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Carb Guys, I need help

8

84mudmachine

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Dec 23, 2003
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I bought a rebuilt 750 q-jet this summer, and it is having some problems this winter. This summer it worked great, but when it turned down below 30 this week it wants to die after it warms up. I go out start it up and let it idle on high for a minute or two and then kick it down and let it warm up for about 10 munites. I drive about three blocks to let my daughter off at school, then it whats to die. I have the choke set right about in the middle, and the trucks idle seems a little high. I don't know if the idle set too high can cause problems or not. I read through the book I have on the blazer, and it tells you how to bend rods to adjust the choke, but I don't know if you have any ideas that I can try. /forums/images/graemlins/dunno.gif
 
Set the choke tighter, with the engine cold there should just barely be a gap between the choke butterfly and the back wall (1/16-1/8). Then adjust your fast idle screw to get your idle set. This is underneath the choke linkage on the passenger side.
 
You should check to make sure that the choke pulloff module is working. It is the module located on the passenger side of the carb, should pull in when you start the engine. /forums/images/graemlins/thinking.gif
 
I checked that, it working. Can you have your idle set too high and have it cause a problem? I have a electric choke and have it set right before the center mark on the choke. I have the fast idle cam set faily high, could this also cause a problem. I think I need to install an rpm guage so I can see what I have the idle set at sometime. /forums/images/graemlins/thinking.gif
 
Sounds to me like your choke flap is not opening up all the way when you kick it off fast idle. Let it warm up on fast idle, pull the top of the air cleaner, kick it off fast idle and see if the choke flap opens up.
 
what is the engine temperature when it dies?
a friend had the choke power lead fuse blow and his choke never released
 
I checked after it got up to full temp, and the choke was fully open. WTF /forums/images/graemlins/thinking.gif
 
Sounds like it's too lean. Did you get the same jetting and primary rods in the rebuilt carb that you had in the original? You can try turning the idle mixture screws out (may require special tool, 5 bucks at AZ). If this doesn't enrich it enough you'll need to change out your jets or rods to get a little richer calibration. Of course this is assuming you've eliminated the possiblity of any vacuum leaks. Did the new carburetor come with bushed throttle shafts? If not check for play there. Also of course check the fuel filter, timing, and make sure that the fuel line isn't laying on anything that gets very hot.
 
Tonight I let it idle for about 30 minutes, and no problems. I took it arround the block and I took the corner a little hard, and then it acted as if it wanted to die. I pulled over to the side of the road and put it in park, and it began to idle smooth again. I wonder if the carb is't getting enough gas or that the floats maybe set low. /forums/images/graemlins/thinking.gif
 
I also wonder if the filter maybe bad. the guy who had the blazer before me put a filter between the pump and the carb, is this ok?
 
That filter will be fine, though if he did that make sure you remove the one in the carburetor inlet, running both is unnecessary and restrictive. The float may be set low, or if it does it going around a bend the pick up in the tank may be clogging or coming uncovered.
 
I removed the one in the carb. Could the cold effect the flow of the gas, because this summer it ran great. The pump does look old and for $20 I can replace the pump and filter to see if that may help.
 
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[ QUOTE ]
I removed the one in the carb. Could the cold effect the flow of the gas, because this summer it ran great. The pump does look old and for $20 I can replace the pump and filter to see if that may help.

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Well the choke can be set less agressively in summer . Also AIR is more dense at colder temps , so mixture technically needs reset with extreme weather changes , unless you have fuel injection /forums/images/graemlins/k5.gif /forums/images/graemlins/k5.gif
 
I would say leaner , since the cold dense air helps burn your gas more effieciently , so it needs more gas . At least that whats I remember from the fast car and late night days /forums/images/graemlins/k5.gif /forums/images/graemlins/k5.gif
 
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