1/8-1/4 throttle bog

[D.T.]

It's me again...

Anyhow, Great site here!

I just got done removing the carbs and vacuum sync them too. It starts great, idles great and rips above 4k rpm. BUT. There is always a but.
It bogs, so I assume it isn't getting enough fuel in the 1/4 throttle range? Should I remove the carbs again? I removed 2 CV slides and cleaned them up, they had a bit of varnish on them. I didn't see any holes in the diaphrams either. Is there supposed to be a pinhole in the bottom of the valve where the needle valve goes through? Will shimming up the CV needle valve make it richer and possibly get rid of this annoying bog? Bike is a 1980 GS850G.

 

[tkent02]

How did you adjust the mixture screws?

Is it too rich or too lean when it is bogging?

 

[Dave8338]

What exhaust and air filter method?

 

[Larry D]

More questions for you....You said you had the carbs off...Did you dip and rebuild them with new o-rings ? And also, while you had them off, did you check to the jets to see what size they are, particularly the pilot jets ?

The wrong size jets or being dirty can cause bogging. Hesitation, bogging or stumbling while rolling on the throttle is generally a rich condition.

 

[D.T.]

I'm 90% sure they are stock jets. The bike is all stock. I just tried adjusting the timing, retarding and advancing (looks like about +/- 5 degrees) didn't help at all. I'm thinking the pilot circut fuel passages in the carb bodies are plugged with varnish.

I don't see the pilot fuel screws on the parts microfishe either. They are the ones in front of the intake boots and on top of the carbs. 3.5 turns out they are set at.

Looks like the carbs come off again. Which o-rings in the carbs are you referring to? Looks like I need to make sure they are all there and in good condition, esp on the pilot screws.

EDIT: I just checked #4 pilot (air or fuel?) screws and the o-ring is in poor condition. Looks like it's not making a good seal. Time for new ones...

 

[Larry D]

There are little orings in the carbs that are +-30 years old, they get hard and leak. Here's where to get new ones. Also, here's the carb cleaning rebuild tutorial.

http://www.cycleorings.com/

http://www.thegsresources.com/gs_carbrebuild.htm

 

[D.T.]

I just looked at all the o-rings in the pilot screws and they aren't WAY bad, so I'm iffy about if they are sealing correctly. Another thing I DID notice is I still have poor sealing from the velocity stacks going into the airbox from the carbs. And I noticed that this bike needs a perfectly sealed airbox to run well. Since it won't even rev with the side airbox covers off. Seems like the CV's need a LOT of velocity to work correctly.

So I'm going to order the 4 "hoses, 2 LH 2 RH" suzuki calls them, even though it's gunna cost $50 big ones.

EDIT: I just removed the crank vent and capped the airbox, then covered the 8 holes in the bottom of the airbox. Best the bike has ever ran. I'd say it's at 98%. But, I'd like to go back a few years and ride a GS off the showroom floor just for a reference!

EDIT: I hooked the crank vent back up and experimented with the holes in the airbox. Bike DOES not bog when I have the 8 holes under the airbox taped over. I remove 1 piece of tape to cover 1/2 of the holes and it bogs again. What are the 8 holes for anyway? There is a hose to plumb away fuel if it does overflow. :-s

 

[D.T.]

Update.

I removed the carbs again. This time I removed the plastic washer on top of all the needles (one was already missing) to raise the needle for a richer mix. Works better. I haven't found some cheap 190 air jets ($10 each) yet and I'm not sure if they will help the stumble, so that's on hold. I left 4 of the 8 holes on the bottom of the air box taped over. New OEM velocity stacks are coming next week. All new spark plug caps.

I'm thinking the bleed holes in front of the throttle plates are semi-clogged. I'm just going to try and ride it (since it's ridable now, actually runs about 95%) and see if it clears out. Put some sea foam in the fuel.