HTRDLNCN

this is a
30 over Mercruiser 502 with a
standard EFI 502 Merc roller cam
HP500 heads,
standard Merc aluminum 502 intake,
standard Merc 454 thunderbolt ignition setup
Lightning headers and
HP500 carb.
I originally had purchased the entire HP500 cam,intake,heads,carb but turned out
cam and intake were not in good shape and since I am short on funds I just went
with stock Merc parts for now. I am not looking for max speed for now either,
this is more of a future build for my next boat that I will be running in my current boat.
My question is how far off will jetting and idle be on my current setup.
Will it be close enough to run it and then dial it in or will I need to reset it up
just to get it running.

Griff

You will probably have to lean out the jetting by a few sizes. It will run, but will probably need some tuning. Do some spark plug readings at cruise speeds and WOT. I would also add an open spacer under the carb.

HTRDLNCN

yes I am adding an open spacer that smooths transition to intake

ezstriper

if you are still running a alpha, hope you are saving up for a drive....

blue thunder

If its a bone stock carb it may have the staggered jets. If so I would change them to around 77p and 91s and do some plug readings. That carb should be a reasonable good match to that engine.

HTRDLNCN

yup still running the original 24y ear old Alpha ,never rebuilt or even repaired.

so far it has outlasted the stock 260/350, a 300/350Mag
and a 454.. If it blows tommorow I would replace it with
another one. Nut holding the wheel has a lot more to do
with how long things last than the machine itself sometimes.

HTRDLNCN

Yes, its a stock HP500 carb and should still have the staggered jets.
Thanks for the reccomendations on the jets.

I spend a lot of time at idle putzing around the lake when I am bored,
on the Holley what would be important to address for good low idle quality besides the jets? (dont want to be fouling plugs)

Griff

They don't run a powervalve in the secondaries. Thats the reason for the big difference. A PV is worth about 6-10 jet sizes.

Jetting has nothing to with the idle.

HTRDLNCN

I know,thats why I asked what else I would need to address
if anything.

Griff

I don't think you'll have any issues with getting it to idle fine after playing with the idle air bleed screws. I ran an HP500 carb(rejetted) on warmed over 454mag with a stock intake and 1" spacer. It idled fine around 850rpms in nuetral/700rpms in gear.