Gas Guzzler!!!!!

[Ben Tade]

I was hoping that someone could help me with a problem that I have? I own a 1969 50hp 500. It is on a 15.5 ft Arkansas Traveler. I took it out for the first time this weekend and I travelled about 6 miles. To my surprise the motor ate all the gas. I mean 0 gas left in the tank. The tank is 15L. I was told that this is not normal at all. I was running at full throttle with my wife in the boat (115lbs) and myself. The boat did not plane out fully. I was told that the compression is great in all 4 cyl.(135) It would be appreciated if someone could give me some direction on how to rectify this problem?

 

[Troy_from _Oz]

Re: Gas Guzzler!!!!!

I have often wondered about this with my boat/motor too. Its a Merc650 65hp on a 14.5ft ali runabout. I also get shocking economy, particularly when i dont have the boat up on the plane. It makes a huge difference if you are pushing the water rather than sliding on the top <br /><br />I would start by questioning why you arent getting up on the plane. id say one of three reasons - others may be able to suggest more.<br /><br />1) motor not propped properly<br />2) motor not in tune<br />3) too much weight in the boat??<br /><br />option 3 is detrimental to your continued boating enjoyment (leave wife at home = reduced chance or "wife approval" for all those extras ya absolutely have to have for the boat - like the nice new shiny thingamyjig)<br /><br />so i guess that narrows it down to options 1 or 2.<br /><br />Have you been able to plane the boat before? Has is been serviced and tuned?<br /><br />you might have to look into these things further.<br /><br />Cheers<br />Troy

 

[Ben Tade]

Re: Gas Guzzler!!!!!

Thanks for the Reply Troy! Option 3 sounded good, but I don't think she'll go for that as she enjoys it as much as I do. As for the boat..I just bought it, and did not give it a tune up at all, just did the ear muffs in the driveway to make sure that it ran good and then took it out for a quick run. It starts great and does not sputter at all. The prop is a 3 bladed prop. I am new to this so I have no idea if it is right or wrong or even the size. I do know that when the motor is under torque it will overspeed. I have the motor sitting at the second to last hole in the tilt?? I have no idea what to call it. I tried all the holes. When the motor is up higher it overspeeds more. The boat does travel at around 20km/h at full throttle but I do know that it should go a bit faster than this. I am new to all of this and I think that I will try to rebuild the engine over the winter and see what happens, I am still open to all suggetions though.

 

[Troy_from _Oz]

Re: Gas Guzzler!!!!!

Ben, <br /><br />What exactly do you mean by overspeeds? Does this happen when you are trying to go up to wide open throttle (WOT) and the engine suggenly runs really fast, but you actually lose speed? If this is what is happening it sounds like a 'spun hub'. This is when the rubber hub that sits between the prop shaft and the propeller starts spinning without turning the prop. The revs go up really high, but the prop isnt spinning. If this is happening, you may have to get the prop re-hubbed. First try tightening the nut up that holds the prop on. <br /><br />20km/h is a little over 10 knots, so id have thought your boat would have been planing about then? Was this speed measured with a GPS?<br /><br />if you do a search for "propeller" and "pitch" on either this forum or the internet, you should be able to find some info about props. not only does the propeller need to be the correct diameter, it also needs to be the right pitch aswell. Pitch is sort of like the angle of the propeller to the shaft. Its actually measured in inches, and refers to the amount of distance the blades would push the boat in one revolution (if it had perfect traction in the water).<br /><br />If your compression is good (and nothing major is wrong with it), it may not need a rebuild - just a good tune. Maybe the carbies need a clean, or the timing could be out.<br /><br />First thing to do would be to get a manual for it if you plan to work on it yourself. Well worth the money. (even cheaper if you can borrow one from your local library).<br /><br />Keep posting - the guys here are a wealth of knowledge and pretty happy to help out when they can. I just wish i knew more so that i could give back some to the board.... <br /><br />Cheers<br />troy

 

[gss036]

Re: Gas Guzzler!!!!!

Ben, while I am not familiar with your motor. You say you have 135 PSI on compression, so why would you consider rebuilding? That is good compression.<br />I would be looking for an oil sheen on the water to see if the fuel is coming thru the exhaust or leaking somewhere else. If you are burning that much oil/gas- 50/1 ratio, I would think your plugs would be fouled or coated with black crud. Sounds like you are getting a 1.2 miles per gallon, which is unreasonable for a 50 HP. I get a little better than that with my 200 hp. How much does the boat weigh?

 

[Ben Tade]

Re: Gas Guzzler!!!!!

Troy and Gss036, you guys are great, thanks again for the reply. Troy, it is doing exactly what you wrote (what I call overspeed?) correct term is??? So I will look at getting the prop done. As for the speed I did not correctly measure this. My friend was in his bass boat cruising beside me and he just measured what he was doing, kind of amateurish but I have no other way. I will take your suggestion and do the search on the pitch and measurement...I can't believe you are being so helpful THIS IS GREAT!! As for the suggestion for the manual, I just ordered one from Amazon.ca it is "Mercury Outboards: 3-4 Cyl 1965-92" by Seloc Publications. Gss036 there is a sheen on the water. I know that a little bit of "rainbow" is normal but it seems to be more than normal, especially on shutdown. I am mixing 50:1 but there is a big "rainbow" when idling or going slow. As for the weight of the boat, it is 800lbs. Thank you again for the quick reply..it makes me so much happier

 

[toomanyboats]

Re: Gas Guzzler!!!!!

as for the older Mercs,try to rebuild the carbs ,it worked for me

 

[rickdb1boat]

Re: Gas Guzzler!!!!!

Sure sounds like a slipping hub in the prop as mentioned and my 67' 65 HP left a pretty big sheen of fuel in the water,too. But it did run great, so I never worried about it. Might have had a leaking float seal, but....

 

[Maximerc]

Re: Gas Guzzler!!!!!

did you take the trailer out from under the boat ?? Ok really how is the bottom of the boat smooth or full of crap ? Have you looked to see what the spark plugs look if you are burning that much fuel they had ought to be soaking wet. Check for a water skier that has not let go next time too. have you checked the air in your trailer tires? Did you put the plug in the back of the boat ? all the gas will run out if you leave the plug out.

 

[DJ]

Re: Gas Guzzler!!!!!

A "sheen" means unburned fuel. That can be caused by carbs that need attention or grossly overloading your engine.<br /><br />Unless your engine tends to rev up high with no apperant increase in thrust-forget the spun prop. theory. <br /><br />My thoughts are, in this order.<br /><br />1. Leaking fuel. Underhood connections. Leaking carb. float needle valve(s).<br /><br />2. Grossly overpropped. Too high pof a pitch.<br /><br />3. Overloaded boat.<br /><br />I supect a combination of #1 and 2.<br /><br />By the way, running a boat at non planing speeds above dead idle is the MOST INEFFICIENT way to operate a boat. Either slow down or speed up.