1956 Big Twin, power issue

[pro-crastinator]

[h=2]1956 Big Twin, power issue[/h] More adventures in boating.... 1956 Evinrude Big twin 30HP, the saga continues....

I think something needs correcting“ here's what I got -

1. Less power than I think I ought to have. 15Mph top speed w mild wind, me& skinny wife. Can achieve 18 in perfect "œwind to our backs" condition.
2. Low fuel consumption. (yes“ low) 2.1 gph wide open. 1.5 gph trolling speed. I read where a 25hp lowest consumption numbers were 3+gph. I need to burn more fuel to generate power. My stainless œsoda keg is one of 4 fuel tanks I have. It allows me to measure consumption numbers with high accuracy. Stainless pick ups are larger than marine tanks = greater flow potential.
3. New inline fuel filter - removed“ with no improvement. Have been filtering fuel prior to putting in tanks. Amazed at the crap that is picked up. Also water in ethanol fuel removal. I am certain that fuel quality is not an issue here.
4. Installed air silencer.
5. Mikuni fuel pump“ rated at 17 liters/hr = 4.49 gallons/hr. Flow is visually impressive.
6. 92+ psi compression numbers“ not measured recently. readings were taken before motor was really run - so I am leaning towards looking at this as a lower than it really is reading.
7. not an attractive looking head gasket“ could this address primary concern in low fuel consumption numbers? I think not but will defer to greater minds., power issue
8. Kinda slow engine starting. Maybe. Sometimes“ when hot - . Problem not consistent.
9. Plugs have a nice tan color on insulator. Looks like the range is dialed in. The fuel that is getting to the combustion chamber is being burned efficiently.
10. Exhaust water feels good and warm.
11. Ran engine with open cowl to check for exhaust leak. I wanted this to work in the biggest way but alas, no improvement.
12. Coils, points, condensers, plug wires, plugs, all replaced new.

Questions:
Does the Mukini pump move enough fuel to get the 30hp up to top performance?
Can the air silencerœslow things down?
Compression numbers weak? (low end of scale)
Check under cowl for kink in fuel line. - done“ looks good.

Iam gravitating toward the reed valves as primary culprit. In the entire fuel system, tanks, lines, carb, everything is Bristol. The reed valves are the only thing in the fuel delivery that has not been fiddled with. Is this a replacement part or is it serviceable?
Fundamental power generation requires the consumption of fuel. More fuel, mo power. Ignition system seems good. Compression system looks ok, I need more fuel to be burned to get to higher power levels. Cant help recall days as a kid with a motorcycle that I also wanted to go faster. Same problem, needed to get more fuel above the piston. Drilled a ½ inch hole in the piston skirt to allow more fuel to get into where it was needed. Worked beautifully. Fear not, I have no plans to deface the Evinrude pistons.

Comments welcome. Thanks in advance. You guys are awesome.

http://youtu.be/DXPMn3RBlO0

 

[Chinewalker]

Is your carb butterfly opening completely? The lever on the port side of the carburetor should be right against the stop at wide open.

 

[pro-crastinator]

Yes. butterfly open looks to be normal - as I observed prior to re install of silencer.

 

[nwcove]

i wouldnt dwell on the reeds being an issue....it would be a rarity. re-check the compression, maybe try a de-carb, things could be restricted on the exhaust side? sorry if i missed it in your post ( tiny font!) but is it a long motor on a short transom? just to much boat for the motor? any idea of what rpm it reaches?

 

[HighTrim]

Yeah, took me half an hour with my face an inch from the screen to read that! Too small for those of us with below average eye sight ! lol

I don't think I have really encountered bad reeds on a 50s OMC. Not to say that it cannot happen, but rare, and not something that I would worry about right away.

I would start by determining if it is indeed running on both cylinders. A cylinder drop test will accomplish this. Run the motor, then pull 1 plug wire at a time. Use insulated pliers. There should be a noticeable DROP in RPMS. If not, the cylinder you pulled was not running.

Also, is the prop hub spun, or partially spun? This would cause prop to free spin, and you would lose thrust. That is where I would look second.

I will also assume you have tuned the high and low speed needles on the water for maximum performance?

 

[F_R]

More fuel does NOT mean more power. In fact it must be within a narrow range of fuel-to-air ratio. That's what the adjustment knobs are for. Don't get caught up in the idea that the carburetor somehow injects the fuel into the engine. Vacuum pulls it in. Vacuum happens as a result of the engine running. A poorly running engine develops less vacuum, thus less fuel/air mix. It isn't the other way around.

 

[pro-crastinator]

Sorry about the font. I'll work on that. - and thanks for the responses.
De carbing the exhaust is intriging. Have not thought of that.
Motor is a short shaft on a short transom. Original engine on the 1957 boat. Word was the daughter of the prior owner skied behind this boat-motor.
Pulling the spark plug wires while running is something I SHOULD have tried. - will put it on the list
I think I dismissed the dead cyl idea when both plugs showed tan on the insulators.
Prop failure. - also on list now.
Balancing the jets - done. re done -. They are good. slightest move right or left degrades performance.
And that brings us to the fuel/power question.
Is my fuel consumption below where it needs to be?

Thanks again guys. I am gonna get this puzzle solved with your most capable assistance.
Will keep you advised. Wont be able to play with the boat for 2 weeks.