Why would the Carb overflow and dump into the airbox/crank case - Suzuki ATV Forum
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post #1 of 11 Old 07-30-2019, 08:42 PM Thread Starter
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Why would the Carb overflow and dump into the airbox/crank case

I have had 2 Eigers. Both 2005. One was a camo edition 4x4 ltf400 and a 2005 Lta400. Both ended up with fuel mixing into the oil. Both Eigers have the raptor 660 mod.

My question is,

If the fuel flows from the gas tank to the carb through an "on/off/reserve" style petcock in the "on" position, why would the float needle and float needle seat not stop the flow???

I have heard a bazillion times that fuel gets into the airbox/crank case because of a disfunctional petcock not stopping the fuel flows when the bike is not on. This seems to only happen with the Eiger because if I leave the petcock in the "on" position on Either of my Dirtbike, my Kawasaki Bayou, or my Suzuki Lt250 fuel never gets to the point of "overflowing.

But for some reason if the Eiger is shut down for 5 minutes with shutting that raptor 660 petcock off, it will flood. It's doesn't even drain from a drain or anything, just goes right into the airbox and eventually into the case.

I would think the float would prevent this.
Could someone please explain to me why???
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post #2 of 11 Old 07-30-2019, 09:06 PM
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The fuel petcock is sealed by way of O-rings only internally. They have very little surface contact in most cases since most O-ring grooves are cut with a standard square nose endmill. Even when a proper ball nose endmill is used there is still clearance but the O-rings can seat better with more surface contact. Because the traditional ring groove allows only a limited amount of sealing surface, when pressurized enough, fuel will squeak past. The reason for the pressure build up is because the fuel tank is probably a sealed unit with no vent around the fill spout or the tank vent is plugged. Carb vents can play a role in this issue too if they get packed with dirt but it is far less likely...although I have seen mud wasps plug a carb vent hose with mud once before, it still had no consequence though as the carb had two vent hoses.

The most probable culprit is likely due to having a half a tank of fuel and allowing the ATV to sit in the sun or any hot or heated environment for any length of time as this will build up surprising amounts of pressure in the tank. There can easily be enough pressure build up to overcome the float spring resistance and pop the needle off the seat. This is where your fuel flow starts and it won't stop until either the tank pressure has been relieved or it drops enough for the spring to take control again which is rare because the less the fuel the higher the pressurized vapour content. If you crack the fill cap you will most likely get a good whoosh of pressure release. A sealed fuel system is mandatory in personal watercraft, so they have special check valves to allow air into the tank but nothing can go out. My ski when sitting in the garage all day with a half tank is enough to give a healthy pressure release when I crack open the fuel cap. Any time I do fuel system work on it I always crack the cap open a touch so the lines don't pour out all over the place from tank pressure.
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post #3 of 11 Old 07-30-2019, 09:22 PM Thread Starter
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If the the Fuel tank cap is off, it still seems to have the same issue. Most importantly, why would my other quads and dirtbikes not experience the same problem? It seems like some kind of engineering fail on Suzuki's part.

I also wonder why there isn't just the simple carb overflow hose/vent that would have the fuel dump on the ground rather than into the airbox and ultimately to the crank case.

I have tracked down the crank case vent that goes up to the airbox. Is there somewhere else I could send that vent instead of the airbox? That would eliminate one route for the gas to go, avoiding an oil change. Then we could let the gas fall out of the airbox with a one way hose vent/valve.
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post #4 of 11 Old 07-30-2019, 09:41 PM
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Just curious to know did you use the OEM "factory" Raptor 660 petcock $30-40 dollar cost doing the mod or the $12-15 dollar aftermarket petcock that looks identical to the factory one? I've heard the aftermarket petcocks are more prone to leak in just a short amount of time.

On a side note even though I have the Raptor 660 mod myself I'll turn off the petcock and run the ATV until it use's all the fuel out of the carb when through riding for the day.

Tony

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Last edited by T.Ray; 07-30-2019 at 09:47 PM.
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post #5 of 11 Old 07-31-2019, 07:01 AM
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The next logical consideration would be that either your needle valve is worn out or there is an issue with the float. A defective float can happen over time by getting a pin hole in it and filling up which in this case looks like that's not likely going to cause this issue, or the float height tab is too high. If the lifting tab on the float is too high it will make the needle pop off the seat early but also not let it return for a good seal. An improper float height will also reduce the pop off pressure on the needle making it lift very easily. Some of the plastic floats sometimes need to be heated by a heat gun just enough to reposition the lifting tab for proper operation. Yours might need to have it lowered a touch more than spec just to give back good sealing pressure. If you find it's a bit too strong of pressure due to a hesitation, you can compensate for that by increasing your low speed jet by one size larger. It would be my assumption at this point that with no tank pressure the leak is caused by either a bad/leaking fuel valve, improper float height or sticking float, worn out needle and seat or a combination of all. Don't get rid of that crankcase vent. It is there to recycle any fuel vapor blow-by from the compression stroke but also allows the crank to breathe and not blow seals.
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post #6 of 11 Old 07-31-2019, 02:50 PM
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Your needle in seat could be sticking open or not seating / sealing completely. The factory petcock is vacuum opperated. If the factory style petcock functions properly it should stop fuel flow after the engine is shut down. With the Yamaha petcock you don't have the vacuum port. So it doesn't close automatically when not running. You have to turn it off manually every time. If you don't it was a waste of time installing it.

My quadrunner had a sticky needle in seat and a leaking petcock. I used a factory style petcock and rebuilt the carburetor and solved my problem. Plus i added an inline shut off valve so i could turn off the fuel for sure when its not being used. Just in case the petcock fails again. I also rerouted my crank case vent so it would not drain into there.
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post #7 of 11 Old 08-01-2019, 06:26 AM Thread Starter
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@440Tim. Where did you reroute the crank vent to? I still want it to function but I want to avoid contamination of the oil.


Also, I have a factory OEM petcock and carburetor on the way. I figured I will just use it and hopefully I won't have any problems. Maybe if I run ethenol free gas it will keep it working longer.


440??? Are you in Ohio?
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post #8 of 11 Old 08-01-2019, 09:11 PM
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I used a longer line and I ran it up by my shifters with the other vent lines.

I've never been to Ohio. I'm in Washington state.
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post #9 of 11 Old 08-01-2019, 10:02 PM Thread Starter
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Quote:
Originally Posted by 440Tim View Post
I used a longer line and I ran it up by my shifters with the other vent lines.

I've never been to Ohio. I'm in Washington state.

I guess you never had an issue with oil swelling that high since you rerouted the vent.

I am installing the Factory OEM petcock and carburetor tomorrow morning. I will also put an inline fuel shutoff to be safe. Hopefully there won't be problems with the new stock parts.

440 is an area code in Ohio.
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post #10 of 11 Old 08-02-2019, 12:42 PM
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The crank case ventilator line should be ok there. It's higher than the factory vent into the airbox. Just make sure it doesn't kink if you run it up there. I didn't plug the hole in the airbox where the line would normally connect because i don't plan on running through water that deep.

As far as running ethanol free fuel it's never a bad idea. Especially if it sits for extended periods and is humid in your area. Alcohol is hygroscopic and can / will absorb water from the air. Water doesn't mix with gasoline so the alcohol water mix will settle down to the bottom of the tank. If this happens you would need to drain and replace your fuel.

The extra fuel shutoff valve is just a precaution. I only used it when i wasn't using the quad.

I plan to do the same thing's with my KQ 300. The Quadrunners engine locked up so it's down for now.

And 440 as in 7.2 liter Dodge big block V8. Other than my quads everything i own is 440 powered.
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