This evening I was trying to do my very first carb sync on my 1998 XJ 600 Diversion (another was done by my mechanic some time ago) and incurred in an unexpected problem.
I had connected my Carbtune Pro and was using an auxiliary fuel tank like this
The tank's petcock was connected to the hose that is normally connected to the bike's tank petcock outlet.
Everything seemed to be going pretty well and was almost done with the syncing when the bike started running rough and then stopped.
I checked the auxiliary tank but it still had plenty of gas, then tried to fiddle with the choke and it started again but running very poorly.
I then tried to fiddle with the auxiliary fuel tank petcock and the bike surged for a second then seemed to stop.
I soon discovered that it could run on choke but I could not use my throttle grip at all because as soon as I turned it , the rpms dropped and the bike stopped.
I tried to lift the auxiliary tank higher, hanging it from the mirror instead of the handlebar grip but it made no difference.
Since I was clueless I tried to put the tank back on and it immediately started with no choke and revved with no problems.
It would seem that it doesn't like to run from the auxiliary tank, but I don't understand why.
Only thing that puzzles me is the vacuum line from #1 carburetor to the fuel petcock; when running with the auxiliary tank I had closed it with a screw since the auxiliary's petcock doesn't have a vacuum line port.
This line has something to do with the petcock, it seems the vacuum it brings to the petcock is needed to keep it flowing gas; in fact without it the petcock doesn't let any gas out even if the petcock is open.
Maybe it is a security feature?
What can it be that it makes the bike behave like this? I'm puzzled.
Pleas HELP!
Thank you in advance
Kind regards,
Michele