Idling issue - Yamaha ATV Forum
 
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post #1 of 8 Old 06-10-2018, 11:55 PM Thread Starter
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Idling issue

First time on here guys. I recently bought a 2003 warrior 350 for $800 it had sat for a year and needed some tlc. I went ahead and replaced the petcock and carb, changed oil and spark plug, and battery as well. It ran fine for a few hours but now it doesn't want to stay running at idle with the petcock on, if I turn the gas off it will run without issue until it cleans the carb out of gas, so I was wondering if I needed to adjust the float height or maybe it caught some trash or something else, I put the carb in straight from the box. Any help would be appreciated!
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post #2 of 8 Old 06-11-2018, 11:54 AM
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i would start with that and make sure you pilot jet is clean
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post #3 of 8 Old 06-11-2018, 02:28 PM Thread Starter
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Is there a good thread on here to read up on for carb adjustments? I've not had much explanation on them before.
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post #4 of 8 Old 06-11-2018, 08:27 PM
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probably but i dont know for sure. l can answer any specific question you have but let me try to give you a general overview of carbs and how they work. and try to dispel some common beliefs. one of the most common things i hear is more fuel is more power and that is the root of a lot of carb problems. more fuel does not always make more power and in some cases can make less power. the same is true of not enough fuel.
your carb is one third of the equation that makes your engine run (we are not talking about electrical or mechanical components) and to adjust it properly you need to consider the other 2. your intake and exhaust are just as important as the carb and all 3 work together to provide the maximum power. the system regulates 2 things air/fuel mixture and mixture volume.
in order for the fuel to burn you have to convert it to a gas, it will not burn in the liquid form. once the fuel becomes a gas it has to be mixed with an oxidizer, in this case the oxygen in the air. that mixture has to be in the flammable range for gasoline. in other words the ratio of oxygen molecules to gasoline molecules has to be perfect. if you have too many gasoline molecules compared to oxygen molecules the mixture is "rich" and wont burn or burns incorrectly too few gasoline molecules and you have a mixture that is too "lean" to burn.
think of your carb as the mixer. the oxidizer side of the equation is controlled by 2 things. the volume of air moving through your carb and atmospheric pressure (this is why a one size fits all jetting chart does not exist) as you get closer to sea level the amount of oxygen in the air increases. the volume is controlled by the size of the intake, the vacuum the the engine creates and the size of the exhaust. all three components must be in balance as the system can only flow as much volume as the the most restrictive piece. with the exception of changing elevation this part of the the equation is generally fixed and why you have to rejet if you change a pipe. (you are changing the fixed part of the equation). the fuel part of the equation comes from jetting. the bigger the number on the jet the bigger the hole and the more fuel it will flow. the tricky part is the vacuum acts as an exponent in the equation. the greater the vacuum the more fuel flowing through the jet.
in general there are 2 circuits that you will need to deal with (some carbs will have more but we will save that for the future) assuming the carb is clean and functioning properly.
the pilot circuit controls starting and throttle through the first 1/4. in my opinion this is the toughest to get correct. with the bike cold it should be hard to start without the choke on. if it starts easily you pilot is likely too big. if it will not idle or idles poorly without the choke it is likely to lean. a bog out of the hole can be either rich or lean and only trial and error can weed it out. since the pilot jet is fixed (no metering needle) you have an air mix screw to fine tune the mixture.
the main circuit controls 1/4 to full throttle. if the machine is flat or has a bog in this part of the fuel curve the first thing you want to look at is the plug. it should be the color of chocolate milk if it is white you are too lean and if it is black you are too rich.
fuel through the main jet is metered by the fuel needle and by raising or lowering it you can slightly swing the mixture rich or lean.

so now that you have some theory lets talk about adjustment
2 turns out on the mix screw and the fuel needle one the middle clip is a good place to start. using the theory above to get it close use the air mix screw to fine tune the pilot circuit and the needle to fine tune the main (moving the needle up/lowering the clip make the mixture richer)

if it is running poorly in the main try putting it on half choke if it gets better you are lean, try taking the air box lid off if it gets better you are rich.

i am assuming you put on a zoom zoom carb and that alone could be you issue. more often than not they are junk and even the ones that are ok still need to be jetted. you said you put it on right out of the box and it ran correctly for a while so my guess is you picked up some dirt. checking the float is a good idea but likely not the issue. if it is too low it will starve on the top end to high fuel will run out of the overflow so if you are not seeing fuel on the ground it is probably fine. it is possible they did not drill the overflow and it is flooding the carb. anything is possible with zoom zoom. check to make sure the needle is seating all the way if it is not it could be overfueling the pilot circuit.

i know this is probably more than you wanted to know but it all plays a part. let me know if i can help
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post #5 of 8 Old 06-13-2018, 10:47 PM Thread Starter
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Not at all I appreciate all information! I'm a how-to addict on YouTube, I just haven't come across any adequate carb videos that explain in detail. Thank you much.
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post #6 of 8 Old 06-14-2018, 09:22 AM
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your welcome
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post #7 of 8 Old 06-18-2018, 10:12 PM Thread Starter
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Ok so I took the float bowl off and checked for debris, I didn't find anything. If I keep even the slightest tension on the throttle it'll stay running but dies at idle. (With the gas on still) but I let it run with the gas off again and it ran for multiple minutes without a hitch, I also tried the reserve setting just for laughs and it chokes it out just like normal on position. And I do believe it's the float myself now because of what you mentioned about the overflow. If I ride it and cut it off it'll drip gas from the overflow tube until I turn the valve off. So if possible, could you explain how to adjust the float height? Or any other thoughts you may have.
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post #8 of 8 Old 06-19-2018, 11:55 AM
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The float has a little tab that the needle sets on. When you bend the tab towards the needle it shuts the fuel off sooner so it will not overflow or flood the engine.

With the carb off you can verify operation by connecting a clean piece of hose to the fuel inlet of the carb, take the float bowl off and turn the carb upside down. Blow in the inlet hose and move the float away from the carb. You should be able to get an idea how high the float has to travel up towards the carb before it shuts the fuel off. I usually try to adjust the float until the top of steel cage that holds the floats(the part the pin goes through) is parallel to the flat spot where the bowl seals to the carb.

This will also verify that the needle is sealing properly in the seat. It should seal with the weight of the float, if not there is something in there or some buildup on the needle.

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