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Rebuilt carbs starving?

  • Thread starter Thread starter sesquipedalian_id
  • Start date Start date
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sesquipedalian_id

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I have an 82 GS650. Perhaps in a whim of overconfidence, I rebuilt the carbs following the procedure found on gsresources.com. Everything went without a hitch for the most part. The bike started right up, but seems to starve out @ around 5000RPM.

I plan on pulling the carbs back out to "bench sync" (didn't do that) and to check some screw settings. I failed to pay attention to how many turns on the air screws. Can anyone offer any guidance here? Any thoughts on the starvation issue?

Thanks!

Brad
 
Start them out at 2 turns out and work from there. Check your fuel line for kinks. If you replaced the fuel line you probably made the new one too long and it gets kinked with the fuel tank.
 
Just curious, but did you put the air box back on? She won't run good at all above those r's without it.
 
Hi,
In addition to what's been said above, did you adjust the floats to the right level? I adjusted mine at 22.3 , this measured on the float itslef, not the flat/hinge part.. And my 82 650 did not like the idle mixture screws at 2 turns out, 1 1/2 was a good starting point . I did not take plugs reading yet though...
 
As I understand your problem, the bike runs OK below 5K RPM? Well, I doubt it is a sync issue (although the carbs should be resynchronized, if the rack was apart). Also, adjusting any "screws" will not help as the only screws I know of adjust the idle mixture. First thing I would look at is fuel starvation caused by low fuel level in the bowls. The method of turning your carbs upside down and measuring from the gasket mating surface to the top of the float is called the "FLOAT LEVEL" measurement. It is easy to do and works great on NEW FLOATS where some previous student of mechanical hasn't bent the floats in the wrong place. You are supposed to bend ONLY the tang; that is, the part over the float needle. I have found using this method is something of a waste of time since most floats have been bent up and have lost their initial reference. I use the "SERVICE FUEL LEVEL" method to set all floats that come through my shop wherever possible. This involves setting the assembly upright and attaching a clear tube to the drain. I use an external gas source but your tank will work nicely as long as it is in PRI position and above the carbs. Anyway, turn on the gas... Hold the hose next to the carbs and DO NOT move the hose around. Gas will fill the hose and come to rest at the same level as the gas in the bowl you are checking. You may have to tap out some air bubbles... in any case, I am guessing that the service spec for your bike is ~3-5mm; that is, about 1/8" below the bowl gasket mating line. If you find it isn't correct, remove the bowl and bend the tang up or down to adjust the level of fuel allowed in the bowl. Bending up = less gas and bending down = more. Replace the bowl and recheck.

The next are things that can make your bike run as you described...
xxx aftermarket air filter w/too much oil
xxx fuel line with a pinch
xxx gas filter in the wrong direction
xxx main jets too small for intake
xxx vacuum lock in fuel tank caused by plugged tank gas cap vent
xxx petcock partially obstructed
xxx carbs connected wrong - see my website for BS series carb connections

Depending on throttle position at 5K for your bike, you are still on the jet needle/needle jet but the main jet is coming into play. You problem will not be in the idle mixture... did you change any settings (as in jet needle clip position) or jets when you were working on the carbs?
 
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