Fuel in air box - Kawasaki KLR 650 Forum
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post #1 of 4 Old 06-23-2010, 09:38 AM Thread Starter
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Fuel in air box

I just purchased a 88 klr 650 with 7000 miles on it. Been sitting for 15 years. Cleaned the carb, tank and change the oil, filter and antifreeze and it ran great for 25 miles. On my way home it started to idle around 3000. Shut if off with I got home and left it til the morning. The next morning there was gas all over. It was leaking from the air box. Went to start it wouldn't crank. Took out the plug and the cylinder was filled to the top with gas. Cleaned the carb again, dipped it, put it back together and and it was tuff to start and ran with a bad miss. Let it cool started it again and it ran better then ever, until I tried to ride it. Stalled then ran crapy again. I noticed the oil was on the high side. Drained the oil and I believe there was gas in it. As far as the fuel in the air box, I believe there was oil mixed with it. What the heck is going on? Absolutely frustrated right now. Any help would be greatly appriciated.
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post #2 of 4 Old 06-23-2010, 10:08 AM
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There has to be a myriad of problems here, and it may take our whole village's input to solve! Here's my 2 cents:

First, that much gas, overnight, is indicative of a total petcock failure. The KLR petcock is supposed to be vacuum operated such that it only flows when the engine is on and there is vacuum to operate it. Yours may have a failed vaccum side that doesn't shut off.

Next, the bowl valve that is operated by the float is supposed to shut the fuel flow off when the floats rise. After 15 years it may have hardened to the point where it doesn't work.

These two things, in combination, would allow fuel to flow into the carb, overfilling it and allowing gas into the cylinder and back into the airbox. It would then fill the crank case and, as soon as you cranked it, puke oil and gas up the crank case vent into the airbox.
Remove the fuel line from the petcock. With the petcock open, if fuel flows you have a bad petcock. I think the most effective fix for a bad petcock is to replace it with a Raptor petcock. Cost is the same, or less, that fixing a stock unit. Search this forum for 'vatrader upgrade' or 'raptor'.
The bowl needle should probably be replaced "just 'cuz".
Hope that helps,


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Last edited by Tom Schmitz; 06-23-2010 at 11:50 AM.
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post #3 of 4 Old 06-23-2010, 11:11 AM
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I agree with Tom's read on this. I suspect your problem originated in the petcock. An old tired carburetor with wore pins and seats that don't seal as well as they did when they were new all contributed, but not the cause. Petcocks can be rebuilt. One problem I see with the stock fuel delivery process on these bikes is the vacuum part of the equation. Anyone old enough to remember vacuum operated windshield wipers would agree that if there is a better way, lets go for it. As Tom mentioned, the Yamaha Raptor petcock is a plug and play replacement, allowing gravity to feed the carburetor rather than the vacuum system pumping the fuel to the carburetor. The only real down side to this is that you will need to manually turn the petcock on and off. If you don't turn it off when you shut down the bike, you could very well be dealing with an engine full of fuel again. And if you miss the signs of a hydrolocked bike, you may be dealing next with a bent connecting rod.

Your call. If you want to rebuild the petcock, we can steer you onto rebuild kits. If you want to modify your current petcock to gravity feed, this is possible, too. If you want to convert to gravity feed only, with the reliability a new petcock and components brings to the table, we can provide you with an affordable solution.

Your float system on your carburetor "shouldn't" allow this. With age and wear, dirt, varnish buildup and bad luck, things hang up and it happens. The best solution to avoiding this in the future is to shut your petcock off every time you shut off your engine.
In the "old days", where ever you saw a bunch of bikes parked, it would be a safe bet that at least one had a bad petcock and was developing hydrolock as you watched.

Last edited by vatrader; 06-23-2010 at 07:39 PM. Reason: speling
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post #4 of 4 Old 06-23-2010, 07:36 PM
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Even with a good float valve a full tank of gas is going to get by the float valve sooner or later if the gas supply is not cut off. If your vacuum valve on the petcock is stuck open just remember to manually turn off the gas when you stop. Shouldn't take too many times of changing the oil and pumping out the cylinder to jog your memory!

Don't try to crank the motor if it's hydro locked, bad things happen... bent valves, bent connecting rod, etc.
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