Johnson 48 hp tune up

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thedude
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Johnson 48 hp tune up

Post by thedude »

Recently acquired a 1993 Johnson 48. I tried to start it when I bought it but it died within 3 seconds or so and never would fire again.

Today I hope to get it running. My plan is to check spark, replace the plugs, clean and or rebuild the carbs, replace fuel lines, replace impeller, and change lower end oil. Got a new can of trufuel premixed so I know I have good fuel.

Wish me luck! Any input on this motor?[ external image ][ external image ][ external image ]

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thedude
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Johnson 48 hp tune up

Post by thedude »

Got it running with new plugs and carb kits!

Bad news is it won't idle. Some gas is coming out of the front of the carbs so I think my electric primer may be open or stuck. The motor has to be choked to run. Will adjust and test the idle jets and run some seafoam thru it.

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thedude
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Johnson 48 hp tune up

Post by thedude »

So I may have solved the idle problem. The cam throttle roller circled in the picture was worn on one side down to the metal. Simply rotating that around made it idle much better. I also adjusted the low speed jet screw but didn't want to tinker too much with it.

The electric choke/primer also was set high on manual setting so reset that to stock automatic setting. I think it was resulting in excess gas sitting in the carb (pictured below). Also seemed to idle better once I got the vacuum hose hooked up to the air cover and got it all buttoned up (I was running with carbs exposed before).

Video of idle.

Also included some pics of my helpers! Good day all in all.

[ external image ][ external image ][ external image ][ external image ][ external image ]

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earl60446
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Johnson 48 hp tune up

Post by earl60446 »

Good for you. I also have a 48hp spl johnson. I like it a lot, had a couple problems when I first bought it, spark plug gap at 60 thou, carbs needed cleaning but that is all at that time.
Yours looks way better than mine, I suspect mine may have been on fire at one point in its life.
Tim
16ft 1989 Fisher SV-2 w 1988 48hp SPL Johnson "CIGAR BARGE"
(engine looks like a wreck but runs great)
Used to have 1972 14ft Lund w 1977 15hp Mariner
(engine looked great but always ran marginal)
XLINE SPORTSMANS CLUB

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thedude
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Johnson 48 hp tune up

Post by thedude »

Update. I got some parts in and took advantage of some temps in the 60s here in Dallas. This morning I installed the new cam roller and wow what a difference it made. I included pics to show the difference and amazed that a 1/16th inch sleeve on the roller makes it idle so much different (new one is the first pic). The previous owner was compensating for dirty carbs and worn cam roller by adjusting the idle screw. As soon as these two were corrected it idled at 2000+ rpms! Scarred the bejesus outta me when it fired. Also replaced air intake and carb gaskets to make sure all was well sealed. Very happy now and took it out on a lake test and getting over 5000 rpms and great idle.

Only one problem remains and that is the broken cmc power trim. It is stuck slightly trimmed up and actuator is not working.

I took a video and you can see the prop spray/blow out at about 3000 rpm or so. Now I have to make some expensive decisions about the trim. There are three trim holes and it is currently in the middle so I could adjust it one more hole down at least temporarily.

[/img][ external image ][ external image ]

water bouy
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Johnson 48 hp tune up

Post by water bouy »

Nice. I had 48 spl Evinrude and liked it a lot. If I remember correctly it's the same as a 50 hp except no tilt trim.
16 ft Sea Nymph w/30 Johnson
14 ft Monark w/25 Merc XD sold
1994 Lowe 1605 w/50 Evinrude sold
14 ft Lone Star w/15hp Evinrude sold

nccatfisher
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Johnson 48 hp tune up

Post by nccatfisher »

You can get a schematic of the CMC online. Most likely a bad relay. I believe that is a jack plate.

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DaleH
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Johnson 48 hp tune up

Post by DaleH »

Plug gap for OMCs should be 0.030” ... not 60-thousandths!

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thedude
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Johnson 48 hp tune up

Post by thedude »

water bouy wrote:Nice. I had 48 spl Evinrude and liked it a lot. If I remember correctly it's the same as a 50 hp except no tilt trim.
Mine still has the remnants of the lift assist tilt but not working. I understood it was only a lift assist with a release valve to lower it (no power).

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thedude
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Johnson 48 hp tune up

Post by thedude »

I have tested and have voltage past the relay. I think my only other troubleshoot is to send voltage directly to the motor and confirm motor is dead.
nccatfisher wrote:You can get a schematic of the CMC online. Most likely a bad relay. I believe that is a jack plate.

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DaleH
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Johnson 48 hp tune up

Post by DaleH »

thedude wrote:I have tested and have voltage past the relay. I think my only other troubleshoot is to send voltage directly to the motor and confirm motor is dead.
Replacement motors here: https://www.boatstore.com/cmc-jack-plat ... t-130.html

I'd check to see if someone could rebuild it first. But try rapping on the housing with a wooden mallet while applying power, as sometimes that "stimulates" worn brushes to make contact with the housing.

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Stumpalump
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Johnson 48 hp tune up

Post by Stumpalump »

DaleH wrote:
thedude wrote:I have tested and have voltage past the relay. I think my only other troubleshoot is to send voltage directly to the motor and confirm motor is dead.
Replacement motors here: https://www.boatstore.com/cmc-jack-plat ... t-130.html

I'd check to see if someone could rebuild it first. But try rapping on the housing with a wooden mallet while applying power, as sometimes that "stimulates" worn brushes to make contact with the housing.
I sold my old boat with a rubber mallet and showed the guy how to thump the trim to get it working. the CMC units are known for corrosion in the motor and that just may fix it.
1991 18' Valco Bayrunner Evenrude 48 SPL

Arizona

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thedude
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Johnson 48 hp tune up

Post by thedude »

Good to know! I will need my assistant to try this since the trim button is by the helm.

I have heard of people rebuilding these and finding similar brushes to replace the worn ones but i have yet to find someone reliable to send it to.

Unfortunately this PT130 has the motor and actuator in one (pic attached) - the only replacement units i have seen come all in one piece and run $400. Not bad considering the price i paid for the boat. I'm referring the link that Dale posted.

I'll try the hammer first and keep you posted if i can find someone to rebuild - at the very least i'll take it apart myself just out of curiosity!
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