Problems with gas tank

Farfignugin · Post by **Farfignugin** » Sat Dec 03, 2005 6:50 pm

My scoot runs fine, as long as the tank is full to half a tank. When the tank gets to just below half a tank it starts to run lean and overheats (even with cold running plug). I think it has something to do with the fact that its gravity fed and as the tank empties the pressure in the fuel line decreases so fuel to the carb decrases and it starts to run lean. Is this normal or is it a fixable problem?

Thanks in advance.

JF · Post by JF » Sat Dec 03, 2005 9:12 pm

The fuel filter in the gas tank, or the fuel valve could cause this problem. I would first drain the tank completely by disconnecting the fuel hose from the carb and putting the end into a gas can. Then, using a vacuum pump on the bottom connection, put like @5 lbs of pressure(it shouldn't take much)on it. If it drains completely, then you go ahead and remove the fuel valve from the tank. If it doesn't drain all the way, then go ahead and remove it anyway. Just make sure that you have some sort of funnel or a pan(and towels) underneath it, otherwise you'll have a lot of gas going everywhere...

Now that you have it off, carefully attempt to remove the fuel filter from the gas tank(I personally haven't done it before, so you'll have to just experiment a bit). Once thats done, check to see if it's nasty, bent, broken and/or has rusty stuff all over it. If it's got junk on it, use an air nozzle on a compressor to blow the stuff out, or use some carb cleaner. If it's broken however, you should either purchase a new one, or install an in-line fuel filter. After that's done, clean out the fuel valve, and put it all back together.

Once it's together, confirm that fuel flows by either using the vacuum pump or turning over the engine. When everything is re-connected, put a little over half a tank in there, and ride it around for awhile.

Let us know what happens, and if there's still an issue, then we'll go from there.

Good Luck,
JF

Farfignugin · Post by **Farfignugin** » Sat Dec 03, 2005 10:27 pm

fuel strainer is brand new, and the petcock works fine.

JF · Post by JF » Sun Dec 04, 2005 9:11 am

Well, thats an interesting problem you have then. Did you check the fuel gauge to see if it is operating correctly(gas in tank is equal to what the gauge is telling you)? If that's not it, then you might need to clean out the carb, making sure the float needle is operating smoothly, and all orifices should be cleaned as well. It also could be some sort of vacuum leak or something thats causing this. I would recommend checking through the entire fuel system from top to bottom, making sure everything is within manual specifications.

Also, do you have the stock air-box setup installed, or is it a high flow air-cleaner setup? If it's after-market, then when the fuel level in the tank reaches a certain level, the vacuum valve tends to not be able to function correctly due to less restriction on the air-cleaner. If that is the case, then try reverting to the stock setup for now and see if that helps.

JF

Farfignugin · Post by **Farfignugin** » Sun Dec 04, 2005 5:26 pm

Fuel guage works fine, vaccume is fine and yes i have stock airbox. Why (other than what I said in first post) would it run fine at full to half tank and run lean half to empty????

hondaman · Post by **hondaman** » Sun Dec 04, 2005 8:24 pm

If everything checks out than it must one of those nasty GREMLINS.
Kick the bike on the rear tire and wave a chicken around your head. That usually scares them away.

darat · Post by **darat** » Sun Dec 04, 2005 8:40 pm

lol
i guess it is time to look on ebay.

JF · Post by JF » Sun Dec 04, 2005 11:33 pm

All I can figure is that there is some sort of problem with the carb, because everything else seems to check out fine. Try throughly cleaning the carb out, check for ANY vacuum leaks, and check the condition of the bottom of the tank. I know you said the fuel strainer is brand new, but if the tank has got any crud in it, it could have partially clogged the strainer already...

If that's not a problem, then try this; Test the fuel flow difference by disconnecting the fuel line, setting the end over a can/bottle/pan, and turning over the engine with a full tank of gas, then try it again with less than half a tank of gas in it. If there is a noticeable difference in fuel flow, then you know that something is wrong before the carb. But if no noticeable difference is seen, then the problem is either in the carb or after it. Try this test and let us know your observations from it.

Good luck,
JF

Post by **noiseguy** » Mon Dec 05, 2005 8:59 am

Any rust in the tank? How's your fuel flow with the fuel line disconnected?

What JF's getting at is that your bowl may be slowly draining out after 1/2 tank, causing the scoot to run lean if the bowl refill can't keep up with usage while operating.

Farfignugin · Post by **Farfignugin** » Mon Dec 05, 2005 4:10 pm

kk will do next time i get a warm day...(sometime next year maybe...) unless this is a warm winter.