bogging when giving the gas...

[Anonymous]

I have been frequenting this forum for the last few years, and I must say that I have learned a lot about my bikes.

I have a 82 GS1100 bored out to a 12, and 2 GSXRs one being a 91 1100 and the other being a 89 1100 frame and a 89 750 motor.

on my 11-7 I am having a problem of bogging, the quicker i give it gas the more it will bog on takeoff. I have the stock carbs for the 750 motor, and stock pipes. I have checked the float levels and jetting, and it is all stock. This was a problem when I got the bike last summer. Over the winter, I took the carbs apart, and found the needles, needle jets, pilots, and mains all too small according to the service manual. I have replaced these all with stock, but I am still getting the bogging at about 1/4 throttle. this happens cold or hot.

Does anyone know if the CDI box have a factor in this? It idles fine, and over 1/4 throttle is fine. I have also backed my mixture screws out 2 1/2 turns, I have heard 1 1/2, 2, 2 1/2 turns, I'm not sure if this will change the 1/4 throttle mark?

Rolling on the throttle slow is the only way to keep it from bogging, not exactly impressive on the track.

I know this is the GS resources, and primarily targeted towards GS vintages, but I thought I would try here, as there are a lot of knowledgeable people on here, and I have learned a lot about my GS.

Any help would be appreciated.

I am in Toronto, Canada

Cheers,

Brad

[ptm]

I'm far from an expert, but it sounds more like a carb problem than the CDI. If you're getting good spark below and above that engine speed, it doesn't seem like it would be bad in the middle, and it shouldn't care if you're rolling the throttle on slowly or quickly.

The carbs, on the other hand, have to deliver very different mixtures at different throttle positions. I'd search this site and the web - use 'mikuni' your carb model and 'tuning manual' in Google, you might be able to come up with something like http://www.nightrider.com/biketech/d...kuni_carbs.pdf) that will give you some ideas.

Sorry I can't help more.

[tfb]

I'm not sure about this idea of mine, so take it in the spirit of self-doubt that it's offered ...

But, could it be that you have some crud in your carbs, so that when you give it some stick (ie. snap the throttle open), the fuel or air velocity lifts the crud to block a jet somewhere? Whereas when you open the throttle in a more controlled fashion, there isn't the fuel or air velocity to pick the crud up and jam the relevant air or fuel jet?

Just a crazy idea...

Mike.

[KEITH KRAUSE]

That's strange that the carbs had smaller jetting than stock? Are you sure these carbs are for your model?
The 1/4 throttle position is mostly the jet needle circuit. There is some overlap from the pilot circuit at this throttle position, but I would focus on the needle. Your Canadian model has adjustable jet needles, correct?? I also assume you cleaned the carbs when you did the other work on them.
Bogging can be used to describe too rich and too lean, I have found by other members. I always thought it best describes a rich condition.
You can temporarily seal up PART of the stock airbox intake holes, and see if the bog worsens or gets better. If it gets worse, that would suggest too rich. If it gets better, to lean. Raise or lower the needles accordingly. You may need jetting spacers made for making 1/2 needle position changes. But a full position richer or leaner, will probably be needed.
I still wonder about the carbs being the right ones though. Seems odd the jets would be smaller. But people do lots of odd stuff. :?