OMC V6 Looper Fuel Usage?? MPG? 29 miles sucked up 19 gallons??? Normal?

[imq707s]

Now that fuel is getting so expensive...I've really started to monitor how much fuel I've been going through while cruising around at the lake. I've got a pretty much stock 89' OMC GT-200 Looper on the back of my VegasXT....aside from Boysen reeds, 2.7 heads, and around 120psi compression. The jetting stock except for smaller idle air bleeds required for the reeds (at least that what Boysen says). I'm running a 40:1 mix for fuel/oil….no VRO.

This thing just seems to drink the fuel...is that pretty normal for the older loopers? My boat holds 20 gallons of fuel, and I was running a 27 SRX prop over the weekend......and after cruising for about 29 miles at around 3500-5000rpms (40-65mph), the motor sucked down close to 18-19 gallons of fuel. It was a little rough so I was on and off the throttle a little, but overall I seemed to stay at a smooth pace. Is that about right for fuel MPG on an older Looper? The motor is in great shape, and it runs like a top. My parents have a big 21’ deckboat with a 150 Merc on it, and it can run all weekend on about 20 gallons.

[bigbore]

U definitly would think u need 2 jet up n down 4 the milled heads but if not she was way fat from the start,how long u been runnin like that?:cool:

[perfmarine1]

Thats about 1.5 miles per gal. thats about right. I figure 2 miles per gal. with a big bore v-6. The merc you are refering to is prob. a 2 liter and they are very good on fuel. I have 2liter 150 and it is very good on fuel,have 48 gal tank and it lasts several weekends of fishing. What you need is a bigger fuel tank! Or spend 15 Grand and buy a e-tech and get 4 miles per gal.! or take your foot out of it!

[imq707s]

U definitly would think u need 2 jet up n down 4 the milled heads but if not she was way fat from the start,how long u been runnin like that?:cool:

According to the OMC factory shop manual, the carbs have the factory size jets in them (62s in the top four cylinders, 65s on the bottom two if I remember right). It's been that way since I've owned the boat...over 5 years. The thing runs great, and the plugs all look perfect. I always hear about the need to jet up when you bump up the compression, but if the plugs look good....why dump more fuel to it if you don't really need it?

BUT...for all I know, the previous owner drilled the stock jets....which wouldn't surprise me since they also put the 2.7 heads on there.

[Lockjaw]

I had a 96 200 venom on my old bassboat, and it went through some gas. I usually burned through 20+ gallons a tourney. My 150 makes gas in comparison.

It should do better then what you are reporting for mileage, especially if you stay around 4K rpms. Maybe Racer will comment on what size jets you ought to have. What do your piston tops and spark plugs look like?

[imq707s]

I had a 96 200 venom on my old bassboat, and it went through some gas. I usually burned through 20+ gallons a tourney. My 150 makes gas in comparison.

It should do better then what you are reporting for mileage, especially if you stay around 4K rpms. Maybe Racer will comment on what size jets you ought to have. What do your piston tops and spark plugs look like?

The piston tops are pretty dark...almost black. The plugs look pretty dark after a WOT run....not black, but definitely not tan either. Kind of a dark chocolate color. I've been running it this way for 5 years, so if it was jetting wrong.....I would think that it would have done something by now :)

I wonder if some of it could be that I'm running about 1" under the pad, and at 4000rpms or so, the prop is still slipping a little (at least more than at 80mph). The boat doesn't really start to get out of the water until around 70....and I never even got close to that because how rough it was. But I always heard that 2-strokes are most efficient around 3500rpms or so....but maybe with a big prop, big motor, and light hull...that's not the case?

I guess I should go out and do some testing....run some distances at different speeds and see what kind of fuel I use. That would be a good excuse to get out and burn up some more gas :)

[mach351]

I think our boats are more efficient at 50-60mph than 30-40mph. Mine sure is anyway. I notice on long runs, when it's choppy and keeps me around 40mph, uses way more fuel than if it's smooth calm and I can cruise 70.

[johnboy 88 vegas]

Thats about 1.5 miles per gal. thats about right. I figure 2 miles per gal. with a big bore v-6. The merc you are refering to is prob. a 2 liter and they are very good on fuel. I have 2liter 150 and it is very good on fuel,have 48 gal tank and it lasts several weekends of fishing. What you need is a bigger fuel tank! Or spend 15 Grand and buy a e-tech and get 4 miles peon r gal.! or take your foot out of it!

I know a few people who have these motors on 18-20' center console boats and they get the same or better than you do. Ya might want to pull the jets and make sure someone hasn't drilled them to some ridiculous size. I have a modified 200 Merc on my Vegas V-hull and I get a hair over 3 mpg as long as I dont cruise above 5 grand with a carb motor so a 2 liter Merc or 15 grand E-TEC is not the solution. You can buy a ton of gas with 15 grand and still be able to work on it without a computer.

[imq707s]

I know a few people who have these motors on 18-20' center console boats and they get the same or better than you do. Ya might want to pull the jets and make sure someone hasn't drilled them to some ridiculous size. I have a modified 200 Merc on my Vegas V-hull and I get a hair over 3 mpg as long as I dont cruise above 5 grand with a carb motor so a 2 liter Merc or 15 grand E-TEC is not the solution. You can buy a ton of gas with 15 grand and still be able to work on it without a computer.

According to the plugs and piston tops, I'm pretty sure the getting is right where it needs to be. I'm assuming that you want the piston tops really dark, and the plugs a dark dark tan color after a WOT run....right?

I'm guessing that I need to go out again and run the same stretch of lake on a calm day.....and see how much fuel I go though. Like I said, it was pretty rough and choppy...so I was running pretty slow most of the time...with the motor tucked in almost all the way. Definitely not the most efficient set of circumstances.

I would love to go out on a calm day and run about 65-70 with the motor trimmed right....and see what that gets me.

What "should" I expect out of that motor/prop/hull combo? 2mpg? more/less??

[racer]

Sounds like the jets have been drilled, installing 2.7 heads generally requires 2 sizes over stock. When I install those heads on an 89 I run 64D in the top 4 and 65d in the bottom. If you are at sea level or close 62D would be asking for trouble and would be light tan on the piston top. On an 80MPH boat you should be well over 2.5

[imq707s]

So as far as efficiency goes...are you better off really "flying" the boat at 75+mph in order to get the best MPG? Or does efficiency start dramatically dropping off after a certain RPM?

[Instigator]

Couple things I've seen......
On a fast boat with the motor up and a good wheel (top end) it will usually be a pig every where else. Watch your rooster tail at 50 compared to 80 w/the same set up. Tall and short at 50 which is wasted thrust. The hull is dragging lumber through the water and the prop is slipping like mad at mid range speeds. Over hub props are even worse. Compare to WFO where the rooster tail should be long and low meaning more thrust is pushing you forward instead of slipping off the blade edges.
Also in rough water. I know in my old Sonic in rough water I'd use more gas @ 30 than I would @ 50 due to in/out of the gas.
My GPS is capable of fuel monitoring on my 24' twin O/B Sonic that I'm just finishing restoring. I've collected 6 sets of wheels to test and will use my GPS to do it.
I think the later era ('93 and up) loopers are more fuel efficient than the earlier ones also. With your mod's you are probably closer though.
If you read some of the water tests that John Tiger used to do in Bass & Walleye mag. they will leave you scratching your head. You see a lot of them gaining efficiency as the speed goes up until about that 60/70% throttle level.
I spent a lot of time w/set up in an earlier, identical Sonic w/o the fuel flow equip and am anxious to test what I think I know w/the new one.
Ian, in my experience a good clean Raker will run right w/a SRX or Chopper everywhere but up top but normally only giving up 2 or so MPH's especially on a heavier boat like yours. My old Sonic was faster w/Choppers (by 2 MPH's) but was a pig every where else with them. At mid range their was no comparison. If I was going to spend the weekend cruising I ran the Rakers. If playing on the river w/car moter boats we ran the Choppers.

[bulldogdaddy]

img, the old nick name for the 235's when they came out was 2 thirsty 5's. when i installed my 225 2.7 1987 on my boat before i broke the #2 piston it would use 6 gals of gas in 15 mins on some speed passes. after doing some porting and removed my airbox,which i was told to get rid of now wish i would have kept it,i have to get the jets redone,fuel pumps(because i didn't relize the fuel rail was in the airbox). so i can only imagine the more gas it will use.Who knows it might do better.But the one thing is i do have a hydraulic jackplate,so if i want to cruse with a 4 blade thru hub and no slip at half throttle,it will save you alot in gas.when i jack it up and use a 3 blade chopper 2 monkeys with gas cans couldn't dump enough gas in it. but glad to see your running.a month or 2 for me.and always rember its better to ask a stupid question than make a dumb mistake like me. there is alot of great help on here.

[LaveyT]

I can get a little better than 3 mpg if I try 3-1/2 mpg about the best , thats with a 225 H.O. on an 80+ mph boat. Less than 2 mpg if Im hammer down.
Im running a Raker most of the time.

[Action Dave]

I usually burn 15-18 gallons on my normal trip from Key Largo to Islamorada and back. It's about a 45 mile round trip. It really depends on the conditions though. If it's relatively calm I can cruise around 4500-5000 RPM's most of the way with an occasional blast to 6400 and it'll sip fuel. If it's rough and I have to tuck the motor under and plow, it'll burn more fuel. Remember, your boat is a lot more efficient when it's mildly aired out as opposed to plowing through the water. My motor is jetted rich too. I'm not interested in dealing with lean conditions and would rather buy new plugs than rebuild powerheads. I usually run a 14 1/4 X 30 MACH chopper and it's much better for cruising than my 27 SRX. Just takes a little longer to get to top speed.

[oldschoolltv]

I ran 80 miles on the suwannee and burnt 20 gals, mostly above 70mph, with a 29 srx, I now have a 32 and would love to do it again and see what it would do, Matt

[perfmarine1]

According to the plugs and piston tops, I'm pretty sure the getting is right where it needs to be. I'm assuming that you want the piston tops really dark, and the plugs a dark dark tan color after a WOT run....right?

I'm guessing that I need to go out again and run the same stretch of lake on a calm day.....and see how much fuel I go though. Like I said, it was pretty rough and choppy...so I was running pretty slow most of the time...with the motor tucked in almost all the way. Definitely not the most efficient set of circumstances.

I would love to go out on a calm day and run about 65-70 with the motor trimmed right....and see what that gets me.

What "should" I expect out of that motor/prop/hull combo? 2mpg? more/less??

Well your right about the rough water being hard on fuel,every time you plow into a wave it slows you down. The best water for speed and fuel economy would be a light chop. As far as reading plugs they should be a very light tan,and that is after wot and turn off key! Any idling will give fulse reading. Go to dave bush racing web site and see how and where to read 2stroke spark plugs. My guess is yours are drilled out! However OMC do come rich from factory from what I have seen.

[Lockjaw]

Motor tucked is bad news for economy. So is pulling something, like tubes. My 200 would blow through some gas if I pulled the kids on a tube. It was awful, if it got 1mpg, I would have been surprised.

Here is what I did with the boat in my siggy.

I got a level and adjusted my trailer so I knew when my hull was level with the floor in my basement, and then put the level on the cav plate of the lower and trimmed it up til it was level, and then checked my trim gauge. If I am cruising, even in rougher water, I try to keep the gauge in the level position, ideally I like to have my boat running where it hops up on the pad, and cruise at that speed, which varies by prop. By the way, level on my gauge was at 3/4 trim.

Just so you know, I have 72D's in my 150, and my boat holds 35 gallons of fuel, and I can usually fish 3 tourneys with it before I need gas. One of these days I am going to track miles with the GPS and see how it does. If I fish guntersville, I usually make a good 15 to 20 minute run, wide open if I can. I probably average between 55 and 60 mph, so I know I cover some territory.

[imq707s]

Well I went out again today, and the water was much smoother! I ran the 27 SRX, and cruised around most of the day at around 4200rpms...about 50mph. I played around a little bit, but mostly kept it slow. I ran 47 miles according to my GPS, and I burned up 15 gallons of fuel....so around 3.1 MPG. MUCH better than I did the other weekend when it was rough as hell and I had to keep it under 30mph most of the time. That SRX seems to hook up really good around 4000rpms. At 3500rpms I'm going 30mph....at 4200rpms I'm going 50. It seems to do much better than I can keep the boat mostly out of the water! :)