carb screw tuning question - please help

[Guest]

so ive restored a 79 gs850 with mikuni carbs to the point where it will start. i know the air/fuel mixture is messed up because i took the carbs apart to rebuild them. heres my question...

i have the outside exposed air screw tuned. (1.75 turns out) but the bottom screws the are inside the carb are just completely closed. i just now figured out that they have to be unscrewed a little to let more fuel in.

of the two fuel "jets" on the bottom (the big center one and the smaller off-center one) i believe they are called main(big) and pilot(small) which one do i adjust? both or just one? and how far out would be a good starting place?

~ also, i currently have no filter on the carbs. im just trying to get the bike to idle. i have new K&N pods on the way though.

thanks for the help!
~Nate

[BassCliff]

Hi,

Jets are screwed in snug. Start with the fuel screw about 3/4 or 7/8 turn out and the air screw about 1 1/2 to 1 3/4 turns out. Adjust the air screw for highest idle from there.

This might also come in handy: http://www.mikuni.com/pdf/vmmanual.pdf


Thank you for your indulgence,

BassCliff

[azr]

It's going to be hard to get her to idle without the air filter set up though but the advice you have already is a good place to start.

[mlinder]

As Basscliff said, no, everything is snug. Jets are not adjusted except by removing them and changing their size.
The airscrew that IS adjustable is on the outside f the carb bodies. I can't remember which carbs are on your bike, but someone here has a pic of what is adjustable, and what it does.
It wont run well (or maybe at all) without airbox/aftermarket filtration, and possibly rejetting.

Again, make sure all your internal jets and such are snug. They will back out and drop once you get running if you don't have them well seated.

[1_v8_merc]

Actually just for "knowledge" purposes....

They can definitely Idle without an air filter and box.
(mine did, but the Idle was higher than normal)

They can even ride without it.

When I first got my GS, and didn't know anything about bikes, we rode it around the parking lot a few times that way.

Then I got the filter back on and oiled up, and put the cover back on.

Your not supposed to ride without them, but it's not that uncommon to buy a running parts bike and find someone riding without it...... It's just going to make the bike run VERY lean and damage the engine eventually. And it's basically just NOT going to run correctly, and you'll probably need Starter Fluid to fire it up every day.

Oh yeah.....never use starter fluid on these bikes, unless it's an emergency situation.

[Bustedknuckles]

thanks everyone

thanks everyone,

i have the jets snug, fuel & air screws adjusted, and filters in the mail, at this point it will start strong then quickly die down after about 4 sec. im going to see if i can get it to idle before i get the filters by closing the air screws somewhat to make the mixture richer. just for fun.

if it idles after this ill know that its not something else thats causing it to stall.. right..?

[Mak]

Nate,
I'm currently doing my first carb rebuild also... Let me know what you end up doing and what your settings will end up being. I'll probably have to do the same thing.

[azr]

What's your petcock set to? if it's at 'Run' and the vacuum hose from the petcock is set up correctly, turn it to 'Prime' and see what it does.

[Steve]

Oh yeah.....never use starter fluid on these bikes, unless it's an emergency situation.

You really need to shorten your advice.

"NEVER USE STARTER FLUID ON THESE BIKES."

If the situation is "emergency" enough to warrant starter fluid, it did not come on suddenly,
and you should have been taking better care of your bike all along.

It is just so easy to do so much damage with starter fluid on these bikes, it's just better to avoid it alltogether.

.

[Bustedknuckles]

re-try

alrighty, so ive turned in the air screws about 1/2 a rotation to compensate for me having no filters on the carbs yet. so they are about 1.25 out. again im just trying to get it to idle so i know theres not something else wrong with it.

its been sitting in the garage overnight so everythings about 50 degrees. for that reason ive got a space heater on itand will be trying to start it again in about an hour.

does anyone know if cold air will have a HUGE impact on it running? i know it will have some but i am unsure if i need to take any other steps to counter this. ill have to open the garage door when i run it and its about 20 degrees outside so the temp in the garage will quickly drop.

also, the bike hasnt run for about 1.5 years. other than the couple short lived (4 sec.) starts ive done in the past week, then the bike drops quickly in rpm's and dies. i know this is a broad (1000 answers) topic. but does anyone know any of the most common issues with these bikes after a long sitting period?

Thanks again! ~Nate

[cowboyup3371]

Look back at Basscliff's welcome site as there's about 15 different things you'll want to look at on your bike.

[Bustedknuckles]

oh yea

hey thanks for reminding me cowboyup, i checked out bascliffs website when i first joined the forum but have kinda forgot about it. i was just looking again now but cant seem to find any kind of long storage link or thread. im just looking for a checklist or something so i can start checking stuff off. might someone be able to direct me please?

sorry, i used the search forum tool and looked through basscliff's site but couldnt find anything.

[cowboyup3371]

From the GSR Greeting (shown as Read Me on Basscliff's page):

***********Quoted from Mr. bwringer************

Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

What I have noticed at the rallies is that very, very few 850Gs are actually running right. Make VERY sure it's actually running the way it's supposed to before busting out the modifications.

Brian's E-Z and fun plan for GS850 happiness:

1) Seal the airbox and air filter with weatherstripping.

2) Ensure no intake leaks. Spraying WD-40 or water doesn't tell you much, since very small air leaks can cause problems even though they won't suck in enough WD-40 to make a difference. Replace your intake boot o-rings and boots if needed, and seriously consider spending the lousy $28 for new airbox/carb boots.

3) Ensure clean carbs with correct settings, new o-rings, and original OEM jets. No, not just squirted with something. I mean completely disassembled.

4) Check/adjust valve clearances (Manual calls for every 4,000 miles. This is not optional.)

5) Ensure healthy electrical system.

6) Seriously consider upgrading coils and plug wires.

7) Install new, stock NGK B8-ES plugs gapped to .031".

8 ) Fine-tune float height and idle mixture screw to ensure best off-idle transition.

9) Clean air filter and reinstall with only the lightest oil mist -- over-oiling and/or letting the filter get dirty is a common and critical mistake, and will make the bike run funny at low speeds and run rich. This may take a few tries.

10) Make sure the exhaust seals are sealing.

11) Ooh, much better now, huh? You're gonna need upgraded suspension - Progressive or better fork springs and shocks. Set suspension sag appropriately.

12) Upgrade brakes with new pads and stainless lines to deal with all that extra speed.

13) Install new petcock, since I'm going to head to the roof with a rifle if I have to read about yet another #2 plug fouling and failed hillbilly attempts to rebuild the petcock and/or deny there's a problem.

14) Oh yeah -- check compression somewhere in there to ensure the valves and rings are reasonably healthy.

15) You'll probably need new OEM clutch springs -- the clutches last forever, but the springs get tired after 20 years or so under pressure. E-Z and cheap.

[Bustedknuckles]

thanks again

that's exactly what i needed. thanks again cowboyup, im gettin to work...

[bwringer]

You know, looking at that list/rant I typed up several years ago, it gives me a warm fuzzy feeling inside. Really.

After years of me and many, many others bludgeoning these items into people's heads, I think we're actually starting to see progress out there.

- Lots more people are actually checking and adjusting valve clearances these days. There's a shim club now and the ingenious zip-tie method has been invented, so there's little reason for even the most dedicated cheapskate to neglect valve clearances. Heck, cheapskates with 16-valve engines can make a valve tool from a square-drive wood screw (maybe two cents, or free if you dive into the right dumpster) and a hunk of a wooden stick.

- More people seem to understand that cleaning carbs means complete disassembly, not just a few spritzes with spray cleaner. On a related note, fewer and fewer people are wasting their money on crappy low-rent carb kits. If there's any justice in the world, Robert Barr's little o-ring kit operation has put his kids through college and built him a new house by now.

- More petcocks and intake boots are being replaced as a matter of course rather than becoming the subject of the hillbilly fix o' the week.