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Dorman10

400ex possible fuel issue

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I need some help guys. I have a 02 400ex with a big bore 440 kit, stage 3 hotcam, ported head, and brand new carburetor currently with a 200 main jet in it, yet it seems like it still running out of fuel on top end. I’ve tried every jet from a 148 to a 200 and I’m having the same issue. It runs good and hard up until I’m going through 4th gear around 60mph and then it just started shutting down like I’m out of fuel. Sometimes if i keep playing with the throttle i can keep it running before it shuts off, but most of the time it just shuts off. It will crank back up without hesitation after about 5 seconds like I’m having to wait for the bowl to fill back up with fuel. There is no black smoke coming out the pipe or anything to show that I’m running too rich. I just need some help, so somebody please tell me what they think is the problem 

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These machines are not my specialty but have you modded the air system at all? Have you tried running it with the air box lid removed or has it been altered?

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Yes i have the lid off, that was one of the first things i tried. That’s the only thing I’ve done with the air system 

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Yes OEM Honda carburetor. The one i took off was OEM as well, that’s why i got a new one to see if that was the issue 

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Gotcha. I would check just to be 100% sure the phillips screws in the carburetor slide arm werent installed loose. Seen that cause a similar issue. I would also suggest checking the filter that is on the petcock. Goes up inside the tank. If its restricting flow to the carb could explain some things. I would try to confirm its fuel starvation first. I would turn the gas off when it dies as your rolling to a stop. Then use a flat tip screw driver to open the bowl drain and see how much fuel you get out. Shouldnt be much if it is running the bowl out.

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The plastic piece sticking up on this picture is the filter. The black line and above filter for the fuel "on" postions. The bottom part will filter the "res" position.

Screenshot_20200321-154412_eBay.jpg

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Filter on the petcock looked good. It’s not clogged.  All the screws in the slide arm are tight. I just ran it until it died and turned the gas off. Opened the drain bowl and almost nothing came out 

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I ran it on reserve and on on, each time it cut off i immediately turned the gas off and it’s running the all the fuel out of the bowl

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Is the fuel cap vent clear?

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^^^that would be next place to look. (Try riding it with cap off) Could be a bad petcock not allowing enough fuel flow? Could try putting a fuel bottle on it and see if it still does it? We are now 100% sure its draining the bowl. Now to just figure out why lol.

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 I have seen the petcock get a clog internally where you couldn't  see it , like a  block artery from eating too much greasey Popeye's chicken , but I am no E man ,  EX or ES 

 

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Sticky needle valve from running ethanal fuel , throw something up there that might stick <*{>>>><  

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8 minutes ago, Fishfiles said:

Sticky needle valve from running ethanal fuel , throw something up there that might stick <*{>>>><  

Sounds to me like it has been doing this on both the original and new oem replacement carb. Wouldnt think ethanol would get to the brand new needle valve that quick would you?

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That sounds logical to me !!!  Excuse me , just the drive by media passing thru , you know sometimes it takes someone to say something stupid , for someone else to think of something smart , carry on , LOL --- clasping fuel hose maybe ? my first thought was the screen in the tank , but I did read he  said it is clean , tank vent clogged , soapy water and a air compressor might show that , but that usually takes a while to happen , I am going fuel hose blockage 

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Thanx for all the input guys, i actually went ahead an ordered a new OEM Petcock and I’m going to try that once it comes in. I have a clear fuel line on there so i can see that the fuel is passing through there smoothly and it is not crimped. I ran it on jack stands to watch the fuel run through the line in all gears. 
Shot in the dark, could it be anything electrical or have to do with the fire. I have a brand new plug in it (was doing the same thing with the previous plug). 

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Posted (edited)

But, running it until it shut off and turning the gas off and seeing that the bowl was empty is definitely telling us that is a fuel issue. Thanx for that tip Slammed Ranger

Edited by Dorman10
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Your welcome! Glad to help!

 

Yeah no doubt about it a fuel starvation issue. You have an odd one on your hands here. Make sure to keep us posted! This one could save someone alot of headache some day.

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I’ll definitely keep y’all posted. Hopefully the new petcock solves it. If not, i have a little fuel pump from Advanced Auto I’m going to slap on there. 🤷🏼‍♂️

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@Dorman10, try unplugging the float bowl vent hose and see if that solves the problem. If so the vent hose is clogged up, quick 'n easy fix.

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Well guys, the new petcock still didn’t do the trick. I’m still starving for fuel on top end. 😞

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Same with the float bowl vent hose disconnected?

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2 hours ago, retro said:

Same with the float bowl vent hose disconnected?

I would imagine the new carb came with all new hoses. What are the chances both are clogged or restricted? This is an odd problem. Wonder if there is like a piece of plastic getting sucked to the pet cock filter or something? I would be putting this bad boy on a bottle and running it down the road. Did you try running the quad without the gas cap? I know its gunna splash gas on your crotch but worth a try.

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I’m going to put a 450 tank on it tomorrow and see what happens. I haven’t tried actually riding with the gas cap off. Then I’ll try a bottle, and then I’m putting a small fuel pump on it. I have to get this problem figured out

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450 tank with a bigger petcock and it’s till starving for fuel. It runs the bowl out in top end

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