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Discussion Starter #1
Hello guys,

I have an 03 trx400ex that has a bogging issue. It has had a small bog mid way up the power band when I got it, but it clears up real fast. I was riding it today and it suddenly bogged down whenever you give it any throttle input. Mainly stock with a top end rebuild maybe 10 hours on it with a hot cams and a new carb. No idea what size jets are in it, but it's whatever it came with. The only thing I can think that the timing chain jumped a tooth. Any ideas?

Thanks
 

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Try adjusting the floats in your carb if you take off the bottom end you’ll see a couple floats in there they may be sticking and allowing to much gas to get in or buy a dynojet kit
 

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Discussion Starter #5
Try adjusting the floats in your carb if you take off the bottom end you’ll see a couple floats in there they may be sticking and allowing to much gas to get in or buy a dynojet kit
idk about a couple floats there is only one. It was really sudden so I'm thinking it was a cam chain jump
 

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Leave the floats as they are, don't touch a thing..!!

Start with the simple things first..

First off, tell us what you know about the ATV, top end build for example.. is it a big bore mod? Is the exhaust stock or aftermarket? How about the inlet... Is it modded? Is there a aftermarket CDI fitted or a tuner? How about the spark plug, is it stock?
Carb jets and carb.... Is the carb OEM? Are the jets OEM, are they stock sizes?

Timing gears and chain... Are they OEM parts or China junk? Are they new?

So many possibilities.. Help us to help you 🙂
 

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Discussion Starter #7
Leave the floats as they are, don't touch a thing..!!

Start with the simple things first..

First off, tell us what you know about the ATV, top end build for example.. is it a big bore mod? Is the exhaust stock or aftermarket? How about the inlet... Is it modded? Is there a aftermarket CDI fitted or a tuner? How about the spark plug, is it stock?
Carb jets and carb.... Is the carb OEM? Are the jets OEM, are they stock sizes?

Timing gears and chain... Are they OEM parts or China junk? Are they new?

So many possibilities.. Help us to help you 🙂
All right so the guy rebuilt the top end with a cheap kit keeping with the stock bore (100 bucks or so). It has the stock timing chain with a stage two hotcams cam. Stock exhaust, plug, and cdi. He bought a new carb for it so probably a cheap one, no idea what the jet sizes are. He gave me the stock one that looks perfectly fine when I took it apart.
 

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Discussion Starter #8
Leave the floats as they are, don't touch a thing..!!

Start with the simple things first..

First off, tell us what you know about the ATV, top end build for example.. is it a big bore mod? Is the exhaust stock or aftermarket? How about the inlet... Is it modded? Is there a aftermarket CDI fitted or a tuner? How about the spark plug, is it stock?
Carb jets and carb.... Is the carb OEM? Are the jets OEM, are they stock sizes?

Timing gears and chain... Are they OEM parts or China junk? Are they new?

So many possibilities.. Help us to help you 🙂
He never replaced the timing chain so it's the stock one I believe.
 

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Discussion Starter #9
Leave the floats as they are, don't touch a thing..!!

Start with the simple things first..

First off, tell us what you know about the ATV, top end build for example.. is it a big bore mod? Is the exhaust stock or aftermarket? How about the inlet... Is it modded? Is there a aftermarket CDI fitted or a tuner? How about the spark plug, is it stock?
Carb jets and carb.... Is the carb OEM? Are the jets OEM, are they stock sizes?

Timing gears and chain... Are they OEM parts or China junk? Are they new?

So many possibilities.. Help us to help you 🙂
It also has a backfire issue when it idles I have a new plug, but no tool to remove it. It has a bog half way up the power band, but it clears up, when I take the airfilter off it seems to help. Now it bogs with any throttle and removing the air filter doesn't help or choke. The gas/air screw is 2 1/2 turns out. It always fires right up
 

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The words Newc carb and cheap don't go well at all.. Sounds Chinese to me especially as you mention a backfire..
you need to rebuild the OEM carb and fit it for optimum performance. You should also replace the timing chain, doing a top end build and using the old chain is a real half ass job!
 

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Discussion Starter #11
The words Newc carb and cheap don't go well at all.. Sounds Chinese to me especially as you mention a backfire..
you need to rebuild the OEM carb and fit it for optimum performance. You should also replace the timing chain, doing a top end build and using the old chain is a real half ass job!
I'm gonna rebuild the oem carb right now and I'll install it in tomorrow. I don't have the funds to replace the top end, but I will replace it when I can. Until then I'll just do the timing chain. Also is it okay to use an oem chain with a hotcams cam? I can't seem to find a hotcams chain.... Am I better off leaving the top end as it is or using a wiseco kit?
 

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If the top end has good compression then go with it, it works. OEM timing chain or DID are best, the chain won't change with the cam.
 

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Discussion Starter #13
If the top end has good compression then go with it, it works. OEM timing chain or DID are best, the chain won't change with the cam.
I used the stock carb and it runs like crap. I've been adjusting the fuel screw and at 2 1/2 turns out it smokes and purges. All the way in it doesn't want to run and 1 turn out it purges. When I removed the cheap carb the fuel screw was completely gone but it ran.
 

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Discussion Starter #14
If the top end has good compression then go with it, it works. OEM timing chain or DID are best, the chain won't change with the cam.
UPDATE!!!!!!

I took the new carb (not the stock one) and tore it apart. The main jet managed to come undone within the bowl so I put that back in and also it was missing the fuel/air screw. I put all the factory settings and put it in and it runs like a top. No more bog at all it runs like a bat out of hell. It does have a sputter at an idle so I'm gonna change the plug when I get the tool in Monday
 
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