass this along to you as a "what its worth" info.
 
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