1984 yz490

[jaykup]

I recently picked up a 1984 Yamaha YZ 490, and it doesn't want to go over idle.

I replaced the plug, cleaned out the already clean carburator, dumped out all the old gas, and cleaned out the petcock and fuel lines.

Its very hard to start, and once you do, it idles really pingy (don't know if this is how it is supposed to be) and when you give it gas it revs a little, but wont get into the higher RPM's and if you try to take off it just dies everytime, even riding the clutch.

The exhaust right off the head leaks, probably half the exhaust (suggestions for fix as well) and the "intake manifold" between the carb and the head seems to be leaking under throttle, like you can see a little bit of bubbles between the seams.

Also, there is a hose coming out of the "intake manifold" thats a good 1/2 inch diamater and its just tapped off.

Last thing is after it runs for a while, gas starts dripping from the air box.

I'm thinking reeds? Its got great compression just by feel, but I didnt test it. I don't know how reeds work, or really even where they are, but I'm guessing they kinda work like valves? Maybe they are stuck/broken?

Any ideas??

[CHAD]

Your reeds are right before the head on the intake side. no leaks are good, i'd fix those leaks then see how it goes, and check your reeds too.

[jaykup]

What am I looking for with the reeds?

[CHAD]

check to make sure they aren't stuck open, broken, cracked stuff like that.

[Kane]

That taped off hose used to connect to a boost bottle. Intake leaks will definately make the bike a bitch to get running right. Fuel pouring from the airbox could be floats needing adjusting or reeds not closing. If it leaks thru the airbox when not running, floats need adjustment. If it only leaks from the airbox when running, the reeds arent closing. Exhaust leaks are real common. Don't sweat it till it's running right. Get that intake sealed.

[jaykup]

thanks, I will try working with that. for the intake, is that a gasket there that needs to be replaced? also, there is a boost bottle sitting there, but I dontk now how well it is hooked up.

thanks, and i will let you know how it all goes.

[jaykup]

i think i am thinking of something else, the bottle goes to the suspension. the air line that was from the intake goes to some seperate air box under the gas tank that is missing.

i tore the intake apart, and it seems one of the reeds (out of 8) is broken off. the thing that worries me.. is where is it? did it get sucked into the engine and just melt or what??

i ordered new reeds and they should be here thursday/friday.

also the intake leak appears to be from both the reed being broken and one of the corner bolts only being hand tight.

hopefully everything turns out ok!

[flotek]

for shits and giggles look inside your intake box and see your cylinder walls and pisto n and rings whats that stuff look like t o you?