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Discussion Starter #1
Just bought a 86 yz490. I fixed a couple minor problems, but its really hard to start. It takes about 15 minutes to start it. Runs pretty well once started though. I took off the carburetor, looks good inside, i could see most of the reeds, they seemed ok. Sometimes i can turn it over 5 or more times before theres enough compression to have to kick it. Its like a valve is stuck open, but its a 2 stroke. I put a new air filter on, put new gas in it (32:1), and i checked the plug, looks new, however wet with fuel. Help please!
 

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I can't even immagine why you would post that here, but I just happened to have sold my '85 490 two months ago and regretting it.. It was bored to 510 with a wiseco and boyseen reeds, and was almost impossible to kick over. I have a scar on my foot where I decided to go riding with hiking boots and the kickstarter managed to lodge itself in my foot. HOWEVER> The '85 had no compression release like your '86 had (was badly needed, because if you wer'nt over 200 lbs, you were not going to get it to turn over, even whith that huge kickstart. If it runs good wonce you get it going, (the bigger problem being staying on with all that damned vibration - don't worry it's normal) The first place I would look is the CR cable. If it's sticky it won't let the valve close properly. Also, you should check the valve itself. Mabee there is a problem there. You should run down to the yammie dealer and grab a gasket set and pull the cylinder off to take a peek. It takes 20 minuts. That valve may be all gooked up too. That happens, just like the newer bikes and their exhaust valves. Gotta love the gobs of tourq the things put out though. Don't try to rev them, you won't have any sensation in your fingers for hours.
 

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Discussion Starter #6
Ya sorry to post it here, you guys have helped me alot with my 240z so i figured what the heck. I know lots of motor heads ride bikes as well. Ive heard elsewhere that the vibration is normal, its pretty annoying though. What is this CR cable you talk about? I dont have the bike here, but i will be able to take a look at it tomorrow. I cant imagine a 490 without a compression release, im 150lbs and have to pretty much jump on the kickstart to turn it over. The torque is crazy, i took it out on the street the other day, did a wheelie on accident. Its a little unstable at speed as well. Thanks for the info though, tomorrow ill have to search for a cr cable. Where does this cable go between? Also, you talk about it not letting the valve close completely. I was under the impression 2 strokes dont have valves, but ports in the cylinder, You must mean some other valve. Sorry i dont know a whole lot about motorcycles, this is my first.
 

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valves

the valves dylan is talking about isn't the ohc valves like what you're thinking. they're in the intake port. probably more like a reed valve to keep the intake charge where you want it. it's kind of hard to explain without pictures. did you try looking for a web site like this one for two strokes, or other dirt bikes? anyways i don't have much info to help with your problems. could be spark like yo said. change spark plugs, wires and coil. good luck.
madcowz
 

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Re: valves

Ah yes those valves. I know which you are talking about now, i took my carburetor off the other day and saw them in there. I figured there would only be 2 or four, theres like 8 of them in there!
 

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You crazy mo fo!!!!

You decided that a 490 is a good starter bike?????????? Just wait till your riding off road somewhere, casually in 4th, with your hand off the trottle (they seem to make all kinds of power at idol) and you give it a little blip to say half, and end up damned near on your a## because it actually hooked up for once. They can be dangerously abrupt off idol. Anyways, the CR cable I was refering to (from under the clutch lever to the cylinder head) is the compression release cable. Beleive it or not, your 2-stroke has a valve in the head, only opens when starting (when you pull that little lever under the clutch) to release compresssion to avoid wrecking your leg. If you kick it over, and nothing is there, and the valve seems reluctant to close, the thing may not want to run because the valve is'nt shutting at that critical first fire. If It seems to run ok once started, that could be what it is. Also, the timing could be all over the place. They have a little tendancy of shearing the itsy bitsy little key yammaha decided to use on their big flywheel, combined with plenty of vibration, things move, but will still run sparaticaly. Also watch for this on your bike : frame cracks around the upper shock mount, cracks at the bracing behind the head tube, cracks across the transfer ports (nasty, I had'em). I think this vibration thing causes a few crack problems. Anyways, how does it sound? It should rev clean and quick with no bogging. If it has any pinging at all (hope your running 90 octane or better) it could be the timing. Also, as one of the other posts mentioned, check your spark. These bikes like to eat plugs, try a new one when you check. It should be an intense blue ball with a bit of a cracking sound. How does it idol?? Are you choking it on cold start?? Does it do the same thing after it's warm??
 
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