1972 50 hp Johnson--NO POWER!!

[rhull39]

Hi Everyone, Just put this motor on a 16' ft Sea Nymph. I cant figure out what's wrong. To start, it has the carbs cleaned, new plugs and coils, and 151 and 143 comression. Problem is, I can't get it to run well above 1/4 to 3/8 throttle. Runs smooth until then. Idles fine and will rev in a barrel. On the water, it cuts and hesitates or just sits at the same rpm as when I have it at less throttle and won't gain any rpm or speed. It seems like it's not getting enough fuel or the timing is off, I don't know. I can't find any air leaks in the fuel line or primer bulb and the fuel line ends see to be fine. The carbs open all the way at WOT. Where should the timing arm stop crew be? Should the arm go as far as possible at WOT? I've tried to push it forward a little more with it wide open on the water---and nothing. Anyone have any suggestions? Really frustrating--I just got finshed restoring the '79 Sea Nymph Fishing Machine I have it on to like new condition and I can't get it to go over 10 mph. Thanks for helping.

 

[nwcove]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

carbs cleaned......or rebuilt? huge difference!

 

[rhull39]

Re: 1972 50 hp Johnson--NO POWER!!

carbs cleaned......or rebuilt? huge difference!

Cleaned well. Completely taken apart, soaked and blown out with compressed air. I'm 99% its not the carbs.

 

[Scott Chinsota]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

check the jets. check to see that they are the correct jets. they are most likely fixed orifice for delivery other than idle speed. once they get gummed up, it's very difficult to get all of it out. then move on to the floats. if they aren't new, buy new ones and make sure they're set right. bad floats are a likely cause of fuel starvation. change the fuel pump while you're at it. one little pinhole in the membrane inside or a broken/worn spring and you wont get the fuel you need.
double check the primer bulb, hose and the fitting on the gas tank. fitting on the tank=same issue...sucking air not fuel. the pick-up tube inside the tanks rot after a few years too.
don't buy anything til you trace the path from the pickup tube in the tank to the jets. good luck

 

[rhull39]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

Thank you. I will do that. Never hurts to clean it again and have brand new parts. The floats to be set right--turn the carb upside down and make sure the float sits level in that position, correct? With the good compression in this motor, it seems like it has been used rarely and should give me some good years of use. Any chance there may be an issue with the timing that would cause the problem as well?

 

[boobie]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

Is the timer base advancing to full wot timing as it should??

 

[RandyJ]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

I don't recall how the timing base works but I have a yamaha 50 hp that had a sticking timing base and would not open up all the way until I freed it up with a little WD 40. I've also got an older 650 Mercury with the same problem... but had carbs cleaned. I happen to also have the exact same motor you have (won't idle but runs good on top end). I have also had other motors that did the same but the problem was fixed by repairing leaks in the fuel lines and fuel line connectors.... wish it was that easy on all the motors I've worked on with this symptom.

 

[rhull39]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

Is the timer base advancing to full wot timing as it should??

It does advance fine, but I don't know where the stop screw should be set.

 

[rhull39]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

I don't recall how the timing base works but I have a yamaha 50 hp that had a sticking timing base and would not open up all the way until I freed it up with a little WD 40. I've also got an older 650 Mercury with the same problem... but had carbs cleaned. I happen to also have the exact same motor you have (won't idle but runs good on top end). I have also had other motors that did the same but the problem was fixed by repairing leaks in the fuel lines and fuel line connectors.... wish it was that easy on all the motors I've worked on with this symptom.

I am going to replace all lines and connectors throughout the fuel system and reclean the carbs. Hope that is it. If anyone has an idea how to set the timing, that would be awesome. Randy, you probably already know this, but my motor was idling badly because i was adjusting the idle screws at the same time the same way. They needed to be adjusted independently via trial and error to get it right.

 

[Scott Chinsota]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

It does advance fine, but I don't know where the stop screw should be set.

mine's a 71 50hp f'nrude. think they're very similar. the stop screw setting is part of the syncronization. to the best of my knowledge it has to be set with a test wheel in place of the prop, aiming for proper wot rpm. i'm gonna pay someone to dial mine in.

something to consider...as you increase throttle the timing advances. over advancing the timing can result in piston and or ring damage which usually scores the cylinder walls. if you tinker, tinker carefully and conservatively. there should be a sweet spot at mid throttle where close to correct runs smooth, retard til you start to lose power, counting full turns advance til you start to lose power again, then retard to half way between. i don't recommend trying this. as i said, i'm taking mine in for sync. not really a diy process.

 

[rhull39]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

mine's a 71 50hp f'nrude. think they're very similar. the stop screw setting is part of the syncronization. to the best of my knowledge it has to be set with a test wheel in place of the prop, aiming for proper wot rpm. i'm gonna pay someone to dial mine in.

something to consider...as you increase throttle the timing advances. over advancing the timing can result in piston and or ring damage which usually scores the cylinder walls. if you tinker, tinker carefully and conservatively. there should be a sweet spot at mid throttle where close to correct runs smooth, retard til you start to lose power, counting full turns advance til you start to lose power again, then retard to half way between. i don't recommend trying this. as i said, i'm taking mine in for sync. not really a diy process.

Gotcha. Yeah definitely don't want to mess it up. I'll just work on fuel delivery for now. Thanks. It's so frustrating doing 6 months of work on this boat and not being able to enjoy it for the big bass bite coming up here soon in PA!! Here are some before and after pics. Tearing it down and building it back up was way more work than I initially thought. The darn fenders were rotting off this trailer so I took the cowl off a 1955 30hp Evinrude and improvised.

 

[tallwill38]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

your advance stop screw initial setting should be 1/2 inch of threads protruding out of cast boss opposite the rubber bumper.This is just a starting point and I am getting this info from a factory service manual for 1972 evinrude models 50272 50273 50202 50203 I think that the johnson should be the same your final timing would be measured with a timing light in the water at 3500 rpm your looking for 19 degrees +- 1 degree .When you go to adjust 1 turn of the stop screw equals 1 degree of timing change.The steps in a link and sync are to set index mark on throttle to align with center of roller just as it makes contact with all the slack taken up.Then connect timing light to top cylinder start motor and adjust idle speed adjusting screw until timing reads 3 degrees +- 1 degree Stop engine then adjust throttle cam yoke (its the fork that pushes the cam you have to remove the cotterpin and turn it to adjust) to align embossed mark on cam with center of roller. Then you set max advance with motor running minimum 3500 rpm to the 19 degrees.I know I am confusing you because I am confusing myself LOL but hopefully you can make some sense out of what I wrote and if you need to more info just ask I'll look it up for ya. Good luck nice looking rig ya got there go catch em'

 

[tallwill38]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

Oh yeah add to post above after you adjust the timing for 19 degrees you may need to readjust the idle speed using the idle speed adjustment screw.Its supposed to idle at 700 rpm max in reverse.There is a tank test prop mentioned in the manual but no info as to diameter or pitch ect... the part# for it is 384769 When I do my motor I am going to set it up with the prop that I run with and will do the adjusting on-at the lake.

 

[rhull39]

Re: 1972 50 hp Jonson--NO POWER!!

Re: 1972 50 hp Jonson--NO POWER!!

Oh yeah add to post above after you adjust the timing for 19 degrees you may need to readjust the idle speed using the idle speed adjustment screw.Its supposed to idle at 700 rpm max in reverse.There is a tank test prop mentioned in the manual but no info as to diameter or pitch ect... the part# for it is 384769 When I do my motor I am going to set it up with the prop that I run with and will do the adjusting on-at the lake.

Thank you very much.