Issue with my '74 50hp Johnson outboard

[Ariesgod53]

Hello to everyone as this is my very first post, with my very first boat so it's a learning experience all around.

I have a 1978 16ft Blue Fin fish and ski with a 1974 50hp Johnson (long shaft), no tilt/trim. The boat doesn't want to get up on plane and I have talked to all the local marinas in my area and they say that it very well should be able to do the trick. I purchased the motor last year and had it completely tore apart to check out everything. I paid $50 for the motor so I had some budgeted money to repair it, but there was very little wrong with it. They had fixed the carbs and put new seals in and a propellar. I purchased a Hardline Tiny Tac in order to get an RPM reading at WOP to see if it is a prop issue as it was suggested that that could be my problem. Currently, I have an 3 blade Aluminum 13 3/4 x 15 pitch propellar and am getting a RPM reading of 7800 at WOP. I called the marina and they said that seems a little high. Well, the manual says I should be between 5000 - 6000 RPM. They gave me a 14 x 17 pitch prop to try and see if that makes any difference. I installed that prop just now and noticed that the nut holding on the old prop was loose and that the sprocket type washer behind that was a little loose as well, could it have been slipping and causing the high RPM's? I am wondering what any of you guys think? Could it be that I have to just find the right prop size for this boat, or do the carb adjustments have anything to do with the RPM's being so high?

Thank you for any help.

 

[junior1113]

Re: Issue with my '74 50hp Johnson outboard

uhhg loose prop or hub in prop probably problem. come back with new wot rpms and speed with the 17 and tighten prop and dont let it go over 6000


2' change in pitch is only going to change 300 wot rpms

be lucky if you didnt blow something by letting it rev that high

 

[Ariesgod53]

Re: Issue with my '74 50hp Johnson outboard

Thanks for the quick response!

This weekend I will get it back on the water, I want to zero in those carbs as well anyways. I noticed that the wire that came with the Tac was a single strand wire and the wire that I substituted to get an extra 6 ft was braided. Maybe that was screwing up the readings? We'll see what happens and I'll get back to you.

 

[Ariesgod53]

Re: Issue with my '74 50hp Johnson outboard

Well we took the boat out and it performed even worse. It seems that the prop (14x17) was too big for that motor and that the Tiny Tac also was defective. I tried adjusting the carbs to see if that would make a difference in anything and following the manuals instructions I couldn't get it to stay running worth a darn. Following the instructions from the "Carb Adjustment" post I couldn't get it to stay running either. It runs so rough and I am at a loss because last year I spent $700 on parts to get it running and it just doesn't seem like it's paying off. So it is now at the marinas, and they are going to take a look at it. They said with labor and what not, and a new prop (used = $75, new = $150), that it would be somwhere between a 2-$500bill. The owner said he has a early 90's 60 hp Mercury coming in and he would be willing to take my motor in on trade. Motor. new prop, tilt/trim tuned and mounted ready to go by next weekend $2000 - whatever trade in value my motor is worth = ? They suggested that the value of my motor would be somewhere in the $500-$1000 range.

So the idea of having a newer motor with a little more power to push my boat sounds appealing, but being that I do not know this market at all and many of you have been boating for some time now, what do you guys think? Should I just drop the money on the motor I have, or should I spend a little more and get a newer motor with a few more horses?

 

[hwsiii]

Re: Issue with my '74 50hp Johnson outboard

I would bet there is nothing wrong with the Tiny Tach, other than you added wire that you can't use on that. Take off the extra length wire you added to it and you will find it works correctly. Then you will have the correct RPM to see if you have the correct prop. Let me know what you find out.

H

 

[Ariesgod53]

Re: Issue with my '74 50hp Johnson outboard

I thought that as well and I took off the wire that I used and then installed it using the wire that was supplied from the manufacturer. It was still reading an idle speed around 2300 RPM and WOT at 7800 RPM, so I am thinking the tach isn't working correctly. To be sure the local marina said they would check the RPM's and if the thing is faulty they would give me my money back. The 14 x 17 prop that they told me to try is too much for the motor, it has a heck of a time getting going, but they are giong to check everything out for me, as well as let me know about that other motor. I'll let you know what we find out this week.

Thanks for the help.

 

[hwsiii]

Re: Issue with my '74 50hp Johnson outboard

You are welcome.

H

 

[steelespike]

Re: Issue with my '74 50hp Johnson outboard

Wire needs to be run carefully to avoid any stray pulses.
Only goes on one plug wire.

 

[Ariesgod53]

Re: Issue with my '74 50hp Johnson outboard

Yep, I made sure of that, I even tried onone plug wire then the other. The guys at the marina said it must be defective and gave me my money back, but I hung on to the prop (14 x 17pitch). I have a line on a 1980 70hp Evinrude. The mechanics are inspecting everything now. They said they'd give me 3-$500 for my motor in trade. I have a question on tilt/trim, but I'll post that in the appropriate forum/thread.