Vintage Dirt Bike Q & A

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PostPosted: Sun Aug 03, 2014 11:52 pm 
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Joined: Tue Mar 11, 2014 8:59 am
Posts: 10
I bought a 84 IT490 the other day. It sat in a garage for two years untouched. The PO said he rode it twice and got hurt both times is the reason it sat. I brought it home started at the tank and worked my way down cleaning the varnish out of the entire fuel system. Checked spark with new plug, blue but not real good. Added 24:1 fuel mix and started kicking. It would just pop about every 20 kicks, did this a long time and finely it started. I let it warm up and took it up the road a mile and back. It idled good and had no hesitation when I cracked it. I pulled in the garage had trouble finding neutral and stalled it and it won't start back up warm or cold. Can anyone help me with this starting problem?


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PostPosted: Wed Aug 13, 2014 1:19 am 
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Joined: Fri Jan 24, 2014 12:39 pm
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First thing I would do is check the compression with a gauge. If thats good I would check the stator and see if it is up to specs. Often a weak stator will not fire when kicked but may start if roll started down a hill. Low compression can do the same thing. You can also check the reeds. If one is broken it wont start. I would check the left crank seal if all those things are good. It may be bad or even popped out. Good luck.


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PostPosted: Tue Aug 19, 2014 1:41 am 
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Joined: Mon Aug 18, 2014 2:23 am
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Hi
i have got 2 IT490s checked the compression on both bikes round about 60psi i think they need to be about 130 psi. The one runs fine but still troubleshooting the other one to get it to start.Does anyone know what the optimum PSI compression should be not the ratio but the actual compression .Possibly need to do top overhaul. :shock:


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PostPosted: Wed Aug 27, 2014 6:04 am 
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Joined: Sun Jul 22, 2012 6:03 pm
Posts: 56
130 PSI would be on the low side. Most bikes have over 150 PSI and after a rebuild some are over 200 PSI. It depends on how the engine is manufactured as to how much it has.
Put a tablespoon of oil in the spark plug hole and check it again. You should see it increase dramatically. Probably enough to make it crank.


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PostPosted: Mon Sep 22, 2014 12:38 pm 
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Joined: Tue Mar 11, 2014 8:59 am
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My top end was worn out. Got machine work and new piston and rings. Got ready to put back together and noticed oil in bottom of crank case not much just touches the fly wheel. Is this a bad crank seal or is this normal? If crank seal is bad do I have to spit the cases to replace?


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