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Old 05-21-2011, 12:51 PM   #1 (permalink)
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Default 2003 LTZ 400 Problem

I recently bought a 2003 LTZ 400. The guy I purchased it from was a real prick.. He made it sound like this quad was in mint condition, barely used, mostly collected dust sitting in his garage. So after an hour and a half of driving to go get this quad its a bit beat up, but anyway... I am having trouble keeping this thing running. There are no real mods to it other than the intake snorkal baffle thing being removed, the exhaust baffle out, and the fuel screw turned to 3 turns out.

This is whats happening:
I turn the choke on and crank over the motor.. after about 5 seconds or so of cranking (long time to have to get an engine started) it'll finally start up (Won't start up at all without the choke), but it wont stay running for long. You'll hear when it starts that the idle isn't really going crazy, but its kind of dropping and raising about 100rpms which is usually normal for when the choke is on. But after about 10 seconds or so of running, the engine will rev down a little bit (about 400rpms) and then the motor stalls and there is this like "BANG!" sound come from the motor, as if the engine slammed to a hault..

This only really happens when it's idling. If I start it up and take off right away, i'll get going, but the quad will bog down a little bit as i am driving and when i let off the gas it'll pop like crazy. And once I get back down in the revs towards idle the engine stalls and makes that "BANG!" noise again. I thought maybe the carb was clogged up, so I cleaned it. I also drained the tank and refilled with premium 93 octane, haven't changed the oil yet because i am waiting on my oil filter to come in the mail along with some other parts to make it look a little better cosmetically. I also just changed the spark plug today, I pulled out the CR7E spark plug that was in there and it was completely black and looked as if it had never been replaced before. I replaced the CR7E with a CR8E since the auto parts store was out of 7s.

The previous owner of this quad was a real moron.. He hard wired the radiator fan so it would always be on, and he cut the temperature sensor light in the process because he was too much of an idiot to test which wire coming from the radiator was for the fan, and which one was for the temperature.. anyway, those are both fixed now, but i'm really concerned about the way this thing is acting. I'm going to do a coolant flush soon, I have a container of engine ice, I just need to get some distilled water to flush out the cooling system with.

Sorry for writing all you guys a novel on here lol, hope someone can help me with this problem....
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Old 05-21-2011, 01:00 PM   #2 (permalink)
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Also, how much noise is there supposed to be in the top end? I just came off a Yamaha Raptor 250, and those valves ticked so loud that I could hear it through my helmet as I was riding. I understand that there is supposed to be some noise coming from there because of the valves and cams and everything, but I just want to know how much is too much..
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Old 05-21-2011, 01:47 PM   #3 (permalink)
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If the guy was a prick I wouldn't have bought it. Sounds like it needs a timing chain or valve adjustment. I would also clean out the carb really good and check the intake boot for dirt. This is where I would start.

After buying my 04 heavily neglected I will probably just buy new next time since I spent more redoing it than a new -z- would have cost. It was nice building it how I wanted it though.
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Old 05-22-2011, 12:13 AM   #4 (permalink)
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The only reason I say the guy was a prick was because he had my father drive out an hour and a half to buy a quad that was supposed to be in "great condition" that turned out to be a real turd. Ended up getting the quad for $1600, so I guess it's not too bad, as long as I can get the thing to run, and fix it up a little cosmetically.
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Old 05-22-2011, 12:41 AM   #5 (permalink)
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I am really hoping that the timing chain does not need replacing, that would be a real pain in the ass. When I can get the quad to actually sit there and idle once its really hot, and the idle is turned up a good bit, it doesn't sound like there are any loud rattling or ticking noises coming from the head. But who knows? after riding the Yamaha for over a year, I can't tell whether or not a tick/rattle should be there, and what a normal "loud" rattle or tick sounds like......
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Old 05-22-2011, 12:46 AM   #6 (permalink)
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Don't feel so bad, great deal, I paid way more for mine. It had some performance parts installed though. I've had to do tons of work on it too. I would get a service manual and make sure the carb is in spec. Also check your exhaust, it might need some work.
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Old 05-22-2011, 08:10 AM   #7 (permalink)
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you need to properly jet the carb for the mods (pilot screw being turned out is only enrichening the pilot circuit, and by the sounds of it not enough)

OR

put the snorkel and baffle back on.
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Old 05-22-2011, 08:21 AM   #8 (permalink)
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Quote:
Originally Posted by zookie400 View Post
you need to properly jet the carb for the mods (pilot screw being turned out is only enrichening the pilot circuit, and by the sounds of it not enough)

OR

put the snorkel and baffle back on.
Yes, I know this... But, since the idle was richened up, and the carbretor was thourally cleaned, the thing should be able to idle properly. But it doesn't. I'll get it started, and if i dont choke the thing for a real long time so the idle stays real high and its blocking air flow, the engine just slams to a hault.. Sounds as if it just went fom 1500rpm to dead in .2 seconds
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Old 05-22-2011, 08:27 AM   #9 (permalink)
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Quote:
Originally Posted by energizer1389 View Post
Don't feel so bad, great deal, I paid way more for mine. It had some performance parts installed though. I've had to do tons of work on it too. I would get a service manual and make sure the carb is in spec. Also check your exhaust, it might need some work.
Where can I get a service manual? Are there any free downloadable ones?
What do you mean by "check the exhaust"?..... The exhaust valves?
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Old 05-22-2011, 09:01 AM   #10 (permalink)
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Quote:
Originally Posted by atv4life95 View Post
Yes, I know this... But, since the idle was richened up, and the carbretor was thourally cleaned, the thing should be able to idle properly. But it doesn't. I'll get it started, and if i dont choke the thing for a real long time so the idle stays real high and its blocking air flow, the engine just slams to a hault.. Sounds as if it just went fom 1500rpm to dead in .2 seconds
how do you know its rich enough? your symptoms are describing a lean condition. this is not a new problem on this forum, people are always taking the snorkel or baffle off and wondering why it doesnt run right. keep in mind these quads are jetted on the edge of being too lean at the factory, for emissions.

there is no choke on your carb. there is an enrichment circuit that replaces old chokes. it basically opens up another jet to allow more fuel in, and does not at all restrict air. if you need the enrichment on, the pilot circuit is not getting enough fuel. since you claim the carb is clean, that rules out there being a blockage or fuel level issue so it must be the jetting.

regardless of your symptoms, you should check the valves on a new to you quad. who knows when they were last checked/adjusted.

you say there is a bang when it stops and it slams to a halt. from idle, these engines dont "wind down" when you turn them off...they stop. i dont know what bang you are describing, maybe a video would help us diagnose that.
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Old 05-22-2011, 09:03 AM   #11 (permalink)
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also, the black spark plug would mean you are way too rich, but its probably from running with the enrichment on. the plug should be a tan coffee color.
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Old 05-22-2011, 09:14 AM   #12 (permalink)
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Quote:
Originally Posted by zookie400 View Post
how do you know its rich enough? your symptoms are describing a lean condition. this is not a new problem on this forum, people are always taking the snorkel or baffle off and wondering why it doesnt run right. keep in mind these quads are jetted on the edge of being too lean at the factory, for emissions.

there is no choke on your carb. there is an enrichment circuit that replaces old chokes. it basically opens up another jet to allow more fuel in, and does not at all restrict air. if you need the enrichment on, the pilot circuit is not getting enough fuel. since you claim the carb is clean, that rules out there being a blockage or fuel level issue so it must be the jetting.

regardless of your symptoms, you should check the valves on a new to you quad. who knows when they were last checked/adjusted.

you say there is a bang when it stops and it slams to a halt. from idle, these engines dont "wind down" when you turn them off...they stop. i dont know what bang you are describing, maybe a video would help us diagnose that.
Trust me man, I know about jetting.. Ive probably torn down my raptor about 12 times to keep changing out the jets till it was spot on.. I only removed that intake snorkal because it was getting in my way with pulling the tank off and putting it back on, so i figured i would remove that to make the job a bit easier.. I will try to post a video later on of the quad so you guys can tell me whats going on...
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Old 05-22-2011, 02:22 PM   #13 (permalink)
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Alright guys, so I just got done pulling the top of the head off to inspect cam chain, and valve clearances. I can't tell whether this motor just has no hours on it or if the chain was replaced. Tension is perfect! The valve clearances too are right in spec.. I am relieved that its not an issue with the head! So this must mean that there is some kind of problem with the carburetor, correct?
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Old 05-22-2011, 07:13 PM   #14 (permalink)
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Alright now 90% of my problem is fixed...
Quad starts up, runs strong. The only problem I am having is when I let off the throttle after acceleration, i get the normal burping effect, but it is followed by a "pop pop pop pop pop"..
Do you think throwing in some bigger jets would help out? I've got plenty of Large Round Mikuni Jets laying around from my Raptor..
Also, do you guys always have to use the fuel enrichment switch to get yours started when the engine isn't warm?
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Old 05-22-2011, 07:19 PM   #15 (permalink)
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Quote:
Originally Posted by mikerocks View Post
If the guy was a prick I wouldn't have bought it. Sounds like it needs a timing chain or valve adjustment. I would also clean out the carb really good and check the intake boot for dirt. This is where I would start.

After buying my 04 heavily neglected I will probably just buy new next time since I spent more redoing it than a new -z- would have cost. It was nice building it how I wanted it though.
this is what needs to be done ^
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