Rebuilt demon carb - now car won't start? But runs fine

After being in service for 10 years on California crappy gas, I decided to rebuild my speed demon 750 carb. I bought a basic rebuild kit (gaskets, needles, floats) and did the job methodically. Now, before I took the car apart, it was running fine, and would fire up at the first turn of the key. I put everything back together, and now it just will plain not start.

I did not change timing, and I checked that I do have spark while cranking. I can reliably get the engine to fire with starter fluid, and so I got the car running and tuned real nice. The driveability is great, idle is awesome, and I’m pulling good vacuum (indicates no major leaks). Once the car is warmed up it starts awesome. It just will not start cold. I checked the choke and it is adjusted OK. Is there something I could have screwed up during the rebuild? I am at a total loss what to check next. For the life of me I can’t figure out how I can have the carb dialed in and working awesome, yet the car won’t start when cold.

Engine combo is a 383 big block, 10:1 compression iron heads with a 230 @ .050 solid roller cam.

Float bowls draining dry when sitting for a while? Sound suspicious for this given that fires right off when warm. What does accelerator pump put out when pumping accelerator when cold? Leave air cleaner off when parking in garage after a run. Can you smell strong fuel odor?

Never owned a Speed Demon carb, have no guesses as to what may be wrong if bowls are running dry except usual gasket or loose fitting inside carb.

Float levels ok?

go through the basic tune once more, setting float levels and especially getting the idle mixture right when it's warm.
imo the correct idle mixture is extremely important in how fast a car fires off.

if that doesn't help, then make sure all yr fuel lines are tight and there are no places you could be leaking fuel. vacuum leaks too...

I forgot to mention that the float levels are properly adjusted. However I'll go over them once more.

I think what concerns me the most is that it doesn’t even want to try and start. Even if I pump it a few times it doesn’t even try and catch. Usually when a carb has been way out of adjustment the car will at least cough and sputter. This time there’s nothing. It acts like there’s no spark – but I’ve checked that. Then once I spray starter fluid, it fires OK and once warmed up, acts totally normal.

i started driving a truck that hadn't been driven in a while. it mostly ran fine, had a demon carb too. but sometime it wouldn't start when cold. not sure what the problem was. i think it was flooding.

another thing it would do, if i would really get on it and get the secondaries open, it would die (while driving) and wouldn't start unless i shot some starter fluid down the carb. i changed the fuel pump and that fixed that.

Is the accelerator pump shooting a good squirt of gas?

Check the choke setting

I’ll check the accel pump. It is working while driving, but I‘ll push the throttle and check for a strong jet of fuel. Good call, if the pump shot’s not working then there is no extra fuel when cold to start it. Which makes sense because I can pump all I want when starting and it doesn’t seem to help.

next time BEFORE you crank it, pull the air cleaner, open the choke & pull the throttle several times & see what you get for an AP squirt. Also when you open the throttle see where the choke stat wants to close the choke plate to

I am guessing the choke is not working or not hooked back up correctly.

Next time its cold, pump the heck out of it and then pump it some more. Bet it starts....

good call on the choke, my carbs don't have them.

another thing you could do it hold the choke open somehow and then give the car a pump or two and see if it fires off quickly.

I live just down the road a bit from Oakland where op is from. Never ever have I used or needed a choke to start any of my old carb'd cars. Temperatures almost never hits freezing levels around here. In fact have always had chokes disabled. Of course all bets are off if I go up into the mountains in the wintertime.

Still suspect dry fuel bowl or accelerator pump as in my original post. Accelerator pump is a long shot as op says runs well when it does start and engine warms up.

Again, pull air cleaner and have a look see into carb while pumping gas pedal after car has sat for a while and won't fire off.

Thanks all, it turned out to be the accelerator pump. During my rebuild I had not seated the small diaphragm 'check valve' correctly. So it required lots of pumping to build a prime and work. Somehow once the car got running it would squirt enough that I didn't notice. Anyways I took the front bowl off and got it fixed, squirts fuel like a banshee and car fires right up.

Glad you got it figured out. Sometimes it's the little things that drive us crazy.