I just put a 4 bbl summit racing 600 cfm carburetor on my 66 289 mustang and its back firing threw the carb and its sluggish.i check and set the timing and checked the spark plugs they are beige in color. One thing i noticed is this carb has double the vacuum then the old 2 bbl is it possible that the vacuum advance is causing this problem now that there is twice as much vacuum? Do i need to retard the timing to compensate or advance it? Thank you in advance.

 

I just put one of these on also. Did you time the car whats it set at. Also did you change any of the adjustments of the carb. If so what? Did you check the site glasses to make sure their about half way i had one stick out of the box. Are you also sure you hooked up to the right port for the vacume. For my car the carb was a bit hard to tune in the smallest adjustments made the car go from running great to not wanting to run at all.

 

I set the dwell to 29 and to the 6 on the harmonic balancer i tried to lower the float level by adjusting the screws on top but its still almost at the top of the window the screws are maxed out i believe clock wise is the direction to lower the float. I have the vacuum hoses hooked up right the advance is going to the distributer, the pcv is going to the pcv on the passenger side and full manifold vacuum is caped

 

well thats no good your needles might be stuck what are you running for fuel pressure. I had mine at about 6.5 and the carb did not like it. Droped it to 5psi and no more stuck needles. You might have to pull the needles you should not have them maxed out out of the box they should be close if not dead on. As i said was secondary was stuck open and would just dump fuel on my carb. I would take it out comes right out the top where you adjust the float level blow it out make sure its not stuck. Also to find out how to adj the float level read the manual says right in it directions to rotate and all. Are both of the sight glasses maxed out?

 

Ya both are nearly past the top of the glass. As for my fuel pump im not sure the pressure its just a basic pump nothing special.

 

Well i would fix that problem first. Might just be that your carb is dumping gas down you intake causing some of the problem. Im sure its flooding it when you shut down the car making it take a while to restart, when it should just pop off right away. I had to remove my needle valve to get it to stop sticking open. Idk why but i removed it blew it out pushed it up and down on it a few times re installed it and somehow that fixed it hasnt stuck since.

 

Ill try that. Thank you.