weird fast idle issue

just got my 82 xj550 maxim on the road recently and went for a good ride this saturday. well after awhile i noticed an idle problem. while sitting at a redlight on level i let off the brakes and just sat there. slowly the engine started speeding up to about 2500 rpm. i tried several things but what made it go back down was lightly holding one or the other brake just enough to turn the light on. it did this at every stop and everytime if i was on the brakes it would go back down and stay at about 1200...

i have no idea on what to check

also my brand new tach cable is leaking oil on the engine side. i checked to make sure it was tight. is there a trick to putting them on that i didnt do?

 

What to check:

-Your valve clearances, so you can sync the carbs.
-Your float levels.
-Your carb synchronization (for which the valves need to be in spec.)
-Your battery.
-The output of your charging system.

The tach drive itself is probably what's leaking, have a look: http://xjbikes.com/Forums/viewtopic/t=19538.html

 

brand new battery. have not checked the alternator yet. will do that soon

 

I edited my reply to include the tach drive oil leak issue: http://xjbikes.com/Forums/viewtopic/t=19538.html

 

Sounds like the classic signs of an air leak, leading to a lean mixture. Mine did it and the temp fix was to quickly hit the kill button off and on while at a light

 

hope its not an air leak. however the partition walls (rubber boots between carbs and head) look slightly dry rotten...

but i still cant undertsand why holding the brake makes a difference. being in neutral or in gear with clutch in doesnt make a difference....

 

Get it running at idle, spray some unlit propane around your intake manifolds. An air leak will quickly identify itself by a raised rpm.