On a ninja ex250 I recently purchased I noticed the vacuum hose which attaches to the pet cock to actuate the flow of gasoline to the carburetor was detached at the connection to the petcock.

When purchased the bike started up instantly without choke and drove great at highway speeds for about an hour and shifted fine through all the gears. No choke used to start no overheating or noticeable rough idle, petcock was set to the on position.

After a more through look over in the garage and starting and stopping the engine several times, the bike was idling quite high ~3k rpms, it would stall when using the clutch to assist walking the bike in 1st gear, and eventually refused to start at all which led to a closer examination.

I noticed the (clear) vacuum hose was not connected where it hooks up to the petcock. After reconnecting the hose to the petcock the bike will no longer start, it will crank until the battery would die. Only once did it sputter then die out. There is plenty of gas and plenty of charge in the battery, starter does not seem to be an issue clutch is fully disengaged and bike is in neutral on the center stand without the kick stand up and out of the way.

How can I get the bike running again after this occurrence? being somewhat of a noob to carbs and motorcycles in general it would be nice to know where the petcock, choke, and throttle should be set when cranking the engine in a relatively warm climate 75 to 85 degrees F.

Is the motor/carb flooded or perhaps missing fuel? The same for the amount of air? If any of this is true how do I correct the fuel to air ratio?

  • If it was running prior to putting the clear tube "back into place", have you tried disconnecting it to see if it would start again? Commented Aug 26, 2017 at 10:04
  • @paulster2 I have tried that with no success.
    – John Dream
    Commented Aug 26, 2017 at 14:29

2 Answers 2


As you stated, the petcock is vacuum actuated. Regardless of position, they only allow fuel to flow when the engine is able to pull vacuum. Like any component, they can fail. The fact that there is clear line running to it means someone has been working on the vehicle. The OEM lines are always black rubber. If the motorcycle ran with it disconnected it has failed. Likely it allows fuel without vacuum and additionally it probably allows some amount of fuel to escape through the vacuum port. This means the motor can ingest additional fuel through that port. Extra fuel or air making it into the intake causes all sorts of problems.

Replace the petcock with a new one. You can probably locate one that would work that is not a vacuum petcock. The bolt pattern in the fuel tank is extremely common. There is no actual reason to install a vacuum petcock on a vehicle. Just turn the fuel off when you will have the vehicle parked for an extended period of time, like overnight.

The high idle is likely caused by the disconnected vacuum tube allowing additional air into the motor. I would locate an appropriate sized vacuum cap from an auto parts store and use it to cap off the vacuum port.

As to why your bike will not start at all now, the engine is likely flooded from the extra fuel and the plugs have become fouled. The easiest route to remedy this is to replace the spark plugs with new ones. Prefer the NGK spark plugs, see this reference. The extra fuel itself should evaporate away.


Replace the fuel petcock as previously suggested, however, also check that your oil level has not increased above its full mark. I have had a petcock and carburetor float issue at the same time and it caused the bike to fill the crankcase with gas. You may also try cleaning the plugs with brake cleaner or carb cleaner.

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