high revving carb question

OK I have an '81 xj550 that I put the carb kit in. Everything is clean put the carbs on hooked it all up (bench sync, 2.75 turns on pilot, dry set floats to 21.5mm) and fire it up. Popped right off and sounded good. Now the issue is that when i rev it up it wond idle down all the time. A few flicks of the throttle and it will drop (not always). I've checked the throttle cable and thers no hang ups. FYI I did the clunk test and they all passed. Is it possible that one of the diaphrams has a hole in it. I didnt see any when i sprayed them all down. Other than that it runs awesome! Seems to be setup right too, no hesitation or sputtering (backfiring). I thought I read about this a while back but couldn't find that topic again, so I started a new one. Any input would be greatly appreciated!

 

Did you check your float hights wet? (clear tube method)

Have you vacuum synched?

 

If the carbs are good check/replace the diaphragm in the fuel petcock. Mine had a small hole in the diaphram, after a short time idleing the rpm would increase (I drove home 35 miles at 6000rpm). When I replaced the diaphram the problem when away. The Yammy dealer want $350 to rebuild the cards again which would have not fixed my problem.

 

I did have the petcock apart to check it out because it would dump fuel in the on position and the diaphram didn't look very good. also the tiny port from the vacuum was dirty. I then slapped it back together just to get her running. (Crossing my fingers it wouldn't leak!) Now I'll have to hit up chacal and see if I can get a rebuild kit from him. Just to eliminate that possible issue.

iwingameover - no i didn't do either of those items. I'm borowing a mercury manometer from a guy at work. I wanted to get it running and at my place first.

 

Make the Carbs IDLE the Bike after Bench Syncing the rack with Strips of 3X5 Card.
Get the Carbs so that when you release the Throttles the Butterflys close right down and depend on Pilot Air & Fuel.
Run-away Fast Idle is generally the result of an AIR Leak.
Be sure the Manifolds aren't letting air sneak into the Engine.

Holes in the Diaphragms would cause you to not be able to get Full Power and cause them to Close or NOT be pulled-up sufficiently during acceleration.

 

It idles great when it slows down. It seemed to have full power on the road when I got on it a little bit it definitely seemed to be all there. It is possible that one of the cracks in the intake manifold is leaking air past. I'm going to try the liquid tape method. There are a pew pics of the manifolds in my gallery.

 

I actually just had a similar problem today. Check to make sure your choke cable is pulling through the sheath the proper way. I had it purring like a kitten yesterday and then I messed with the headlight and speedo, restarted and it was revving high. Somehow the choke cable was still pulling on the enrichment valve when it was all the way off at the handle. I had to reach down and manually push down on the enrichment valve and I could feel the cable slide a bit and the idle immediately settled.

Also, make sure your intake boot clamps aren't rubbing on any moving parts of the carbs otherwise you could be getting a little bit of a stick or a rub which could cause a bit of high idle.

 

Take the extra few moments that they couldn't ... when these Bikes were moving-down the Assembly Line and secure the Choke and Throttle Cable to the Center Tube.

Keep those two Cables from moving-around and changing the way the Bike is running.
I've seen guys trying to maneuver out of a tight spot have the Throttles get revved-up because the Throttle Cable got yanked.

The Choke Cable gets pulled and often gets moved because the Cable End Attachment lets the Cable slide within the Mount.