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06 dvx 400 fuel problems


toomanytoys
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I have a 06 dvx 400 that has a strange fuel problem. It seems that there isnt any flow coming from the tank when the valve is in the "res" or "on" position. The only time I get any fuel is when the valve is turned to the prime position. And its only a trickle at that. I tookthe valve off of the bottom of the tank and it is clean inside and out. Has anyone else had this problem? Im having a hard time keeping this thing running like this.:confused:

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Dream Car Giveaway

There should be more than a trickle coming out when the petcock is in the prime position. It is, however, normal for no fuel to flow out when it is in the on or reserve positions since the petcock is vacuum operated, it only flows when the enginge is running. I would check the vacuum line first like Ajmboy advised. If the line is ok then you likely have a bad petcock. Make sure your gas cap vent isn't clogged.

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Could be a leak in the carb, it could just be the signal hose or an air leak somewhere else in the intake. There are many things that could cause low intake vacuum, I would start with the most simple thing, the signal hose or a loose or leaking intake boot. How did you apply the vacuum to the fuel valve? It could still be that the fuel valve is the problem, it may just be taking more vacuum than your engine can generate to operate the fuel valve.

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I used a vacuum pump to test the valve. It opened at about 2 inches of vacuum. I tested the hose and there were no leaks either. I will check the intake boot. It seems to be really lean right now. I have to put the choke on and hold the throttle wide open to get it to start. It will not stay running at idle. I dont seem to have any control with the idle screw either. Its either racing or stalling. Im getting alot of backfires now as well.

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Heres an update : I got a rebuild kit for the carb and when I opened it up I found lots of dirt in the float bowl and some scale throughout. After a thorough cleaning and a rebuild there is no difference. Its still hard to start and once I get it started it wont idle. I have also changed the vacuum hose and the intake boot is in great shape with no leaks. Im starting to wonder if I have multiple problems here. Could there be a crack in the head maybe?

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Did you try a new spark plug. a partial fouled spark plug will cause a hard starting problem and a poor idle issue. how is the compression. if you do not have a compression tester put 3 or 4 squirts of oil in the cylinder, the same in all cylinders if multiple. if you have a ring problem this will take up the worn ring clearance. and up the compression. if it starts easier then you have poor compression. if your ring seat is poor enough you will also lose vacuum because it canot draw enough intake air.

Did you clean your fuel tank out? you could have some grime in the bottom of the tank. also you fuel cap could be partialy pluged as well.

Edited by GEARHEAD01
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I started thinking about the compression as well. I just dont get how it went from running fine to not running at all in less than 5 min. When I first started it that morning it fired right up and settled into a nice idle and after letting it warm up I started down the trail. About a quarter mile later it just shut off and the problems started

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I would check for spark. If you have spark, put in a new set of plugs anyway. They are cheap and I have seen them just quit or have to weak of spark. Spark plug gap could also be too wide causing the coil to work to hard and over heat. At any rate I would start with spark.

Your Friendly Neighbourhood Journeyman Mechanic :)

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I took the bike out for a ride with some friends this weekend. It ran perfectly. Lots of power. I had a hard time keeping the front tires on the ground. It just wouldnt idle. I could pull the motor down in gear until it started bucking and it didnt stall. But if I put it in neutral it tried to stall. How about the valves? Could I need an adjustment? Can they be adjusted? The top end of my motor is a little noisy compared to my friends 06 kfx400.

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I would definately check the valve clearance, improper valve adjustment could definately be at least partially to blame. The valves can only be adjusted by taking the cams out, removing the bucket tappet from above the valve and replacing the shim that sits between the tappet and the valve. If the valves are tight, you use a thinner shim, if they are loose, you use a thicker shim. I am also wondering if you got the carb completely clean? Did you remove the pilot screw and clean the pilot circuit? Did you poke something throught the jets or did you just spray everything or soak it in cleaner. You need to manually poke throught all the passages in the carb and make sure they are clear.

Like I said before, your fuel valve could still be the issue here, the fact that you have more problems at idle and at low engine speeds makes it seem more likely. When the engine speed is up, the vacuum is sufficient to keep the petcock open, when you have the machine at an idle, it isn't quite enough to keep the fuel flowing through the valve.

Edited by DirtDemon
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