Ghostrider

G'day all,

Here's a situation for you to ponder.
I am no expert on Holley or any other brand of carb for that matter. I can rebuild one, tune one and fix most things but whether or not I'm right is a different matter.

I am running a Gen VI BBC, 468ci 10.5:1 comp, RPM Air Gap intake, Vortec heads, Crower (for now...) 01404LM cam - 292/303 Dur, .585 / .612 Lift and a holley 850 HP D/P carb.

I get about 4-5 inches of manifold vacuum from the vac port on the carb base plate and I think my power valve is a 35 but I'm going to check tomorrow.

All that asside, I now live in Darwin, Australia, which is hot all the time and more humid than a hippo's armpit during mating season. It is however; at sea level.

Anyone with any good advice as to what jets I should be looking at and any thoughts on the merits of dropping to a 25 power valve?

The boat is a Stinger 222 and I've got a B1 24P, a P5 23P and a Mir+ 25P, so far I've only really tested the 5 Blade and it was slower to get up on a plane than I expected and topped out at (GPS) 62mph at ~4250 rpm.

Any advice or input would be greatly appreciated!

Cheers,
John

ezstriper

4-5 inches at idle ?? if so you have a problem, should have twice that...fix that first...Rob

getrdunn

iTrader: (7)

I would think you would at least twice that also. With your cam it would seem like you'd have 10 - 12 inches of vac. You sure your vacuum port isn't pinced or do you perhaps have a leak somewhere. Sounds like your on the right track with lowering down to a 25 though based on your vac numbers. Half the vac is typically a good starting point. There was a thread here not long ago and an individual on the board was really helpful on the subject. It's a good idea to also have the vac gauge visable when running at various RPM's to know for certain when your PV is opened and closed.

Good luck Mate!

PS I would also check it in and out of gear at an idle.

Ghostrider

I thought about running the gauge up the inside of the scoop so it's visible with the hatch down for the next time I take her out for a test. I might have used the wrong port on the carb for vacuum, I checked the manual and it referred to it as the 'timing / vac adv port' which has limited vac at idle so as not to advance the dist (if used).
I'll try today on the other port and see how that measures up.

Cheers,
John

getrdunn

iTrader: (7)

You got it. Just make sure you use one on the bottom of the base plate and not one on your intake runners. Pull the carb off and look at the bottom to be certain you have the right one. What rpm does it idle at?

bajabob

you got to put a smaller prop mirage is the way to go prop it so the rpm are higher that motor needs to see 5200 to 5500rpm you are way off at 4250rpm the motor is dogging !!!!

Ghostrider

Okay, so I tested again today...

Managed 8-9 inches vac (on the correct port this time!) I tried all sorts of adjustment of idle an mixture but 9 is the best I could do while still having the motor at idle.

I then pulled the carb off and tore it down, here is what I learned:
Jets: #86 on all four corners (I'm hoping their not #98s but they look too small!)
Power Valves: 65 on both ends.

Now with my way of thinking, to get a boat out of the water and up on plane, you'd need large primary jets right?

Given that I managed to only muster 9" vac, I'm planning on going with 45 PVs and then trying a set of 92 primary, 90 Secondaries then doing a plug check run to see how that feels.

Any thoughts on that idea?

Linster

You are getting close to the right idea. Generally for a a marine carb you go up 2 jet sizes on all 4 jets. If you want to be real safe, go up 4 jet sizes to start. No matter what, do all 4 jets the same. Say if it came with 86 squared go to 90 squared. If it came with 82 in the fronts and 86 in the rears go to 86 in the fronts and 90 in the rears. On the power valves, you go down 4 sizes from the low vacuum level. You say 8-9 inches, its calling for a 4 or 3.5 power valve. A 4.5 might work. A power valve adds about 8 jet sizes of fuel when it drops below its rating. they generally start opening about 2 sizes above its rating. The vacuum keeps it shut. The valve should never open at idle, only WOT. Set the idle screws no more than 1 turn out then adjust the idle.

The cam seems a little large for that size engine. I would suggest you only time the engine at 32 with that compression unless running good fuel(92+) You will need premium at minimum. You should also not install over a 140 thermostat. Good Luck

Ghostrider

Thanks Linster, that advice seems solid to me.

I run 98 PULP in the boat just to be sure, my current timing is set to 34deg (total.) I run the Crane HI-6M and use advance curve 6 (NA motors). Setting 6 has my base timing at 14 deg BTDC with 20 Deg advance in the curve. I am going to try adv curve 8 (high HP NA Motors - High idle advance) next time out which has a base of 24 BTDC and 10 Deg adv curve. We'll see how that goes.

I'm not running a thermo at the moment as I'm worried about my cast alloy exhaust. I have a 140deg which I've drilled out but because the water here is so warm all the time, I don't seem to have trouble getting engine temp up a bit and steady.

I'm going to get a pair of 35 and 45 PVs to see how they go. I'll also get a set of #90 jets to try and see if they work any better.

How would you know if a set up should / shouldn't have different / offset jet sizes in it (ie: 92 & 90)? What difference would it make in a marine engine? How will I be able to tell if that may work for me?

Thanks for all your help so far, sorry to hit back with more questions but I'd like to tget this right!

Cheers,
John

ezstriper

try advancing the base timing and watch the vac gauge, 9 still to low, see if that raises it ? also do you have another carb you can try ? what idle speed are you at ? but you should be in the low-mid teen in vac at idle..so something no right...Rob