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Discussion Starter · #1 · (Edited)
ok I just bought this quad the other day.

anyways I didnt notice much when riding it, cause I was in a parking lot and also didnt have anywhere to really rip it.

anyways, back at home, in the yard and it will hardly spin a tire, and falls on its face and misses out from anything over idle to 1/8 throttle.

mods are white brothers full exhaust, k&n filter, cut air box and jet kit with 125 main jet.


thats what i started with. cleaned carb, changed the main jet to a 130, with no difference, and to a 135 with no change. still acting up at half throttle, almost sounds like a rev limit that changes slightly with throttle change, but hold it in on place and it sounds like a rev limit, and I know its not the reverse limiter, that sounds way difference than this.

so I started messing with the (pilot?) neddle and notice it was 3 up from the top, so I took it to 5 from the top(all the way) and didnt really seem to change much of anything, so I took it all the way to the top, seems to rev up a little bit higher, but still cut outs really bad.

i checked spark plug, looks decent, maybe a little dark from this larger main jet. also checked spark and it seems decent to maybe a little weak??

I am kinda lost on what to do next, valve lash was checked and was .004 intake and .006 exhaust. right within spec.

anyone have any idea's before I bring a awesome running stock 97 300ex and start pulling parts of it till mine runs right....

thanks in advanced!

here is a video to clear up whats its doing, with everything I have tried, this is about the best its ran yet.
http://www.youtube.com/watch?v=2tKQnTdqeYM
 

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Did you check the rubber carb/intake boot to make sure it doesn't have a hole in it?
 

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Discussion Starter · #3 ·
Did you check the rubber carb/intake boot to make sure it doesn't have a hole in it?
I didnt see a hole, and spraying carb cleaner(ran out of starting fluid) didnt seem to change much.

now my question is, there is 2 tubes coming off the carb, are they both vent tubes? cause both were connected to nothing at the other end...
 

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Did you check the rubber carb/intake boot to make sure it doesn't have a hole in it?
I didnt see a hole, and spraying carb cleaner(ran out of starting fluid) didnt seem to change much.

now my question is, there is 2 tubes coming off the carb, are they both vent tubes? cause both were connected to nothing at the other end...
I think the 300EX has a vent line on the carb body and a overflow/drain that comes off the carb bowl.
 

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The valve adjustment is wrong. .004 on both intake and exhaust I believe to be correct same as the 250X until 2007. you are correct on the lines Helmut pull the air box lid off and see how it runs also check your choke lever make sure it's all the way down they have a tendancy to wear on the plate that holds the lever
 

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The valve adjustment is wrong. .004 on both intake and exhaust I believe to be correct same as the 250X until 2007.
Yep, that's correct, both valves should set at 0.004 according to my factory service manual.
 

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Discussion Starter · #9 ·
ok both set to .004, with no changes in how it runs.

after throwing big jets at the carb with no difference, me and a buddy are starting to think weak spark... is there problems with these coils often? or the CDI boxes??

hope to get a good running 300ex over here tomorrow and start swapping parts lol
 

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I guess it's possible that it could be a bad ignition coil or a bad stator. I doubt if it's the CDI, because usually when they go bad, they go bad all at once and the ATV just won't start.

Did you pull the sparkplug and check your spark? You should have a good, bright blue spark. If it's orange or red looking, it's too weak.
 

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Discussion Starter · #11 ·

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I would say that would work fine.
 

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CHeck the resistance in the coil and in the coil wire have you tried running it without the airbox lid? you should only be jetted at about 130 main and 40 on the slow jet with 3 turns out from seat on the pilot with the little mods you got.
 

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CHeck the resistance in the coil and in the coil wire have you tried running it without the airbox lid? you should only be jetted at about 130 main and 40 on the slow jet with 3 turns out from seat on the pilot with the little mods you got.
My factory service manual don't have a resistance test for the coil, it just has the peak voltage test. I've noticed the old manuals have resistance tests for the ignition components, but the newer manuals just have peak voltage tests.
 

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Discussion Starter · #15 ·
heading over to my buddies house in the morn that has a good running 300ex and doing some parts swapping in the morn, with the coil being first.

I will let you guys know what turns up....
 

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CHeck the resistance in the coil and in the coil wire have you tried running it without the airbox lid? you should only be jetted at about 130 main and 40 on the slow jet with 3 turns out from seat on the pilot with the little mods you got.
My factory service manual don't have a resistance test for the coil, it just has the peak voltage test. I've noticed the old manuals have resistance tests for the ignition components, but the newer manuals just have peak voltage tests.
Yeah I noticed that in the 300EX manual I have but I would think you could still check the resistance between the 300EX coil and the 250X I will post the procedure on my 250X after church. I'm pretty sure the coils are the same?
 

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CHeck the resistance in the coil and in the coil wire have you tried running it without the airbox lid? you should only be jetted at about 130 main and 40 on the slow jet with 3 turns out from seat on the pilot with the little mods you got.
My factory service manual don't have a resistance test for the coil, it just has the peak voltage test. I've noticed the old manuals have resistance tests for the ignition components, but the newer manuals just have peak voltage tests.
Yeah I noticed that in the 300EX manual I have but I would think you could still check the resistance between the 300EX coil and the 250X I will post the procedure on my 250X after church. I'm pretty sure the coils are the same?
Yeah, I would say that they are the same coil. As long as you have the specs for the resistance test, it should work.
 

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Measure the primary coil resistance between the connectors you should read 0.1 - 0.2 ohm at 68 degrees F. Then remove the boot from the spark plug and measure the secondary coil resistance between the plug boot and green terminal you should see 8.8 - 14 k ohms. If the resistance is out of range unscrew the boot from the wire and measure the secondary coil resistance you should read between 5.8 - 7.2 k ohm if it's out of spec then the coil is no good.
 

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Yeah, it could be just the sparkplug cap/boot bad, too. I've seen those go bad and cause the same symptoms you describe.
 

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Discussion Starter · #20 ·
well tried everything that could unbolt off the perfect running 300ex. coil, both black boxes, the carb, rectifier box. battery.

out of idea's at this point. quad runs way worse trying to ride it rather than sitting there with it running. starting to think maybe it jumped time??? what do you guys think?
 
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