1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics

[DIZZYSPOTS]

YES! I let off the throttle...25 in a tiller steered 12ft tinnie is scary fast..a little chop on the lake, not bad...dont know what the other 700 would have got me...not looking cuz i'm happy...gets on plane quickly even part throttle is a nice clip

1987 Johnson 20 hp 30 hp carb and intake swap

 

[Johny25]

Ok that's right, sorry I have so many motors and mods in my head I cannot remember one from the other any more So yeah with that 2.15 gear case you should be able to turn that 14 pitch to 5500-5800 and probably hit 28-30mph.....and yes that is scary fast in a 12' tin with tiller steer :lol: You will have to open it up one day in calm water and post results.

What was your top speed prior to the mod?

 

[Jay D]

I have a 1988 25hp evinrude, what would it take to boost it to a 35hp evenrude? If you already answered this please forgive me.

 

[DIZZYSPOTS]

top speed before the mod..hard to get to 18...but had fuel issue" bad"(old) bulb and hose, then bad gas...it got to 20mph..but only once and it took the length of the lake to do it....Now? twist the grip and you're on plane, seconds later 25!
If we get a glassy day in Baja, Ill try to get a real top end for ya


PS 25 days until fresh fish tacos and cold cerveza on the beach...

 

[Johny25]

I have a 1988 25hp evinrude, what would it take to boost it to a 35hp evenrude? If you already answered this please forgive me.

I made this whole thread from the exact year and HP motor you have Jay. Start at the beginning of the thread where I layout and have pics of your exact motor converting into a 30hp. It will never be a 35hp since the 35 was re-badged to a 30hp in 1985 when OMC prop rated the HP on there motors. The old 35's were only cranking out 30hp at the prop hence the reason it was labeled the 30hp after 1984. Read the first page of the thread and let me know if you have any questions

 

[Johny25]

top speed before the mod..hard to get to 18...but had fuel issue" bad"(old) bulb and hose, then bad gas...it got to 20mph..but only once and it took the length of the lake to do it....Now? twist the grip and you're on plane, seconds later 25!
If we get a glassy day in Baja, Ill try to get a real top end for ya


PS 25 days until fresh fish tacos and cold cerveza on the beach...

I remember my first day out with mine Dizzy, had an 11pitch Stainless on it. The freaking thing would get up on plane and hit 25mph so fast that it was SCARY. Like a damn rocket. Of course I was way under propped and the motor was turning 6290rpm lol not good. So the 14 stainless was put on which made time to plane much longer but top end was increased about 5 mph. FYI I have had my 14' tin completely out of the water and airborn when running WOT in rough water, that is an awesome feeling. My 6 yr old loves when we wave jump.

I am glad you are happy Dizzy. Don't worry, you will get used to the extra power after a few trips and start thinking of a 40hp on there just like me :lol:

 

[DIZZYSPOTS]

actually just thinkin of bigger boat...more room to share fishing with a total of 4 grandkids....

 

[Johny25]

I hear ya, Ive been trying to find an 18' or better. And bigger boat means I get to play with bigger motor

 

[DIZZYSPOTS]

Just got back from Gonzaga Bay in Baja...had perfect flat, windless seas...can you say 35 mph in a 12ft tinnie...YEEHA! actually kept up with my buddy's 17 ft bayliner...till I chickened out ")

 

[Johny25]

35mph in a 12'tin is butt puckering fast! :mrgreen:

 

[nick4203]

lol my buddy gots a 77' johnson 35 on his 14 foot valco always the fastest tin boat on the lake he keeps talkin he wants a 50 i told him i wont go with him any more haha

 

[DIZZYSPOTS]

bigger boat gets picked up sat...74 Wellcraft Airslot 185...Evinrude 140 clean...2nd owner covered and in AZ its whole life...so about this 140 hp......

 

[Johny25]

Depending on the year of the 140 it will decide whether it is a crossflow or looper. Needless to say I am jealous

 

[Charger25]

35mph in a 12'tin is butt puckering fast! :mrgreen:

Yeah it is ......... but I bet he had monster grin from ear to ear !! I know I would. :LOL2: :LOL2:

 

[DIZZYSPOTS]

yeah so did my son in the front of the boat...maybe that was from the wind


PS think the 'rude 140 is a 87 or 89..168 hrs on it...dont have serial number in front of me...VRO blocked off using premix

 

[Johny25]

It is a looper then, and if it is an 88' or later it is a big bore looper

 

[Plasticmotif]

Just joined to say Thanks for this thread!

I've got a 93' Grumman 1465 with a 90' Evinrude 20HP. The boat's a bit heavy and will only do 10 mph going upstream against generators. On the lake, it's fine. I'll probably end up doing this switch to a 30HP.

Do you have any other notes?

 

[Johny25]

Well if you want just a little more power you can just bore out the backside of the 20hp carburetor to make it into a 25hp. This is the only difference between the 20 and 25 if memory serves me correct on the 90' models. If you want the extra ten HP then intake and carb will be needed. The 20 had a restricted small hole on the backside of the carb where it attaches to the intake manifold, bore it out to match intake hole size and you got you a 25hp. Don't get any metal into the crank case though so remove carb to do this and clean well.

 

[Plasticmotif]

dbl post

 

[Plasticmotif]

Thanks for the fast reply.

I'll be on the lookout for a 30HP Carb and intake. What years work? Also, If you could point me to where I could find model numbers, I'd very much appreciate it!

I want to be doubly sure before I go buying anything. I've got a CE20CRESB.