Very hard cold starts after dyno tune

[EMCD]

My 408 stroker has been dyno tuned and since I changed from the 670 Holley to the 770, it's a bear to start when cold. The 670 would fire up great, the larger carb won't run w/o my foot on the gas. It also shakes and acts very unhappy when it warms up. Any clues?

[jimynick]

Does the carb have a choke? Do you apply it fully or partially? Do you have a pressure gauge at said carb to determine if you have the appropriate fuel pressure at it? Have you experimented with different starting procedures? Some like nothing, some like one kick and some want 2 or 3 kicks, try some out and see. From the rough running comment, it may be rich; is there black smoke upon start up? Perhaps just putting the pedal to the floor and holding it is what it wants. Look down the carb-wearing safety glasses- and see if there's fuel dribbling out the boosters at idle. That's a few thoughts, anyways. Good luck 

[EMCD]

It has an electric choke like the 670, but that carb warmed up and started the car on the first click w/o any troubles. The car smells rich, but it always has. The dyno outputs said I wasn't running rich, but it smells like a old carb car.

[brads70]

I bought an A/F ratio gauge. I've found it to be a great tell tale/ tuning aid?

[Chryco Psycho]

sure they tuned it leaner on the dyno for more power & efficiency so either the choke needs setting or you do not have a choke

[Jamiez]

I'm no expert but when mine was hard to start, I rebuilt the carb.  That fixed the starting issue, but then it wouldn't idle until it was completely warmed up and it was rough even then. I hooked a AF meter up to it just to see where it was at, and it was way out.  I set the float level and then used a vacuum gauge to dial in the idle mixture screws.  That got it running well, but I took the time to adjust the timing and fine tune it.

It wasn't very difficult and there were a lot of helpful people here. 

[EMCD]

The carb is completely rebuilt less than 200 miles on it. If I use the car every day it starts with no problem. If it sits for the week, it takes a few cranks and light throttle pressure to keep it going. I never had to do this with the smaller carb. My guess is that the choke is not working.

[Chryco Psycho]

Or not set quite right , not closing enough or coming open too fast

[jimynick]

OK, if it sits for a week, then take the air cleaner off before you do anything and 1- check the position of the choke blade; it should be closed and 2- manually opening the choke blade, look at the accelerator pump nozzle and give the throttle a whack open. It should squirt; if it doesn't or is spotty, there's likely a small internal leak that drains the fuel down and requires you to crank it to refill the float bowls. The electric choke heats up to pull the choke off and the cold, default position should be lightly-snug closed. Check to make sure the cold idle cam is engaged with the cold idle screw. It should have graduated steps that the cold idle screw adjuster touches to apply various levels of throttle during warm up, with the last position completely off and on the warm idle cam/screw for normal, warm running. Like the other lads said, check the timing and tune the idle mixture screws with a vacumn gauge and tach, looking for the highest vacumn and then adjusting the idle speed to spec or where ever you like/need it to be. Good luck 

[Chryco Psycho]

Or with all the alcohol in the fuel it is evaporating off after a week

[EMCD]

I bet it's the alcohol in the fuel. If I run it on Friday, and go to start it on Saturday morning, it starts on the 1st click.