I am experiencing spitting back thru the throttle bodies once the motor is thoroughly warm. This happens randomly at all load positions except idle. I am running an msd ignition and have tried with the box out of circuit and the problem remains.
Any ideas anyone?

Do you mean backfiring, popping through the throttle body???

If so, it could be a cam lobe, broke valve spring or in the ignition.

As Griff said, sounds like it's in the valvetrain. Check the cam lobes really good. It's a flat tappet cam and they have been known to flatten a lobe. You can put a dial indicator on the rockers and check the total valve lift. Should be .530 on the intake and .551 on the exhaust.
Also check for a broken spring(s).
Eddie

Thank you for the suggestions, my thoughts too except why no popping while it's warming up?

When it's warming up, the ECM is throwing more fuel
at it, and on these engines, they tend to throw alot at them.

That might be masking other issues.

throttle bodies will fart and pop when you have low fuel pressure..check the fuel pressure first,,will be OK when cold but as it warms up it will pop and fart from low pressure..

If i can rely on my fuel pressure guages, the fuel pressure is normal.
This is quite tricky for me as here in Europe no one has any experience with these motors and as soon as i mention 575SCI everyone runs away!!
I forgot to mention these motors have the ASM pulley and ecm re-progamme and they dont run rich.
I am thinking electrical still, maybe the magnetic pickup in the dizzy, cracked cap, even the coil, perhaps because these are easiest to fix!!

ok? what is your normal fuel pressure?

If it spits at you spit back!

Thank you guys for all your suggestions, and i have found the problem.
One injector on each throttle body was not firing. I decided to check if switching the wires on the injectors would move the problem to that injector but......as soon as i tried that they all started working!!
Now the motor runs perfectly, but i do not know why the injectors stopped or why they work again. That is the real question????