Not getting fuel & stalling out while riding.

Hey everyone,

I'm riding a 1978 KZ650. It was my father's bike and he kept it pretty cherry. I recently had the carburetors fixed and the bike had been running great. I was riding down the highway when I just started losing power and the bIke eventually just stopped running as I was going up the off ramp. It seemed like it just wasn't getting any fuel. I pulled the in-line fuel filter off, and tapped it out but there wasn't anything in there. I put the fuel filter back on and it started right up, and ran for 9 more miles. Same thing happened again, so I did the same thing with the fuel filter and it ran fine. This time though I ran it with the choke on a little, and with the petcock valve turned to prime. I replaced the fuel filter and I was able to ride it 60 miles back home. Every time I was at a stop light it wanted to stall. Ive adjusted the idler and it's where it needs to be, but still wants to stall.

I thought it might be the gas tank being rusted out and gumming up the works so I cleaned that with Cider vinegar, putting metal nuts in and shaking them around, and rinsing with distilled water, but there was very little residue that came out.

What else could it be, and how do I check it? The needles and springs in the carbs were just replaced.

Keep in mind the bike never sputtered, or backfired when it was stalling out, it just quit. Also I had some issues getting her started, and used the Kickstarter a few times then the regular electric starter worked. I also trickle charge the battery regularly.

Any thoughts would be greatly appreciated.

If the engine is running out of fuel there are a few likely suspects.

The first is that the fuel line between the tank and carbs has a kink in it. If this is the case the bike will start after it sits a while (assuming the kink permits at least some fuel to pass through) but then the engine will starve for fuel after running a while. I had this happen to me once on my KZ650 when I had fiddled with the tank & fuel line. Make sure there are no sharp bends in the fuel line and that the fuel line has no obstructions inside.

Another fuel starvation problem possibility is the fuel cap vent is not venting. This can result in a vacuum inside the tank as fuel runs out of the tank but is not replaced by air. This is easy to test; just run the bike with the fuel tank cap cracked open and see if the fuel starvation problem persists. If that stops the problem the cap should be disassembled and the vent cleaned.

One other possibility is that the vacuum operated petcock has a problem. If the diaphragm or other parts inside the petcock are not permitting full fuel flow when the petcock is in the "ON" position and the engine is running the carbs may not receive enough fuel to support the engine's requirements. This also is easy to test; just put the petcock in the "PRI" position and see if the problem goes away. If the problem goes away with the petcock in "PRI" the vacuum line from the #2 carb to the petcock should be checked or replaced, or the petcock should be rebuilt or replaced. Ed

Your tank strainer is probably clogged. Your tank can look very clean but still have fine debris that will clog the strainer.

How to solve this, I do not know. I myself have removed the rust and flushed my tank 6 times and the strainer still clogs. I have eventually resorted to removing the strainer and relying on an inline filter instead.

Could also be a cheap paper filter, or more likely a fuel filter designed for a pressurized (has a fuel pump) system. Been there.

TexasKZ wrote: Could also be a cheap paper filter, or more likely a fuel filter designed for a pressurized (has a fuel pump) system. Been there.

Exactly what I've had happen.
This video shows the filter not flowing until tank is pressurized.


I use the scintered brass filters with cleanable/replaceable elements, and I also use disposable metal screen filters on other bikes. They both seem to work ok. The disposable one was cheaper.