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carbs rebuilt, now what?

  • Thread starter Thread starter Anonymous
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Anonymous

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I have my carbs back together after cleaning, replacing jets needles etc. This is my first time doing this. After putting the carbs back on the bike it idles very smoothly but when throttle is applied it slows down almost to dead then revs up as it should. It will not hold revs at any throttle except idle, it races and comes close to dying sometimes. Floats are set to Clymer spec and the mixture screws are all 2 1/2 turns out. Any ideas?

BTW I am speaking of an 80 GS1000G with BS carbs.

Thanks
 
Stock airbox? If it is, you'll need to make sure it's sealed so that air only gets in where it's supposed to.

What do the plugs look like?

And, of course, you'll need to synchronize the carbs before anything else.
 
Sorry I omitted some information. The carbs have been synchronized. The airbox is stock with a K&N factory style filter. There are no apparent air leaks. The plugs are gray-black in color but have not been replaced since the carbs were rebuilt.

Thanks
 
Are you letting it warm up enough? When the choke is on it will not respond well to the throttle. Often using any throttle at all at first will cause it to stall.

Does it do any better if you roll on the throttle v e r y slowly?
 
It performs this way after warming up for several minutes, last I tried I let it idle for 10-12 min. and it still performed the same.

If I roll on really slow it will rev up better than just laying it on, but it will still get to a point where it wants to die. About 3500-4000 rpm but I'm not swearing by the accuracy of my tach.
 
I would double check the float levels. I rebuilt the carbs on my girlfriend's gs450 and had the exact same problem.... would rev to about 4500, then just bog.

I had adjusted the floats to what I thought was the spec, but I really don't know how anyone knows the difference between 25.0 and 2.53mm, but I digress.

I took the carbs by our local shop and the guy took off the bowls, pushed up the floats and blew in the fuel tube. He dropped the floats slowly until the air stopped. He said they were too low, adjusted them and then sealed them back up and put them on a tank of gas in the shop to make sure they didn't overflow when level.

Worked for us.

I also remember someone saying that a misaligned, or a diapragm with a hole in it, would react similarly due to the
 
Check fuel flow from the tap first,you could have a prob there.
Also make certain the vent hole in the fuel cap is clear.
Easy stuff first
 
benbottles said:
Sounds like a very concrete method, but what is too low?
Click to expand...

I may be that the floats are shutting off the flow of gas into the bowls too early, therefore there's not enough gas to run over 4000RPM... if you try and ride it you'll probably start bogging at 2500 or lower.

First, as gspaul mentioned, try the easy stuff like making sure it happens with the gas cap removed. If it runs fine, then your cap isn't venting and a vaccuum is getting built up in the tank, not allowing fuel to flow into the carbs.

Next, pull the fuel line and the vacuum off at the petcock (not the carbs!) and attach another set to the petcock. Put the fuel line into a bottle and suck on the vacuum line. If you get gas in your mouth, your petcock diaphram is bad. If not, you should get a constant and heavy flow of gas from the fuel line. If it just trickles out you're petcock is clogged.

If all else fails, take the carbs off and double check everything. Pull off the bowls and blow into the fuel tube. Take each float and lift it until you hear the air stop from that carb. If the air stops flowing before the float is about horizontal, then bend the tab away from the needle an repeat. I can't remember the precise angle of the float relative to the carb body when they were set right, but you can figure it out by a process of elimination. Put the bowl back on and test to see if the float is set too high (i.e. gas pouring out the overflow). Since you have your tank off the bike at this point, you can set the tank above the carbs, then attach the fuel line. Turn it to prime and let the carbs fill up. If the don't leak, then at least the floats aren't too high. You can also blow into the gasline once the carbs are filled with gas to test for leaks.

If you take them off, also double check that the slides are installed so that the little tab is in the correct position and the black membrane is completely sealed once you tighten them back up.

I'm pretty new to this too, so if any of the more experienced ones out there have any suggestions or comments, I'd like to hear them as well!

Chris
 
Alright, progress! I readjusted the floats using the above method and the bike is running way better now. I get smooth acceleration when throttle is applied. It starts easier and idles smoother than it ever has since I've owned it. Thanks a lot for the help.

However now I am getting "pops" on hard accel and on decel. I have read in other posts that this is a lean condition. Is this so, and if so can I solve it by adjusting mixture or do I need to consider rejetting to increase fuel?
 
Make sure the intake boots are not leaking, with all the carb work you may have caused one of the boots to crack. You might have bad O-rings on the intake boots, spray wd-40 around them while idling and see if the engine changes speed.

Are the carbs properly seated in the boots? Are the air cleaner boots pinched underneath where you cannot see them?

Leave the jets alone, you cannot solve a problem by tuning around it
 
benbottles said:
Alright, progress! I readjusted the floats using the above method and the bike is running way better now. I get smooth acceleration when throttle is applied. It starts easier and idles smoother than it ever has since I've owned it. Thanks a lot for the help.

However now I am getting "pops" on hard accel and on decel. I have read in other posts that this is a lean condition. Is this so, and if so can I solve it by adjusting mixture or do I need to consider rejetting to increase fuel?
Click to expand...

Check your plug color. Tan is good, while white/grey is lean, and blackened is rich. To clarify, lean=too much air, rich=too much fuel.

Also, exhaust can affect the lean condition. What type of system do you have? Were the carbs ever rejetted if the system is non-stock?

Brad tt
 
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