Will carbs hang if....

[Calliway]

So my 77 GS400 is driving me nuts. The bike has 8000kms on it and I have spent the better part of a year redoing this bike. I have not cracked the engine as it ran before I started the rebuild. It is a lovely bike and I really like it.

I got it running after my rebuild with pods and exhaust. It keeps hanging. it idles very nicely but hangs and once you go over 2500rpm it will climb by itself up to about 4000rpm.

I completley dissassembled the carbs and cleaned them out. The floats were a bit off so I set the floats according to the Clymer manual and made sure that everything was clean and moving.

I found that there was a hole drilled in the slides beside the need hole so I filled it as it appeared to be home done....

I changed the manifold gaskets and the boot o-rings and when I spray around the boots no change to rpm.

I removed the pods and put the stock airbox back in. Everything seems to be nice and snug. The throttle snaps back so its not cables or linkage

So what am I missing? I have a bit of an exhaust leak at the connector pipe which I will fix tomorrow but will that cause hanging throttle? The petcocks on these bikes are just plain weird but if they aren't working will that cause it?

I can't figure it out and it's driving me around the bend a little.

[Nessism]

Did you go though the carb rebuild tutorial (linked in my signature) page by page and make sure everything is taken care of properly? Where are the mixture screws set?

[Steve]

Remove the slides, drill that hole back out.

Note that the stock hole is drilled at an angle, not straight in.

Without that hole, there is no way for vacuum to get above the diaphragms to lift the slides.



Now, that will help with airflow at higher throttle settings, but your "hanging" problem is likely a lean condition.
You say you have "pods and exhaust" on it. Did you re-jet for them?
Another possibility is an air leak from a broken o-ring on the intake boots.

.

[Calliway]

yes i read all of the articles on this and have searched this out on the forum. I will clean out that hole but in no pictures that I was looking at was there a second hole in the slide.

I HAD pods but I put the stock airbox back in and yes I have rejetted appropriatly. I am no stranger to carb work as all of my bikes are carbed. My Bonnie runs perfect and it is dual Keihen CVK 36mm which are almost identical to the Mikuni carbs on this GS.

As far as the o-rings go - they are brand new and so are the gaskets between the intakes and the head.

Hanging has to be some sort of vacuum leak or mechanical issue with the cables/linkage. Cable and linkage is fine. The only thing I haven't done is rebuild the petcock. Since it is a vacuum style petcock is it possible that it could cause the throttle to hang. These bikes are annoyingly sensitive....

[thewiz]

Are you using an auxilliary gas tank? If so, make sure you plug your vacuum outlet that normally goes to the petcock. If not, make sure you vacuum hose is secure and not broken or split. Simple things first.

[Calliway]

Stock gas tank and stock pet cock. That is why I am thinking there is an issue with the pet cock. Maye that is where it the vacuum leak is.

[Steve]

yes i read all of the articles on this and have searched this out on the forum. I will clean out that hole but in no pictures that I was looking at was there a second hole in the slide. ....

There is, of course, one hole in the center, for the needle, but there should be a second hole to transfer vacuum to the top of the diaphragm.

On most of the slides that I have seen, that hole will be toward the engine side of the slide.

.

[Calliway]

Thanks for that. That is the whole I plugged up. It looked really raw and "home drilled". I'll unplug it and recheck the floats and recheck for vacuum leaks. Just getting tired of chasing the same demons.

There is, of course, one hole in the center, for the needle, but there should be a second hole to transfer vacuum to the top of the diaphragm.

On most of the slides that I have seen, that hole will be toward the engine side of the slide.

.

[1948man]

If there was ever a Dyknojet kit in the carbs, the stock hole was probably drilled out larger. If you have gone back to stock jetting, exhaust and airbox the drilled hole might be a little large. Not sure if that would have an appreciable negative effect.