1979 Johnson 75HP Stinger starting/idling issues and control relay rusted out

ctdude

Cadet
Joined
Jun 13, 2015
Messages
28
Hi,
I'm new to the forum, but my research has shown me that this is the best online forum for boats with the most knowledgeable contributors, so hopefully someone can give me some good advice and help get me back in the water.

I've decided to try and get my old faithful going again after a few years of her sitting around. I've given the old boat a good clean and am now in the process of getting the motor started up again and hopefully fix a few starting and idling issues. First things first, the control relay (the thing on the interior transom that all the wire and controls run through) is totally rusted out, and I have no idea how it should be wired. I might be able to work it all out, but would at least appreciate if anyone could advise what current rating relays for trim/tilt should be. Same goes for starter motor etc, as all the wiring goes into a rusted out box (see photos).

The issue the motor had was it started pretty well from cold and would idle nice to warm, but once she was running she struggled to idle and required extra revs to stop her stalling. Also, it would be harder to start once warm/hot. Any idea what might cause this?

I've included some pics in case that helps with identification etc.

Thanks in advance for any helpful suggestions.

I will be on here a fair bit over the next few months I expect, as I have the whole boat (14" fibreglass runabout) to work on, but I want to know I can get the engine back up and running smoothly before investing a lot of time and money into everything else.

Cheers,
Chris D.
 

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ctdude

Cadet
Joined
Jun 13, 2015
Messages
28
I did compression testing today, have figures of:
Cylinder 1: 112psi.
Cylinder 2: 108psi
Cylinder 3: 120psi
That all sounds ok to me, they are all pretty close and all over 100psi. I did a test by just cranking it for about 1 second per cylinder, but then gave cylinder 3 another crank and it went from about 110psi and topped out at 120psi. The point of the test wasn't so much for 100% accurate measurement but more to know if this motor is worth spending more time and money on.
Its all sounding good so far!
 

ctdude

Cadet
Joined
Jun 13, 2015
Messages
28
The rusted out part is the trim up relay...easy fix
OK, thanks for that, so how do I fix it?
I can buy a new Johnson relay for about $50 online, or I can buy a relay at the electronics shop for about $5. Do you happen to know what sort of current it draws?
Does it need to be anything "special"? Mine is sitting safely away from fuel, UV and water at the rear of the boat. I just want to get everything running and tested before I start spending big money.
Thanks.
 
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