Author Topic: Gravity feed floods even with needle set to leanest position  (Read 14685 times)

fl250noob

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Gravity feed floods even with needle set to leanest position
« on: August 20, 2012, 02:43:26 PM »
Total newbie here, both on the forum and with the fl250.  It's actually my father-in-law's and he said I could have it if I could get it running. It has a rigged gravity feed tank at the top of the seat and feeds directly into the carb. It would start first pull and idle fine, but out on the trail it would smoke excessively and flood at anything over 1/2 to 3/4 throttle.  It would recover when letting up on the throttle and idle fine, the just start to flood and smoke when pulling anything past about 1/4 throttle.

The throttle needle was set in the mid position, so I moved it up to the leanest setting at the top. It ran a lot better, but I still couldn't get it to really open up at full throttle.

On one run, the thing just picked up and hauled. Just like it was supposed to. No stuttering or pause on throttle. Well, it ran out of gas right after that.  So I got to thinking about the gravity feed setup and how the pressure of the fuel down the line may be causing excess fuel to be injected into the carb.  As it was almost out of gas with no fuel pressure from the tank, I figured that was the cause of the problems.

I have the OEM tank so I pulled off the fuel pump as I read on several posts that you should run the pump even with gravity feed. I hooked up the pump to the gravity tank and ran a line back up to the tank.  Fuel trickles out of that hose when running and the odyssey start and runs about the same as using the straight gravity feed set up.

I then decided to test my empty tank theory a few times by shutting off the fuel at the tank and just running the fuel in the line (with the pump) without any pressure from the tank.  It ran better, not quite as well as the one time when I ran out of gas with the gravity feed, but it could take full throttle without flooding or sputtering too badly.

So I'm at a loss as to what is causing the excess fuel in the carb. The gravity tank is near the top of the roll cage, so it has about 3' of hose to the carb (or fuel pump). When I move the throttle needle back to middle position it runs real bad, smokes and floods.  I can't even get close to full throttle and barely even get it back to the shop.

Any ideas out there on what would be causing this excess fuel?  I'm in Nebraska, so the factory jetting should be fine, but i don't know where else to control the fuel as it comes out of the bowl.  I've gone through the whole carb and it's spotless.  It's almost like if there was one more notch at the top of the needle, that would be the perfect setting.

Thanks for your input on this. 

girth first

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Re: Gravity feed floods even with needle set to leanest position
« Reply #1 on: August 20, 2012, 09:06:17 PM »
Could the float be out of adjustment. manual says it should be 20mm or .079 in. also are ypu running a recirc "t" in the fuel line

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #2 on: August 21, 2012, 05:11:39 AM »
I do have the Clymer manual for it, and I did read about the 20mm.  But I wasn't sure how to measure it because my carb is not the same as the stock carb in the manual. The float design is a little different than the pictures.  I wasn't sure which part of the little flap could be adjusted, whether it was the two prongs that get lifted by the floats, or the smaller center prong that triggers the shut off valve in the bowl.

Yes, I have the T valve in the line, and it does feed the excess fuel back through the hose leading back up to the tank.

LiveWire

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Re: Gravity feed floods even with needle set to leanest position
« Reply #3 on: August 21, 2012, 11:38:30 AM »
Bend the tang that presses on the needle toward the needle. That will put more pressure on inlet needle for a given fuel level and prevent the flooding. I would put your jetting back the way it was. Fix the fuel flow issue first then move to jetting.

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #4 on: August 21, 2012, 12:12:46 PM »
I'll give that a shot.  I wasn't sure if the level of fuel in the bowl had any effect on the flooding issue so I hadn't messed with it other than cleaning it out and making sure the floats were free.  I figured as long as there was enough fuel in the bowl to get sucked up into the carb that the level didn't matter.

TEXASBAGMAN

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Re: Gravity feed floods even with needle set to leanest position
« Reply #5 on: August 27, 2012, 06:11:13 PM »
Check float for a whole in it. Put in a container of gas and see if it floats, push it down and see no bubbles. if it is filling with gas it rides on bottom of bowl not shuting off fuel supply. Float level will make rich/lean to some degree but engine should run if float is bent to rich side. I would put clip back in center position. is your air filter clean? Check your exhaust pipe make sue its clean, cheap 2 cycle oil will cause carbon build up, dirt dobber etc. Depending on what fuel pump you have , diaphram could have whole in it, engine vacum will suck gas into bottom of engine but it should not run at all. Try gravity no pump to be sure. make sure carb vent is clear. Is fuel running out of over flow at bottom of bowl?

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #6 on: August 27, 2012, 06:30:41 PM »
I bent the tang up towards the needle and tested with no significant change.  I didn't want to break that off so I then bent the outer arms that contact the floats downward too. I still couldn't get it to run quite right with the needle set to anything richer than the leanest setting. The air filter is clean, but not sure about the exhaust.  I have noticed some oil dripping out of it and it smoked excessively before when it was running too rich.  So I should probably clean out the pipe. 

I started this whole process with gravity feed and no fuel pump and it was running too rich. I then put the fuel pump with the gravity, and am now running the stock tank with the fuel pump. I don't know why it had been replaced with the gravity tank to begin with. I reasoned that the gravity tank was just feeding too much gas due to fuel line pressure and no pump/bypass.

It's definitely running better than when I started, but it's just not quite right.  I shouldn't have to run with the needle clip at the top, so I'm trying to figure out why so much fuel is getting into the engine.  I'm running 20:1 but not sure what kind of oil it is.  Some 2 cycle oil that my father-in-law had.  I'm going to try some 91 octane and maybe 32:1 mix or even 40:1. 

I can spin cookies nicely now, but WOT is still just not there.  It just has a stutter that keeps it from full power.  But dropping the needle clip causes it to flood from about 1/4 throttle and up.  So the saga continues!

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #7 on: August 27, 2012, 06:31:59 PM »
Oh, and have never had fuel overflowing from the carb.

hoodlum

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Re: Gravity feed floods even with needle set to leanest position
« Reply #8 on: August 28, 2012, 05:16:46 AM »
Have you tried dropping the main jet a size and see what happens?

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #9 on: August 28, 2012, 05:28:45 AM »
I thought about that, but don't know where to get a different jet size. 

odypilots

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Re: Gravity feed floods even with needle set to leanest position
« Reply #10 on: August 28, 2012, 10:52:21 AM »
If his main jet is so big that he needs the needle to drop into it to reduce fuel flow, it seems he's way too big on the main jet. It could have a winter jet in it. I would buy a jet two sizes smaller than what's in it, then 4 sizes smaller to test the "too big of a main jet" theory. Just be aware that if the "main jet is way too big" theory is wrong, you could be driving on possible too lean a fuel mixture, and could melt down your engine. If it's super clean and crisp running, BE CAREFUL!!! Most people tend to think" It's running great!". Think, " If I'm very lean, it WILL melt the piston." And they can run very good while jetted dangerously lean.

What size main jet is in your carb? I don't know 250 stock sizes, but what's in it is something to work from. Do you know if your lower end is sealed up? Any time a two stroke runs erratically, a vacuum leak should be considered.
« Last Edit: August 28, 2012, 11:11:00 AM by odypilots »
The usual 'my two cents' disclaimer applies. :)

fl250noob

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Re: Gravity feed floods even with needle set to leanest position
« Reply #11 on: August 28, 2012, 11:46:37 AM »
I haven't pulled the main jet out yet, but it's on the agenda. Haven't done any kind of pressure leak test either. Don't have the equipment to do it yet and need to read up on exactly how to do it. So much to do, so little time  :-\

odypilots

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Re: Gravity feed floods even with needle set to leanest position
« Reply #12 on: August 28, 2012, 12:09:20 PM »
Trouble shooting without 'being there' is tough. Some video should get you more accurate responses, but posting video to the internet can be as difficult as working on the buggy!
The usual 'my two cents' disclaimer applies. :)

TEXASBAGMAN

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Re: Gravity feed floods even with needle set to leanest position
« Reply #13 on: August 29, 2012, 09:56:01 PM »
you did find the fact service manual on the forums right? the fuel screw will only adjust the idle. 1.5 to 2 turns out. if you are are sure main jet is the original don't change it. clip on pin will do more or as much. carb kits are available for sale at most aftermarket dealers for $20-25. i like the K&L kits best. Maybe you are not running rich i bet your pipe is stopoped up with carbon or even a dirt dobber. if you have the factory pipe NOT A CHROME DG OR FMF. YOU CAN TRY THIS. OLD BIKER TECH. I DONE IT AND A FEW TIMES AND IT WORKS. REMOVE EX PIPE BUILD A LARGE CAMP FIRE PUT PIPE IN THE FIRE A LET IT GET HOT AN BURN OUT CARBON.IT WORKS I HAVE DONE IT. Torches or propane burners don't seem to work as well as a couple hours in a hot fire. use good 2 cycle oil and mix it exact. USE PREMIUM GAS engine will run better and cooler. ???

TEXASBAGMAN

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Re: Gravity feed floods even with needle set to leanest position
« Reply #14 on: August 29, 2012, 10:04:31 PM »
1 more thing. SPARK PLUG i use NGKs. In my ODYSEE i like the SPLIT FIRE. Once you foul a plug they are never the same as a new one! Be careful but you can go 1 step hotter plug that may help.