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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10621
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 71 Jonson 50hp starts good and runs good in neutral

Customer Question

I have a 71 Jonson 50hp starts good and runs good in neutral and runs out good but when moving it will not run out good rpm dosnt come up seems like it has no power
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is***** will be assisting you. Do you have spark on both cylinders? When you are running the boat squeeze the primer bulb when the engine is acting up. Does the engine run better? If no change choke the engine when the engine is acting up. Does it run any better? Do you have a timing light?
Customer: replied 1 year ago.
I don't have a timing light and if I close the choke it dies. I haven't tried squeezing the Bulb with it running. And yes have spark On both cinders
Expert:  Tan replied 1 year ago.
Ok we need to try the primer bulb. Choking eliminates the carburetors as an issue. Leaving the fuel pump, a restriction or spark. If squeezing the primer bulb helps then we have a restriction or a bad fuel pump. Run the engine on another fuel tank this will eliminate a fuel restriction.If there is no difference we will need to get a timing light to check spark when the engine is acting up. Most auto parts houses will rent tools.
Customer: replied 1 year ago.
ok I will try that and get back with you
Expert:  Tan replied 1 year ago.
Ok great. Have a good evening.
Customer: replied 1 year ago.
I forgot to mention I put a new set of plugs in it and it runs great has all the power it should for about 4 miles then they foul up and lose power again
Expert:  Tan replied 1 year ago.
We still need to do the tests I posted. Sounds like you are loosing spark on one cylinder.
Customer: replied 1 year ago.
Ok done some looking and found that it dose just have spark one one cylinder. Could this be from the power pack?
Expert:  Tan replied 1 year ago.
Power pack, ignition coil or the sensor under the flywheel. Swap the ignition coils does the misfire move to the other cylinder? Do you have a volt/ohm meter?
Customer: replied 1 year ago.
Yea I have a multi meter
Expert:  Tan replied 1 year ago.
Ok do the coil swap we have to eliminate the coils as a possible cause.
Customer: replied 1 year ago.
I have already put new coils on it
Expert:  Tan replied 1 year ago.
Ok we need to disconnect the sensor coils from the power pack. These are the white/black and the black/white wires test between the 2 wires with ohm meter. You should have 10-20 ohms. If the ohm spec is good then the power pack is bad. If the ohm spec is not in the range the sensor is bad. Post back with questions. There is no test for the power pack only inputs.
Customer: replied 1 year ago.
Ok I checked the trigger it has 16.6 ohms
Expert:  Tan replied 1 year ago.
Ok the power pack is bad replace the power pack.
Customer: replied 1 year ago.
Ok I will get one some time this week and get back to you
Expert:  Tan replied 1 year ago.
Ok that is the only thing left that it can be by the tests we did. The coils are new and the stator and the trigger tested good leaving the power pack as the cause of the loss of spark on that one cylinder.
Customer: replied 1 year ago.
Well that didn't help it any
Expert:  Tan replied 1 year ago.
Do you have spark on any cylinder? Then that leaves the timer base/ trigger. It passed the ohm test that is why I said the power pack. It won't be the stator as you would have no spark and you said you replaced both coils. Leaving the only 2 things the power pack and the timer base which tested good.
Customer: replied 1 year ago.
Do you know if there is any place online that I can get a manual for it I haven't been able to find one for that year and motor size.
Expert:  Tan replied 1 year ago.
Here is a link to the manuals. http://www.marineengine.com/parts/johnson-evinrude-manuals.php?Year=1971&HP=50&Model=50ES71

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