So after reading all these posts, I have a few things to try out. I want to describe my problem so you all can let me know if this is anythign out of the ordinary. I hsave not read about low rpm bogging, mostly people with problems in the high RPMs. Here is my problem:

The bike runs nothing short of excellent, it had been sitting for 6+ months when I got it. I pulled the carbs and did some standar cleaning of most of the parts etc... Great! Now the bike actually runs, but it has this terrible bogging problem at LOW rpms. Lets say you are idling at 1200, and you dump the throttle full on - *put* *put* *cough* - almost dies - VRRRRRROOOOOOOM! up to 12k rpms. It takes about 3-4 seconds from when it you open it wide up until you get to 12k....only takes about 1 second to get to 12k.

Now, once the bike is warmed up (20 mins of idle choked/partial choke), this problem is almost un-noticable. It has almost no problem revving up in the low RPMs. This is what baffles me.

So I hope all you fine GS Carb mechanics (god knows owning a GS means you become a carb master) have some suggestions for me on what I can do.

Oh yeah, new plugs, new oil, new tires, new chain, new battery, new fuel, old air filter still.....I figure a K&N will do when I get a minute to order one.

Did it always do this or is this a new "feature" after having sat for a while?

I'd start by adjusting the idle mix screws.  Do the slides flutter when you open it up suddenly?

Bike started out totally dead.

After doing everything but pulling the carbs, it ran like total crap.

I pulled the carbs and cleaned out the needle jets and a small chunk came out of each. This helped things alot. Then I cleaned up the gunk on the slides and cleaned as many surfaces as I could. That is the current state of the carbs. Pulled slides/cleaned, pulled out other brass things/cleaned...got some sticky gunk off a few parts. That was basically it.

I'm not sure what you mean by flutter exactly, how can I check this? Where is the location of the mixture screw, I do not believe this has been messed with yet. I have tried to adjust the idle but that doesn't really do much to help the problem.

Thanks!
Matt

Flutter can be seen with the airbox off - http://www.gstwin.com/carb_work.htm

ahhhh this is the picture I was hoping for - thx scratch.

Matt,
I was thinking that the carbs are out of sync or out of adjustment (idle mix).  Using this picture, look to see if the carbs have the idle mix screw covers removed.  The tower labeled "air/fuel mix screw" will either have a plug in it or it will be open and you can get a screwdriver in there.  If they're open, then lightly bottom the screws, and back them out 4 turns or so.

Adjust the idle to about 1,500 or so and starting with one side, turn the screw in slowly until the rpm's start to drop - then back it out a hair.  Do the same with the other side, readjust the idle to 1,500 or so and repeat as many times as necessary to get them good. 

Assuming the carbs are close to being sync'd to each other in the first place and there are no vacuum leaks, this should get you most of the way there.  You can cover a bit of hesitation from this setting by backing out the screws 1/8th turn each.  If it isn't working good here then you've got other issues.

Ok, I have an update: I pulled the carbs last night because those stupid little brass discs were in the way of the fix/air mixture screws!!! 

I was unable to remove them. How can I go about removing those little discs?

On another note...I looked at the air intake side of the carbs where the slides are, and the 2 little holes at the bottoms of the silver intake concavity - the left side carb had the non scre hole blocked by brown stuff so I cleaned that out. The bike got a little better, but as I was test riding it, I was going about 60 mph after gettign on the bike hard and it started bucking and died. I've read a little bit about this -- is it something that messing with the air/fuel mixture screws can help fix?

Quote from: praefex on January 28, 2006, 02:32:39 PM
The bike runs nothing short of excellent, it had been sitting for 6+ months when I got it. I pulled the carbs and did some standar cleaning of most of the parts etc... Great! Now the bike actually runs, but it has this terrible bogging problem at LOW rpms. Lets say you are idling at 1200, and you dump the throttle full on - *put* *put* *cough* - almost dies - VRRRRRROOOOOOOM! up to 12k rpms. It takes about 3-4 seconds from when it you open it wide up until you get to 12k....only takes about 1 second to get to 12k.

Now, once the bike is warmed up (20 mins of idle choked/partial choke), this problem is almost un-noticable. It has almost no problem revving up in the low RPMs. This is what baffles me.

I have a similar issue with bogging down at low RPMs. This is what lead me to rebuild the carbs last week.
But get this ..  She still boggs down every now and then, just as you describe.
Since I couldn't figure it out, I went crying to daddy.

He said when she is running perfect (warmed up and no symptoms) disconnect the spark plug cable and see if these are the same symptoms.

Sure as s***, she was bogging down at low RPMS.

So the next step was to wait until she was bogging down again. Then pull one spark plug- If it still runs, pull the other plug. (plug the other back )

If she dies then you know you have an ignition problem not a carb problem. (because one spark plug is not firing)

I am going to trouble shoot this next week when I tear into her again to replace the clutch cable.
It could be the ignition module or the coils. We'll see.

Good luck

Ok - so the trouble shooting pattern is - warm up bike... (ride home from work)

Then turn off bike, pull off 1 spark plug cable, start bike. Bike bogs or not bogs.

Turn off bike - pull off other cable, reattach first cable - turn on bike. Bike bogs or not bogs.

So basically this will test the coils to make sure enough juice is getting down to make a spark and the coils are working?

Quote from: praefex on February 02, 2006, 02:52:53 PM
Ok - so the trouble shooting pattern is - warm up bike... (ride home from work)

Then turn off bike, pull off 1 spark plug cable, start bike. Bike bogs or not bogs.

Turn off bike - pull off other cable, reattach first cable - turn on bike. Bike bogs or not bogs.

So basically this will test the coils to make sure enough juice is getting down to make a spark and the coils are working?

mostly NOPE!!

but you got th gist.

sorry If I mislead you.
----
start her up. (no warm up)  if she is boggy then pull a plug.  If she dies then she was only running on that cylinder.  makes sense?

If she doesn't die reattach the plug and pull the other plug. If she dies then she was only running on that cylinder.  makes sense?

-----

The whole warmup deal is just to be sure that your symptons are consistant with running on one cylinder.  If not then nothing I have told is worth a sqaut. --Sorry--

Godd luck and keep us posted

like I said, I will trouble shoot mine later.
This problem only comes up durring warmup and not all the time.  I might have a loose cable or just condensation in the coils.

you said you were going like 60mph and she bucked and died.  I am no expert but I think a lost cylinder might cause such a symptom at speed. maybe a loose connection or semi-shorted wire in your ignition system.

again just a guess.

This is very curious behavior, I'm interested in testing this out, thanks for the further explaination. I'll report back!

Ok I went out side and tried this. I put the choke on and started the bike up.

Pulled off left plug - makes clicking noise coming from the plug and shocks me slightly when coming in contact with the frame or tank or other metal stuff. Turn off bike to avoid more shocking. Put plug back on, turn bike back on.

Pull right plug. Bikes dies a second or two later.

So I *think* this means there could be a problem with the left side coil? Battery is brand new BTW.

Ok...does the engine rev up normally if you roll on the throttle normally (ie if you control the throttle smoothly instead of trying to snap it wide open..)
? Does it idle nice and even... no hanging rpms or weirdness at idle?

When you snap the throttle open you let the engine take a big gulp of air and you get an increase in airflow through the carbs...as more air moves into the carbs  more air also  pushes on the diaphragms opening the slides more to keep the air flow at a closer to optimal rate for the engine...(CV carb...constant velocity..).

If you have the needles set wrong -when the throttle is open the diapragms may move up too early /open too far too soon and the motor falls flat on it's face and then it kind of catches (You're still at WFO on the throttle..) and the motor screams.

Make sure your needles are set correctly..... also double check all the small passages in the carbs  and make sure your pilots are really clean.
Fresh plugs?

Yeah fresh plugs...everything on the bike is the fun bags when its all warmed up. I'm really interested in the ignition coil test that obviously failed on one of the coils. The carbs have had very little work done to them...the bike is a 96 with 3300 miles on it.

When the bike is warm it revs up like a champ (hardly any hesitation at all but still more hesitation than my ducati)

I'm pretty happy with the carbs at this point - I'm hoping for something in the electrical realm at this point as I'm sick of pulling the carbs LOL.

I got another suggestion from a motorhead.

go here----   http://www.gstwin.com/ignition.htm

Look at the picture "this is what you see after cover is removed"

In this picturre you will see two small black squares on either side of the shaft.  THese are magnets that "read" where that metal tab is and tell the ignition module when to fire.
one for each cylinder.  (makes sense, right?)

one of these square magnets may be dirty or something. causing the bike to be a bit advanced at warmup.
Try this before you pull your coils. just pop the top and check for dirt or damage.

I am at work :laugh:and wont be able to try this until lunch time.

let me know what you find.
3imo


(I am no expert any help from anyone who knows more about this is greatly appreciated) 

Interesting... I'll open it up and see if its clean. I'm meeting up with a guy who used to race GS500's - I think he was AMA - anyway, I figure he's got a fair amount of knowledge focused on the quirks of the GS to share. I'll let you know what happens.

Great. see if you can get a pic of his GS.

I love seeing them all decked out for a race.

BTW, I checked out those magnets and they look fine. nice and purdy.

I am bummed out though.  she runs great after warm up which, to me, seems to point to the carbs.   But when she is boggy, one cylinder is not firing.

see what your freinds says.   thanks.  3imo

Quote from: praefex on February 02, 2006, 04:44:34 PM
Pulled off left plug - makes clicking noise coming from the plug and shocks me slightly when coming in contact with the frame or tank or other metal stuff. Turn off bike to avoid more shocking. Put plug back on, turn bike back on.

Ok, I want to clarify something - When 3imo states to pull the plug, he actually means to pull the sparkplug wire (leaving the sparkplug), unless he meant to look at the condition of the plug (Did you, 3imo?).

Pretty sure he meant just the wire on that one, pulling the plug I think would cause compression loss and mess it all up.

Ok, cool, just wanted to make sure.  I was trying to follow along the diagnostics and got caught up/stumped at the terminology.

Is the old airfilter clean?