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Lack of power under load

mmiloser

New member
I recently became the owner of a 1969 Evinrude Sportsman 155. It has the Buick "Nailhead" V6. We were told that the boat was lacking power and the thought was that it needed a valve or piston job. After sitting for about a year, it started right up in the driveway with the hose attached. Right away we could hear a tapping noise and suspected a valve issue. Upon further inspection, we found that the exhaust manifold had a small hole and when patched with high temp JB Weld, the noise went away and the engine for its age was quiet. We took it to the lake and began our first test run to see how it handled. The boat powered right up and went on plane and we were shooting across the water. Unfortunately, the fuel tank even though it was reading full, was empty. We ran it completely out of gas. Luckily a friend was with us and towed us in. The very next day, I took it to the gas station and filled up with 18 gallons of gas. We took it back to the lake to continue our test and for some reason, the boat would not go above 2800 rpm and would not go back on plane. We looked at the fuel filter and there was very little gas in the filter. More investigation found that the fuel pump was bad and the fuel filter had dirt in it. We changed the fuel pump and filter restoring the flow of gas to the engine. Once again we connected the hose and started it in the driveway. The engine ran strong, smooth and quiet. We could push the throttle open full and the tach pegged out at 6000 rpm. We decided to go back to the lake and test. We backed it in, ran at no wake for about 5 to 10 minutes, once the no wake zone was cleared, we throttled up but it would not go above 3000 rpm. After several up and downs on the throttle, back to neutral shifting forward and reverse and once again attempting the throttle up again, still no higher than 3000 rpm. Placing back in neutral, we did a throttle up again and it went up to 6000 rpm. Returning home, I figured that it was not an engine issue but maybe a Sterndrive problem since we had not changed any fluids yet. I did an upper and lower gear case fluid replacement. Both upper and lower fluids were a yellowish milky consistency. I replaced with Type 'C' lubricant and trecked back to the lake. Unfortunately, it was the same result. No more than 3000 rpm were achieved under load. In neutral however, full rpms. I am at a loss, can anyone offer me any assistance as to why the boat would go up on plane and run fast until we ran out of fuel and now I can't get above 3000 rpm when in gear.
 
In neutral however, full rpms. I am at a loss, can anyone offer me any assistance as to why the boat would go up on plane and run fast until we ran out of fuel and now I can't get above 3000 rpm when in gear.

Ayuh,..... In neutral is irrelevant, it'll rev to the moon, runnin' on 2 cylinders,.....

My 1st guess is, yer carb is fulla the crap that killed the fuel pump,.....

Did ya set the points, 'n timin',..??
 
I have not. My next step is to check the points, timing and such. Looking for a carb rebuild kit before tearing into it to clean.
 
Rebuilt the carb. Did a compression test, (all cylinders are within range). Still no help. You can get to about half throttle, about 2500-3000 rpm, then nothing more. Thinking maybe to replace the carb altogether?
 
The compression readings were from lowest 125 to highest 150. We also found that the timing was quite retarded. We advanced the timing back to normal and I also drained, cleaned and refilled the fuel tank. Planning to take it for a run again hopefully today. There was quite a bit of dirt and a deteriorated gasket in the tank so that has all been removed. Hoping for the best. It just makes no sense that it ran perfect until it ran out of gas.
 
Check the ignition coil. Usually if there's oil coming out of the coil tower, the coil is breaking down. You can check the primary or secondary resistance. Or, could just throw a coil on it. Also, make sure the distributor cap doesn't have any carbon tracking, and the rotor doesn't have a pin hole in it causing the spark to go to ground through the distributor shaft. An easy way to check the ignition rotor is to remove the coil wire from the dist cap and hold it a 1/2 inch away from the distributor rotor while someone cranks the motor over. Either the spark will jump onto the tab and jump off the tip of the rotor, or, it will just disappear right into the rotor grounding on the distributor shaft. I'm assuming the plugs are good and the gap is only about .035. You might want to check your fuel pressure. Or, you could have one person drive the boat with the engine cover off, and another holding a can of carb spray over the mouth of the carb....and when the power problem starts, dowse the carb spray into the mouth of the carb. If it doesn't pick up substantially in power, it's NOT a fuel delivery problem. If the power picks up big time, you just found your problem....fuel delivery. You could also use a propane torch to provide enrichment to the carb while dynamically testing it in the water.
 
Would also be good to verify the timing advances w/ RPM...

agree. especially after hearing the timing was off.

chances of the advance weights and springs being all gummed up with 50 year old oil residue is high. Easy to take the points plate out and clean with parts cleaner and lube it fresh.
 
I realize that the OP has not been back since 09-17-... but here are my thoughts.

Its supposed to be brown...."milky" usually suggests water has entered the gear case.....
Agreed!

Would also be good to verify the timing advances w/ RPM...
Ditto!
What Mark means, is to check not only BASE advance, but to look further (dynamically) at what the Progressive and Total advance are doing.
In other words, connect your standard strobe style timing light, and strobe your timing marks at BASE RPM, 1,000 RPM, 1,500 RPM, 2,000 RPM, 2,500 RPM, 3,000 RPM and 3,500 RPM.
You should see that the advance is progressing from BASE value up to the 3,500 RPM range.
This can be done while on the water muffs.

No gasoline engine will perform well if the ignition advance is not progressing as it should be.

See your OEM ignition advance specs for this data.

*** Also worth mentioning..... if memory serves me, the Buick V-6 is an "odd fire" engine. Not all of them.... but many were.
It is a 90 degree V engine, but the crankshaft does not bring each of the 6 pistons up to TDC C/S using equal degrees of separation.
This means that the cylinders reaching TDC C/S do not follow the typical 60 degrees of separation.

The ignition distributor must also follow the odd cylinder compression stroke and firing arrangement.
In other words, correctly indexing the distributor housing per the odd fire, is extremely critical on this engine.


The compression readings were from lowest 125 to highest 150.
Your lowest and highest readings are more than 10% from each other. Not good.
However, on a small hull like this, I would think that it should still reach WOT RPM.


We also found that the timing was quite retarded. We advanced the timing back to normal and I also drained, cleaned and refilled the fuel tank. Planning to take it for a run again hopefully today. There was quite a bit of dirt and a deteriorated gasket in the tank so that has all been removed. Hoping for the best. It just makes no sense that it ran perfect until it ran out of gas.

See above *** and verify before you take it back out for another test run.
 
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