Upgrading 20 HP Johnson (J20CRC0S) to 35 HP

[Vibemanrts]

Thanks in advance for any help... I'm trying to source the correct intake manifold (395626, 396790, 391054) and 35 HP Carb for this conversion. Any guidance on where to look? So far my internet searches have come up empty.

Thanks

Steve

 

[jimmbo]

You will need more than that to change a 20 into a 35.

 

[kbait]

https://forums.iboats.com/forum/eng...rude-outboards/449716-salvage-yards-by-wilde1

 

[Vibemanrts]

Thanks for the responses

I'll keep looking...

 

[Willyclay]

If you have not already seen the thread at the link below, you might want to read it. Good luck and let us know what you do!

https://forums.iboats.com/forum/eng...ds/281518-converting-a-20-hp-johnson-to-35-hp

 

[Vibemanrts]

Have read that one several times! I also have an Evinrude 15 hp (15804B) and when I placed both of these engines on the ground next to each other I was shocked at how much bigger the Johnson 20 (J20CRC0S) was. Thus started the internet searching as to why. i.e. 35 hp block/motor being used as a 20 hp.

My Father bought the Johnson in the late 80's and used it for several years on a fresh water lake. For the last 10 years it has been sitting outside in my Brothers backyard unused. I finally convinced him to give it up (along with the 13 foot Boston Whaler it was attached to) and have started bringing them both back to life. The armature plate was frozen (black goo from the electronics had leaked onto the bushing) so after I got that freed up I put it in a garbage can and fired her up. Ran fine at higher RPM's but did not idle at all.

I decided to go through all of the normal steps to bring the engine back to 100%. New fuel lines, spark plugs, water pump, fuel pump rebuild, compression (~105 psi each), spark test, carb rebuild, changed lower unit oil, new spark plug wires..I'm sure I left something out.... And reamed out the existing intake manifold to match the carb opening maybe getting me to 25 hp.

Will get the lower unit back on this weekend and see if I can get it to idle. Or work for that matter after everything I did to it!!!

 

[Willyclay]

I have a J25RLCOS and will be following you closely. Your compression sounds great and I am sure you can whip the bad idle issue. What year is the BW? Hopefully, it does not suffer from the "saturated foam disease" like most older Whalers. Good luck!

 

[Vibemanrts]

Willyclay... After all the above described work the idle still has not improved (or only improved slightly). One thing that surprised me was that the new spark plug wires (Sierra 6 inch) had about 250 ohms of resistance where the old wires showed only a few ohms. I did a lot of looking on-line and it appears that the ohm value of the new wires is correct.

I also checked the coils with an ohmmeter and they checked out good.

I'm going to redo a few steps (compression, spark) just to verify that what I found before is still good. And I'm going to rebuild the carb again. I was thorough the first time (removed all of the welch plugs) and used carb cleaner and compressed air but did not soak the carb overnight. I also did not remove the lead shot (not sure what is under that).

I found a nice topic from Psteurer on this issue from 2008 (1989 Johnson 20 HP not idling) that makes me wonder if I missed some hardened crud in the carb. I'm going to check the small holes described in that article as well as the needle valve and seat.

Not sure of the year of the Boston Whaler. Bare bones basic though.. small storage locker in front, 2 wooded slats for seats, no console.

Steve

 

[Willyclay]

I also am surprised at the 250ohms resistance in those brand-new Sierra spark plug wires. I will check mine tomorrow and advise. FYI, it took me three carb cleanings to get my RDSL-21 to idle and the last time included using non-metallic, gunsmithing picks to get the "hardened crud" out of the low-speed orifice. Hang in there, you can do this!

EDIT: Here's a link to a good source of info for your BW: http://continuouswave.com/whaler/

 

[Willyclay]

I am unable to get a reliable reading from my plug wires due to possible corrosion from having spent all 33 years of it's life in saltwater. Guess I need new plugs wires. If another member doesn't jump in here with help, you may have to start another thread regarding that particular issue. Good luck!

 

[Vibemanrts]

Thanks for trying to measure the resistance of your spark plug wires.

I've got the carb soaking and a new rebuild kit on the way. Was way cheaper to just buy a new rebuild kit then to purchase the Welch plugs by themselves.

The slow speed holes (three under the top Welch plug) seemed clear. I'm actually starting to wonder if this rough idle issue might have to do with the slow speed needle valve bearing. I'm having a hard time determining (seeing) if there is one installed or not. I've tried several different sized screws that would engage a new one and they seem to "bite" into something but I am unable to remove whatever it is biting into. I see in previous posts that a 4x41 tap is the way to go... I'll pick one up and give it a try.

Steve

 

[Willyclay]

Be careful with that "bearing" because if you get too aggressive trying to remove it, you may damage the orifice. Good luck!

 

[Willyclay]

A thought fell out of the empty space between my ears and hope I have not confused you. I verified we both have the same carburetor on our motors and I cannot find anything identified as a "needle valve bearing". Our carbs have a "needle valve retainer" that is removeable and is non-metallic, not sure what material exactly. The "retainer" functions like fiber packing washers in older-style carbs, i.e., RD-series which also had a threaded, removeable, aluminum, needle valve BUSHING. I believe the needle valve threads in our carbs are in the upper, carb body and are NOT removeable!

 

[Vibemanrts]

Willyclay... I believe that you are correct. I've looked on marineengine.com at the parts lists for both of our motors and it does appear that the carbs are the same and do not have the Needle Valve Bearing shown in the carb repair kit generic drawing. Should have looked at that .. Thanks

 

[Vibemanrts]

Normal Spark Plug Wire Resistance

I decided to replace my old spark plug wires because when I was measuring them with an ohmmeter I was getting very inconsistent readings.. Anywhere from 3 ohms to infinity.

I purchased sierra 6 inch wires (Sierra International 18-8816-1 Premium MagForce 6" Marine Spark Plug Wire Lead for Johnson/Evinrude Outboard Engines) and when I measured their resistance I got a very consistent 250 ohms.

Looking on-line this seems like it could be a reasonable number but I'd just like confirmation from this more experienced group.

Thanks

Steve

 

[F_R]

What is the model number of the motor you intend to put them on?

 

[Vibemanrts]

J20CRCOS. Johnson 1985 20 HP.

 

[Willyclay]

FYI, if you have not already seen this in the FAQ's:

(Replacing Regular Spark Plug Wires)​

(J. Reeves)​

If you also need the spark plug boots and the spring terminals that connect to the spark plugs, purchase them from your local dealership (OMC Part #581027). This includes one boot and one spring connector. Price is about $3.25ea.​

Purchase whatever amount of spark plug wire you need. Be sure to purchase the kind that has a steel (or copper) twisted wire leading through the center of it....... not the carbon type plug wire that many automobiles now use.​

Using your old plug wire, cut the new wire to a length about 3/4" to 1" longer. If you have no old plug wire, just make sure that the wire is longer than you'll need as you can trim the other end later.​

The rubber boot, spark plug end.... With the wire cut to the length required, trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above. Holding the spring wire terminal, estimate where the prong should be inserted so that the spring will be flush against the exposed wire. Hold the spring terminal away from the wires end (sideways) and insert the prong into the insulation and into the center wire, then swing the spring terminal in front of the exposed wire portion (makes a tight fit for continuity purposes). Spraying the inner portion of the boot where the wire will insert with a small amount of WD40 makes the installation of the wire a easy project.​

Now, the other end that slides into the magneto coil... Look into the awaiting hole of the coil and you will see a somewhat threaded tapered prong. Double check to make sure that the wire is cut to the length required (better slightly longer than shorter), trim back 1/4" insulation again but do not solder tint the wires. Simply fan out the wires and fold them back against the insulation, cutting the excess off as explained above, then simply slide the wire into the coil so that the inner wire core of the wire is impaled by the tapered prong within the coil. That's it.... you're done.​