RPM's with choke? GS400

[MrZig]

What should the RPM's be at with the choke fully engaged on a cold 1980 GS400? It's about 3 degrees celsius outside.

When I choke it, no throttle and hit the starter button, it starts instantly and idles around 1500 RPM for a few seconds, then drops down to 1000 and finally to around 800 where it wants to die, and quite frequently does.

The only way to get it to warm up is to keep restarting it to the point where it will finally take throttle, and then slowly nurse it up to about 2500 RPM for awhile to warm things up.

I've rebuilt the carbs, recently just sprayed the crap out of the choke tubes with solvent, and still no difference. Any ideas? The carbs are synced and the pilot screws are out 2 turns each. Idle screw set to where it idles hot at 1100 RPM.

[Big T]

The engine's response is pretty normal

When the revs start to fall, try edging the choke about 20% -30% of the way back towards off. I'll bet your revs will rise

After a minute or so, do it again

I'll bet your revs will stay up

The motor is slowing down because it's running too rich. This technique will make it less and less rich

My GPZ is really sensitive to this.

[Nessism]

That kind of behavior is not normal for a GS; typically the rpm's screem with the choke on.

When you rebuilt the carbs did you competely break them down and soak the carb bodies in carb dip? Did you replace all the O-rings inside the carbs, and on the intake pipe boots? Vacuum sync the carbs after reinstallation?

[chef1366]

Did you clear the brass choke rods (jets) that dip into the float bowl? Fuel also travels through the float bowl itself and that needs cleared also.
I agree, the motor will scream with the choke all the way on. It should not back off and die.
Ever check your valve clearance?

[Steve]

Try turning your idle mixture adjustment screws (you called them "pilot screws") out another turn.
You may find that you won't need as much "choke" to start the bike.

What are you doing starting the bike anyway? Are you actually going for a ride or just doing maintenance?

Hopefully you are not just starting it "to keep things moving" or whatever excuse you might find. Starting the bike like that will never get warm enough to burn off the condensation that will form. You should not start the bike unless you are going to ride it for over 15 minutes. Half an hour is even better.

.

[MrZig]

Thanks for the replies. Valves are adjusted. Float bowl and choke tube are all cleaned out.

I didn't soak the carbs but I did tear them apart completely and spray the absolute crap out of them and used shop air to clean every passage. New carb O rings as well.

The exhaust inside is pretty rotted out so any condensation that forms in there won't add any more harm, and the reason I'm starting it up is so I can make sure it's in sellable condition as I'm going to list it real soon.

[Steve]

... but I did tear them apart completely and spray the absolute crap out of them ...

Probably did not do all you wanted, but since you will be selling it, ...

Even "spraying the crap out of it" does not keep the solvents in contact with the crud long enough to soften them into submission.

Especially with the weaker solutions available today, there is no substitute for TIME.

Hope it sells well.

.

[sscott]

You can check this link for better and preferred ways to clean the carbs. Shop compressed air wont clean the jets properly. Not to mention "spraying the crap out of it".

http://members.dslextreme.com/users/bikecliff/images/vm_carb_rebuild.pdf

Please remember as you are "warming things up" by letting it run its an air cooled engine and its cooking. Using a fan on high setting blowing right on the engine will help your engine a lot.

[MrZig]

Every jet was taken out and cleaned completely, same goes for the needles. Each passage also flowed.. I dont think I did a bad job. This seems really weird to me.

[chef1366]

Every jet was taken out and cleaned completely, same goes for the needles. Each passage also flowed.. I dont think I did a bad job. This seems really weird to me.

Well hell than they should be perfecto!

[donimo]

mine can be finicky with the choke too, it has a "sweet spot" that it likes, any more and it shoots for redline, but it may just stall. I find it barely needs any choke except first start after sitting a while (week or more)