A similar post: http://s7.invisionfree.com/XJOWNERS/index.php?showtopic=123

I am tuning up my '82 XJ650LH Maxim and I had just finished cleaning up my carburetor and got it running wonderfly when I noticed that gasoline was pouring from my left-side exhaust just at the intersection (my bike has 4 pipes to 2 pipes). When I rev the engine there is an instant increase in gas flow from the pipe. At high revs it even sprays. To put into perspective the amount of gasoline flowing, I would estimate the rate at 10 ounces per minute.

Me and a friend checked the plugs and electrical system but could not find a failing. I will do more tests to make sure my plugs and cables are working but I do not think that is the biggest issue here. We found that it was the #2 cylinder that was causing the problem by removing the plug completely and running the engine. Compression was good and gas mixture was just right (very dangerous though). While we ran it like this no gas came from the exhaust. So what is bizarre to me is that if it leaks a torrent of gas with the plug inserted and acts normal when it is removed; what is causing this leak?

Perhaps the release of pressure in the cylinder during our test caused the carburetor to act differently? Perhaps the float needle is blunt and is malfunctioning? Maybe the needle slide in the carb is stuck. If so, is there a lubricant I can use? They did seem just a little bit un-smooth after the rebuild.

I have made sure that gas is not running down the pipe from another source. The thing is, the bike still runs great...it just leaves a trail of certain doom behind me. I am not riding it now because of this and it's a real drag after finally getting my jets unclogged.

Another thing to note is that opening the choke at all will kill the engine immediately. before the carb rebuild it functioned just as it should and I did not even touch the choke assembly. All exterior components are in great condition. Engine starts the moment I touch the ignition and the only other problem I see is that the idle is way too low at startup and gradually weakens but does not die. I will try to adjust the idle to fix that but I hope all this information can help diagnose the problem.

Kind of a strange problem. The reason the bike doesn't gush gas when the spark plug is removed is because there is no longer any vacuum in the cylinder to pull gas into it.

10 ounces a minute is a lot of gas. Sounds like you still have some issues in that #2 carb. I think a damaged/worn float assembly is a good place to look first. Then make sure your needle is in good condition and is seated properly.


Double check to make sure the #2 spark plug is firing correctly.

I agree with the above. I've seen that with a stuck float or a bad needle in the carb. Might want to check your oil also. I've been there too.

You could start the bike back up and see if the exaust on #2 gets hot. Mine seemed to run smooth but was missing on that cylinder.

Its hard to hear the miss because #2 fires at the same time as #3.

Sure sounds lokw a float problem. Be careful, don't start the bike with a cylinder full of fuel.

Another question for you, cruhmm: if you remove the airbox/air filters from the carbs and turn your fuel petcock to "prime", does fuel eventually come out of the #2 carburetor while priming? That would be an excellent indication that your float needle is sticking open. At least that's my experience.

I just rebuilt the carbs on my '81 XJ550, and that's exactly what happened to me, but a few taps with a rubber mallet or the like freed it up.

Another possibility for the extra gas is the o-rings around the float needle seat can go bad, allowing fuel to come in around the seat, no matter what the float level is. (I also learned that one by experience!)