question for carb gurus

[zblip2]

I own a gs850g since last year. I recently changed the carb boot o-rings. All 4 of them were split and flattend out and must have been like this since before I bought the bike. Now that I changed the o-rings, the bike obviously runs ritcher and over all smoother EXEPT on the highway at about 45 mph to 65 mph. The best way to describe this is to say that after settling at crusing speed the bike feels like I'm hitting wind gusts and air pockets exept there isn't any. The speed is varying constantly and in some cases, if I wack the throttle while at 45 mph the bike dosn't pick up and something weird goes on in there like the motor is drowning. Another clue is that if I stop the bike for a minute and then take off, it runs like a champ and then after a minute or two at 45/65mph it starts acting up again. Also, if I drive faster than 65mph, the bike behaves normally.

My theory on this was that the previous owner adjusted the carbs to cope with the ''failed O-ring sindrum'' and now that I have fixed the O-rings, the mix is too ritch...

Here is What I tried:
I raised the flotes clearance 2mm to make the mix leener, and turned the mixture screw 1/4 turn clockwise to make the mix leaner also. But then realised that turning the mix screw clockwise actually make the mix ritcher... finally I had to go to work so I couldn't rectify my error. I went to work on the bike and I must admit that the adjustments I did have not helped perfomance. The motor lost what it had gained from fixing the O-rings. The motor seems to strain more and at I dle, if I do a quick rev up, the Idle drops afterwards and the motor almost dies... By the way I cleaned the carbs today.

I'm starting to think now that I went the wrong way with this and that the highway speed variations were actually caused by starving since the carb uses more gas now that the mix is ritcher and therefore the flotes needed to be actually set to richer insted of what I did...

Sorry for the long post, hope some one who understand these things will help.

Thanks

[kparkfan]

Whens the last time the carbs themselves were dipped and the o-rings in them changed?

[TheCafeKid]

Start from the begining. I am assuming that your bike is stock since you made no mention of any pipe or intake modifications such as pods. Going with that assumption, I suggest you set the screws all the way closed (lightly seated! Dont screw em in too tight, or you'll break the tips off the screw) and then open them all to TWO full turns out, and go from there. Two turns out is a good starting point. You then, once the bike is warm and idling nicely without choke, adjust the screws SLOWLY one at a time, listening for the idle to raise to its highest point. Once youve turned the screw so that it no longer raises the idle speed, cock it back an 1/8th of a turn and leave it. Then move on to the next. You have to do this fairly slowly because it will take a second for the bike to compensate for your adjustment. Once you have THAT done, to get the bike running its smoothest, you'll need to vaccum sync. If you dont have one, or have access to a set of sync gauges, you'll be ok, it just wont be as smooth as it could be. The surging you're talking about sounds indicitive of it being a bit rich in the pilot/just off pilot section of the carbs, which is what the screws have most effect over. Your float levels sound just about right, its what I generally set mine to, splitting the difference of the +/- 1mm the manual calls for just about. But, you need to be SURE that they are all set the SAME, or one or more cylinders might push a lil harder than the others. The vaccum sync will also help in ensuring that they are all working equally. Hope this helps.

TCK

Oh BTW, i DONT claim to be a guru by anymeans, but ive done this with stock bikes enough to know that its a good way to go. Now, when you get into tuning for pods and pipes and stuff, *I* still need help with some of it..

[BassCliff]

Hi,

Make sure your carb vent hoses are properly connected and routed. See the "Where Do These Hoses Go?" article on my website.


Thank you for your indulgence,

BassCliff

[Steve]

What year is the 850?

PLEASE PUT THIS INFO IN YOUR SIG LINE.

If you have a '79, then, yes, turning the AIR screws on the sides of the carbs IN will richen the mixture, but if you have an '80 or newer, the IDLE MIXTURE ADJUSTMENT SCREWS on the tops of the carb outlets will lean the mixture when you turn them IN.

Rather than throw a box of Band-Aids at the carbs, set them properly to factory specs, except for the pilot mixture. For that, the factory had them set rather lean and they can stand to be richened up to make them run better. Set the floats at the proper level. If you have a '79 with the VM carbs the floats should be at 24mm. If you have an '80 or newer with the BS carbs, the floats should be at 22.4mm.

When you experience this surging, immediately pull the clutch, hit the kill switch and pull over to a safe spot on the side of the road. Pull a spark plug or two to see what color they are. If they are dark, yes, you are running rich. My guess, though, is that you are running lean, and they will be rather white.

Besides mixture problems, you might also have a poorly-venting gas cap. When you pull over to check your spark plug color, open the gas cap, listen for a big WHOOSH when you open it. If you hear that, your cap vent is not working properly.

.

[TheCafeKid]

What year is the 850?

PLEASE PUT THIS INFO IN YOUR SIG LINE.

If you have a '79, then, yes, turning the AIR screws on the sides of the carbs IN will richen the mixture, but if you have an '80 or newer, the IDLE MIXTURE ADJUSTMENT SCREWS on the tops of the carb outlets will lean the mixture when you turn them IN.

Rather than throw a box of Band-Aids at the carbs, set them properly to factory specs, except for the pilot mixture. For that, the factory had them set rather lean and they can stand to be richened up to make them run better. Set the floats at the proper level. If you have a '79 with the VM carbs the floats should be at 24mm. If you have an '80 or newer with the BS carbs, the floats should be at 22.4mm.

When you experience this surging, immediately pull the clutch, hit the kill switch and pull over to a safe spot on the side of the road. Pull a spark plug or two to see what color they are. If they are dark, yes, you are running rich. My guess, though, is that you are running lean, and they will be rather white.

Besides mixture problems, you might also have a poorly-venting gas cap. When you pull over to check your spark plug color, open the gas cap, listen for a big WHOOSH when you open it. If you hear that, your cap vent is not working properly.

.

I disagree with you only here... what he is describing is exactly how my ES felt before i adjusted the floats. Its quite possible the PO did exactly as he said in order to compensate for the leaking boots. (Good call on the possibility of them being VMs however, didnt even occur to me boots leaking and VMs...so to the original poster, disregard my settings on the carbs if you have a 79 850, they're not right) However, without actually FEELING what he's talking about, i cant say for sure, so you may very well be right Mr Steve....

BTW, THIS guy is the one who taught me what I DO know bout carbs that i didnt figure out myself thru beating my head against the workbench

[1978GS1000custom]

when you set the floats did you measure from the carb surface at the gasket base (the surface the gasket sits on)to the floats bottom? did you make sure the gasket was not in the carb when you set them? the gasket is between .032 and .062 in thickness and that will throw your setting off. most of the time the gaskets stick to the carbs and its really easy to overlook this. also, did you use the correct o-rings? they can very in size just a little bit and throw things off. the o-rings in these carbs are metric not standard. the standard ones are a bit smaller and will allow leaks. cliff

[zblip2]

Whens the last time the carbs themselves were dipped and the o-rings in them changed?

Well, that I don't know, but two times this month, I opened up the carps and unscrewed everything in there and shot carb cleaner and air in every hole possible. I gess that's enough no?

[zblip2]

Start from the begining. I am assuming that your bike is stock since you made no mention of any pipe or intake modifications such as pods. Going with that assumption, I suggest you set the screws all the way closed (lightly seated! Dont screw em in too tight, or you'll break the tips off the screw) and then open them all to TWO full turns out, and go from there. Two turns out is a good starting point. You then, once the bike is warm and idling nicely without choke, adjust the screws SLOWLY one at a time, listening for the idle to raise to its highest point. Once youve turned the screw so that it no longer raises the idle speed, cock it back an 1/8th of a turn and leave it. Then move on to the next. You have to do this fairly slowly because it will take a second for the bike to compensate for your adjustment. Once you have THAT done, to get the bike running its smoothest, you'll need to vaccum sync. If you dont have one, or have access to a set of sync gauges, you'll be ok, it just wont be as smooth as it could be. The surging you're talking about sounds indicitive of it being a bit rich in the pilot/just off pilot section of the carbs, which is what the screws have most effect over. Your float levels sound just about right, its what I generally set mine to, splitting the difference of the +/- 1mm the manual calls for just about. But, you need to be SURE that they are all set the SAME, or one or more cylinders might push a lil harder than the others. The vaccum sync will also help in ensuring that they are all working equally. Hope this helps.

TCK

Oh BTW, i DONT claim to be a guru by anymeans, but ive done this with stock bikes enough to know that its a good way to go. Now, when you get into tuning for pods and pipes and stuff, *I* still need help with some of it..

MAN!! What a great and simple post!!! This post should be a permanent text in the how to section of the site. Now I see the light!!

Thanks a million! I'll go and do exactly that!

[zblip2]

Hi,

Make sure your carb vent hoses are properly connected and routed. See the "Where Do These Hoses Go?" article on my website.


Thank you for your indulgence,

BassCliff

Sure thing, thanks. It just occured, is there a chance that I cracked a carb boot while fighting with the carb boot screws? How can I check this?

[zblip2]

What year is the 850?

PLEASE PUT THIS INFO IN YOUR SIG LINE.

If you have a '79, then, yes, turning the AIR screws on the sides of the carbs IN will richen the mixture, but if you have an '80 or newer, the IDLE MIXTURE ADJUSTMENT SCREWS on the tops of the carb outlets will lean the mixture when you turn them IN.

Rather than throw a box of Band-Aids at the carbs, set them properly to factory specs, except for the pilot mixture. For that, the factory had them set rather lean and they can stand to be richened up to make them run better. Set the floats at the proper level. If you have a '79 with the VM carbs the floats should be at 24mm. If you have an '80 or newer with the BS carbs, the floats should be at 22.4mm.

When you experience this surging, immediately pull the clutch, hit the kill switch and pull over to a safe spot on the side of the road. Pull a spark plug or two to see what color they are. If they are dark, yes, you are running rich. My guess, though, is that you are running lean, and they will be rather white.

Besides mixture problems, you might also have a poorly-venting gas cap. When you pull over to check your spark plug color, open the gas cap, listen for a big WHOOSH when you open it. If you hear that, your cap vent is not working properly.

.

Thanks man for the great insight! I'll try all of this!

[zblip2]

when you set the floats did you measure from the carb surface at the gasket base (the surface the gasket sits on)to the floats bottom? did you make sure the gasket was not in the carb when you set them? the gasket is between .032 and .062 in thickness and that will throw your setting off. most of the time the gaskets stick to the carbs and its really easy to overlook this. also, did you use the correct o-rings? they can very in size just a little bit and throw things off. the o-rings in these carbs are metric not standard. the standard ones are a bit smaller and will allow leaks. cliff

Thanks for the input. First, I did not mesure the actual flote height. I just rased them roughly 2mm higher than what they originaly were (not very scientific)

But, if I was to set them I would do it according to this: by the way is this a good source?

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html

[curseboy]

at 45mph...my guess is that the pilot/floats have very little to do with it...the RPM and throttle are probably in the range of the needle jets.

My guess is that to compensate before, the needles were raised excessively and maybe the needle tube o-rings might be leaking as well. I am not a carb guru but i am also not going to regurgitate the "dip'em clean'em and sync'em" that many people do. Carbs can take some guesswork, even if you know what you're doing (which i not always do)