i just replaced a burnt intake valve in my 1990 250 4 stroke, it starts good, but will not open up, pleasw help

 

I'm a 2-stroke guy, but I'll try to give you a little help here. Two things to check is the gap between your rocker and the top of the valve. Set to the manufactures recommendations. The second thing could be the cam lobe is worn off, and isn't allowing the valve to open all the way. Had that problem on a Polaris 425 where the cam was starved for oil. I don't know why your valve burnt up, but you may need the cam replaced, just check it with a micrometer, and check in you tolerances in your book.

Oh and the obvious thing to check is your timing, but I'm sure you've done that. Don't know if it can be adjusted on your quad, I'm not to familiar with that model[img]i/expressions/face-icon-small-smile.gif[/img]

 

I checked valve clearance & timing, all is good, when i leaned the mixture , open up, then booged, i think carb. is problem, any suggestions? i found the problem, it was the diaframe ic carb. tks.[img]i/expressions/face-icon-small-cool.gif[/img]

 

Make sure your floats are floating, it kinda sounds like a main jet issue ie: clogged passage way, choke on, to fat of a needle jet position or to fat of a main jet. pull out your spark plug and see how it is running. If there is a carbon build up, or the plug is wet, check your needle jet position. Makes sure the needle is in position # 3 (center) and then lean your pilot and main jet down one, then see how it runs. I had the same problem with my lt230 after i rebuilt the motor, and as far as I know, they both use the same carb and motor, just diff bore.

 

tks. quadsportfreak, i moved needle jet to 4 , adj. air screw 2 turns, works fine now, only problem is starts a little hard when hot. comp. is good.[img]i/expressions/face-icon-small-smile.gif[/img]

 

if it is starting hard whel it is hot, you are running your pilot jet too lean. I fould this out after i rebuilt my quad and it took 1/4 to 1/2 throttle to get it started when it was hot. I would try riding it around under 5/8 throttle, so all thats feeding your carb is your pilot. then check your spark plug. If it looks like it has been sandblasted on the end, then jump up 1-2 sizes on your pilot. Other than that it should be smooth sailing.