1987 Johnson 70 HP Outboard Loss of power

[chrisk15]

I have a 70 HP Johnson on a 15 foot Bomber. When I got the boat, the motor had a few issues starting, dirty carbs, low fuel pressure, and the timing arm was stuck in the rear position (I didn't know the latter until later after running the motor for a while.) However at this time, once you got the boat started it ran like a champ with full power and at full speed, but it would die at idle. I would have to slam the choke down as I pushed on the throttle.

Fast forward 2 months, I bought two brand new batteries, three new spark plugs, adjusted the idle to where it would not die at idle, replaced the ignition, replaced everything to deal with the fuel system (i.e. all hoses, pump, filter, clamps, everything). I cleaned all the carbs, to include taking them apart as far as they can go, I did this three times. Then I discovered my timing arm was stuck in the rear position, I lubed it got it unstuck and it works correctly now. After all this work I got the boat starting correctly, and running better at idle. It still occasionally dies at idle but fires right back up.

Then a new problem occurred. I lost power in the motor, It feels as if I have lost 60 percent speed and power in water at WOT. I spark tested it and all three spark great, I compression tested it and all three were between 115 and 120, fuel pressure is perfect, I then took it to the dealer I bought it from. He re-worked everything I did. Between multiple test runs and going back to the lake what seems like 100 times he is clueless on what to do next. The last thing we did was put shims in the prop to make sure it was not slipping and losing power that way. Also during this process the throttle cable, choke, idle lever, throttle body valve were adjusted multiple times. Mechanically everything looks and feels like it is working properly.

Any other suggestions. I just want my speed back.

 

[flyingscott]

Did you do a cylinder drop test. Sounds like you are not running on all 3. How did he adjust the choke you don't have one. What is a throttle body valve

 

[chrisk15]

I may have the nomenclature wrong, I am no boat mechanic just a tinkerer. By choke I mean the cold start lever cable was adjusted. By throttle body valve I mean the lever inside the throttle body. I have a link to the picture below. One of them had a slight gap and it was adjusted. at full throttle it is wide open.

http://www.google.com/url?sa=i&rct=...3F2b5e7DrFz9fivYkMEaVHCw&ust=1467313691725996

 

[flyingscott]

You do not have throttle body you have 3 separate carburetors on your motor they are NOT the same. You do not have a cold start cable that is the actual throttle cable. Your picture shows a car throttle body for Fuel Injection nothing in common with your motor. You need a new mechanic and was a cylinder drop test or spark test done. Was a link and sync done

 

[chrisk15]

Thanks for the reply, and negative on cylinder drop test, not sure what that is. A spark test was done and all three spark plugs spark a strong bright blue.

 

[flyingscott]

Does the spark jum 7/16" gap, the drop test is done while it's running pull the spark plug wires off one at a time if the idle changes they are good if not you have a dead cylinder. Use a plastic pliers or good insulated set it will zap you. Get a factory manual for the link and sync and make sure all 3 carbs are opening all the way and at the same time you cannot adjust just one.

 

[chrisk15]

I checked the carbs with the mechanic. All 3 are wide open at full throttle. So if the idle does not change on one of the cylinders it is dead. Does that mean it needs replaced?

 

[Bosunsmate]

Have you checked timing? When the electronics got changed out if the flywheel wasnt retorqued properly the flywheel key may of sheared

 

[racerone]

There is no choke lever on this motor control box.------There are no choke flappers in the carburetors.------The engine has an electric primer valve.---------For cold start you lift the fast idle lever.------Then push key in while cranking the motor over.-------Find an owners manual as mistakes do get expensive in a hurry.

 

[flyingscott]

You will not know until you have done all the tests if your compression is good and spark is good then could be a fuel issue. Hard to tell I am not there next to the motor. You also cannot shim a prop hoping to fix it

 

[chrisk15]

I am certain fuel is not the problem, I personally pre-mix the fuel to a 50:1, replaced every line, hose, clamp, pump, and checked pressure and it was fine. I guess I am leaning toward the dead cylinder. I will check this weekend when I get it out again. Unsure on timing, I can relay that to a competent mechanic.