Low power question

[Bussard87]

70hp Evinrude 1976
Just replaced the switch box after the cylinders cut out one by one and now all cylinders are firing but it won't accelerate. That's to say that I can't get any RPM's out of it on the water. Had this happen on an older 30hp once and never figured it out. Any suggestions?

 

[F_R]

Water getting into cylinders (???)

 

[Bussard87]

Runs smoothly... how would I know if it did? It happens when you want power. I've tried working the throttle and timing by hand on the water and there's just not much power produced. No adjustments were altered when replacing the switch box.

 

[racerone]

How did this motor run for you last season ?----Post the results of a compression test.----Does spark jump a gap of 3/8" or more on each lead ?----Does bulb on hose go hard when you operate it.------And stop running this motor till you find the issue.-----A blocked carburetor will starve one cylinder of oil !!-----Did this motor sit for years ?----Is timer base rotating ?-----Flywheel key in good shape ?

 

[Bussard87]

I checked the flywheel key, no damage. It ran perfectly the previous season when the switch box began to fail one cylinder at a time shutting down. Come Spring I'll do the compression test. Starving for fuel is a possibility my hose and bulb are old so I'll start with a new assembly and see if that cures it. I already don't trust them. The entire mechanism is free moving. The manual turning of the spark advance and throttle opening had very little effect on its operation during attempted half and full throttle operation. Seems all the more fuel starved now that I think about and write this down...fuel line is next. I'm still going to check compression. I know that I did check it and it was within spec.. Runs smoothly but wants to die at idle in gear.

 

[stresspoint]

did you get the correct CDI unit for your model motor.

 

[Bussard87]

Ordered it from Van's Sports in Grand Rapids MI via the website based on model and serial.

 

[airshot]

When you replace the fuel lines, also replace the short sections of fuel line inside the motor. When these hoses degrade small pieces flake off and cause blockages. You entire fuel system needs to be flushed and cleaned thoroughly. Probably will need carbs removed and cleaned as well. Once these hoses go bad they go quickly and can cause lots of blockages

 

[Bussard87]

Very interesting. I'll clean and back blow the carbs. I never think about those on-engine fuel lines! Thank you for that.

 

[F_R]

Post #2 was a serious suggestion. An all-too common problem with those motors. Exhaust plate warps and water squirts in through the exhaust ports. Result is complete destruction of the powerhead.

 

[Bussard87]

Ah ha! I did find a leak in there when I replaced those gaskets. A warped plate would make sense. I'll look at the color and condition of the piston tops with my borescope.

 

[racerone]

I agree with water possibly getting in there.-----Did you get rid of any flaws / warpage on the exhaust plates ?----Did you use top quality gaskets ?-----Test run with a timing light.----One cylinder at a time.----See and report how spark behaves as you speed up the boat.

 

[Bussard87]

Ooo good diagnosis tip. Thank you. I'll have to wait for the ice to melt so I can run it in a lake. Engine acts fine in a tank.

 

[racerone]

Do what you like or think is correct.-----But if water got inside the engine and gets on the bearings , major damage can occur.

 

[oldboat1]

Good to hear Vans is still in business. You might also find water in your gas tank (sample in a glass jar. When settled out, water will be seen at the bottom.)

 

[stresspoint]

Ordered it from Van's Sports in Grand Rapids MI via the website based on model and serial.

check the part numbers with what you had and what you are using.