More carb fun

When rebuilding the YF carb for a 74 w/258. There is the metering rod screw inside that is an adjustment you make typically when you rebuild the carb. IIRC you push down on the pump until the needle seats and turn the screw the specified number of turns.

Questions are:

1. How many turns of the screw should you do?

2. What does this adjustment change?

3. What are the symptoms of this adjustment being wrong?

Sorry about all the questions on a Monday morning...

 

Back off idle speed screw until throttle valve is completely closed. Then bottom metering rod and then turn screw 1 turn. This is initial adjustment and is somewhat sensitive, although I have never had one need more than 1 more turn(usually 1/4 turn or so either way more). This screw adjustment can sometimes help eliminate "stumble" upon initial throttle opening.
PS. I still will get that spring linkage bracket sent to you, I thought that I had 2 styles but can only find 1 style.

 

Thanks Cam. Thats sort of what I thought. It almost seems like this acts as a accel pump adjustment. I know it has to do with the meetering rod, but the more turns on the screw the bigger the pump shot right? Or do I have that backwards.

 

The metering rod has mechanical assistance and also utilizes vacuum to lift it off it's seat thus enrichening the mixture. It is a taperered or stepped rod to control mixture at all speeds except idle. I guess I would say that it more operates in conjunction with the accelerator pump. I don't think the adjustment changes the size of the pump shot, it just enrichens the mixture more. (sort of accomplishes the same thing) When the adjustment screw is backed out it does make it richer. Hope my convoluted explanation makes some sense.

 

It makes sense. I am thinking about opening her up and turning it in 1/2 a turn as I think she runs rather rich. When I throttle it to about 2500 RPMS it runs ok but it is really not running to smooth. It just sucks that you have to have a bunch of gaskets it on you if you want to make a few adjustments.

 

If it is running too rich you want to close(tighten) the screw, thus lowering the metering rod. Also you can most of the time get by reusing the gasket if it isn't damaged.