CV Carb illustration needed

[DaveDanger]

I did it again. Unintentionally HiJacked someone else's thread on a carb related topic.... so I cut and pasted and moved mine back here as a new thread....

<DaveDanger> Does anyone know where I can find a really detailed couple of photos of the CV carbs on my 81 GS850? Or a book that details this type of carb? an internet article? A child's crayon drawing?
I want to be able to determine exactly what adjustment screws and jets are where. Several views and angles, with everything marked with arrows and such. My Clymers gives me just enough information to be irritating, and the Suzuki shop manual I ordered for my year model came in as a 79 GS850 manual. It illustrates nothing but the other style carbs.
I currently have my carbs disassembled for cleaning again (5th time) and I still don't know exactly what is referred to when someone advises me to adjust screws and jets and needles. I've never had to do these adjustments on any bike I've owned before and it's frustrating the fool outa me. Mostly because I can't identify specific locations on the carbs.


<Spchips> http://www.thegsresources.com/images...ed%20view1.jpg
This is slide 65 of the carb cleanup series on the main GSresources site. This one picture does a good job of showing everything and the whole assembly, while the guide goes through the entire carb very thoroughly

I've gone to this photo. It doesn't point out one particular adjustment screw in particular that I need to identify.
If you're looking down directly from the top of the carburetor, there is a deep port on the top, front, center of the carb body with an adjustment screw down inside it. It is directly behind where the intake rubber slips over the carb throat outlet. It is accessible without disassembling the carb in any manner, but the tank does have to be off to get to the screws. On mine, the screws on #1 & 4 are capable of moving, whereas #2 & 3 are stuck tightly. I have soaked them for days in penetrating oil. What are these screws??? What do they adjust???

When I started this post a week ago... I had pulled and disassembled my carbs for cleaning and rework again. A major problem with my pickup truck left me with no wheels at all, so I quickly reassembled the carbs and got the GS running again so I could get back and forth to work. Problem is, I messed with those un-named screws a little bit while I had the carbs apart, assuming I'd be able to get them out and clean behind them. At any rate, they're apparently badly out of adjustment now and I can't seem to figure where to start to get them, and all the other carb adjustments back to where they should be. (They've never been correct since I got the bike back this past fall, but they were infinitely better than they are now).
I am going to start this morning with checking and adjusting the valves before I get into any more carb tweaking. I absolutely know that my intake tube rubbers and o-rings are tight and not leaking. There are no mods on my system. Completely stock air box (sealed tightly) and stock 4 into 2 exhaust. I have set the float levels per the manual.
I badly need to determine where to start with these carbs as if they just came out of a box and have never been adjusted. Some of you brave types grab a 6-pack and sit down with me for a while

[Boondocks]

...If you're looking down directly from the top of the carburetor, there is a deep port on the top, front, center of the carb body with an adjustment screw down inside it. It is directly behind where the intake rubber slips over the carb throat outlet. It is accessible without disassembling the carb in any manner, but the tank does have to be off to get to the screws. On mine, the screws on #1 & 4 are capable of moving, whereas #2 & 3 are stuck tightly. I have soaked them for days in penetrating oil. What are these screws??? What do they adjust???...

Sounds like you're talking about the pilot screw (sometimes called pilot air screw or pilot fuel screw). See Pilot Screw and Removing Pilot Screw and Pilot Screw Removal and Assembly.

The screws are normally have caps above them. Yours have already been removed. They are capped because they are adjusted at the factory to meet EPA requirements, and the screws underneath are sealed with a permanent type thread sealant which can be a bear to remove. Heat works to remove the sealant, also carb cleaner might work but if you're not careful the carb cleaner could damage the O-rings at the bottom of the screw.

The screws adjust the fuel flow for low to mid speed operating conditions. The bikes typically come too lean at low speed from the factory in order to conform to the EPA regs. A good starting adjustment is to lightly and carefully turn the screws all the way in. Too much pressure can break the sharp point on the end. Back them out about 2-1/2 turns for an initial adjustment and see how it goes from there.

[DaveDanger]

Thanks Boondocks!
That sounds like step one that I need to start with. I will see if I can find something, up to and including heat that will loosen the rest of those screws. I don't mind at this point if I do dissolve out the o-rings beneath them. I already have a new set of o-rings on the way from Mr Barr, and I want to clean beneath those screws.
I'm going to go through all the rest of the engine setup first, but the carbs are coming back off tomorrow for yet another clean and reassemble.

[KEITH KRAUSE]

The screws you describe are the mixture screws. They fine tune the pilot circuit mixture for each cylinder.
These screws should be set using the highest rpm method. The engine has to be running well before this adjustment is done of course.
On a stock bike, I'd initially set them at 1 turn out.
Start the bike up and warm it up completely on the centerstand. Adjust the idle to 1,000 rpm's.
Starting with any cylinder, slowly turn the screw in either direction. At some point (usually between 3/4 and 1 1/2 turns out) you should hear the rpm's max out. Try it back and forth a couple times if you like and find the sweet spot. Stop turning as soon as the rpm's max out. Re-set the idle to 1,000 rpm by using the idle adjuster knob. Go to the next cylinder and repeat until all four are set for best idle. Final set idle to 1,000 or what your factory manual says. This is what's recommended before any vacuum synch too.
The screws can be very stiff as you've found out. Heat may help as has been suggested. Be sure to use a proper fitting tool, not just the closest fitting tool in your box. I always turn the screw IN first, not out. Turning out first causes the sealant to jam/ball up in the threads. Turning it in will expose some of the factory sealant jammed in the threads and you can pick any out with a straight pin. LIGHTLY seat the screw. Continue any cleaning. Once clean, the screw should come out with the correct tool. If you do get about 1/2 to 2 turns out and it jams up and you're sure the head will strip, I suggest leaving it be unless you want to risk looking for a replacement carb body/bank. At this point of being stuck, you'll still be able to make a range of adjustment. Only possible problems are that you can't service the o-ring inside (if it needs it) and you can't properly blow out the passage that this screw regulates. Of course, it's always possible no problem exists in that passage. It's always a gamble.
After hopefully making these adjustments, test and see how she runs.
If you're already breaking down the carbs, I'll try to help later.
There are sites that you can search to learn about CV carbs. I have a factory manual that explains basic operation with decent diagrams. It's for the '80 models but your '81 will be nearly identical.
I'm computer illiterate though and I'm not sure of the best way to send typed info. If I take a few pics I don't know if the sent pics will be large enough to read, etc? Unless someone else can help with this soon, I'll try to take the pics and have my son help post them and we''ll see if that helps you.
I can also describe basic operation of the different jetting circuits and how they work at various throttle positions.
If you want to start from absolute scratch, we can do that too. Starting with parts/jet identification/verification and correct assembly order (need Mikuni site illustrations or factory manual), unless you KNOW the carbs history and are sure they are jetted as stock and nobody has taken them apart in any way. You need to know exactly what you have before rebuilding.

[KEITH KRAUSE]

Just bumping this up Dave. I plan to post some pics/info in the morning.

[KEITH KRAUSE]

Some factory manual pics of BS34 carbs from an '80 GS1000. Should be identical to yours, except exact jetting.
Basic operation:



Closer ups:




This site says it limits you to four pics in a post, so I'll post again to get all the pics here. Forgive my computer skills.

[KEITH KRAUSE]

Slow, or better known as the pilot circuit:
Fuel/air mixture arrows have small dots in them (hard to see).


Pilot circuit operation:

[KEITH KRAUSE]

Main/jet needle operation:



Main/jet needle operation:

[KEITH KRAUSE]

Just to put into different words/simplify but still the same thing...
For the pilot circuit, closed/nearly closed throttle position, the fuel enters the main jet and is regulated by the pilot jet. Fuel goes up the passage and mixes with air from the pilot air jet. This mixture enters the main bore, but a secondary passage to the main bore is regulated by the mixture screw. The mixture screw allows for small differences in each cylinder and allows for fine tuning of each carb/cylinder.

Jet needle/main jet circuits...
Remember, fuel flow will always be regulated by the SMALLEST passage.
At throttle positions of just above idle to about 3/4, the jet needle regulates flow. The jet needle is tapered. The needle jet it slides up and down in is straight. The widest part of the jet needle will be the smallest passage for fuel (between the jet needle and needle jet) and the regulating point.
Fuel enters through the main jet and up through the needle jet. Air coming in from the primary air jet mixes with the fuel. As you open the throttle, the tapered needle rises out of the jet. The opening, or space between the needle and jet increases. As throttle position increases, the flow increases.
At about 3/4 throttle position, the opening, or space between the jet needle and jet becomes larger than the opening of the main jet. At this time, the smaller passage of the main jet will regulate fuel flow up to full throttle.
Hope this helps.

[DaveDanger]

Thanks Keith
I'm printing this all out as you send it, and I'm studying it in depth. makes sense so far
The photos make a world of difference as well.

Again, I appreciate your time!

DD

[KEITH KRAUSE]

OK. Sorry it took so long. If you have questions during your carb work, just ask.

[Joe Guilbeau]

Keith,

I have a 1981 GS11--EX with a big bore kit (Wiseco...don't quite know which big bore kit was installed.)

I have a 142.5 main jet

I have Vance&Hines 4-into-1 pipes.

To properly tune the carbs....

I have been doing this

1. Set the Needle with the C-clip so that idle is giving me smooth response as I try to hold idle, and the plugs are tan.

2. After reading your post, I will go to the No. 2 Carb and set the idle at 1000rpms and adjust in till I get max rpms. Then follow up with other three carbs.

3. Go for a ride and whack open the throttle, and kill engine at 8000-9000 rpms, glide to a stop and pull plugs. If rich, I will go down in Main Jet size.

Finally I will sync the carbs.

Is this correct?

[KEITH KRAUSE]

For a bore kit and pipe with completely stock intake (lid still on too), I would check with what mains are used in stage 1 jet kits for your model. I'm sure someone here runs/owns a stage 1 kit and can tell you what sizes they supply. Just guessing, I'd go up 1 step size (2.5) for the bigger pistons and an additional 7.5 (1 1/2 full sizes) or 10 (two full sizes) for the pipe. So that's 10 to 12.5 larger than what your stock mains are.
Forget about rpm's. It's about throttle position. Test the mains by running at full throttle on a level or uphill road is fine. "Chopping off" to read the plugs means quickly closing the throttle/pulling in the clutch and turning the key off, coasting to a stop with the clutch lever pulled in. Be sure the motor is completely warmed up.
Test the same way at 1/3 throttle to see how the jet needles are doing.
Test at minimal/steady throttle in 4th/5th gear (about 35/40 mph) to see what the pilot circuit is doing.
Mixture screw adjustments may help with tuning the pilot circuit and to a lesser degree, the jet needle reads. If the needle reads are lean, you'll need to raise them. Hopefully you'll be OK with them and not need to.
If the pilot circuit reads are lean, mixture screw adjustments should help.
You may need to go to larger pilot air jets but again, check with stage 1 kits to see what they suggest/supply.
BEFORE JETTING, always adjust the mixture screws using the highest rpm method/1,000 base idle and THEN vacuum synch. BEFORE SYNCHING, the valves and timing must be adjusted correctly too and make sure you have no intake leaks.

[jager1313]

I still don't get it.

I must be pretty dense, but after reading multiple carb synching posts I still don't understand.

I took apart all four carbs last weekend, then put everything back together exactly as it was. I counted every turn as I unscrewed things, Most everything was screwed all the way in, so as not being able to be screwed in anymore. The only adjustable screws were on the top engine side of each carb. I have highlighted it on #1 carb in the picture below.

http://i218.photobucket.com/albums/cc65/jager1313_photos/Picture035edit.jpg

Each "air screw" as it is called on the carb clean up series is almost all the way screwed out. Between 5 and 7 full turns out from the bottom. I have seen posts saying that default is only 1 turn out. How could mine be so far off? I'm pretty sure I learned how to count...

My bike is a 1981 GS 550L that was running perfectly. I only took everything apart to learn.

Can someone show me which other screws I need to adjust to get me running? I have not attempted to start the bike yet, because I am having massive trouble squeezing the whole carb set back into place. I could possibly be doing it all wrong. Is there a way to remove the air intake boot thing so that it all fits in nice, then place the air intake back in?

Is there a pictorial carb synching tutorial like the one for carb cleaning and the ones for changing oil? If not someone should make one...

[chef1366]

Make sure you are not counting half turns as full turns. Those are not sync screws but idle mixture screws. Set them at 1.5 turns out to get started.
These carbs are a known pita to re-install. The only help I can be is make sure the air box is as far back as possible and start with the airbox side of the carbs in the boots and the intake side below the intake boots and angle them up till they pop in.