Weak spark on 1973 20 Hp Johnson

[fleetwin]

OK, found the ebay auction….He wants big money for that piece…You may want to reconsider buying it…

[Evinrude 25]

Here is the link. After reading all about this topic. It is very interesting of the great sharing knowledge of the member of this site.

https://www.ebay.com/itm/Johnson-Evinrude-20-Hp-Ignition-Plate-Coil-581131-Driver-Coil-581130-Stator/112343166324?_trkparms=aid%3D777001%26algo%3DDISCO.FEED%26ao%3D1%26asc%3D225085%26meid%3D32294b78a32a4ef3899e391a462f97b1%26pid%3D101213%26rk%3D1%26rkt%3D1%26mehot%3Dnone%26itm%3D112343166324%26pmt%3D1%26noa%3D1%26pg%3D2380057%26algv%3DRecommendingSearch%26brand%3D&_trksid=p2380057.c101213.m46344&_trkparms=pageci%3A784dc604-cba0-11ea-a591-74dbd1809b84%7Cparentrq%3A737750cd1730abc5a60099a0fff24afa%7Ciid%3A1

[fleetwin]

Just emailed the seller and asked for more specifics about this set up….Will let you know what he has to say….

[fleetwin]

OK, seller replied. He said that the other driver coil is not used for ignition purposes…It is for a AC lighting coil, which makes some sense. Plus, I can see the two terminal ends from this coil coming out of the wiring harness…I am used to see only double wound alternator windings or AC lighting coils, but this mag plate would not accept that piece. So, this was some sort of accessory for overseas engines….
Makes sense now, I just assumed that other coil was used for ignition….
But again, this item seems a bit over priced…Unless it is in absolutely perfect condition….

[Evinrude 25]

Is it possible to gain 5 hp more when installs a 25 hp carburetor on 20 Hp? I saw a 25 hp carb on sale “JOHNSON EVINRUDE 25 HP 385815 CARBURETOR 1973 TO 1976 YEARS GOOD CORE 2 REBUILD”. It is interesting to know if it is just simply swap the Carb or more things involved to get additional 5 Hp.

[fleetwin]

Sometimes these engine have an intake manifold with a restricted/small diameter inlet. Installing the larger throat 25hp carb might not work out very well…Not saying it won’t work, but you should have a look at the intake manifold and carburetor throat first. It’s not always as simple as the seller claims… How much does he want for this “core”? I wouldn’t pay too much for it, consider it a gamble that might not work out.
I would get the engine running properly with its original carburetor first before attempting to swap out the carbs…

[Phil Budne]

The 25hp 22ci engines had a number of changes other than the carb. I seem to recall they include (at least):

Balanced crank
Piston pin location changed (for porting and/or compression)
Different cylinder head
Exhaust tuning

And maybe also improvements in the lower unit (gear case)

http://www.omc-boats.org
http://www.aerocraft-boats.org

[Evinrude 25]

Hello All,
Her is the update the status of my 20 Hp Johnson:
1) Compression: 114/112 psi
2) Have spark on both cylinder. With the help of this forum, I will be able to get the spark of both cylinders. The update of the hardware: two new Mallory Marine Ignition Coil 9-23106, OMC OEM Outboard Tune Up Kit 172523, The driver coil (old) is still there even though I bought (OMC COIL #581130) but did not install yet. I did timing of the point based on the you tube that use ohm meter. So far I got good spark!
3) Clean the old carburetor and put it in, I could get it run for but it is hard to get it running but whenever it runs it runs good. Note: the Carb is not in good shape. I have 3 spare Carb from 1981 70 hp Johnson. By the look they are the same as 20 hp carb. I could take one of them and try out. There are a couple external hardware different and the butterfly plate which I could swap them out to match.
What do you think?

[fleetwin]

First, please don’t every try to swap throttle or choke shaft components by removing the butterflies. The butterflies are staked in place for a good reason, you sure wouldn’t want the screws to get sucked out and gobbled up in the powerhead….Plus, the butterfly could get jammed in the WOT position, usually at the most dangerous moment.
What I’m hearing you say is that your engine is hard starting when cold, but once warmed up it starts fine, do I have it right?
If so, I would have a look at the choke linkage, some of these designs are not the greatest…Some of the chokes rely on the choke knob bushing to hold the choke completely closed….So, I would have an assistant pull the recoil while you ensure the choke is completely closed.
The carbs from the 1981 70hp will not work on your 20hp….Completely different design, even though it might “bolt up” OK.

[Evinrude 25]

Yes, initially it was hard to start, 10-20 pulls to get it run but when it ran, I could start again with a couple pulls. The idler needle sets out 2 turns from fully seated some time I had to back out 1 more turn to make it run. Ok I heard from you to give up using 1981 carb. I will order the carb kit and rebuild it. I may redo the cleaning again when the new kit coming. The choke linkage was not a clean design!
Note: the bottom part of the 1973 Carb is the same part number of 1981 carb.

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