How can fiddling only with Pilot Air screws cripple my gs850

[RandyRex]

I've been getting my ass kicked by this. It's a long story, but I found a beaut, and got taken for a ride on it ... been through 2 shops, both pronounced it "good to go", the second one even showed me the fun dyno printout ..I was driving trucks, had no time to mess with it, trusted a shop, but after taking it for a ride on the freeway and hearing the "marbles in a jar" issue again, I messed with the Pilot Air Screws to get back home. Bike shop said "you blew the guarantee" and now I can't get it to run properly, either at idle speeds or the freeway, am about ready to shoot this bike, but I think she's only a couple of adjustments away from humming like she should. I'm no carb guy, but have been getting up to speed through the fantastic resources I found in here, but even armed with everything, I'm baffled. I quit my job driving trucks last month, as I thought I had my ducks lined up for a ride from Ohio to NY, which I still want, but am now on limited resources. It is a 1979 GS850 with Mikuni VM29s ( I think, not one schematic matched up exactly). It was running like a Swiss watch around town, but not on the freeway (high end of the Jet Needle/Needle Jet) but as it was idling high and making the "marbles in a jar" noise (at about 5K ... 1/2 throttle), I tried to be clever and I twisted the screws shut (thinking to lean it out a wee bit, but without counting ...like a dumbass. However, the 4 screws seemed to bet set at different amounts of turns, second dumbass award for not realizing that high idling and throttle hang was a sign of lean-ness) after that, I tried backing them out 1.5 turns, to start with, but haven't found the original setting, boots and O-rings are good, comp test showed acceptable readings (according to the first shop) boots are soft and fresh. Valves are unknown, but it was running tight around town, so I haven't checked the valves. It has pods, and the jetting was (supposed to be good, as per the second shop) seen to, as per having pods. Had the carbs somewhat apart, I checked the Pilot Jets, new condition, new Main Jets, floats all balanced and set, points all set right, which they weren't, even though the dyno said "good to go ...) after dishing out about $3K to shops, I'm starting to go through it myself, now. I used to be a competent car mechanic, but 4 carbs ... i yi yi ... almost forgot, I did NOT touch the ... Pilot Fuel Screw (?) that is in front of each bowl, underneath, I left them alone ... I read that one cannot have both a Pilot Fuel screw and a Pilot Air screw, but this seems to dispute the doctrine I have no vac gauges, but the slides are synched, I check openings with a feeler gauge, hillbilly, I admit, but the slides were spot on identically set. So, I dropped the bowls to check float height, and they were not balanced, which they are now, floats are even and set. But, with clean Pilot jets and and no blockages, my bike will not run at idle now, any suggestions?

[Nessism]

You have VM26 carbs.

The pilot fuel screw which comes up from the bottom of the carbs should be set at 7/8 of one turn open. The pilot air screws are on the side of the carbs should be at about 1.5 turns open so it sounds like you are fine there. Of course there is a lot more than a simple screw setting that goes into assuring your carbs are working properly. I won't get into it here but please check the Newbie Mistakes thread linked in my signature and search out Basscliff's website which has a wealth of information, including a VM carb rebuild guide.

Good luck

[Steve]

First thing to do is to verify which carbs you have. VM29s might be a bit much for the bike, it came stock with VM26 carbs. After you verify what carbs you have, it would be necessary to verify jetting. Keep in mind that 29s will require different jetting than 26s, so it's critical to know what you have.

Valve adjustment is critical. If you don't know the clearances, it's best to check and verify. These valves always tighten up, and the standard clearance is really tight, so if you haven't checked them, the might be TOO tight.

.

[Big T]

Post up a pic of your carbs for starters
VM 29 float bowl held on by one large but
VM 26 float bowl has 4 screws and a brass drain bolt

[Big T]

Also, more likely a points issue

[RandyRex]

Thanks guys, I'm reading your replies now

[RandyRex]

You have VM26 carbs.

The pilot fuel screw which comes up from the bottom of the carbs should be set at 7/8 of one turn open. The pilot air screws are on the side of the carbs should be at about 1.5 turns open so it sounds like you are fine there. Of course there is a lot more than a simple screw setting that goes into assuring your carbs are working properly. I won't get into it here but please check the Newbie Mistakes thread linked in my signature and search out Basscliff's website which has a wealth of information, including a VM carb rebuild guide.

Good luck

Oho, it was one of the first pages I read Thank you for it. I've got her running now, I made the floats all identical in every way, and oddly, #1 float tab was pinning it shut(fixed now) , odd as I set them all identically. I'm EMO like that =D I got the screws to 1 1/2, went around the block a few, and am letting it cool now, for another plug check. It was stumbling a bit at around 1/8 - 1/4 throttle, but on the freeway, it pulled nice, so my mischief was limited to the idle circuit, which will need a wee bit of more fiddling, and the marbles noise ... originally thought it was the main (noob award #3 ... ) but now realize that after learning y'alls "smart guy wake-ups" that it might be a simple jet needle drop to reduce the amount of fuel it's getting, until the rpms can devour the right mix.currently thinking that the #1 float might need a bit of adjusting, too, as it was not seating like the other 3. Thank you for the input ..

[RandyRex]

First thing to do is to verify which carbs you have. VM29s might be a bit much for the bike, it came stock with VM26 carbs. After you verify what carbs you have, it would be necessary to verify jetting. Keep in mind that 29s will require different jetting than 26s, so it's critical to know what you have.

Valve adjustment is critical. If you don't know the clearances, it's best to check and verify. These valves always tighten up, and the standard clearance is really tight, so if you haven't checked them, the might be TOO tight.

.

Thank you, I understand. I have Mikunis, the reason I say VM29s instead of the 26s is because of the throttle cables and the pullout slides, which mine lacks. As to the jets, I was told that it takes #115 mains, and the pods have leaned it out, so it has 120s in it, at the moment. I have 130s and 135s for mains in a bag, but am dealing with the Pilot circuit, too. I'm pretty sure I have the 29s because of the layout, which most closely resemble the pics in the carb rebuild manual from this forum. As to the valves, I am a believer, I've read about them tightening up, so will check them, too, but my first problem was the Pilot circuit, I rarely even get to the mains, this old girl wants to run wa-a-a-y fast =D and the Pilot was preventing me from tuning her, but she's purring at the moment at idle, with hesitation around 1/8 throttle.

[RandyRex]

Post up a pic of your carbs for starters
VM 29 float bowl held on by one large but
VM 26 float bowl has 4 screws and a brass drain bolt

These are my carbs, 26s? I have the 4 screws ...

[RandyRex]

Also, more likely a points issue

It might have been that, too, I addressed the points/cond last night and today. Put an inordinate amount of time in setting them just right, too. Ended up replacing most of the stripped screws holding my points sets down, as the bike shops ... must have missed this important feature ... they were out of adj, too grrr ..

[Steve]

These are my carbs, 26s? I have the 4 screws ...

Yep, those are stock VM26 carbs.

Stock jetting includes #15 pilot fuel and 102.5 mains. With pods installed, a 115 might work fine, but plug checks will need to be done. Might also need to raise the needle one notch to ease the transition to mid-range.

.

[RandyRex]

Yep, those are stock VM26 carbs.

Stock jetting includes #15 pilot fuel and 102.5 mains. With pods installed, a 115 might work fine, but plug checks will need to be done. Might also need to raise the needle one notch to ease the transition to mid-range.

.

Well, I haven't achieved the fullest understanding, then, as I had intended to drop that needle down a notch, as one of the original maladies was the "marbles" issue, which I had thought to be too much fuel being dumped in, too soon. I was told that it came from the factory with #115 mains, and the marbles noise appeared when I drove it, after having the #135s installed, which I changed down to #120s, before I realized that I was still having my problems in the Needle Jet/Jet Needle zone, not the Main Jet zone. So, I'm working several issues at the same time, with only the understanding that I've picked up in the last 4 days, from here. But, I'm wrapping around it now, and I appreciate all the help you guys are giving me! Right now, I'm still facing the idling issue, but think I'm on track, now. After I get the idle back to nice, I'm going to rethink the marbles issue, which I thought to be too much fuel. Am I wrong there? And, thank you for identifying those carbs, I was guessing ... =D

[Big T]

These are my carbs, 26s? I have the 4 screws ...

VM 26

Obviously, the shops you trusted led you astray.
Take off the points cover tomorrow, fire up the bike i n the dark and see how much sparking is going on

[Steve]

I was told that it came from the factory with #115 mains, and the marbles noise appeared when I drove it, after having the #135s installed, which I changed down to #120s, before I realized that I was still having my problems in the Needle Jet/Jet Needle zone. So, I'm working several issues at the same time, with only the understanding that I've picked up in the last 4 days, from here.

The '80 and later 850s came with a different series carb, which did come with #115 mains, but your '79 was the only year to have the VM-series carbs, which came with 102.5 mains.

Jetting is (almost) always "fun". However, I tell people that if this is your idea of "fun", don't bother to invite me to any parties. One of the cardinal rules in jetting is CHANGE ONLY ONE THING AT A TIME. In other words, if you want to raise the needle and try the 115 mains, change just the mains, then do a test ride. If it's better, great. Then you can try the needle to see if it makes it any better. Also, record your starting settings and your changes. If you don't keep track, you will eventually forget, so record what you changed, how much you changed it, and the results of the test ride.

.

[RandyRex]

The '80 and later 850s came with a different series carb, which did come with #115 mains, but your '79 was the only year to have the VM-series carbs, which came with 102.5 mains.

Jetting is (almost) always "fun". However, I tell people that if this is your idea of "fun", don't bother to invite me to any parties. One of the cardinal rules in jetting is CHANGE ONLY ONE THING AT A TIME. In other words, if you want to raise the needle and try the 115 mains, change just the mains, then do a test ride. If it's better, great. Then you can try the needle to see if it makes it any better. Also, record your starting settings and your changes. If you don't keep track, you will eventually forget, so record what you changed, how much you changed it, and the results of the test ride.

.

Any suggestions on raise the Jet Needle? Mine seem fixed to the slides. Unless, (my guess ...) the slidie thingies have to come out first?