Fuel Problems

Hello there. I'm a proud own of a 1985 xj700x. I am not very mechanical savvy but i try to do what i can. My bike was running fine until i took the tank and fenders off to get it painted. Now it is running like crap. I think it isn't running on all cylinders or maybe not getting enough fuel. I recently had the carbs cleaned and synced so i don't think it's that. I think it is a problem with the petcock. I took out the vacuum line and sucked on it and i couldn't get any gas to come out. I ordered a manual petcock to replace it, but I'm not quite sure how to install it. Do I just plug up the vacuum port and just install it to the line going to the carbs? Also any suggestions about why it's acting like it is. Also when i had the bike running it would idle fine when i just start it but when it was hot it would rev a bit high like 2k rpm rather than around 1k rpm. Any help is much appreciated Thanks.

 

Yes, plug up the port on the intake manifold where the vac line used to run.

Either it's not really in sych, or the pilot circuit screws are out of proper adjustments, or the vac pistons are sticking, or a vacuum leak exists somewhere.......

 

the high rev would come from the vacume port exposed, that would be the simplest and hopeful solution. The manual petcock you've ordered shouldn't come with vacume port/line so just plug the one on the intake manifold. if the problem persists after the petcock replacement go back to the person who worked on the carbs i guess. good luck

 

if the carbs were synced with a bad petcock chances are that carb is off due to a vac leak. i know mine are out of sync my idle hangs up a little then drops off

 

How many miles are on it? I'll betcha nobody's ever touched the valves...

 

I think you might have several issues to deal with, ...
And, as the New Owner of a Max-X
Do a Full Monte Tune-Up.

Adjust the Valves.
Clean the Carburetors and Polish the Carb's Bores.
Bench Sync
Vacuum Sync
Adjust the Idle Screws
New Plugs

Have fun all Summer long getting to the next red light faster than the guy next to you.

 

Have you taken the petcock assembly out of the tank? Maybe when you removed the tank you may have stirred up a bunch of sediment and now it has been sucked through into the carbs as well as choking the filter.

 

Thanks for all the input guys. I just got the manual petcock assembled and plugged up the vacuum port and now the bike runs great. The high RPM was as simple and adjusting the idle screw and it ran great. Not bad for a 25 year old bike with 46k miles on it. My next project will be to check the valves this winter. Thanks again.