Need help with my gas hog(boat)
 

Let me start by saying, i have no issue feeding it,just seems a little excessive.
I have a 20 ski brendella comp boat. was bought with a cracked block. Had a customer back out of a engine deal and bought his motor.its a .30 over 350. compression ratio specs out to be just under 10.23-1. Iron eagle heads with stainless 202 &160 valves, Cam is a 383 fastburn roller from Gm and i believe is 510 on intake &547 on exhaust. Carb is a 725 Marine from a 460 ford which was used by omc. it has 92 primary jets and 88 on the seconderies. plugs look awesome color just a tad to medium brown. Motor runs flawless all day long. but seems to like the gas station more then i think it should. not in any way complaining. but looking for a honest feedback. it will burn a 22 gallon tank pulling the kids around on a tube in about 3-4 hours. what do you guys think.

i think your one of the luckier oso members who doesnt have to spend over a grand a day to be on the water!!!!!!!:lolhit:

22 gallons in 3-4 hours is nothin. That looks like a pretty stout SBC and probably making 350+ HP. At WOT it would probably burn 30 gallons per hour.

I agree. If you can get an enjoyable day on the water for less than a hundred bucks....your the one livin the good life sir. :drink:

primary jets seem way to large...but also might try a newer holley 650 or so DP...

please understand, i agree its not like my big boat older scarab with 509 s from a well known builder but just seems high on the consumption. this engine idles perfect never ever loads up, can idle around lake which has a shorline of 15 miles and sits right at 620 rpms in forward and never miss a beats. so its definately not over jetted on the idle side. Now i did run a marine edlebrok 600cfm out of the box and it was more then lean, had to close choke butterfly to keep it running. I was thinking of buying a new holley marine, but really not to shore on cfm, yeah do the normal cfm rating to match cubic innch but this a healthy small block, if anything, would rather over cfm it and jet it to what motor likes to run at.

Pulling kids around on a tube all day can eat through some gas - I know from my experience with my 25 Baja and 454. I can cruise around at 3000 RPM and not burn near as much gas as slogging around at 20 - 25 mph with the boat barely on plane. I'm sure yours is set up more for skiing, but it's still not a very efficient way to run. Factor in all the stops and starts you probably make for wipeouts, and I can see where you could burn through a tank of gas. Take it on an easy cruise for a known distance and check your mileage. You might be surprised.

I also agree that 92 on the primaries seems excessively rich. Have you tried running it leaner?

I agree that the jetting looks pretty rich, but stepping it down will have little effect on fuel usage. The carb is a on the large side for your cubic inches, so that is why you have to increase jetting.

The carbs jetting has absolutley nothing to with idle. The idle circuit is completely separate.

Nothing wrong with that fuel burn at all. I'm only making about 320 hp and WOT is 30 gal/hr. Cruise at 3500 is about 10 gph on plane all trimmed up

Well, I'll throw in here from my ski days. We used to run a Mastercraft comp ski boat all day long and around 20-25 gals, can't remember. 8 hours or so of slalom & wakeboarding, with 5 people on boaRD. Ski boats have fairly easy planing hulls (lots of flat area in back).

Now, this was before the days of water bladders to kick a big wake - if you are running one of those (or the fins that pull your hull into the water), your fuel use will skyrocket. If not, it sounds like you are running too rich. So, I'd try a smaller carb and get the jetting right.

I would venture that the engine in your MC was probably a stock 350 Chevy or 302/351 Ford. His motor is significantly beefed up from stock - bigger heads, much more aggressive cam, etc. All of this adds up to more fuel being used. I do agree that the jetting seems rich. Those jets are bigger than what I plan to run in my 489 big block.

you start pulling people gas goes out the window, think you are about right

I pulled the carb off and put a stock off the shelf 650 holley marine on it and took it out for a spin, very light acceleration runs ok, get on it like your going to pull a slalom skier up and just forget about. it aint happening. I also lost almost 400 rpms at wot. it did seem to idle a tad better, put anything off of idle and it was not a happy camper. I am going to lean the original cab down on the primary side and leave secondaries alone. what would you guys suggest i jet the primary side to. thanks guys....

Maybe try going down 4 jet sizes to match the rears and then go from there based on plug readings.
Plug readings need to be taken after a 1-2 minute run at the rpm right before the secondaries open. This is for jetting the primaries. You need to come off plane and then shut it off and check the plugs.
After the primaries are dialed in, then run it at WOT and check the plugs.

With todays fuels, you really should not see hardly any color on the porcelain.

Griff, thats exactly how i did it to set carb the way it is now. it took about 15 hours to get some color on the plugs with the current jetting in the carb has now.

fuel burn doesn't sound too bad to me, I can burn through more then 22 gallons in 4 hours on my seadoo.

so, sense i am tired of playing carb games. I called my buddy at the machine shop down the street. I called on a favor. I am pulling motor from boat, which takes me about 30 min. and we are going to put it on the dyno and carb it correctly. this way there wont be any issues or headaches. my risers have predrilled holes for egt probes and will try our best to set up that way, he sugested if we have problems doing that. we will either throw some stock exhaust manifolds that he has that are drilled in each exhaust port for probes or last stick a set of block hugger headers and do it. so out it comes friday evening and onto the dyno saturday am. I believe very strongly this is the best way. sense in a comp ski boat we concentrate on all around driveability and not so much on peak hp but more on the torque curvr through rpm range for pulling skiers and tubers. ounce again, thanks for all the help guys.

For what it is worth, probably about 10 yrs ago now (before I got into the real deal) I had a 17ft manatee with a 75 hp johnson outboard and that would run through it's 14 gallon fuel cell in a day when running around and pulling tubes/skiers and such.

Mind you it never really came off of WOT with a top speed of 28 mph but in comparison I don't think your doing bad.

had my formula out this holiday weekend, 130 gallons on saturday and then 68 more on monday.

I think our boat sounds like it is running nice!

well motor got dynoed today. So hear is what we came up with.We are able to drop the jetting in the carb on the primary side to 2 jet sizes and 1 on the secondary side. and got it to run reall close 14.5 a/f ratio all thru rpm range. took timing up to 36 degrees total @ 6000 rpm. the torque curve was a tad bit lower then i wanted. but its all good. made max power at 5803 rpms and was 402. this is at 1100 above sea level. its back in boat and going to the lake tomorrow morning. with the flow scan hooked up, it burning 7.3 gallons a hour on the dyno. so its going to go thru a 22 gallon tank pretty quick. its all good.