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Discussion Starter #1
Like to start out by saying any help is appreciated.

Problem started a month ago and just got worse. Pretty sure it is a carb issue but little stuck on where to go now. Bike is a 2003 400ex. Bored to 416 with JE 10.8 :1, stage 2 cam, p&p head. K&N air filter.

Started running rough on trail when riding. Would have to hold it past 1/4 throttle to get going. Sounded like it was loading up bad. Took carb apart to clean. Has a 42 pilot and 165 main. Put everything back together and ran and idled.

Now it will not start unless its wide open. Fuel spray from intake tube, getting waaay too much gas. The kicker on it is i can turn the fuel on and fill the bowl. Shut the fuel off and when the carb is emptying it runs like a top.

Now my question being. Will a worn needle jet cause this or is it time to buy a new float needle and see if this is the cause?
Was not suspecting the float needle do to the fact the carb bowl does not overflow.

**Update. Today I dropped a the oil from tank and crankcase as well as the filter. As suspected was cross contaminated with gas.
 

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Yeah - you obviously have a carb issue - when you shut the gas off and as the float bowl empties at some point just before it runs out of gas, air starts to mix with the fuel being drawn up through the needle jet holder and the mixture leans out. If it runs good for quite a while as it lowers the fuel level in the bowl until it eventually runs out of fuel, then the problem is simply float and float needle related. The float and needle are replaceable. but the needle seat is part of the carb body - if there is a defect in the seat it needs to be reconditioned by a machinist or the carb replaced.

Now, the question is what kind of air filter box do you have, how is the engine vented and what kind of configuration are you running on the intake? Another question is how did the oil get contaminated with fuel? The best way to contaminate oil with fuel is by not shutting the fuel off when the vehicle is parked overnight or longer or having a defective petcock on the fuel tank. Alcohol blended fuel will damage the rubber seal in the petcock allowing it to flow fuel even when shut off - might want to check that - just remove the fuel line and see if it runs or drips steadily in the off position.

Alcohol blended fuel will also damage the float and float needle. I worked on one onetime that acted like you describe and it turned out to be that the float had swelled from exposure to alcohol and was touching the inside of the float bowl preventing it from rising sufficiently to press the needle into the seat at the specified level - when the carb over filled, the float would rise from the extra pressure of fuel displacement and shut off the fuel, but the fuel level was too high causing rich running - because it would rise to shut off fuel when overfull, two things happened - when the float popped up from the obstructed movement, it dropped the fuel level slightly due to being higher in the float bowl and less fuel was displaced by the less submerged float and because it would pop up and stop the fuel flow at the same time lowering the fuel level a mm or two, the carb never overflowed.

Now if it's not an internal carb problem; having fuel in the oil and if the crankcase is vented to the air box, as the engine and oil heat, the fuel in the oil will vaporize and be drawn into the air box where it enters the engine with the air being drawn through the carb - since the engine runs on vapor and not liquid fuel, the fuel vapor from the oil being drawn into the air box will cause rich running.

I suggest you change the oil, disconnect the crankcase vent hose from the intake and try running it - if it's still the same, repair the carb.
 

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Discussion Starter #3
Thanks for the input. Also to answer question. Everything as far as air box configuration is stock except the K&N filter.
Also oil contamination i believe is do to faulty shutoff. I checked thats when I took the tank off. Also noticed this morning that I had a little fuel in the garage under the tank where it had dripped out of shutoff.

The needle valve and float looks like it may have been changed out before. Possibly that it was done with the wrong year? To my recollection isn't there a specific year that the needle valve was slightly longer or shorter?

Needle valve for float looks slightly worn when I removed. It has a small indent around it from where it seats. Possible it is not seating fully in the seat. Float is the molded plastic with no fuel inside it. However, will be replacing this also.

On a side note. Remembering back the quad would act like it was starving for fuel with the petcock either in the on or reserve position. I do not recall at the moment. Will be taking that out and looking at filter.
 

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Discussion Starter #4
Ok got the quad running. Put the 152 main back in as well as putting a new needle valve and needle jet in. However, it will only run with the intake boot for the air cleaner off the carb.

So my guess is it wants more air because it is getting too much fuel yet. Is this possible with the main jet being a 152? Or did I miss something when cleaning the carb?
 

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The stock main jet was a 148 and a 152 would be about the right size for a change of the intake to allow more air in, but jetting is not written in stone - it has to be adjusted for the individual set-up. Take it back to a 148 and try it and continue to adjust until it is right.

Back in the 70's when I started racing, we never changed the jetting of a carb until after we rode it after the engine changes were done. In some cases we jetted up and in other cases we jetted down. The rule was to jet in steps of two until it was too rich and then jet back down to the point where it ran best without being too rich, but I was working with two strokes and they were fuel hungry. With a four stroke, the jetting is more sensitive. I will start with stock and jet up until it's too rich then back down one size at a time until it performs as desired, and when it runs optimal, I go down one more size as long as one size smaller does not cause some other undesirable characteristic.

Of course it's always possible you missed something when cleaning the carb and the only thing you can do is try cleaning it again and see how a second cleaning changes things - maybe a good change and maybe no change - if no change then quit worrying about the quality of the cleaning and just work on the jetting until it runs right.
 

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Discussion Starter #6
Thank you for the reply.

I am almost 99% sure I have a jetting issue at this point. Being that it wants to run with the front side of the carb completely open allowing more air to compensate for the extra fuel.. I have had the carb apart and cleaned about 3 times now. I will go back to the 148 jet and see how it runs.
 

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I had a motorcycle that no apparent reason started running rich and had to be jetted down to run right again - I always kinda suspected an air passage that got clogged and could not be cleaned, but I got it jetted to run right and it ran that way for many years.
 

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Just for shots and giggles I pulled the vent tank from the intake. Quad runs amazing as soon as I hook it back up runs like shit. Where do I go now?
 

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That means your oil is contaminated with fuel (my first post near the bottom) - as the fuel vaporizes from the fuel it is drawn into the intake and walla, the mixture is rich.
 
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