Hi folks, I'm new to the forum and need some help with my new Speed Demon carb. The basics: 1969 383, stock heads, purple cam[specs unknown], headers, performer rpm intake, 74 stock electronic ign. , with a speed demon 750 vacuum sec carb with their idle-ease adjustment. All basic settings are set per the manual, fuel is at the bottom of float window. The car will start and rev cleanly with ether but with gas it floods, cant even get it to idle. Will only run for a few seconds at a time while jazzing the gas. The rare times I've gotten it to idle by screwing open the throttle blades, the idle mix screws are useless. Any help out there? Thanks, Scott

 

Was the engine able to idle with another setup? [befor you went to this carb] or is this a fresh build. Maybe a giant vacuum leak somewhere?
If the cam seems large, bump the initial timing up 5 or 6 degrees [12*]
Check the pcv valve.
6 to 7 lbs. of fuel pressure.
Check firing order.

 

Wires, triple checked, timing at 10-12 degrees. Came with victor jr intake and leaky gummed up holly. Installed performer rpm and 750 demon. Checked for vacuum leak with starting fluid but couldnt reach underneath between intake and valley pan. Pvc is hooked up to carb basplate, all unused vacuums plugged. Regarding fuel pressure, if it was too high, wouldnt it be raising the float level and coming out the overflow/vent tube? Or is there a fuel passage drilled before the fload needle that would allow it to flood without affecting the float level?

 

No other passages unless the power valve is bad.[dont think thats it]
I was thinking that the pressure might be high, but just a little, enough to force extra fuel through the jets. What pump are you using?
Do you have a manual choke or electric?

 

Factory mechanical pump and electric choke.

 

Just got a return from my question to barry grant tech. "Just the basic stuff, recheck everything, rebuild the carb,did I check the air in the tires"etc. Not very helpful. But they did go back to the fuel pressure issue. In my view, if the fuel pressure is not blowing the float needle off of the seat,and raising the float level, how can the pressure be an issue? Unless someone out there comes up with the magic bullet, I guess I'll start with a pressure guage and move on to arebuild after that.