Evinrude 50273c, 50hp '72 no power, swilling fuel

[kippstakes]

Have been working to get my engine up and running for a while now and finally thought I had it. Got it back from the shop, they claimed it was working fine under load and was ready to go.
Second time at the shop, actually. Took her in the fist time and they got the idle set, new plugs/caps, tested power pack and coils, and some wiring work done. Took her out next day, bogged down like crazy. Popped carbs off day after that and realized the nozzle gaskets hadn't been installed! Put the gaskets in thinking I had solved the problem, but took it back to the shop for them to give it an official thumbs up, which they did.
SO, got her out on the water a few days later and she would only make about 10mph with current, with the throttle wide open, AND was using more fuel than I imagine is to be expected (be this as it may, she did run MUCH better, however). Note: the engine runs like a top and sounds like a chainsaw when out of water.
We made it about 9 miles on 5.5 gal of gas before running out (and having to be towed in- uuugh).
Now I have little basis for comparison but it seems to me that a 50hp two stroke on a 15 foot boat with two people aboard should get better mileage than that-- that's under 2 mpg, which is about half the fuel economy of a military Humvee.. not too hot. What's going on here??

A little maintenance history:

The carbs are clean, very clean- right down to the fast jets. All new gaskets and fuel line. New inline filter and pump diaphragm is in excellent shape. Bulp becomes tense quickly and seems to move fuel effectively. Both carbs and cylinders seem to be getting adequate fuel, so that shouldn't be a problem (judging by my mileage they'd better be).
Plugs/caps are new installed by the shop, no signs of fouling that I can tell. As mentioned earlier, the coils and pack were both tested fine.
Compression tests fine also, can't remember exact numbers, but it was adequate to indicate a solid head gasket. Also, I am seeing no oil in the pump indicator water.
The boat seems to porpoise a bit, but I think that might be due to low forward power- can't get enough speed to get on top of the water. The cav plate is aligned with the boat's keel angle, which I've heard is default, so it should be okay at least.

This engine has been giving me the business for a while, but I feel like it's on the verge of actualization and it's just a step or two away from being great.. just need to figure out the steps.

ANY IDEAS?

Thank you

 

[F_R]

Re: Evinrude 50273c, 50hp '72 no power, swilling fuel

Well #1 thing you should check is to see if it is running on both cylinders. I'll make a bet that it isn't. Remove and ground one spark plug lead and run it. Then do the same with the other one. Chances are, it will make no difference with one of them grounded, but won't run at all with the other one grounded. That is the good one.

Next thing to do is figure out why the one cylinder isn't firing. Any engine needs compression, fuel (in the right amount), and spark. Plus, a two stroke engine needs crankcase compression. I can't check it from here, that has to be up to you, or that shop you have been taking it too. Kind of makes me wonder about their qualifications.

BTW, "sounding like a chainsaw out of the water" makes my hair stand up on end. Don't be revving it like that under no-load conditions, or someday you won't have to worry about it. Just pick up the pieces out of the yard.

 

[kippstakes]

Re: Evinrude 50273c, 50hp '72 no power, swilling fuel

That would definitely make sense, and it was one of my first concerns when I started troubleshooting as well, plus one of the first questions I asked them when they started looking at my boat ('am I running on both cylinders??'). They tested it by, what appeared to be, the same method you just described. However, I will test it again tomorrow to be sure, because you are right, all signs point to a failing cylinder.
Have heard many positive reviews about the shop, but I'm also having second thoughts at this point.
Where would crankcase compression likely be lost? And since the crankcase is mostly uncovered by a water jacket, wouldn't a failing gasket be evident by oil/gas leakage? she seems pretty dry from what I can see.
We'll start with the cylinder functionality first though.

 

[pn]

Re: Evinrude 50273c, 50hp '72 no power, swilling fuel

take a look at your motor wiring to see if its in good shape, connections clean, grounds grounded, spark plug wires clean and crack free, no scuffies. also, while bogging on the water try pumping your primer bulb to see if it's lack of fuel. good luck. about gas mileage 2 mpg is average id say for any boat but going at speed and not at 10mph. does the engine smoke alot? your float bowls might be set too high allowing fuel to be sucked in, too rich

 

[kippstakes]

Re: Evinrude 50273c, 50hp '72 no power, swilling fuel

she doesn't smoke at all. tried pumping the primer last time we were out with no change in performance.
can check float levels. anyone know what they should be set to? have set my motorcycle before, but have no idea how to level a boat.
thanks