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Discussion Starter #1
Hey guys,

Brand new to the forums, but I've had a lingering problem with my atv.

Basically, I got this quad off a friend when he blew the motor on it. I bought a used motor and swapped it right in. I did a leak down test and adjusted the valves. Don't know the hours on it. Figured it would be a cool project.

Got it running. It idles great, but would bog down and almost die when I open up the throttle. Does ok when you lightly push in the throttle, but when you slam it down for power, it Boggs out, usually dies if I leave it wide open.

Here's what I've tried;
Cleaned the carburetor. Took it completely apart and soaked everything in carb cleaner bucket for about 10 hours (while I was at work) then put it back together, and it idled better, but had the same problem.

Then I bought a brand new carburetor for it. Just wanted to cut out the tinkering and was frustrated. Installed it, and still have the same problem. Starts right up. Idles great, let it get to operating temperature, then push the throttle down, its spits and sputters till it dies!!

I'm really stuck here guys. I've come to the forums before and found some great tips without even posting..I'm stumped! Any help would be appreciated.
 

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welcome to the site,m just to be clear this is a 01' TRX400EX ,
MY next question will be , was the motor you put in it, the same YR, as if NOT the cdi electronic's might not match up and that's your issue?
on a more simple side of things, is this NEW fresh fuel, or??
as fuel can be bad in NO time, so, trying new fuel and plug, might help if its a fuel issue?
 

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Discussion Starter #3
Thanks for the reply.

The motor was out of a 2003. I could be wrong, but I used all the original electrical components. It could be the issue, but I'm not even sure where I would begin to diagnose that.

The fuel is a couple months old now. It's been an ongoing project. I replaced the plug when I first installed the motor. I haven't checked it since.. it may have been fouled. But I predict it's probably black. From the sound of the bike bogging, it's probably running rich.
 

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To me it sounds like a jetting issue of some sort. Almost sounds like its acting like the choke is stuck on. Is the plug gapped right? Choke off?(sorry have to ask though) Any aftermarket pipe or filter? What size are the jets in the carb?

Oh and welcome to the forums! Always forget that part haha
 
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the plug was gapped to the specs i read online. on one of the forums actually. it has a stock air filter and a DG slip on exhaust. Im hoping this is just a carb adjustment issue that im overlooking (im too stubborn to bring it to the pros). next week im buying a couple new plugs and a angled screwdriver (that idle screw is a bitch to adjust while the quad is running)
 

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Haha yep had my motion pro for years and i have used it literally 1000s of times. Try removing the airbox lid and see if it makes a difference. What size jets are in the carb?
 
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i tried removing the airbox lid, didnt really make too much of a difference that i could see. the jets are stock, so 148 Main, and 38 piolet. when i bought that new carb, ive only messed with the idle screw a little bit.
 

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With a slip-on your gunna need at minimum a 155 main jet. Expecially since they are so lean from the start. Ive had to put a 165 on a quad with just a slip-on before. If you dont give it enough fuel at WOT it can bog just like if its to rich. Most of the time if its a rich bog you will get some black smoke/soot coming out the exhaust.
 

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Discussion Starter #9
(hopefully i dont sound like an idiot) what do i have to do for a 155+ main jet? is that just an adjustment? or is it a whole new jet i need to buy?
 

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No such thing as sounding like an idiot on this forum bro. Its a keihin small hex jet. You can get them at almost any powersports store. Or order them from jetsRus or ebay. Generally jets are around 3-4 bucks a piece
 
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haha good to know, guess thats what these forums are here for. so ill try getting a jet kit and a new plug. that will be sometime next week. thanks for all the help so far, but my gut tells me that this wont be the only problem ;)
 

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Haha no problem! Keep us posted!
 

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Man I have an 05 400ex and it's doing the same thing as what his is doing. But, I just recently got this 400 from a guy and he totally kind of been through the whole bottom and top end and rebuilt it several times before I got it ,so it was running like a beast at first I think it has a 450 Honda front end on it anyway it was ticking the other day, started doing this ticking sound? and the oil is full ,dude said it leaked. give me a gasket kit with it said I need to put a gasket kit on it sometime soon for a small oil leak whatever but the leak has stopped? and it's been full of oil maintaining for 2 weeks but the ticking got like to be a worrisome amount of ticking going on, so I quit running it and I my three-year-old daughter want to take a ride down the road so I just kinda cruised along and I noticed if I gave it anything past a third of the throttle it would just do that backfire bog down barely want to go almost died but if I feather it and it would go eventually get up to speed is it like a a roller maybe? a push rod? perhaps a jetting issue ?could a jetting issue cause a tick or that's that's my bottom end huh? It's a fast ticking sound kinda like the way a baseball card sounded in your bike spokes when you were a kid. Any diagnosis!??
 

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Seeing how this post is 2 weeks old, I’m not sure if you have gotten anywhere with it. I would start by tearing the carb apart and cleaning everything. My girlfriend’s son has one that he used to like playing in the mud with, then it started acting up. The jets, float bowl, and everything else had mud in it. Spent a couple of hours cleaning it and it ran like a champ. While you’re in there, check to see what main jet you have in it. I would go up to a 152 to help with Honda’s lean settings. You may also want to consider backing out the air fuel screw a 1/4 turn. On the top of the carburetor is a silver plate with 3 small Phillips head screws. Remove the plate and take a peek down in there. There is an arm with a small plastic linkage and spring that attaches to the slide that I have seen come apart. This causes the motor to be running just off the slow jet and will bog at roughly 1/4-1/2 throttle and feel like there is no power. As for the ticking, take a long screwdriver and put the tip against the motor with the handle in your ear like a stethoscope. put the tip in as many different places until you can figure out where the sound is loudest and clearest. It will help you narrow down the source. The cam on these have an auto decompression mechanism that can wear out and cause the noise but is difficult to narrow down. It could also be valves out of adjustment causing the noise. For the most part I doubt that it is in the bottom end, but things happen. Hope this helps. Let me know what you find on it.
 

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Hey guys,

Brand new to the forums, but I've had a lingering problem with my atv.

Basically, I got this quad off a friend when he blew the motor on it. I bought a used motor and swapped it right in. I did a leak down test and adjusted the valves. Don't know the hours on it. Figured it would be a cool project.

Got it running. It idles great, but would bog down and almost die when I open up the throttle. Does ok when you lightly push in the throttle, but when you slam it down for power, it Boggs out, usually dies if I leave it wide open.

Here's what I've tried;
Cleaned the carburetor. Took it completely apart and soaked everything in carb cleaner bucket for about 10 hours (while I was at work) then put it back together, and it idled better, but had the same problem.

Then I bought a brand new carburetor for it. Just wanted to cut out the tinkering and was frustrated. Installed it, and still have the same problem. Starts right up. Idles great, let it get to operating temperature, then push the throttle down, its spits and sputters till it dies!!

I'm really stuck here guys. I've come to the forums before and found some great tips without even posting..I'm stumped! Any help would be appreciated.
Hello so I've been night riding alot and my lights started dimming an flickering sometimes now its all the time if I stop come to an idol the lights get bright but still kinda flicker then now when my lights are turned on and there dimming out an I goose the throttle it bogs out like a Rev limiter so was playing with the light switches maybe there bad and noticed when I turn my lights off I got full power to the motor again atleast but dano whats causing it yet havnt looked at it yet I'm thinking voltage regulator is going bad maybe but are problems are all similar but everyone's a Lil different it seems lol
 

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Seeing how this post is 2 weeks old, I’m not sure if you have gotten anywhere with it. I would start by tearing the carb apart and cleaning everything. My girlfriend’s son has one that he used to like playing in the mud with, then it started acting up. The jets, float bowl, and everything else had mud in it. Spent a couple of hours cleaning it and it ran like a champ. While you’re in there, check to see what main jet you have in it. I would go up to a 152 to help with Honda’s lean settings. You may also want to consider backing out the air fuel screw a 1/4 turn. On the top of the carburetor is a silver plate with 3 small Phillips head screws. Remove the plate and take a peek down in there. There is an arm with a small plastic linkage and spring that attaches to the slide that I have seen come apart. This causes the motor to be running just off the slow jet and will bog at roughly 1/4-1/2 throttle and feel like there is no power. As for the ticking, take a long screwdriver and put the tip against the motor with the handle in your ear like a stethoscope. put the tip in as many different places until you can figure out where the sound is loudest and clearest. It will help you narrow down the source. The cam on these have an auto decompression mechanism that can wear out and cause the noise but is difficult to narrow down. It could also be valves out of adjustment causing the noise. For the most part I doubt that it is in the bottom end, but things happen. Hope this helps. Let me know what you find on it.
My lights are dimming like crazy shut off basically and like retards my motor to runs great till about half throttle then cuts out like a Rev limiter and I shut my light switch off its fine but I'm a night rider havnt looked at it yet think it might me the voltage regulator for the lights but don't get why that would retard the motor like that
 

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It sounds like you have a short in the electrical system that is grounding power for the lights to the frame. I would start by taking the all the plastics off and tracing every wire to see if there is a bare one anywhere. There isn’t a regulator for the lights in the circuit at all, so it won’t be that. Also, if you have a multimeter, check your battery voltage with the key off. Then check it with the key on, engine off, lights off. Check it again with the key on, engine off, lights on. Write all of these numbers down so that you aren’t trying to remember what each was. With the lights on, if there is a really quick drop in battery voltage, you have something in the circuit grounding out and draining power. With the key off your battery should have around 13 volts. To check the charging system, start the engine, lights off, and check battery volts again. If the stator is working as it should, battery voltage will be closer to 14.5 or a bit higher. Start there and see what you find, then get back with me.
 

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I have a 2002 400ex just had top end rebuilt will start up and idle fine but it cuts out at half throttle all it has done to it is a slip on I have cleaned the carb tore it back down to make sure timing is right and still does the same thing as before any suggestions?
 
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