I was fooling with my CS-590, which has a CS-620P carb, and I realized it had a dribble hole in the check valve to prevent people like me from leaning the saw out too much. I had read this would make tuning difficult, so I decided to close the hole.
I ordered a new valve (Walbro 86-578-1) with no hole, but in the meantime, I decided to stick solder in the old valve's hole, and it looks like I did not do any damage that would impair the valve's function. I'm having some trouble tuning it, though.
The new valve is here, and there is a second difference between it and the old valve. If I understand the parts I'm looking at, the hole that holds the valve has a tiny gas passage entering it from the side, and that passage has to be lined up very closely with another hole in the side of the valve. If you were to clock the valve wrong or fail to push it in to the right depth, the carb's gas passage would be blocked. It would not line up with the hole in the valve.
The new valve seems to be designed much more intelligently. The ends check out at about 5.43 mm in diameter, but in the middle of the valve, it's a lot thinner. It has a recess machined all the way around it. If you line up the gas passage in the carb body with any place in the recess, gas can go into the recess, travel around the side of the valve if necessary, and enter the opening on the side of the valve.
So why would Walbro/Yamabiko make a valve that has to be inserted to exactly the right depth and be clocked to within a few degrees in order to work, if it's just as easy to make a valve you don't have to clock?
I wonder if it's possible to close up dribble holes with a TIG torch and no filler, without taking the valve out of the carb. I don't know why I didn't think of that to start with. I guess I'm not used to thinking of TIG and brass together.
Maybe the heat is not great for the screen. I wonder if I messed up my old screen by applying a soldering iron.
I ordered a new valve (Walbro 86-578-1) with no hole, but in the meantime, I decided to stick solder in the old valve's hole, and it looks like I did not do any damage that would impair the valve's function. I'm having some trouble tuning it, though.
The new valve is here, and there is a second difference between it and the old valve. If I understand the parts I'm looking at, the hole that holds the valve has a tiny gas passage entering it from the side, and that passage has to be lined up very closely with another hole in the side of the valve. If you were to clock the valve wrong or fail to push it in to the right depth, the carb's gas passage would be blocked. It would not line up with the hole in the valve.
The new valve seems to be designed much more intelligently. The ends check out at about 5.43 mm in diameter, but in the middle of the valve, it's a lot thinner. It has a recess machined all the way around it. If you line up the gas passage in the carb body with any place in the recess, gas can go into the recess, travel around the side of the valve if necessary, and enter the opening on the side of the valve.
So why would Walbro/Yamabiko make a valve that has to be inserted to exactly the right depth and be clocked to within a few degrees in order to work, if it's just as easy to make a valve you don't have to clock?
I wonder if it's possible to close up dribble holes with a TIG torch and no filler, without taking the valve out of the carb. I don't know why I didn't think of that to start with. I guess I'm not used to thinking of TIG and brass together.
Maybe the heat is not great for the screen. I wonder if I messed up my old screen by applying a soldering iron.
