Desperately need help with pit bike

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zpitfighter

zpitfighter

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Alright to save my fingers from cramping Im going to link you guys to my thread on thumpertalk.com that I have been updating with what I am doing. Unfortunately no one is helping me out over there because its a chinese bike. Somebody please help me, could it be possible that my problem is a bad cdi box, it is getting spark because it is starting but Im thinking its a weak spark because it is dieing when I give it throttle. SOMEONE HELP ME! Ima bout to pull my head off with this thing!
http://www.thumpertalk.com/forum/showthread.php?t=1004468
 
Probably the wrong carby for the engine, or the wrong manifold for the carby or the wrong jet sizes mate.
 
Hey mate, firstly welcome to M.R ... I'm thinkin carby as well by the sound of it but it's always hard to say without being able to see the bike. Can ya post a pic of the bike or motor as well ? I only know what jets work on my bikes I'm not one of the gurus here ... but hang tight someone will be along soon ... we got guys here that know what goes on what and what jets to run so relax we'll get her running ... but yeah pics always help.
 
firstly are you sure your operating the choke correctly. if your unsure remove the air filter and check the butterfly.. open is off and closed is on.. these carbs dont like the choke left on..

failing that its now process of elimination. change spark plug, coil, cdi, check all your wiring for good connections and then lastly check the stator plate coil..
make sure you only do one item at a time.

also unplug any kill switches and ignition switches..

now if you go thru all that and still have same result then its fuel related.. maybe even a bad/blocked air cleaner which will starve it for air.. manifold gaskets, orings and the plastic spacers can be a problem too..
 
Alrighty I went out and took some pictures, It is a kc 70, they were sold at pep boys, I believe it is a baja motorsports motor. here are the pics
100_4423.jpg

100_4424.jpg

100_4425.jpg

100_4426.jpg


spark plug has been changed, I will unplug the kill switch. how do I check the connections, I changed the spark plug, and the air filter is brand new that can't be it. How do I check the stator plate coil. I am using the choke properly. btw does it matter what type of cdi I buy, does it make a difference to buy one of those racer ones or just get a regular one?

EDIT: Just ordered a new cdi, and coil
 
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the plastic carby spacer with the o'ring is missing from between the carby and manifold.
it's possibly is getting a vacuum leak there.

craig
 
also where is the pipe that runs off the intake manifold go to? is it to a boost bottle?
there are no air leaks there? splits in the hose, cracks in the seam of the bottle etc

start the bike and let it idle,
then grab some wd40 spray or crc or even carby cleaner.
spray it on all the joins where the carb meets the manifold, and then manifold to head.
if the idle changes in any way at all when you spray it, there's your vacuum leak.
replace that gasket or seal then try the spray trick again
once you have it sorted, you will need to adjust the air screw to set the mixtures and get some response when you blip the throttle.
the needle in the carb ma even need the clip raised of lowered to get the best out of it.
if you do move the needle, the air screw will then need to be adjusted again.

goodluck, and be sure to post an outcome after trying those things out.
craig
 
The tube that runs off the manifold runs to what I think is some time of emissions control, ill take a pic of it. And Ill run through that stuff today. Im assuming that this is what I need between the carb and the mani,20mm INTAKE MANIFOLD GASKET SEAL PIT BIKES CRF XR 50 70 | eBay

I couldn't get it to idle long enough to test to see if there is a vacuum leak, Ima go ahead and just order the gaskets, considering I need them and I don't have them. Ima try and take a video later of me trying to start it and what happens, that might give you guys a better idea.

Here is a video of it, some times it will run longer, but it always dies out. when I get it to run here for a second I am giving it throttle, then after I try to get it to idle on its own but it won't, sometimes it does sometimes it doesn't
trying to start pit bike - YouTube

I got it to run at an idle, ill see if I can do it again and get it on video

Edit: so there is not rubber spacer between the carb and mani, and there was not gasket between the mani and the head, I did the little spray trick, and it might been in my head but I think I might of heard a difference, I ordered the gaskets, along with a new cdi and coil so we will see what happens
 
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^^^^ that'll do it every time...

i saw on thumpers you said you'd buy some gasket material and make some gaskets.
i presumed you had done this for the carb / manifold.
mentioning you have no gaskets there, earlier, would have had things diagnosed a bit quicker i think.
while you wait for the new gaskets to arrive, pull the manifold off and make some.
just use some cardboard from an old cereal box, couple of layers thick on each end of the manifold.,
cutout the holes to suit.

the new manifold spacer may reqiure new longer bolts, i cant see from your pic if your bolts are long enough.
the new spacer is about 5mm thick.
dont over-tighten the carb-manifold bolts after fitting the plastic spacer either, the spacer will crack easily, and you might lose bits down the manifold into the head.
 
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so not having a gasket on either of those would def cause something like what was in the video, using cardboard to test it won't hurt it right??? so hopefully the gaskets and cdi, and coil should make it run like new!?!?!?! I really honestly just want to get it fixed and out of my hands so that I can get my yamaha far


btw the bolts are plenty long
 
well the make shift gaskets didn't help at all, things seem worse now, its almost like Im getting no spark because I know Im getting gas and its a new plug, I'm just hoping when the real gaskets get here along with the cdi and coil it will work.......if not I don't know what ima do
 
i have run home made gaskets to get me out of trouble plenty of times, without a problem
in fact some are still there years later, lol
maybe wet them up with some oil to help them seal.
how accurate did you make their shape?

what gap do you have on the stators' pulse pickup to the flywheel?
pull the cover off the lh side of the motor , sprocket side (2 or 3 bolts usually) and have a look at the small black magnetic pickup to the rh side of the flywheel,
there will be a green and a blue (or white with blue stripe) wire coming out of it
turn the motor over by hand and check the gap when the little bump is lined up with the pickup. it should be about .12mm or a slightly bigger gap, just enough so it doesnt touch
these 2x things will give you the best spark

do you have a multimeter? if you dont, grab a cheapy ( under $10 from your local hardware or electronics shop)
if so check the measurement of the pickup running off the stator
set the multimeter to 200 Ohms,
unplug the wiring coming from the stator and put 1 lead from the multimeter to the green wire the other lead to the blue or the white with blue stripe
(depending on your wiring colours)
you should get a reading of approximately 100 - 130 Ohms give or take..., if so that is good
if not within that range, and you get a high reading or low reading you need a new stator or just the pickup at the least

with the sparking issue,
what size gap are you running on the spark plug? .7mm or .6mm recommended
pull the plug out and kick it over with the plug still connected to the coil and the plugs' electrode sitting on the motor, a bolt that holds a side cover on is a good earth usually.
check for a good blueish spark.
a faint tiny yellow spark is no good,
sometimes i need to cover the bike with a rug/blanket to make it dark and put your head under to actually see the spark it is so bad/faint
could mean you have a faulty coil, a faulty coil earth (take it off and rub back any paint under the mount with coarse sandpaper to help the coil earth properly)
a faulty spark plug lead,
a faulty cdi,
a faulty kill switch (you can just unplug it, then kick start it to see if it makes a difference, then plug it back in to turn the motor off)

post up your findings

craig
 
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I don't think there is a problem with the kill switch seeing I used it when I had the motor idling and it killed it and then when flipped back aloud me to start it again. I do not have a multimeter, but will get one if it comes to that, I will check the measurements between the stator plate, and the contact point on the flywheel. the new coil, cdi, and gaskets should be here by friday my guess. The make shift ones were not perfect, my cuts were pretty dang close.

Edit: alright I just went out to check my spark and I believe we I might have found the issue, ugh I feel like an idiot. I took the spark plug out and grounded it to a bolt, no spark at least that I could see. just to make sure I was testing it right, I took my weed eater which I know works, and grounded the spark plug to the socket wrench, I got a nice little blue spark with that. After that I took the plug from the pit bike and grounded it against the socket wrench and still no spark at least that I could see. Im thinking I might have a bad cdi, or coil, which I have in the mail. is it possible for me to have little to no spark and still get the engine to start like I was???
 
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a bad coil or stator will spark when ever it wants to.. you got the coil n cdi coming so hopefully that does the trick. if it doesnt then move on to testing the stator.

i had a bike the other day give me spark while testing but yet wouldnt fire. rechecked the spark and it was gone.. replaced the stator and bingo all good
 
is it more common for the cdi and coil to go bad or the strator???
 
I personally view the coil as the easiest to go bad.

Especially with all these dodgey cheap ones, I've had a few bad in my experiences
 
Just wondering hahaha, thanks

Edit: well just checked it, and we should be finding out later today if the cdi and coil are the issue, because they should be in the mail today, ok so here is the deal, I got them in the mail today, put the new cdi on with the old coil and gave it a shot, I got a couple of sparks, and then nothing, so I tried wiring up the new coil with out mounting it and still nothing....btw the new coil wasn't an exact fit with the one I have right now, the only difference was the green wire connecter, one was like forked, and the other was a little circular thing. So in order to test it I just made sure the circular thing was making contact with both of the forks. This pit bike is starting to get on my nerves......at least now I know its the stator, only problem is I can't get the flywheel off without a puller, and I really don't feel like spending another 20 on a puller and 20 on a stator, this is just pissing me off. is it possible that the stator just popped out of timing

picture explanation=

this is the old coil, and my current electricals
100_4430.jpg


The new coil which is slightly different from the old, explained better in video which I got cut off on
100_4429.jpg


green wire connector coming from stator
100_4441.jpg


green wire on new coil
100_4437.jpg


Way in which I tried to hook them up to test it, not sure if this works or not??? hopefully you can see what I did.
100_4440.jpg


Video where I try to explain, but my camera cuts me off before I can finish, Im really getting pissed
 
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