Alright OSO peeps...I have 509ci(started as hp500's gen 6 blocks) motors that made 650hp on the dyno. Their naturally aspirated with a single carb. The Carbs are Holley 950 hp's. Runs great. Problem I have is getting it started after it sits a week or more. I have to crank and crank and crank. I have tried all the different methods I can think of. From just a small bump of throttle to wide open and I havnt found anything that really works. Eventually they always start but no rhyme or reason when. Once it starts the first time, just bump the key the rest of the day and they fire right up. Ignition is MSD AL6, Timing advance is locked out and set to 36. My initial thought is the timing being locked to 36 is the culprit. Thoughts? What are my options if it is. I can provide other motor details if needed. Oh, fyi the motors have solid lifters and are running with 4-7 swapped in the firing order if that matters.

John

do you have an anti-siphon valve in your fuel line? sounds like fuel system might be draining back to the tank.

There is no anti siphon. But I have had the air cleaner off prior to any cranking and when I give it a little throttle it squirts fuel. So I know there is at least fuel in the bowls.

I have to crank mine 4-5 times around then give it 3 or 4 full throttle pulls on the sticks and it pops off, what are your fuel pressure gauges reading while cranking. BBC like fuel @ start up.

2 quick short pumps and a shoulder roll.

is your msd box hooked straight to battery or down on starter + lug ?

Try about four full throttle cycles while watching down the carb . That's what my 540 takes to fire off .......but my bowls will be empty because of the already mentioned antisiphon valve .
​​​​​​​I put a button on the dash to run the pump ( electric) in my case but if you are mech. you will need the valve

Even with a mechanical secondary carb ? ie: two accelerator pumps ?

You could have gas in your spray jet for one pump. Have someone pump the stick 3 times to see if your carb has fuel in the bowl. I agree it takes a few pumps for cold start. Lots of great advice already given in this post. Put your flame arrester back on before trying to start. Good luck

hummmm.fuel pressure gauges im not positive. I know the regulars are 8-10ish psi idle. Ill have to watch next time.

Midwest - I have mechanical fuel pumps high flow holleys off the sea water pump. 3-4 pump scares me to flood it. But I am open to ideas. On the hose at home ill try it.

The MSD boxs are wired into the standard merc wiring harness. Direct to battery not sure, but pretty sure they dont go to the starter. Can you explain how that would matter? It starts instantly after the first time, I would think its either good or its not.