Update: 1982 XS400 still only running while on 'prime'

crib20

XS400 Member
Messages
11
Reaction score
0
Points
1
Location
Bradford, Ontario, Canada
Quick background:

One day I was riding and all of a sudden the bike stalled. I could start it again after a few seconds, but it only went a few kms before it stalled again. After a little while, it started stalling after only about 30 seconds (after priming some fuel into the carbs). I have now realized that I can run the bike on 'prime', but if I take it off prime it will stall after a short period of time.

My first reply here said to check the pin hole in the tank cap to make sure it wasn't clogged: that was not the problem

The second reply said to clean the carbs, I did that and they were spotless: that was not the problem

The third reply here said to remove the fuel petcock because the screen must be clogged. That was not the problem, as the screen was super clean.

So ... really hoping someone else has a solution. It seems like there is an issue with the vacuum that sucks fuel into the carburetor, but I could be off base.

Thanks for any help!!
Rob
 
You might want to pull the petcock apart and check if the vacuum diaphragm has a hole or something. I know when mine went bad, I put a longer hose on it and just gave it some suction with my mouth but I got some fuel instead, yuck! Or pick up a harbor freight vacuum tester gun and see if it will hold vacuum.
 
I second the petcock issue as the best possible suspect at this point. If the vacuum signal is not opening the valve fully, you will starve the carbs of fuel. The prime position does not use vacuum to operate.

Personally I dislike the vacuum operated petcocks and never rebuilt the one that came with my bike, but replaced it with a manually operated petcock that relies on me to shut off fuel after a ride, but has never failed to deliver fuel when I ride.
 
Back
Top