ENFORCER24

OK , with all the help from my friends here , and Ebay
i'm getting close to the end of my engine freshen upgrade
but have 1 more question (i hope)

i have to re-build and re-jet a holley 750 DP , that used to be a blower carb (got it cheap)
the engine was a stock 330 1989 mercruiser 454
engine ran fine last year , just wanted a couple more ponies
changed heads to large oval early GM heads (casting 781)
stock re-build with the small valves , Intake is a victor jr 454-0
exhaust is 496 mag/ho (individual runners / dry joint / stainless risers) look very similar to Gil manifolds
a kick a$$ looking flame arrestor too
and the HP500 valve covers
and the carb is Holley 80557 , blower carb
cam is stock , as is the complete lower end
i finally started it today after tracking down a week ground for the ignition module that i mounted to the port manifold
iT IS A TORK MONSTER , WANTS TO ROLL OF THE TRAILER WHEN YOU GOOSE IT !!!!
e-nuff bragging , its running super rich , which i expected from the origin of the carb
after writing this novel , i'm taking the carb to a drag racing friend of mine and having him re-build it and re-jet it
where should i go with the jets?
how about the power valves?

KAAMA

iTrader: (1)

Don't really know what to tell you on the jet sizes----maybe 1-2 jet sizes smaller until you find the size your engine likes/can live with. Perhaps someone else can tweek you in here.

Anyway, nice job on the Merc 330 rebuild/upgrade. You will probably see more of an increase in the midrange vs top end especially with the stock cam, but who knows---it will be interesting to hear the feedback from you. I am curous if you bowl/pocket ported the heads. (???) Have fun.

ENFORCER24

completely stock heads , no porting at all
next year i plan on stroking the bottem end and going larger valves and porting the heads
in the real world i'm hoping on 50-70hp with the mods i have done , doesnt sound like much but will probably feel alot different
and i WILL keep everyone up on the process of re-propping the boat and what this all net's me at the end in MPH

cuda

I have a carb from a stock HP 500, on my 1982 330 horse. In 82, they came with the large oval ports. I also changed the intake to a Performer "O". A carb guru I really repect, told me to try running 75 jets in all four corners. I can't tell you if it works or not, because right after swapping out, I burned up a solenoid, and just got the replacement.

ENFORCER24

Thanks cuda , any and all help is appriciated

98itrwhite

that thing looks sweet! nice job

jeff1000man

Glad to hear you got that stuff done.

Those big ovals will be a night and day difference.

Did you put in new pistons? or did you just rebuild the top end?

That 454-0 intake is a mean mutha. It will fight you a little getting on plane, but look out on the top end.

Most of the time if those carbs have been manipulated for blowers, then the metering blocks have been driller out for bigger fuel flow.

Check that first.

Also, take the power valve out of the secondary. It will give you better control of your fuel situation.

After you build it, start jets around 80-86, if you have a 6 power valve. I am running that combination in a similar engine with a bigger cam.

You should be a little fat right now, but that is not a bad thing.

Run the engine on plane but at about 1/2 throttle, to keep the secondaries from kicking in for around 15-20 minutes and then turn it off without idling much.

Check the plugs. re jet until plugs turn golden brown. I like them a litle darker than they are supposed to be.

After you get the primaries adjusted, re jet the secondary for the amout of the power valve in front and run the boat at WOT for 20mins or so and then re check plugs again. Don't let it idle much or it will change the plug color.

Re jet until you get it right, but it should only be the amount of the power valve in the primary.

Good luck with this.

It sounds tedious, but it is not that bad.

blue thunder

Assuming the carb has not been drilled on.... here is the best starting point. Call Holley. Ask them what box stock 750DP marine carbs come with for jets and PV. Use the PV they call for. Add 5 jet sizes to the primary and 5 to the secondary to maintain p to s balance. Then procede with plug readings. You should be a little rich which is where you want to start.

BT

jeff1000man

Last one I got was 74 - 80

ENFORCER24

All the help is great , this weekend is gonna be in the high 60's so i'm gonna try for some time on the water and see how she goes
the carb is in serious need of a kit at least , she's loading up at idle bad , made is hard to set timing cause i couldnt get her to idle below 1000 rpm
i'm not too concerned with the intake fighting me getting on plane , the boat only weighs like 3500lbs , and last year she got on plane with little more then 1/8th throttle , its a modified V that might not be the best in offshore water , but loves 1-2ft chop

oh yea , this year was just top end , next years budget will be you (JEFF1000MAN) building my bottem end