Choke setting at start up

[Halstead666]

Hello, New guy here......I have a 1996 v-8 5.7 mercrusier that starts a bit rough. i recently rebuilt the carb (2brl) following Mike's carb rebuilt instructions to a tee and have the mixture screw set at 1.25 turns and idle screw at 2.5 screws. When cold Choke plate open from running the previous day but closed completely just prior to start up, following start up procedures I pump throttle in neutral fully once and leave it 1/4 open, when doing this the choke plate is kicked up a bit as per instructions although it then closes completely. I usually have to pump a couple of more times before I can get it to turn over and it runs very rich as I just dumped more gas than needed to get it started. It runs rough as The choke plate opens up as engine warms up over the next few minutes and the black smoke it cleared. It seems that the choke plate should remain open on the initial bump with the throttle.......currently the choke setting is at 2 to the right more lean setting..........I am wondering if I should set it so the plate opens and stays open slightly during start up which is quite a further setting then the 2 to the right?

 

[CFM56-7]

Hello! The idle cam is attached to the choke actuator. At idle, the idle screw applies pressure to the idle cam which basically pins the choke into position. When you move the throttle off idle, you relieve pressure on the idle cam and allow the choke plate to move to the position dictated by the choke thermostat spring. After this initial throttle movement off idle, throttle position no longer has any affect on the choke position.

If you are seeing lots of black smoke at startup, I would recommend moving the choke thermostat to a more open cold position. If my throttle is off idle, and the choke thermostat is close to 70 degrees fahrenheit, my choke plate is just slightly open. She starts easy and idles smooth after a brief warm up.

Good luck!

CFM

 

[Halstead666]

Thanks for responding, my choke plate closes when the cam is released then kicks open slightly when the throttle is fully extended, but when I bring the throttle back up it closes completely. The suggested setting is 2 lean (more open) position. In order to get the plate to remain slightly open I need to keep turning past the 3rd setting and what would be maybe a 5th or 6th setting (if there were ones). I guess it does not seem correct to move it so much more than directed, is that normal?

 

[CFM56-7]

When the throttle is held wide open, the choke unloader activates and if set properly, should open the choke just ever so slightly. This feature enables you to work through a flooded start condition. After the throttle comes back from the full position, the choke unloader tab is no longer engaged and the choke plate returns to the position commanded by the choke thermostat. When you pump the throttle once prior to start, you are unloading the idle cam so the choke is set, and activating the accelerator pump to prime for the start. Hitting the choke unloader at full throttle happens when you do this, but doesn't do anything to the choke for your start unless you are cranking with the throttle wide open during an abnormal flooded start.

I'm not sure what is normal, but that is what it took on my Mercarb after I put an after market rebuild kit on it. I had the same rough start, black smoke condition you had. After setting as I described above, she runs like she should.

CFM

 

[Bondo]

When the throttle is held wide open, the choke unloader activates and if set properly, should open the choke just ever so slightly. This feature enables you to work through a flooded start condition. After the throttle comes back from the full position, the choke unloader tab is no longer engaged and the choke plate returns to the position commanded by the choke thermostat. When you pump the throttle once prior to start, you are unloading the idle cam so the choke is set, and activating the accelerator pump to prime for the start. Hitting the choke unloader at full throttle happens when you do this, but doesn't do anything to the choke for your start unless you are cranking with the throttle wide open during an abnormal flooded start.

I'm not sure what is normal, but that is what it took on my Mercarb after I put an after market rebuild kit on it. I had the same rough start, black smoke condition you had. After setting as I described above, she runs like she should.

CFM

Ayuh,..... Great post,.... Many folks don't understand that,.... Proper Choke operation,.....