Question about 1981 Yamaha XJ 650

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Gasoline is leaking from a point not determined. Cannot see anything coming from the carbs, but gasoline is running down the left intake manifold. No fluid leaking from the fuel supply valve either. I'm stumped.

Posted by Anonymous on


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  • Yamaha Master
  • 41,794 Answers

Hi, Anonymous and the usual suspects are:
1. Damaged or restricted fuel tank venting system.
2. Loose float bowl screws.
3. Damaged float bowl o-ring.
4. improper fuel level in the float bowl.
5. Worn or dirty inlet valve or seat.
6. Damaged or leaking float assembly.
7. Particle contamination in inlet fitting cavity.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have nice a day.
Carbs leaking Here is how to fix it
1985 XJ700 Carburateurs Overflowing
Yamaha XJ750 Owners Workshop Manual
OEM parts for Yamaha

Posted on Jun 20, 2016


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Posted on Jan 02, 2017

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SOURCE: fuel leaks out what looks like a vent tube coming from the carbs

Hi ...... Sounds like float levels are set too high or debris in float chamber. Switch petrol off from/at tank and drain fuel from float bowls, if you use the cap off a paint can etc you can catch it and look at it to see if any water or debris present. Retighten drain screws, switch petrol back on and see if it still overflows.

Posted on Dec 30, 2008

  • 72 Answers

SOURCE: Motorcycle leaking gas from an unknown tube.

sounds like you got a cracked gas line or it needs a clamp on it,1.if it a line running from each carb. that is the overflow lines.2.if its one big one coming from the breather box it is a catch holes, and you open it to let whats in it run out.

Posted on Mar 27, 2009

ollie reece
  • 1167 Answers

SOURCE: I have an abnormally strong smell of gasoline

is the smell coming from the exhaust also check to make sure nothing is leaking out the pipes then get back to me if not

Posted on Sep 02, 2009

  • 10 Answers

SOURCE: lots of fuel leaking out of fuel vent on carb. XTZ 750

Sticky float needle valve probably caused by dirt from the fuel / tank or accumulated fuel gum build up. Try tapping the float chamber. Failing that pull the float bowl off and carefully clean/ flush with carb cleaner spray.

Posted on Mar 23, 2010

  • 426 Answers

SOURCE: Hi I have bought a 1985 700 maxim watercooled it

If I understand "the petcock was in prime position and it eventually quit dripping."
Prime = on
Sound like the needle rubber was hard and after a while they soften up enough to cut off the fuel.
Keep an eye on it and ride safe.

Posted on Feb 03, 2011

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If the fuel pressure in your car is too high (above 7 psi) that may cause gasoline to get into the engine oil.

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An inoperative injector system can also cause this problem, because if the engine is not firing appropriately, the gasoline will end up running down the walls of the cylinders.

Check to see if the float in the gas tank is rising the way it should be rising or if it needs an adjustment. You will not be able to look at your gas gauge and get an accurate reading If the float is not functioning properly.

Your engine may be running rich, with too much gas going into the engine and too little air.

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Two ways to tell if you may have a problem with gas in your engine oil are:
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If this is a new installation, your carb may not be jetted correctly or if the carb has been running for a while, you may have a vacuum leak somewhere. Your carb should be jetted 29.5-31 on the slow jet and 72-74 on the main with your 88" engine. If you've modified the exhaust, the jetting could varry a bit from that.

If your carb has been running for a while with no problems and you haven't changed anything and it's suddenly started running lean, I'd remove the carb and go through it. Check all the jets to make sure they aren't partially blocked. Check or replace the intake manifold gaskets where they join the heads. The carb has a vacuum takeoff point as well. It should have a hose supplying vacuum to your VOES and the vacuum operated petcock unless these items have been removed or replaced. Make sure that hose is in good condition.

Also, when you pull into a gas station, look on the pump and see what percentage of ethanol has been added to the fuel. Although I haven't seen it and cannot verify it, I've heard talk of some stations selling fuel that has more than 10% ethanol blended in with the gasoline. Since ethanol is basically alcohol, it will run leaner than gasoline with the same jets.

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