Jonsered 490

[Tony Snyder]

490

490 circa 1985. Piston ported, open loop scavanged.

There is no reed valve.

A couple of hints:

I wouldn't use starting fluid. If you must do similiar, use fuel mix.

Unfasted fuel line at carb, tip saw if necessary, but there should be a pretty good small stream of fuel. If it is a slow, drop , drop you probably have, a fuel line problem, a plugged fuel filter, or the fuel pickup has got out of postion at the bottom of the tank and can't get fuel.

Get a test plug, or make one by cutting the side electrode off af a new plug. Take the existing plug from the cylinder and lay it aside. Hook up the the test plug and ground it anyway you can. If the spark jumps this large gap in open air, your ignition is probably O.K.

I'd better stop this, or they may blackball me for teaching propriatary stuff.

 

[stihltech]

490

OK back to basics. We need air, fuel, and spark. Sounds like it is fuel we lack. Carburetor, fuel line, filter. Takes care of delivery. Intake boot? ( sorry not famliar with model, but they all work the same, just different versions). Reed valve? never had one not fire because of it, usually bad idle or top end. Leaking seal or gaskets will cause fuel not to pump.
I know this seems basic, but when one stumps you, the answer is usually there.
Make sure spark is bright and jumps an extended gap. Seen a weak spark keep the plug looking dry, but not fire.

 

[stihltech]

490

Proves one thing snydert, great minds think alike.

 

[johnb]

Saw trouble???

Take the flywheel off and check the keyway on the crank. I had a husky that broke the keyway yet it was tight enough to fire the plug. Only thing was it was firing off time. It wouldn't fire a lick on any fuel. after fixing the keyway it ran like a top. It sounds like everyone else has covered it pretty well. good luck! The Hoosier