Question about Suzuki RM-Z 250 Motorcycles

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When I turn on the petcock on the bike a steady flow of fuel comes out of the overflow tube. When I turn it off the bike starts and runs fine. I let it run for 15 min before it stopped with the fuel turned to the off position

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David Belcher

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You have rust in your gas tank causing the needles to stick open. Check the filter on your fuel petcock or add an additional inline filter. Or you have worn needles in the carburetor. Disassemble clean and replace. You possibly have a malfunctioning vacuum fuel petcock that is bleeding fuel past vacuum diaphragm. Rebuild the vacuum petcock with a K&L rebuild kit or replace it with a new petcock that will also have a new fuel filter on it.

Posted on Sep 24, 2010


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1 Answer

2002 Vulcan 1500 Classic has fuel pouring from the overflow tube that leads from the carb and routes down by the battery.

bad needle for the float control
there is a small rubber insert on the needles and over time it dries out and cracks

Apr 12, 2017 | Tank Motorcycles

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Gas leaking out overflow tube as soon as petcock turned on fuel running out of overflow tube,running or not

If you are saying the fuel is leaking out of the carb overflow tube it would likley be that the float and/or needle and seat are stuck or defective

Jun 10, 2014 | 2004 Harley Davidson FXDWG - FXDWGI Dyna...

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2005 Harley Sportster 1200 Custom stalls at highway speeds

The diaphragm petcock operates by vacuum.
Sometimes, the vacuum line comes unhooked, cracked or broken.

Check the vacuum line.

Also, the diaphragm petcock sometimes dies, and needs replacing.

The reserve DOESN'T operate by vacuum.

Feb 12, 2014 | 2005 Harley Davidson XL 1200 C Sportster...

1 Answer

Why would there be oil coming from the overflow tube on my 86 Suzuki gs450l

Hi Michael the problem with many older motorcycles is usually gas working its way from the fuel tank and dirty or worn carbs into the engine check your oil level and to see if it is overfull and smell it for fuel. Change the oil and refill to the proper level then you need to check your fuel system.
1. check to see if your fuel petcock is not flowing and the setting is on on or reserve. If it is still flowing then the vacuum diaphram needs replacing.
Position PRI is for when you run out of fuel and needed to prime refill the carbs to get the bike running then turn to reserve. hope i Explaned it clearly enough hope this helps.

Oct 28, 2012 | Motorcycles

1 Answer

XJ 700 N Carb issues

1. If it only runs in the pri position, that means that the petcock small rubber line is not connected to a vacuum port which is normally in the engine side of the carbs. If you unplug the fuel lines at the petcock and place a vacuum on the smaller rubber line (coming from the petcock)using a hand held vacuum tool or your mouth, the petcock should flow gas each time a vacuum is created and stop when the vaccum stops. If the petcock does not stop flowing gas when the vacuum is released or does not start flowing gas when a vacuum is applied, then the petcock needs servicing or replacing.

2. The fuel is still spilling out because the float is sticking or out of adjustment, or the needle&seat has trash/rust in it or the needles&seats are bad. The float should swing freely on its pivot shaft. The needle sometimes has a spring loaded plunger in top that should freely move back and forth when pressed with the finger and if not replace it or free it up. Setting the floats will vary with manufacturers so consult you service manual for the proper procedure. If the floats are set too high, gas will continue to come out. Some floats have no adjustment.

3. If the tank has rust in it, replace the tank or put a rubber liner kit in it so that it ceases to release rust back into the carbs. Filters will not normally stop rust so the tank needs to be free of rust or fixed with a liner kit.

4. The 4 tubes (if coming from the bottom of the carb fuel bowls) are just overflow tubes and hang down on the backside of the engine. If these 4 tubes are coming from the sides of the carb (about midway up the carb body), these are also vent tubes and just hang. These 4 tubes in question should be smaller than the fuel lines on the carbs and about the same size (maybe a little smaller) as the small vacuum tube coming off of the petcock.

5. If the bike is still boggy and/or hard starting when done correcting the fuel spilling issue, that is because the carbs are still partly plugged. Most carbs do not get cleaned out correctly because most consumers do not have the proper wire drills to go through the jets to get them cleaned out. Some jets get under .010 inch diameter which is really small. The only other way to properly clean the carbs are to totally disassemble them and soak them in a caustic carb cleaner made for cleaning and removing fuel deposits

Jul 24, 2012 | 1985 Yamaha XJ 700 S Maxim

1 Answer

Hi, my description is lengthy, but I tried to provide as much detail as possible for troubleshooting. I'm seeking technical input re: a continuing carb issue w/my '96 Magna, which would not turn...

Reserve tube is usually set at a 1 gallon level in the tank, if you only added a gallon to an empty tank,I would fill the tank at least half full, If that doesn't fix the issue then replace the petcock, It's not a carb issue if it runs fine in reserve.

Jun 28, 2011 | 1996 Honda VF 750 C Magna

1 Answer

Fuel over flows thru overflow tubes only when motor is running. motor off ignition on it stops.

Your gas tank petcock is diaphram operated.
there is a vacuum line coming off the intake, that goes straightb to the petcock.
when you turn the motor over a vacuum is created, pulling the petcock diaphram back and allowing fuel to flow to your carburetor. when you turn the motor off the vaumm is gone and the spring behind the diaphram pushes it closed and stops the fuel flow to the carbs.

Now the reason the carbs are overflowing is because the floats valves are not closing, in other words the floats are sticking.
Usually a good carb clean will cure the problem, especially for that year.
the older ones usually require new float valves/seats that are usually found in a good carb rebuild kit. You shouldn't need one.

If your really broke try tapping on the bowls of the carburetor lightly, while the engine is running, sometimes the vibration will vibrate a particle loose that may be holding open the float valve.
if it works then the fuel should stop overflowing while running.

if you know how to work on it, try this, with the engine off.
open the carburetor drain screws so that fuel will run out the carb. drain. flush out the carb.
get a container to catch the gasoline.
while fuel is flowing tap the carb bowls a few times then closed the drain screws.
clean up any spilled gasoline .
start your bike.see if they stop leaking and the floats are closing.
if it still leaks, you'll need the cleaning.

Happy Riding
Best Regards
Big Al

May 22, 2011 | 1997 Yamaha Royal Star XVZ 1300 A

1 Answer

I ran out of gas, now it won't start. what do i do?

Okay....I think your bike may have a vacuum operated fuel petcock.....which is the fuel valve on the bottom of the tank. It shuts the fuel off automatically when the engine stops and the hose from the intake to the side of the petcock loses vacuum.
So when you restart the bike the petcock is closed till the engine starts...which is okay because there is a small amount of fuel in the carb.........until you run out of gas....then the engine quits and the carb is empty.
To handle this situation, typically there is a prime position on the petcock that allows flow without vacuum to "prime" the empty carb......usually marked as PRI on the petcock,
So rotate the lever on the petcocck to prime....wait a couple minutes....get the bike started and set the petcock back to the normal setting....don't leave it on PRIME as fuel may flow overflowing the carb.

Apr 04, 2011 | 2007 Yamaha XT 125 X

1 Answer

When i start the bike cold or hot i have black smoke from the exhaust pipes..choke on or off and cant get bike to idle..i turn off the petcock and after a few seconds the idle starts to come back to...

Black smoke indicates that your mixture is way too rich. Now, you didn't say what carb you're running, stock or aftermarket. But, what it sounds like to me is the needle and seat in the carb is leaking fuel and overfilling the float bowl. When you're running down the road, you'll using enough fuel so that the float bowl does not overfill. When idling, you don't use as much fuel, the bowl overfills, and fuel flows into the carb creating a very rich mixture. Is you overflow hose that connects to the bottom of the float bowl connected, clear and open? If so, turn the petcock on without the engine running. If the overflow is clear and the needle valve is leaking, you should see fuel start to flow out of the overflow hose. This is very important that it do this. If the overflow hose is blocked and you forget to turn your petcock off, you could wind up with a couple of gallons of fuel in your engine. It will leak out of the float bowl, into the carb past the intake valves, past the rings and into the engine. I've also seen it get into the primary drive case as well. I'd put a new needle in the carb and check the float setting according to the book. it's sets with the carb on an angle if the carb is the original Keihin CV.

Good Luck

Jan 29, 2011 | 2003 Harley Davidson FLSTFI Fat Boy

2 Answers

When i turn the fuel on to start the bike gas pours out the clear tube that comes from the carb to under the bike some were is this line dis conected or broke or is it something more

it's probably just your overflow from the float. it doesn't connect to anything, it just let the fuel overflow come out when your float level is high. if you turn on the fuel petcock and it starts pouring out, your float needle is sticking. clean the carb and the float needle valve assembly and see what happens.

Dec 30, 2009 | 2003 Yamaha TT-R 125

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