I am having problems tuning a new 500 cui stroker...

Engine specs: stroked 383 with a 4.25” crank, forged pistons, hydr. Roller cam (Comp XR292HR-10) installed @ 104° icl, Indy 440 ez heads, Hughes roller rockers, MSD ready to run dizzy / ignition set @16° btdc - 34° full mechanical advance no vacuum adv. as of right now, new Holley 870 street avenger.
Pulls about 10” vacuum

Engine starts without problem when cold, but won’t when warm / hot. Haven’t had the LM-2 on it to measure emission, but it smells way rich…
Idels nice @ approx. 800-850rpm

When I try to start when hot, the engine does not catch any spark at all, it behaves like it has no spark at all (but it does)…
What should I look for?
Thanks,
Frank

Before you do anything else, do you fully understand how a carburetor works, and how to operate one, both in theory AND with today's fuels?

I have to ask because so many of these types of questions are from young people who have never operated anything without fuel injection.

yes, I do know some, isn't the first engine I put together and I set up a variaty of different carbs. But this situation confuses me...

Well, it could be as simple as your re-starting procedure---assuming like you say you have spark, fuel and compression.

Example. One of my motors i built, after it was warmed up and run, to restart it---say after a 10-15 minute sitting, you either had to just turn the key, or maybe givie 1/4 pedal at best to get it started. Anything else would make it crank all day long and not start.

Another engine i built (very tall intake), easily had to give it 3/4 pedal then crank it while easing back into the throttle. Again, anything else and it was a struggle to get started.

Being a new engine, you might just have to find what it likes when warm.

Now my only other thought is (and i am not familiar with your distributor) is a pickup or what ever your ignition box is. Years ago i had a Holley annialator ignition (similar to the MSD 6AL)---hot, it would not start for anything, once it cooled down some---anywhere from 5-15 or so minutes---then it would fire up and run fine. It still had spark when it wouldn't fire up, but it seemed to be very weak. I eneded up swapping back to good old Ma Mopar stuff and never had a issue after that.

Just some food for thought for ya. Good luck.

Yep. Big Block characteristic. Even Mr.Angry got screwed with this one. You have to figure out what works. Let us know when you do.

Just came back from the garage. Went 6 steps richer on the primeries (LM-2 showed about 16:1 A/F @ 2500-3000rpm) whiche helped a lot with starting behavior.
I managed to get the engine going once or twice when hot. If I barley touch the throttle it won't start at all. The two times it fired I didn't give any gas at all. But it appears, this does only work if the engine fires right away. If I need to crank it some - no chance.
Any input from the board about carb mods to cure this?
Thanks,
Frank

Start by leaning out the mixture while it's running... simply get it going and 1/4 turn at a time lean out each side until you hear a difference. Then turn it back until it's just at the cusp before you hear the difference. If you're running rich you're running hot. Make sure your carb's bowl isn't evaporating the fuel. (do you have fuel when you try to start it up warm?) The high ethanol content of today's fuel makes it very sensitive to heat.

fuel is there, I feed the carb via electric pump, regulator and return line. I'll try to lean it out...