Merc 2.5 carb questions?

[16ft superboat]

Building a 2.5 200FF block. Porting it between 225-245hp block. The past season I ran these carbs with .68 main jets. Since the engine is going to require more fuel and air I was curious if these carbs will work fine if I re-jet them or should I go to a larger style carb maybe a wh20 or stick with the wmh? Thanks guys

[mach351]

Stick with those....leave them jetted the way you have them. 68’s will support plenty of hp....that’s stock jetting on a 245.

[eli]

Have 2 ff blocks ported 260 and run same carb off my 245,s 68 main ,60 idle no back draft , think 50 off idle ,

[wogi]

Are you running a 245 cross drilled seven peddle intake? what is your elevation above sea level? Eli and I are at roughly 750 ft

[rjdubiel]

I have not ran it yet, but I have a stock 245 which has a crossdrilled intake and I got it with WH31 carbs with 94 main jets. I am swapping to a WH20 carbs and will see where the 94 mains put me at. I am guessing they will be rich but will find out in a few months once the water is not so hard (Frozen)!

[eli]

Wh 20 and the ones you have the venturi #84 are 1.315 ,i did try briefly wmh 47,s off 3 liter 1.465 venturi # 94 worked well if i was racing all the time but gas milage wasnt as good and i like to cruise

[wogi]

I have not ran it yet, but I have a stock 245 which has a crossdrilled intake and I got it with WH31 carbs with 94 main jets. I am swapping to a WH20 carbs and will see where the 94 mains put me at. I am guessing they will be rich but will find out in a few months once the water is not so hard (Frozen)!

I'm thinking that going to be fat, just my 2 cents

[eli]

I would say so it will run like the choke is on

[tux974]

I ran .72 breaking and .68 on all my 245’s. Actually kept the .72’s on my Howard after break in due to today’s fuel.

[wogi]

According to the factory service manuel, 72 are break in jets for a 245

[rjdubiel]

yes, 72 and 68 are the WHM carbs, but with the WH series I am guessing I will end up somewhere in the ballpark of mains for a carb BP. I think mid to upper 80's. I am not worried about fuel mileage, mainly will be setting up for 800 foot drags and the occasional run on the weekend, which will most likely call for a main jet change.

But run the WHM Superboat and let us know how ya like them.

[mach351]

If you’re going to run a WHM with jets in the 80’s you’re gunna be awfully disappointed. Remember, 2.4 porting is nowhere near as efficient as 2.5 porting. It’s not the extra 100cc’s of displacement that took mercury race V6’s from 2.4 245hp (if you were lucky) to 2.5 worked drags making 350+. It was the more efficient port design. This, by nature will use less fuel. Not to mention 80 jet sizes were needed for a completely different carb type (WH).

I ran a ‘05 280 on carbs for awhile.....stock WHM 21’s (200 carb)....jetted at a 64.....and turned 8000+ rpm with a 33

[rjdubiel]

The original question is should he run WHM carbs or WH carbs with his mod FF block. My guess on my 2.5 245 running WH carbs is i will end up in the 80's on the main jets. If running WHM carbs I am thinking everyone is onboard with the mid 60's to low 70's mains. Thats all, no one is running 80's mains in the 3 circuit WHM carbs.

[Dave Strong]

Early 245hp with pumper carbs ran .072 mains, later non pumper style ran .068.

Dave

[mach351]

The original question is should he run WHM carbs or WH carbs with his mod FF block. My guess on my 2.5 245 running WH carbs is i will end up in the 80's on the main jets. If running WHM carbs I am thinking everyone is onboard with the mid 60's to low 70's mains. Thats all, no one is running 80's mains in the 3 circuit WHM carbs.

Sorry, Guess I misunderstood what you were saying.

Anyhoo, yeah, I’ve got wh20’s now on a steel bore 2.5 ported past 245/260 specs and am running 82’s.