‘78 GS1000 Throttle Valve Adjusting Screw

[DeegzARG]

Hi Folks,

I picked up a “barn” find GS1000 that I’ve been working on these past few weeks. It was more a cosmetic restoration as the engine was running smoothly….running smooth until I touched it of course. 
 

Im hoping to get the bike on the road before the season is up and was working on getting the carbs synced. I started playing around with the throttle valve adjusting screw and now the bike barely idles. Does anyone know how to bring that setting back to stock? Like I said bike was running pretty smooth before I touched it. 
 

P.S. I’ll add some photos of the bike on another thread. 
 

Any help is appreciated!

 

All the best,

 

Carlos

[TonyGee]

I assume you are using balance gauges ?   if so raise the idle more till the carbs level out. 

[DeegzARG]

Im using a carb tube pro.  when I raise the idle and sync the gauges it seems ok but once I lower the idle, everything goes out of wack

[BigT]

How low of an idle are you talking about? Idle should be 1,100-1,200 rpm for VM carbs

[DeegzARG]

When I was “syncing” the carbs I had the idle at about 2,000rpm and once I had the gauges (vacuum) roughly at the same level I tried to lower the rpm to 1,000 and the bike would just stall. 
 

what I’ve done since is try to reset the throttle adjusting screws equally and turn the air screws 2 turns out but I’m still having issues when I lower the idle to 1,000rpm.  Should I be turning the throttle screw to a certain position?

is there an order of adjustments?

I really appreciate the help

[BigT]

1. Clean the carbs  -http://members.dslextreme.com/users/bikecliff/images/vm_carb_rebuild.pdf

2. adjust the valves

3. Bench sync the carbs

4. Set fuel screws at 7/8 turn out, air screws at 1 1/2

5. install carbs

6. tune to high idle with air screws

7. Vacuum sync the carbs- they should be close from the bench sync. adjust any carb

Your syncing at 2,000 rpm is correct. Opening the air screws made the idle mixture leaner, is that what you wanted to do? and, why?

If it won't idle, your idle circuits are plugged

[DeegzARG]

Thanks BigT.

When you say tune to high idle with air screws would I be turning them out more than the recommended 1 1/2 turns? 

I don’t want the bike to run lean I just read that 2 turns out was a good starting point, I’ll try the 1 1/2 turns that you recommend.

should the throttle adjusting screws be at a specific setting? I feel like that’s when the bike started to run like shit, when I started messing with those settings. Now Im backpedaling trying to get the bike back to stock settings as it was running pretty well  

Lastly, Should the choke be off while making all these adjustments?

 

Edited September 16, 2022 by DeegzARG

[dago]

All mixture adjustment should be done with a warm engine, same for carb balance. The choke richens the mixture making any adjustments void,

[DeegzARG]

On 9/16/2022 at 2:44 PM, dago said:

All mixture adjustment should be done with a warm engine, same for carb balance. The choke richens the mixture making any adjustments void,

I’ll make all adjustments with no choke. 
 

Does anyone have any pictures of roughly where the throttle adjustment screw should be? Or measurements by any chance 

 

Thanks!

[DeegzARG]

I’ve made some progress but it’s not 100% yet. I’ve got it idling at 1,100rpm and sounding smooth. Only issue is when I give it throttle too fast it bogs, when I give it throttle smoothly no issues. I’ve changed the exhaust gaskets, synced the carbs and turned the air screws at 1 3/4 out from lightly seated. 
 

any ideas why Im getting the bog?

[Gixer1460]

I don't think those carbs have accelerator pumps like the RS series do, so you can't 'snap' them open like a CV carb - they have to be opened progressively! It becomes a riding style thing that you'll get used to!

[BigT]

What 1460 says.

You get the adjuster screws close by doing a bench sync. If the carbs are still on the bike, just tweak until they're even

Edited September 19, 2022 by BigT

[DeegzARG]

Oh ok, I feel like I’ve got those adjusted fine at this point. 
 

What would be the reason for the bike wanting to stall when I open the throttle too quickly? Should I turn the air screws clockwise to fix that issue?

 

thanks again for the help!

[Gixer1460]

Simple physics lesson coming up!

All carbs have a restriction in their bore called a venturi (narrowing of bore). Due to the restriction this causes, air has to speed up through it and whilst speeding up the pressure lowers - called depression. The depression is what 'sucks' fuel out of the jets. So, imagine the carb sitting at idle, the slide is down, restriction is massive but airflow is low so the jets only meter enough fuel to suit the airflow. If the slides are lifted too quickly, the restriction is removed, airflow 'should' increase but as its at idle, it can't accelerate quick enough to breathe deeply and airflow stalls. At the same time, because the restriction has disappeared, the airflow slows and because of that its pressure increases (loss of depression) and as a consequence fuel is not drawn out of the jet so readily.

Hence you have to match the slide opening speed to engine speed to depression and fuel flow. RS carbs artificially add extra fuel into the airflow using accelerator pumps giving richer mixture to wake the engine up. Long answer for simple question LOL!

[BigT]

23 hours ago, DeegzARG said:

Oh ok, I feel like I’ve got those adjusted fine at this point. 
 

What would be the reason for the bike wanting to stall when I open the throttle too quickly? Should I turn the air screws clockwise to fix that issue?

 

thanks again for the help!

Making the mixture leaner won't solve that issue. Gotta be over 3,000 rpm if you want a good response

 

[DeegzARG]

Appreciate the info! 
 

I’ve run into a different issue now. Not sure if it’s carb related or a little more serious. I had the bike idling and pulled the plugs to make sure all the cylinders were running ok and the 3rd cylinder was not firing. Really bummed about it as I was getting the bike close to road worthy. 
 

I removed the spark plugs and took photos. What should my next step be and what are your thoughts on the plugs?

 

Thanks!!

 

 

 

[TonyGee]

its running rich on no3, (over fueling)  could be a leaking float valve. 

[BigT]

Also could be a bad fuel trap, and fuel is running down the vacuum line into #3.

check the vacuum line for fuel. 

[DeegzARG]

I’ve pulled the carbs out and they were very dirty. I guess the residue from the tank was not cleaned properly. Now I’m working on bench syncing the carbs, which I’ve never done before. 
 

I’ve attached a photo and had a question regarding the components. Should they all be seated all the way down or should any of them be turned out a little. What are the names of the components in the photo? 
 

again, thank you all for the help. 

[Gixer1460]

See Image - all identified.

All have to be 'lightly bottomed out' in their working condition except the Idle mixture jets / screw which are usually between 1.5 - 2.5 turns out from seated point to adjust the idle mixture (really clever naming huh! LOL!) I like to remove the MJ's from the emulsion tubes before fitting the ET's so they seat correctly with decent pressure then MJ's go in and get lightly tightened, enough to avoid vibration loosening!

[DeegzARG]

Thank you Gixer1460! That illustration is perfect. I’m a newbie with these carbs so that’s very helpful.
 

Questions about the air/fuel mixture idle jets; should they be perfect? I noticed one of them is in rough shape compared to the others. Should I replace that and is it something that I can walk into any bike shop and pick up or are these special order items. 

Edited October 7, 2022 by DeegzARG

[Gixer1460]

It's likely been over tightened! They are pretty much 'order in' items, unlikely a normal bike parts place would have them on the shelf.

[dago]

You can probably get them from https://www.allensperformance.co.uk/ probably also worth getting new o rings

[DeegzARG]

I’ve attached a couple of pictures. Does the first one look right to you folks? Lightly bottomed pilot and main. 2 turns out for mixture idle jets

Second photo is a reference to the screw on the side of the carbs. How many turns out do you folks normally go for when bench syncing?

 

thanks!

 

[Gixer1460]

First - is the Idle screw I identified accessible externally when the bowl is in place? Second - I should have realised these were Slide carbs (not what I'm used to) so the idle jet setting may be waaaay off ! Third - Looking at my Haynes Bike Carb Manual and GS1000 fiches, that external screw in 2nd picture is titled an 'Adjuster' by Suzuki LOL! Haynes indicates it is probably a Pilot Air Screw. I guess its function is to widen the mixture range of the Pilot Fuel jet which has a fixed orifice, changed only by swapping jets.

If you haven't already - GET A MANUAL ! ! !  It will help a lot.