OK. Now we are getting somewhere. I have my initial timing set as high as possible. In the neighborhood of 18. Basically I set the idle to 36 degrees while running engine at 3000 rpm to make sure I got max timing at RPM. When the engine is at temp it starts at the touch of the key. Anymore timing and it drags.
The build was based on a recipe from a Marine engine builder. Custom cut cam, AFR 195 heads, EMI Thunder exhaust, Edelbrock performer RPM air gap intake with the 750 carb topping it off. 509 HP was suppose to be the outcome.

If the thunderbolt ign won't give me the timing required, where do I go from there.

This boat was originally an Alpha boat. Swapped out many years ago to Bravo's.

There is no 'basically' nor 'in the neighborhood' in tuning vocabulary, especially with timing.

Most TBIV advance modules do not stop advancing at 3000rpm. Some go as high as 4200rpm before advance hit's it's peak timing.

Keep reving the motor until it stops advancing and then rev it 200-400rom more to double make sure the advance has stopped increasing.

Does your carb have 2 or 4 corner idling mixture screws ?

Damn this is like dragging the info of what happened in a wreck out of the person that caused the wreck...lol.. The no alpha drive info would have been good 10 posts back. If its ANYWHERE close to 500 hp, for a 383 this would have a cam so big it is probably reverting water and putting out the plugs as soon as he puts it in gear.

Chris

"This boat was originally an Alpha boat. Swapped out many years ago to Bravo's." - I guess thats where the interrupters came from...

Can you get the #'s on the stick? - all the timing in the world at idle may not save you.

I ended up running the whole engine advanced a few degrees which got it to work down low with my top end combo.

SBC - 4 corner idle - on a marine 750? Cool - didn't know they had it. Have it on my demon.

"EMI Thunder exhaust," - and 500HP out of a small block 383 are two things Ive never seen co-exist on an actual dyno chart.

I'm guessing if it was even dynod it was done on a dry exhaust.

UD

All small blocks are 500hp. Did you not know that ?

Only If they have lots of chrome on them and a double-stacked air filter.... Everyone knows that..

OP, throw the interupters in the garbage

I am still wondering if no alphas how did testing the shift interrupter switches come into play and tested good ? post # 1

Mercruiser offers a 383 and has been for years. I think you still can get a carb app 383 - it comes out of their reman / repower division and is a drop in.