Vacuum Leak and High Idle After Carb Rebuild

So here's a fun one that's been puzzling me. I've got an 82 XJ650 Maxim I've been working on for a while now, got it cheap, went through the works undoing things from the PO and rebuilding things, starter, carbs etc.

I rebuilt the carbs, all went well, did bench sync with feeler gauges, once again went well. Once I got the bike started again, it idles high, only once warmed up. Goes to about 2k, regardless of if I touch the throttle or not. I can pull the idle control screw all the way with no change. After I've rode it for around 5+ minutes, it idles at 4k. Vacuum sync readings are good as well, all cylinders are very close in vacuum, until it gets warmed up and 2 and 3 read all over the place. It also has low power until warmed up.

My first thought was carb boots, replaced them with no effect. Same symptoms, same severity. Made sure all the valve clearances were in spec, they are. Anyone have any ideas what this could be?

 

Can you do a compression test cold and then hot.
Might help to remove a question if nothing else.

Although it does sound like a sync issue.

 

Throttle cable is not suck on the top of the holder at the carb? Not too sure how many of these carbs you have cleaned. I will tell you the first set I did, I cleaned them six times. I kept missing little things. Once the carbs are good and the cables are all properly seated and adjusted issues should go away. I see you are new to the board only reason I am asking if you have cleaned these type of carbs before. That little jet in the bottom of the float bows is a bugger to get clean.

 

in my opinion - intake gaskets.
I had similar issue only while hot. [1/2hr into riding] except the low power thing.

 

I replaced them, theyre sealed tight.

 

Cables are good. Moves freely, plus the other two carbs, which have interlinked throttles of course, are not experiencing this.

 

I don't get the bench sync with feeler gauges, bits of wire etc. Do it by lining up on the edge of the first hole, foolproof method.

 

Check with propane wafted over them to see if the idle revs pick up.
It's not unknown for the flanges to be distorted and bowed in the middle.

 

hey any new updates? I am having the same issue and posted about it.

 

Posted? where? not here?

 

My bad, I posted as a conversation not in the Xj tech chat...