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1973 50hp johnson

C

curly01

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I have a 1973 50hp Johnson that does not accelerate properly. When trying to raise rpms under a lo=ad it seems to bog down and then slowly (very slowly) accelerate. I have new coils, plugs, power pac and the carbs are spotless and adjusted properly. The timing is set at the proper specs and the advance is working correctly. Stumped.
 
You say the advance is working correctly, ....but are you sure? The spark must advance all the way before the carburetors are opened wide open.

Have you run the motor on this same boat before? Hate to suggest it, but is in underpowered? Or are there 50 gallon of water trapped under the floor? Boat bottom clean? Just a few guesses.
 
thanks fdrgator for responding. The things you mentioned have been checked and checked, I even made sure the anchor is inside the boat and the trailer wasn't still strapped on . I have had this boat for 18 years with the same motor. the compression is 140 on both cylinders, the tank was replaced with one from another boat that ran fine. I've pretty much done all that can be thought of even taken to a marine mechanic shop. However I'll look for any ideas at this time. Don't want to scrap the engine. Thanks again curly01.
 
curly01 said:
thanks fdrgator for responding. The things you mentioned have been checked and checked, I even made sure the anchor is inside the boat and the trailer wasn't still strapped on . I have had this boat for 18 years with the same motor. the compression is 140 on both cylinders, the tank was replaced with one from another boat that ran fine. I've pretty much done all that can be thought of even taken to a marine mechanic shop. However I'll look for any ideas at this time. Don't want to scrap the engine. Thanks again curly01.
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Thanks for the amusing reply. Sure glad it wasn't the trailer. And after 18 years, you certainly should know it well. I think boobie made a good suggestion but you probably are ahead of us on that too. I would have guessed a trashed piston, but not with 140 psi. Let us know what you find.
 
Even though the carbs are "spotless" there's always the chance of that one little piece of crap in a carb high speed jet.
 
boobie and all who have responded thanks you. I will check a couple of the ideas mentioned, however it may be a couple of days. Today is the Lord's day and we will worship in Church, hope you will also. As for the cylinder drop test already checked, odd that after a sluggish take off on top end it runs fine, boat runs about forty mph which is to fast for this old man. I appreciate all the response will keep checking and let everyone know should we discover the problem. Thanks Curly01
 
Well its Monday and time to piddle again since the weather is bad. kimcrwbr1, your suggestion sounded good, I hadn't thought about the thermostat so we pulled it out and it checked good, wasn't stuck open, however since going to all that trouble decided o put in a new one. I don't know but I think I found something that may affect my performance, the intake manifold box gasket was broken and out on the bottom of the box. I ordered a new one and will give this a try. Thanks for all the response from every one. will let you know how things go. curlt01
 
???--------There are huge holes in the intake box for air to enter.-----I do not think a bad gasket there is a performance problem !
 
time to get back to my problem. Think I'll check the valves, but not sure exactly how. Could use a little help. thanks curly01
 
Sorry, should have said reed valves, forgot to engage brain this morning. Howerver as things go around here I never got to the shop. Thanks, curly01
 
O.k. been a little while. However did check the reed valves and all is well. Opened the carbs again and cleaned and flush everything again and we did check the high speed jets, all seems to be clean. Put every thing back togeather, put it in the tank and the same old problem. So I give up. Probably going to juck this one and replace it with something else. I appreciate all the help everyone has offered to me but crappie season is here so gota get something going. Thanks again everyone. curly01
 
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