350 Mag Weber Jetting ?

[offthehook2]

Hello I'm rebuilding a 350 Mag engine for my boat its 1994 engine but updated to vortec heads and intake I'm down to rebuilding the Carb its Weber 9770SA I've got it cleaned up ready to go back together but confused on jetting it has .104 primary jets and .107 secondary on the Starboard and .101 port ? only info I can find is the primary should be .101 with 6850 metering rods and secondary .092 jets
1) is the info I've found correct or did they have some odd staggered jetting on the secondary's maybe TSB update ?
2) only fuel around here is 10% ethanol (argh) do I need to bump both sets of jets 3% or did mercury already account for that possibility ? if not maybe that would explain the primary's jets being .104's already

 

[offthehook2]

Anyone have suggestion on starting jet sizes ?

 

[Scott06]

Hard to say considering it is a modified engine - you could look up jet sizes for a 357 alpha which is essentially your engine (vortec), sites with parts break down give just a merc part number for primaries, list a .092 secondary. Edelbrock 1410 which is a 750 cfm has .113 primary /.071x.047 step up rods, .107 secondary jets.

If it were mine try whats in there and see how it runs, read the plugs. If off buy an edelbrock jet kit, read the plugs and use trial and error. I tuned in a 1409 on my 5.0 was fairly easy with the edelbrock manual https://www.edelbrock.com/pub/media/...ers-manual.pdf

id use the 1410 chart to go richer or leaner, fairly obvious if you go a step rich or lean and observe the results. Google plug reading chart and you'll see pics of foul to lean plugs. Mine looked leaner than they actually were, fattened up both primary (2steps) and secondary (one) got a stumble and went back lean a notch on each and runs great. Lots of folks who've done it and can walk you through it.

 

[Fun Times]

Scott06 suggestion was along the lines of what I'd meant to say a few days ago but failed to get back to you on.

Using either 350 (4 BBL) Gen+ Crate Engine - ALL & Up , 357 Alpha 4V parts guides you'll find the carburetors used for the Gen+ (vortec) remanufactured engines which will show the Merc part numbers...Some websites will show the jet sizing numbers as well so you could try searching all the Merc part numbers you may be interested in online to see the sizes from the following site links as it will help you make the choices you'd like to go with, etc..

Carburetor, 350 Alpha
Carburetor, 350 Gen Plus
^From https://www.mercruiserparts.com/350-...n-crate-engine

Carburetor, Four Barrel, Alpha
Carburetor, Four Barrel, Bravo
From https://www.mercruiserparts.com/357-...4v-1g400000-up

Bear in mind there's a difference in jet sizing just between a Bravo engine setup vs the Alpha engine setup. .098 vs .092....Plus I'll add the Weber carb's always seemed to run a bit richer than most owners liked from new.

The above sizing starting point,
https://www.mercruiserparts.com/part...cturing-produc

 

[offthehook2]

Thanks Thought the 9770SA weber was a 600/625 CFM ? depending on who you talk to ?
Anyway I'd like to put it to stock calibration and go from there Well I guess update it to 357 mag calibration

Here is what I know about the 350 Mag Vs 1409
edelbrock the edelbrocks calibration is a bit off from mercruisers
Primarys 9770SA has 6850 metering rod .068 x.050 with 101 jet
edelbrock 1409 (600) uses .068 x.047 rod .098 jet
close but looks little leaner on the high vac/cruise side
Secondarys
9770SA calls for 092 jet
Edelbrock 1409 101 jet
whole lot more fuel on the secondary maybe they jet them way up for safety they will run on anything?

old saying "lean is mean but fat is where its at "definitely don't want to be hurting any parts burnt valves or holes in pistons make for bad day

I'm sure I can dial it in just need a starting place I guess I should have just bought a Holley for it I have tons of parts and jets from them but hate the idea of changing jets on boat with one gas going everywhere with every change on Holley just can't catch it all

I think this is where I need to start or 3-5% fatter work down
what I've found 357 mag alpha motor
Primary jets 809769 but cant find a size ????
Secondary jets 811657 and is .092
Metering rods and springs are 809068

Anyone know with size the 809769 jet is
What about the metering rods P/N or sizing ?
Anyone have one laying around they can check ? rod # and if the plain or pink spring?
(they are use in 97798 and 9780s)

Thanks