1980 XJ650 Maxim

Hey guys. I need help with this one. I am stumped. I have been working on cars for over 20 years. But I am a novice when it comes to bikes.


I have a 1980 Xj650 maxim. Bike has run great for the 2 years that I have had it. Last year, I swapped out the petcock for the newer Harley style. I just didnt like the vacuum design. I rode it all year last year without a problem. Over the winter, I took the tank off and had it cleaned, relined and also treated it to a fresh coat of paint thanks to the local body shop. I put it all back together with a new filter. In the morning, I can ride the bike to work without a problem (its about 15 miles). In the evenings, when I go home its a different story. After about 10 miles, it starts to spit and pop, when I let go of the throttle it will back fire. I have installed a clear filter. When I stop, I can see its empty. I opened the cap, thinking it was vaporlocked, or not venting properly, but no change. I pulled the line off the petcock, and its flowing. But I put it back on the petcock, and nothing. Filter remains empty. After sitting for about an hour, the filter fills back up and the bike will run long enough to get me home(about 5 more miles). Yesterday, I just let it run in the driveway. After about 30 minutes, same thing happens. I tried blowing through the fuel lines, and I get flow. I am at a loss. I know its a fuel issue. But cant figure out what. Anyone have any ideas???????????? :?

 

How full is your gas tank?

Maybe without a vacuum drawing the fuel through the lines there isn't enough pressure pushing it through...

 

Tank is full. Or very close to full. the vacuum didnt pull the fuel through. All the vacuum did was actuate the petcock so fuel didnt flow unless the bike was running. I looked into that. Thats why those petcocks were Off- Run- Prime. But it happens with tank full or with 1/2 tank.

TheBostik

How full is your gas tank?

Maybe without a vacuum drawing the fuel through the lines there isn't enough pressure pushing it through...

 

It doesn't pump it with the vacum, it just opens a valve to allow for gravity feed only when it's running, but you don't have vac operated petcock right ?

You might have a float or 2 sticking... Next time it does it, put a tubes on the float drains routing them into an approved container...and open the float bowl drain screws one at a time and see which if any are dry.

Funny how it doesn't do it in the morning, might try driving it further in the Am and see if it does it further down the road.(dont be late for work... 8O )

 

I've noticed when setting float levels or trying to drain the bowls through a clear fuel line a bubble will slow the flow to almost nothing.

I suspect you have some air trapped in your fuel line. I'd suggest filling the tank full, prop the back up so the line is all a downhill run. Set to "ON" and start tapping things to get the bubble to rise through the fuel valve.