Replaced the carbs...right track?

[randyshipp]

We replaced the carbs on my 1980 GS850GL today with a set from my 82 GS850GL that had recently been cleaned and rebuilt. Before putting them on, we set all the butterflies to the same opening (this is "bench syncing," right?) with a piece of wire. We set all of the air screws to 1 1/2 turns out. Upon putting the carbs and tank back on, we set the petcock to Prime, gave it some choke, and cranked for a bit (not too long) and the engine roared to life. After some time, we were able to shut off the choke, and it idled at about 1800 RPM. All the pipes got hot enough for spit to bounce off, so, even though it sounds pretty rough, they must all be firing. Attempts to bump the throttle a little bit caused it to want to die, then the engine would race for a few seconds when the throttle was released.

Does this sound about like what you'd expect? Is this something that syncing the carbs is going to smooth out, or would you expect the bike to run well enough to ride right after putting the new carbs on?

Randy...

P.S.-- there was a fair amount of rusty looking crap in the bowls of the old carbs, so this was probably a good idea.

[frosty5011]

You'll have to do a few plug reads, but sounds right now like the carbs are set up too lean.

Synchronize the carbs....and if you're really sure the float heighths are set correctly, you should be able to adjust with the mixture screws.

(This is assuming you don't have any intake leaks)

[randyshipp]

I'm pretty confident of the float heights, which were set with a nice dial micrometer marked in thousandths, so I'm sure they're good. I'm hopeful that all the leaks are gone. And besides, it's running worse than before, but with arguably better sealed boots than before, so I think it should be just an adjustment thing. Hopefully I can get help this weekend to sync them.

Randy...

[mark]

If I'm stating the obvious, I apologize, but when you fired up the bike, you're airbox was on right? Won't run real well without it...........

[randyshipp]

If I'm stating the obvious, I apologize, but when you fired up the bike, you're airbox was on right? Won't run real well without it...........

Everything was back together. The only thing that was a serious biatszch was getting the airbox boots back on the carb. I think the design is crap. The flanges on the back of the carb should extend at LEAST another 1/4 inch so that the clamps have more to grab onto. Anyway, rant over. It took a while to get the clamps tight enough without them slipping off the back of the carb, but I feel like we got it all together eventually.

So...based on your question, should I assume you'd want it running better at this point than mine seems to be? Would there be any use in shooting a video clip of it running so you can hear it?

Randy...

[Billyboy]

I'm in process of doing this to my bike, so I'm real interested in the result.

[Nessism]

Did you replace the carb boot O-rings yet? They often cause air leaks which lead to problems like you have described.

[randyshipp]

Did you replace the carb boot O-rings yet? They are sure to allow an airleak which leads to problems like you have discribed.

An answer and a comment:

No, I didn't replace those O-rings. The bike was not running so terribly before, so I don't know that they would cause the really rough running now. Now, if you're saying that old carb boot O-rings could have been causing the old symptoms, then I suppose that's possible, though I have an easier time believing all that crap in the carbs was responsible. Still, I'll look at replacing them sometime if we can't get it tuned.

Thanks for the advice!

Randy...

[mark]

Is this something that syncing the carbs is going to smooth out, or would you expect the bike to run well enough to ride right after putting the new carbs on?

Try the synch and see what happens. It's cleared up a lot of problems with my carbs (I have VM's though, they aren't the same as yours). Get a couple of good fans and make sure you plug your petcock vacuum line.

[GS850_Coug]

I would work on getting the mixture correct before even worrying about the synch. If you had a definite miss on one or two cylinders, the synch could help even out this kind of problem.

First thing you should do is adjust the mixture screws for highest idle. Then readjust base idle. Then do your plug chops to verify proper fuel mixture. The last step would be the vacuum synch for optimum performance.