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Horrendous fuel consumption....help !

L

leokow

Regular Contributor
OK guys, lets see if you can help me out of this jam. Please. I have a 1990 31 boston whaler, weight 13,000, powered by twin 454 crusaders with AFB carbs. It holds 325 gals. of gas,and just turned 1000 hrs. I tried to go outside with it a couple of weeks ago for Tuna, WOW ! What a suprise, We burned 23gals per hour at 3100 RPM, ON EACH ENGINE ! We traveled approx. 140 miles on all the gas we had , save 29 gals. when we got back to the fuel dock. I checked the timing, it's at 10 deg.. I checked the bottom and props , bottom ok, props just tuned before the season. Replaced the plugs , wires, distributor caps and rotors. Changed all the filters . Other than actually weighing the boat I can't actually confirm the stated weight, but I feel pretty comfortable that the hull is in good shape, had it surveyed last Sept. when I bought it and nothing out of the ordinary was found. I love this boat , but honestly , at this rate , I can't afford to drive it. I was hoping for around .9mpg and would be happy if I could get it to that. I got a hold of Chuck at crusader and he sent me the an article containing all the specs at different RPMs, that was written back in 90 when the boat came out. My boat is averaging about 1/2 of the results that they got. At WOT it pegs the floscan out at over 32 gph/per engine. I know that there is an answer somewhere, I'm just having a hell of a time finding it,and so the call for help goes out to one and all,could the answer be those 20 yr old carbs ? I think I need some more info before I spend on new carbs. Here's hoping that somebody out there has some ideas to help track this thing down.....thanks....Lee
 
Twin 454s on a 31 footer! That's massive power for such a relatively small boat and it should get far better mileage.

I'll bet your props are tuned to the "standard and acceptable" dogma of obtaining the maximum rated rpms at WOT, right? Well, mine are not (a 32 footer with twin Chrysler 360s). You'll get a ton of grief on this from the "experts" out there, but if you add a couple of inches of pitch to your props, your gas mileage (and engine life) will improve noticeably. (It's like shifting into overdrive with your car or truck.)

Let's face it; your boat is far from underpowered (as is mine). My Marinette will plane off with the butterflies open so little, you couldn't slip a pencil between the wall and butterflies--I've marked the throttles and tried it. At this throttle setting the boat planes off within 200 feet, runs 18 to 20 mph at 2,500 rpms, and gets 1.2 MPG. WOT rpms are around 3,900. "Normally" propped Marinettes (WOT 4,400 rpms plus) have to turn 3,000 rpms to make 20 mph while giving up engine life in the process.

Again, if you mention this heresy, you'll get a ton of grief from the "experts" out there, but others--with boats that are NOT underpowered (an important point)--have added pitch and got similar results. Try it and you'll like it.

Jeff
 
Thanks for the reply , Jeff.....maybe just maybe with the guys on this site I might get somewhere with this boat. All of the experts that I talked to about this problem went to the props, first thing ! The props are 18x20's, which is what the boat was shipped with, I should reach 4200 rpm's on both engines but only the starboard will get there, the port just about makes 3900. At WOT she'll do 25knots, which is still 5kts. off the project boat and double the gas consumption. The next expert solution was the" Timing has to be off" I checked it at the balancer and it was right on 10 degrees. I then took a compression test on both engines and got between 150 and 135 for the lowest, I felt ok with that. My prop guy says the props are just fine, so I know what you mean with the heresy thing. You're saying add a couple of inches of pitch and I'll gain in the middle where most of us drive anyway, but I'll lose on the top end where I very rarely drive, especially at over 64 gph ! Now all I have to do is convince him to go along with this idea. What's your suggestion for the size I should move up too ? Thanks again ....Lee
 
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If the engines check out ok, start looking at what you lugging around. A full fuel load is just under 2000 Lbs. Add 40 Gal in the fresh water tank that's another 300 Lbs. Ice, bait,rods & crew all add up. A boat with lots of storage is great. You accumulate all kinds of stuff. However, you burn fuel to move it. Get rid of stuff you don't need and distribute the load so the boat is in trim & gets completely up on plane. If you have trim tabs be sure your using them correctly to fine tune trim,not correct improper loading. Tabs create drag to lift that squatting stern, lower the sky high bow or correct that list to port.Take a look at your wake at cruise speed. You should not be leaving mountains behind you. Your target MPG of .9 @3000-3500 20 Knots seems about right after you burn off some fuel. Check the bilges make sure there is no secret compartment full of water trapped some where due to a clogged drain. Do you fly more canvas than a sailboat? A full bridge enclosure in a head wind can cost you a few knots.
 
the AFB's in the 90's air horn would warp after time, letting fuel run through the system at mid and full throttle, they would idle fine. this was on cars and trucks, i assume that the marine version being built at the same plants would have the same problems. just a thought.
 
Lee,

I used Jeff's prop idea a few years ago and went from 18x20 on a Silverton 34C w / 1992 454's to 21x23 4 BLADE. Honestly it performed well and with full enclosure hit .8....bite was really good is slow speed docking and the idle speed went from about 3 knots to about 4.4 with topend cruise about 25??? I could not reach 3000 WOT and it spun a shaft key about 1 mile from the inlet so on the haul out, we had another small set of 4 blade props 20x21 and used those to date........happily. On any cruise today we reach about .6 mpg at 3200. out wot has hit 4200 again. Our weight is about 15,000 running with our usual crew of 4. We bought and sold our props in order to walk away with minimal expense or it can be an expensive trial and error
 
Is this boat kept in the water? Whalers are rather known for foam absorption of water into the hull below the waterline; look for small cracks or thruhull sealing issues. It would be great to weigh the boat.
 
Since no one has mentioned this, I will. Did you check the total advance (TA). You say the base advance at idle is right on at 10 degrees, but the total advance may not be there, although your top speed probably indicates that it is. Double check the plug wires for proper rotation also.
 
erich.....yes I've checked the T/A and it rotates up about 30 degrees, just guessing at that as the mark rotates to just out of sight. and my plug wires are right on the money. Thank you.
Diver Dave.....I was afraid you would mention that, I've been afraid of that being the reason ever since I discovered the problem, only one of my other buddies mentioned it and it's left me with a queasy feeling ever since...There's the Viking yacht plant not to far from me and I have a friend that works there. I'm going to see if they have the capability and if so I'll see if I can work something out with them for getting the boat weighed . Ocean yacht is also close by , so maybe one of them can do something for me, like they don't have anything else to do.\
Knuckle.....I really like Jeff's Idea and I'll probably end up doing something along those lines If I can't find the real problem. I just hate to modify something to correct a problem caused by something else. This ran correctly at one time and now somethings happened to change that. I would really like to solve the real problem if I can then implement jeffs idea if I can't find it. If diver dave is right that would be one way to partially correct it. I have to admit ,,,,thinking of that foam filled with water scares the s... out of me. One thing I did notice and that's that the water line is in it's original place and the boat sits just perfectly in the water, if I had picked up a lot of weight from water soaked foam I think the boat would be sitting a little low above the water line , don't you ? Thank you all for trying to help, I will continue to try to weigh the boat but in the mean time I'll just keep hunting....Lee
 
rfdlou.....I checked the boat out before the test run to make sure we wern't carrying a bunch of extra junk and removed just about everything . There were only 2 of us on the boat and the 325 in fuel was the same as the test boat. The boat is a hard top express so I don't have a lot of canvas flying around. Also I checked and I was wrong about my carbs being AFB's they are Q jets.
 
qjets didnt warp the air horns, but the well plugs for the metering rods leaked, we would epoxy the plugs with every carb overhaul we did on the quad jets, not saying thats your problem as your not complaining about a black toilet ring from running rich, but they had there leaks also.
 
I would contact by phone & in writing the company that surveyed the boat and ask what tests they did to check for water in the foam core. As Dave stated "Whalers are rather known for foam absorption of water into the hull below the waterline". You hired them for a professional opinion,they should have known this is a common problem and tested specifically for it. You may very well have a claim against them for the repairs if this worst case scenario comes true. Contact Boston Whaler also,fortunately you have a boat where the company is still in business. Whaler may have tests to verify the problem. Who knows they may have a "secret" warranty or offer reduced cost repairs.
 
Lee,

Sounds like were are only a few miles apart. Viking is only a few miles south of us. off Rt 9 What size shafts do you have?
 
Roscoelab...When I changed the plugs most of them were black, telling me it was running on the rich side. Not a big carbon build up ,just more on the black side than the tannish orange they should have been. So maybe you have something there.

rfdlou...I looked at my survey report and it says they performed tests using a moisture meter to look for water or moisture in the hull. I don't know if this would have told them anything but I will look into it.

Knuckle....you're right we must be close. I'm in Mystic Islands, Little Egg Harbor...Osborn Island to be exact. My shafts are 1 1/2". Thanks again everyone for the help, makes me feel like there's still some hope for this boat ....Lee
 
Concur on your desire to find the real issue before trying to compensate elsewhere.

First (easiest), verify you are getting full advance on the ignition timing. Either break down and spend a few buck for a timing tape or just scribe the damper (or paint a line). An advance timing light is another option if you know how they work.

Next item to check is the "sight tube" from the fuel pump to the carb. if it has fuel in it, the pump's diaphragm has ruptured and is the likely cause of the rich condition.

Another possibility...bet the OEM carbs were Q-Jets...the 170 series rarely had issues with the main well plugs even though www-based urban legends continue. anyhow, the original performance data was likely taken with those carbs. it is possible whoever did the swap never jetted the AFBs correctly, for the specific application. another option is the float/needle/seat are due for replacement, especially the float if made of foam.

If these aren't the issue, I'd run the boat with vacuum gauges hooked up, recording intake manifold vacuum at various rpm's and post the numbers...a very good indicator of overall health of the engines and the load they are seeing. Your hours of run time indicate the top end is approaching the end of a reasonable service life...if the previous owner hasn't performed regular maintenance with quality products, it could be time already.
 
Thanks for joining in Mark, I was hoping to peak your interest with this one. I was wrong when I said the carbs were AFB'S, they are Q-JETS. I corrected it later in the posts but I figured you missed it, anyway we can skip that problem unless you think I may have a problem in the Q-JETS...
I'll begin to do the things you asked this afternoon and see if I can find my vacuum gauge from long long ago, or just get a new one before I waste too much time looking. This may take me a couple of days to do, but I will post the results when I'm finished so I can get the forums opinion on what I found. I think a vacuum reading at 500 RPM increments should give us enough info. to see what's going on......Thanks again...Lee
 
I just did a sea trial of a 32 edgewater, it had about 300 gal of fuel aboard, and measured almost 10mph shy of what the "test results" showed. Engines were healthy, props were OK, no canvas, clean bottom paint. I think the disparity was due to fuel load and "marketing". 1800# of fuel is a lot of load on these deep V, 30 something boats, and really cuts top speeds.
 
We're about 2 miles apart, just the other side of the Osborne Island Bridge. We usually winter at Tommy's (Great Bay)
 
Knuckle....we'll have to get together one day. I've been up at Tommy's for 15 years now, Anna and Tom know me real well, they're great people. I winter over there too, and the guy that bought my 30 Pacemaker is also there.
 
Just an update so you guys don't think I fluffed off all the suggestions you gave to me.
Jeff....I have a chance to pick up a set of 18 x23 props, do you think that's enough to go up or too much at one shot ?
Also , I picked up the timing tape and some vacuum fittings to do the rest of the tests that were suggested. I had planned for this weekend but the weather did me in. Thank you all for the suggestions....Lee
 
leokow said:
Just an update so you guys don't think I fluffed off all the suggestions you gave to me.
Jeff....I have a chance to pick up a set of 18 x23 props, do you think that's enough to go up or too much at one shot ?
Also , I picked up the timing tape and some vacuum fittings to do the rest of the tests that were suggested. I had planned for this weekend but the weather did me in. Thank you all for the suggestions....Lee
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3 inches more pitch and you are slow and going only to 3900 now with too much fuel flow?? I vote a strong no to changing the props right now, at least until you debug the boat/motor system.
 
Dave....I had intended to do the debug on the engine first and then if things worked out go for the props later, but a deal came up on the props and I didn't want to pass it up if they were worth getting. I would really like to get the boat back to where it was originally before I fool with the prop issue.
Also ...I checked the sight tube from the fuel pump to the carb and it's fine no gas in it. Thanks....Lee
 
erich said:
Since no one has mentioned this, I will. Did you check the total advance (TA). You say the base advance at idle is right on at 10 degrees, but the total advance may not be there, although your top speed probably indicates that it is. Double check the plug wires for proper rotation also.
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Bingo, with yet a few unknowns!
Improper TA, and you will not get the perforance from either engine.

leokow said:
erich.....yes I've checked the T/A and it rotates up about 30 degrees, just guessing at that as the mark rotates to just out of sight.
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Lee, all due respect, but this is nothing to be guessing at.
It's all about LPCP (Location of Peak Cylinder Pressure) at/neat 12* to 14* ATDC.
Gas/Diesel.... doesn't matter! As long as we're talking piston engines, this is extremely important.
For our gassers, this is the sole function of our ignition systems.

Now, note that the outer ring of the harmonic balancer can slip.
If these were not punched from day one, we will not know if the TDC marking is dead-on or not.
Without an accurate TDC mark, we can't time these with any accuracy.

I'm not suggesting that this IS your issue, but it would certainly be an item to check from your P of E list.
You may even need to do a PPS procedure to see if these are OK.

Water logged core foam is certainly something to consider also.
Marine growth on the hull would be another.

Sump'n aint quite right here.

.
 
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